Advance Solar Photovoltaic Thermal Energy Technologies: Fundamentals, Principles, Design, Modelling and Applications (Green Energy and Technology) [1st ed. 2023] 9819949920, 9789819949922

Citation preview

Green Energy and Technology

Gopal Nath Tiwari

Advance Solar Photovoltaic Thermal Energy Technologies Fundamentals, Principles, Design, Modelling and Applications

Green Energy and Technology

Climate change, environmental impact and the limited natural resources urge scientific research and novel technical solutions. The monograph series Green Energy and Technology serves as a publishing platform for scientific and technological approaches to “green”—i.e. environmentally friendly and sustainable—technologies. While a focus lies on energy and power supply, it also covers “green” solutions in industrial engineering and engineering design. Green Energy and Technology addresses researchers, advanced students, technical consultants as well as decision makers in industries and politics. Hence, the level of presentation spans from instructional to highly technical. **Indexed in Scopus**. **Indexed in Ei Compendex**.

Gopal Nath Tiwari

Advance Solar Photovoltaic Thermal Energy Technologies Fundamentals, Principles, Design, Modelling and Applications

Gopal Nath Tiwari BERS Public School (BPS) Ballia, Uttar Pradesh, India

ISSN 1865-3529 ISSN 1865-3537 (electronic) Green Energy and Technology ISBN 978-981-99-4992-2 ISBN 978-981-99-4993-9 (eBook) https://doi.org/10.1007/978-981-99-4993-9 © Bag Energy Research Society 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Use renewable energy sources to conserve fossil fuel and save eco-system (Gopal Nath Tiwari)

I have been always blessed unconditionally by

Guru Ji Padma Shri Prof. M. S. Sodha Guru Ji: Professor M. S. Sodha was born in Ajmer on February 08, 1932, Rajasthan and pursued his education from UP, including his higher education from Allahabad University in Allahabad (UP), India. His father was a teacher in a government school in UP. After completing his Ph.D. from Allahabad University, he secured a job in the Defense Research and Development Organization (DRDO) in New Delhi. Before his joining, he sought the blessing from his father and his father shared the following advice with him:

(a) If someone comes to you for any kind of help, think that God blessed you to be in a position to help others. (b) Before taking any decision, place yourself in his position and expect the results from your boss. Our guru ji has followed his advice throughout his life and celebrating his 92nd birthday in the year 2024. Be happy with good health to help Nature for longer life.

Preface

The formation of the SUN, EARTH, and ATMOSPHERE took billions of years. The first living organism (algae) was created by greenhouse effect on the planet Earth due to solar energy coming from the sun. Solar energy is basic source of all renewable energy, which is free and environment friendly. If it is harnessed directly to meet the energy demand of any individual, it is most economical, and it will help to conserve limited non-renewable energy sources (such as fossil fuel), which is responsible to pollute environment since WW-II. In this book, I have made an attempt to discuss advance developed technology based on solar energy. Basically, we receive solar energy in terrestrial region through atmosphere, which consists of greenhouse gases [carbon dioxide (CO2 ), oxygen (O2 ), ozone (O3 ), carbon mono-oxide (CO), water vapor (H2 O), sox (SOx ), nox (NOx )]. The solar energy mainly consists in the form of electromagnetic (e/m) wave and many photons. The electromagnetic wave provides us energy in the form of thermal energy and vitamins, and the photon provides the life on the planet Earth. Further, there are many technologies based on electromagnetic (e/m) wave and photons, which includes water/air heating to provide thermal energy and solar cells to provide electrical energy. This book consists of 11 chapters. Chapter 1 discusses basics of solar energy available on any surface on Earth, global greenhouse effect, and ecological balance, while the quality of water needed for all living organism has been discussed in Chap. 2. There is a brief discussion on working principle of solar cell and its basic parameters including electrical efficiency fill factor, generation of solar cell, and applications in Chap. 3. The photovoltaic (PV) module based on solar cell, types of PV module (opaque and semitransparent), its design parameters, solar energy-based energy balance, etc., have been covered in Chap. 4. In order to increase agricultural product to meet the food security, a greenhouse concept has been developed throughout the world. So, in Chap. 5, I have tried to explain the greenhouse concept along with its various types and applications in food industries including aquaponics, solarization, transparent plastic mulching, and solar greenhouse drying. The working principle, construction, and design of advance greenhouse integrated semitransparent photovoltaic thermal (GiSPVT) system have been discussed in Chap. 6. The GiSPVT ix

x

Preface

system provides thermal and electrical energy, and hence, it is referred as PVT system. The cultivation of off-season vegetables, namely bottle gourd (Lauki), French beans, tomato, capsicum, cucumber, and broccoli within GiSPVT system including sowing, transplantation, and climatic parameters along with thermal modeling of GiSPVT system have been discussed in Chaps. 7 and 8, respectively. The concepts of earth air heat exchanger to be used in heating/cooling of GiSPVT system and basic heat transfer coefficients (convective, radiative, and conductive and overall) have also been discussed in Chap. 8. Another application of GiSPVT system is solar drying which has been covered in Chap. 9 which includes its working principle, types, heat transfer for drying, thermal modeling, parametric studies, etc. Chapter 10 discusses in brief (i) steady-state thermal analysis, (ii) transient analysis, (iii) quasi-steady condition, and (iv) periodic condition and its appropriate application in thermal modeling of solar technology to optimize various design parameters. The periodic thermal modeling of uneven greenhouse semitransparent photovoltaic thermal (GiSPVT) system has also been done by using matrix inversion method for time-independent and—dependent parts of modeling. The discussion about another application of PVT technology in area of aquaculture, water/air heating, and its uses in space heating, biogas heating, and swimming pool heating with advantages and disadvantages has been covered in last Chap. 11. I have taken the help of many literature published online, and in my own books with appropriate acknowledgment. If anyone’s acknowledgment is left, I express my regret for the same, and I will request to all concern one to drop me a letter to rectify the acknowledgments in the revised version if any comes in future. This book will cater to engineering students, faculty, researchers, and entrepreneurs in building basic knowledge useful in design of solar energy system. However, it will be very useful for teaching engineering students in B.Tech. and M.Tech. programs. The energy engineers can also take the advantage of this book. Examples in each chapter at appropriate section if required are given along with problems and objective questions at end of each chapter. S.I. units and conversion units (Appendix A) have also been given at appropriate places when it is required. The main physical and chemical constants used in the book in approximate multiple three have also been given at beginning of the book. I have used conventional symbols, but I have given the list at beginning for users of this book. If any symbol is left, then let me know. I am extremely thankful to Ms. Swati Meherishi, Editorial Director, Engineering, Springer, New Delhi, India, for her support and encouragement during the preparation of manuscript. I will fail in my duty if I will not acknowledge those who inspired me to write this book and their help in the form my Ph.D. student’s examiner, unknown reviewer of my papers, research collaborator, and colleagues. These include Profs. T. Muneer (UK), Brian Norton (Ireland), Christophe Menezo (France), Sparber Wolfman (Italy), Koji Matsubara (Japan), T. T. Chow (Hong Kong), and Danny Hin Wa Li (Hong Kong) Al-Helal (King Saudi University). I am also thankful to my colleagues for their moral, financial, and physical support given to Bag Energy Research Society (BERS) from time to time. These include Dr. Alok Srivastava, Chief Guest, SOLARIS-2024

Preface

xi

(USA), Prof. V. K. Srivastava, New Delhi; Prof. Emran Khan, JMI; Dr. Vineet Saini, New Delhi; Dr. Vivek Tomar (Hong Kong), Dr. Neha Dimri (Switzerland), Dr. Prabhakant, IRS; Prof. Vijay K. Dwevedi (Gorakhpur), Prof. Sarat Panda, IIT Bhuvneswar; Prof. Subhas Solanki (Indore), Dr. Manoj Gaur (Gwalior). I am dedicating this book to my Guru Ji, Padma Shri Prof. Mahendra Sodha on his 92nd birthday (February 08, 2024) for his contribution to shape my academic carrier in Solar Energy since 1977 as a mentor, and I have a privilege to get unconditional blessing always from him. Further, I thank my family members Mrs. Kamalawati Tiwari, Mr. Ghanshyam Nath Tiwari, Ms. Ritu Mishra, Ms. Gopika, Shrivats, Shri Ganeshu, and Ms. Shrivani (lovely princess) for keeping patience during these periods and helping in so many ways required by me. Last but not least, I express my deep gratitude to my late grandparents and parents Pt. Ramdhari Tiwari, Mrs. Suguia Devi, Pt. Bashisht Tiwari, and Mrs. Bhagirathi Tiwari for their blessing which helped me to achieve my target in teaching and research. Ballia, India

Gopal Nath Tiwari

Important Constants

Approximate values of some constants in renewable energy sources which is multiple of three Constants

Actual value

Approximate value

A

A

A

Absorptivity of bare surface

0.3

Absorptivity of blackened surface

> 0.9

Altitude of ozone (O3 ) layer present in stratosphere

12–25 Km

12–24 Km

Average heat flux from center of Earth to Earth’s surface

0.06 W/m2

0.06 W/m2

Average temperature of the Earth 298 K (≈ 25 °C)

300 K

B

B

B

Band gap for silicon

1.16 eV

1.2 eV

Black body temperature of the Sun’s surface

5777 K

6000 K

Basic convective heat transfer coefficient from outer bare surface with zero wind velocity

2.8

3

Boltzmann constant

1.38 × 10–23 J/K

12 × 10–24 J/K

Broad classification of thermal comfort (Physical, physiological, intermediate) parameters

3

3

C

C

C

Central core (0–0.23R) temperature of the Sun

8–40 × 106 K

9–30 × 109 K (continued)

xiii

xiv

Important Constants

(continued) Constants

Actual value

Approximate value

Convective heat transfer coefficient for air with V as a wind velocity

2.8 + 3 V

3+3V

Convective and radiative heat transfer coefficient from bare surface to flowing air

(5.7 + 3.8 V) W/m2 K

(6 + 3 V) W/m2 K

Cooking time by solar cooker

2–3 h

3h

Climatic zone in India

6

6

D

D

Diameter of the Sun (2RS )

1.39 ×

2

Distance of the Sun from the Earth

1.5 ×

3

Diameter of the earth (D = 2R)

13000 km

1

4

5

D 109

m

1.5 × 109 m

1011

m

150 × 109 m 1.5 × 106 m

Density of air

1.2

kg/m3

1.2 kg/m3

Density of water

997 kg/m3

990 kg/m3

Dry biomass in biosphere

250 ×

E

E

E

Energy generated at center core of the Sun

90%

90%

109

ton/year

Effect of climatic parameters on yield

240 × 109 ton/year

9–12 %

Effective density of states in conduction bands

2.82 × 1019 cm3

27 × 1018 cm3

Emissivity of surface

0.9

0.9

Efficiency of solar cells in standard conditions

15%

15%

Efficiency of PV module with Si solar cell

12%

12%

Energy contained in visible region

47% (502.6 W/m2 )

48%

Energy contained in infrared region

51.02% (697.4 W/m2 )

51%

Energy produced in one fusion reaction inside sun

26.7 MeV

24 MeV

F

F

F

Fermentation temperature of slurry for biogas production

37 °C

36 °C

Energy contained in ultraviolet (UV) region

Fin efficiency

0.9 (continued)

Important Constants

xv

(continued) Constants

Actual value

Approximate value

Flat plate collector (FPC) efficiency factor (F' )

0.7

0.6

Flow rate factor (FR )

< 1.0

< 0.9 ≤3

FPC connected in series G

G

G

Gas-turbine operates

600–1200 °C

600–1200 °C

Geothermal energy from the Earth

300 × 1012 W

300 × 1012 W

H

H

H

Heating concepts (Direct, indirect, and isolated)

3

3

Heating value of coal

29000 kJ/kg

30000 kJ/kg

Heating value of biogas

20000 kJ/kg

20000 kJ/kg

Heating value of wood/straw

15000 kJ/kg

15000 kJ/kg

Heating value of gasolene/ kerosene

42000 kJ/kg

42000 kJ/kg

Heating value of methane

50000 kJ/kg

51000 kJ/kg

High-temperature geothermal well

≥150 °C

≥150 °C

Hydropower system electrical efficiency (Pelton wheel turbine base)

90%

90%

I

I

I

Ideal efficiency of solar still

60%

60%

Intermediate comfort parameters

6

6

Insulation thickness

0.10 m

0.09 m

J

J

J

Junction thickness near n-type semiconductor in Si

0.15 μm

0.15 μm

L

L

L

Latent heat of vaporization

2.3 ×

Long wavelength radiation from Earth

10 μm

106

J/kg

3 × 106 J/kg 9 μm

Long wavelength radiation 60 W/m2 exchange (ΔR) between ambient and sky

60 W/m2

Low-temperature geothermal well

≤ 150 °C

≤ 150 °C

M

M

M

Mature tree consumed, CO2

12 Kg of CO2

12 Kg of CO2 (continued)

xvi

Important Constants

(continued) Constants

Actual value

Maximum temperature in concentrating collector

Approximate value 3000 °C

Maximum wind power extraction a = 1/3

a = 1/3

Maximum hydropower mechanical factor

ut = uj /3

ut = uj /3

Maximum power coefficient (WECS)

59%

60%

Maximum efficiency of WECS with ideal Pelton wheel curved turbine

100%

90%

Mean sun–earth angles (three w.r.t. center of earth and three w.r.t. observer on earth)

6

6

Methane presence in biogas

60%

60%

N

N

N

Number of sunshine hours (average)

5

6

Number of solar cell in standard PV module for 18V O

36 O

Optimum till angle for maximum Φ±15 solar radiation, degree Order of radiation heat transfer coefficient

6 W/m2 K

O Φ±15 6 W/m2 K

Order of convective heat transfer 100 W/m2 K coefficient between hot plate and water

(90 – 300) W/m2 K

Overall heat transfer coefficient for glazed FPC single glazed

6 W/m2 K

Optimum temperature for body of human

35–37 °C

36 °C

Optimum depth of water in basin 0.02–0.03 m of solar still

0.03 m

Optimum wind velocity for wind 10 m/s turbine

9 m/s

One photon has energy

3.2883 eV

3 eV

OTEC power generation, ΔT

≥15 °C

≥15 °C

P

P

P

Physical comfort parameters

9

9

Physiological comfort parameters 6

6

Propane in liquefied petroleum gas (LPG)

90%

90%

(continued)

Important Constants

xvii

(continued)

7

Constants

Actual value

Approximate value

R

R

R

Radius of Earth (R)

6500 km

6.5 × 106 m

Rate of evaporation from free water surface (q˙ ew )

0.016 × hcw × Pw –r Pa

0.015 × hcw × Pw –r Pa

S

S

S

Saturation current in reverse bias 10−8 A/m2 (I o )

0.1 × 10−9 A/m2

Sky temperature (°C)

(Ta -12)

(Ta -12)

Solar constant

1367 W/m2

1500 W/m2 900 W/m2

Solar intensity in terrestrial region Solar energy for photosynthesis

30 × 1012 W

30 × 1012 W

Solar energy for wind and wave conversion

300 ×

300 × 1012 W

Solar energy for hydropower

40 × 1015 W

30 × 1015 W

Solar energy for sensible heating

80 ×

W

90 × 1015 W

Specific of water

4190 J/kg °C

4200 J/kg °C

Specific heat of air

1 kJ/kg K

1 kJ/kg K

8

Short wavelength radiation

0.23–2.6 μm

0.3–3.0 μm

9

Sunshine hour at equator

12 h

12 h

10

1012

1015

W/m2

W

and 25 °C

900 W/m2 and 24 °C

W/m2

60 × 10–9 W/m2 K4

Standard test condition

1000

Stefan–Boltzmann constant

5.67 ×

Sunshine hour at north pole

24 h

24 h

T

T

T

Thickness of n-type semiconductor in silicon solar cell

0.2 μm

0.3 μm

Thickness of p-type semiconductor in silicon solar cell

0.50 mm

0.60 mm

10-8

K4

> 150 W/m2 > 150 W/m2

Threshold intensity (a) Winter (b) Summer The rate of heat generated by healthy person during sleeping

60 W

60 W

The rate of heat generated by healthy person during hard work

600 W/m2

600 W/m2

The body temperature of human being

37 °C

36 °C

Thermal conductivity of insulating material (K)

0.03–0.04 W/m K

0.03 W/m K (continued)

xviii

Important Constants

(continued) Constants

Actual value

Approximate value

Transmittivity of window glass

0.9

0.9

The rate of ventilation/infiltration 0.33 NV (Tr − Ta )

0.33 NV (Tr − Ta )

Tidal power from planetary motion

3×

Thermal solar energy absorbed by earth

120 × 1015 W

120 × 1015 W

Type of radiation (beam, diffuse, and reflector)

3

3

U

U

U

UV solar radiation

0–0.30 μm

0–0.30 μm

V

V

V

Vehicle using gasoline produces

2.5 Kg of CO2 /liter

2.4 Kg of CO2 /liter

V group impurity concentration

1015

1015 cm3

Velocity of light, c

299,792,458 m/s

3 × 108 m/s

W

W

W

11

Wein’s displacement law

λT = 2897.6 μm K

3000 μm K

13

Wavelength radiation from the sun

0–30 μm

0–30 μm

1012

W

cm3

3 × 1012 W

Contents

1

2

General Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Greenhouse Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.1 Global Greenhouse Effect . . . . . . . . . . . . . . . . . . . . . . . . 1.1.2 Ecological Balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Microclimate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Solar Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.1 Solar Constant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Earth-Sun Angles and Conversion Factors . . . . . . . . . . . . . . . . . . 1.4.1 Earth-Sun Angles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.2 Conversion Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.3 Total Solar Radiation on Inclined/Tilted Surface with Any Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 3 4 5 5 6 7 7 10 15 19

Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Water Quality for Human Consumption . . . . . . . . . . . . . . . . . . . . 2.3 Water Quality for Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Electrical Conductivity (EC) . . . . . . . . . . . . . . . . . . . . . 2.3.2 Water Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 Sodium Adsorption Ratio (SAR) . . . . . . . . . . . . . . . . . . 2.3.4 Residual Sodium Carbonates (RSC) . . . . . . . . . . . . . . . 2.3.5 Turbidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.6 The pH of Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.7 The Color of Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.8 Alkalinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.9 Ion Toxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Water Quality for Aquaculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.1 Total Alkalinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.2 Ammonia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.3 Dissolved Oxygen (DO) . . . . . . . . . . . . . . . . . . . . . . . . .

21 21 23 24 26 28 28 29 29 29 30 30 30 31 31 32 33

xix

xx

Contents

2.4.4 Hardness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.5 Nitrite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.6 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.7 Carbon Dioxide (CO2 ) . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.8 Chlorine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.9 Hydrogen Sulfide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Instruments to Measure Water Quality of Aquaculture Water Pond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.1 Temperature Measurement . . . . . . . . . . . . . . . . . . . . . . . 2.5.2 Measuring Dissolved Oxygen (DO) of the Water . . . . 2.5.3 Measuring pH Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.4 Measuring Conductivity and Salinity . . . . . . . . . . . . . . 2.6 Experimental Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.1 Internal Uncertainty/Error . . . . . . . . . . . . . . . . . . . . . . . 2.6.2 External Uncertainty/Error . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Solar Cell and Photo-Voltaic Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Basics of Semiconductor and Solar Cells . . . . . . . . . . . . . . . . . . . 3.2.1 Doping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Fermi Level (E F ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 The p–n Junction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.4 The p–n Junction Characteristics . . . . . . . . . . . . . . . . . . 3.2.5 Photovoltaic Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.6 Solar Cell (Photovoltaic) Materials, Tiwari and Mishra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Basic Parameters of Solar Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 Overall Current (I ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.2 Short-Circuit Current (ISC ) . . . . . . . . . . . . . . . . . . . . . . . 3.3.3 Open-Circuit Voltage (V oc ) . . . . . . . . . . . . . . . . . . . . . . 3.3.4 Maximum Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.5 Fill Factor (FF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.6 Solar Cell Electrical Efficiency (ηec ) . . . . . . . . . . . . . . 3.4 Effect of Solar Cell Temperature (Tc ) on Its Electrical Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Generation of Solar Cell (Photovoltaic) Materials . . . . . . . . . . . . 3.5.1 First Generation of Solar Cell . . . . . . . . . . . . . . . . . . . . 3.5.2 Second Generation of Solar Cell . . . . . . . . . . . . . . . . . . 3.5.3 Third Generation of Solar Cell . . . . . . . . . . . . . . . . . . . . 3.5.4 Fourth Generation of Solar Cell . . . . . . . . . . . . . . . . . . . 3.6 Applications of Solar Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

34 35 36 37 38 38 39 40 40 41 42 44 44 45 48 49 49 50 50 52 52 53 54 55 57 57 58 58 59 60 60 62 64 66 66 66 66 67 71

Contents

xxi

4

Photovoltaic (PV) Module and Its Panel and Array . . . . . . . . . . . . . . . 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.1 Photo-Voltaic (PV) Module . . . . . . . . . . . . . . . . . . . . . . 4.1.2 Photo-Voltaic (PV) Panel and Array . . . . . . . . . . . . . . . 4.2 Materials of PV Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Single Crystal Silicon (c-Si) Solar Cells Module . . . . 4.2.2 Thin-Film PV Modules . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.3 Single and Multi-Junction PV Modules . . . . . . . . . . . . 4.2.4 Emerging and New Organic PV Module . . . . . . . . . . . 4.3 Design Parameters of PV (Module .......................... ) 4.3.1 Packing Factor β c of PV Module . . . . . . . . . . . . . . . . 4.3.2 Electrical Efficiency of PV Module . . . . . . . . . . . . . . . . 4.3.3 Electrical Load Efficiency . . . . . . . . . . . . . . . . . . . . . . . 4.4 Energy Balance Equations for PV Modules . . . . . . . . . . . . . . . . . 4.4.1 For Opaque (Glass to Tedlar) PV Module (Fig. 4.1a), Tiwari and Sodha . . . . . . . . . . . . . . . . . . . . . 4.4.2 For Semitransparent (Glass to Glass) PV Module (Fig. 4.1b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.3 Series and Parallel Combination of PV Modules . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

73 73 73 77 79 79 81 81 82 82 83 83 84 85

Concepts of Greenhouse and Its Application . . . . . . . . . . . . . . . . . . . . . 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1 Classification of Greenhouse . . . . . . . . . . . . . . . . . . . . . 5.2 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.1 Crop (Vegetables/flowers) Production . . . . . . . . . . . . . . 5.2.2 Aquaculture (Fish Production) . . . . . . . . . . . . . . . . . . . . 5.2.3 Aquaponics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.4 Solarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.5 Transparent Plastic mulching . . . . . . . . . . . . . . . . . . . . . 5.2.6 Solar Greenhouse Drying . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Greenhouse Integrated Photo-Voltaic Thermal (GiSPVT) System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

99 99 99 102 102 103 106 108 110 111

5

6

Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic Thermal System (GiSPVT) . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Low Technology/Low Cost Greenhouses . . . . . . . . . . . . . . . . . . . 6.2.1 Wooden/Bamboo Base Greenhouse . . . . . . . . . . . . . . . 6.2.2 PVC Pipe Structure Greenhouse . . . . . . . . . . . . . . . . . . 6.3 Medium Technology Greenhouses . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.1 Quonset Greenhouse . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.2 Even Type Greenhouse . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.3 Ridge and Furrow Type Greenhouse . . . . . . . . . . . . . . . 6.4 High Technology (Hi-Tech) Greenhouses . . . . . . . . . . . . . . . . . . .

85 89 92 96

113 117 119 119 121 121 121 123 123 125 129 130

xxii

Contents

6.5

Greenhouse Integrated Semi-transparent Photo-Voltaic Thermal (GiSPVT) System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.1 Working Principle of GiSPVT . . . . . . . . . . . . . . . . . . . . 6.5.2 Layout Plan of GiSPVT . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.3 Foundation for GiSPVT System . . . . . . . . . . . . . . . . . . 6.5.4 Semi-transparent PV Module South Roof . . . . . . . . . . 6.5.5 Medium Tech GiSPVT . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6 Photo-Voltaic System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6.2 Description Specifications of Each Component . . . . . 6.6.3 Description of Solar Power Plant Generation System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7 Junction Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8 AC Distribution Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.9 Cabling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.10 Fire-Fighting System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.11 Data Logger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.11.1 Erection and Commissioning Phase . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Cultivation of Vegetables in Winter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1.1 Root Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1.2 Climatic Controlled Condition . . . . . . . . . . . . . . . . . . . . 7.2 Basic Parameters of Summer and Winter Vegetables Crop . . . . . 7.2.1 Bottle Gourd (Lauki) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.2 French Beans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.3 Tomato . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.4 Capsicum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.5 Cucumber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.6 Broccoli . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Root Media for Planting Vegetables and Temperature of Soil, Inside Medium Tech Greenhouse Room Air . . . . . . . . . . 7.3.1 Root Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.2 Soil Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.3 Greenhouse Room Air Temperature . . . . . . . . . . . . . . . 7.3.4 Solar Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.5 Relative Humidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.6 Electronic Weighing Machine . . . . . . . . . . . . . . . . . . . . 7.3.7 Harvesting of Vegetables . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Cultivation of Vegetables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.1 Sowing of Seeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.2 Transplantation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.3 Growing of Various Planted Vegetables . . . . . . . . . . . . 7.4.4 Maintenance of Inside Greenhouse . . . . . . . . . . . . . . . .

131 131 132 133 135 137 139 139 141 141 147 148 148 149 149 149 154 155 155 157 157 157 157 158 159 159 160 161 162 163 164 164 164 165 165 166 166 166 167 169 170

Contents

7.4.5 Cultivation of Vegetables . . . . . . . . . . . . . . . . . . . . . . . . 7.4.6 Fruiting of Vegetables . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5 Measurements of Climatic Parameters . . . . . . . . . . . . . . . . . . . . . . 7.6 Harvesting of Vegetables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.7 Electrical Output (Generation Off-Grid) . . . . . . . . . . . . . . . . . . . . 7.8 Conclusions and Recommendations . . . . . . . . . . . . . . . . . . . . . . . . 7.8.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.8.2 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.8.3 Suggestions to Farmers . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Thermal Modeling of Greenhouse Integrated Semi-transparent Photo-Voltaic Thermal (GiSPVT) System: Quasi-Steady-State Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Earth Air Heat Exchanger for Thermal Heating/Cooling . . . . . . 8.3 Working Principle of Greenhouse Integrated Semi-transparent Photo-Voltaic Thermal (GiSPVT) System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4 Basic Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.1 Conduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.2 Convection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.3 Radiative Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.4 Mass Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.5 Total Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.6 An Overall Heat Transfer Coefficient . . . . . . . . . . . . . . 8.5 General Thermal Modeling of Quonset GiSPVT . . . . . . . . . . . . . 8.6 Thermal Modeling of the Uneven GiSPVT . . . . . . . . . . . . . . . . . . 8.6.1 Analytical Expression for Water pond’s Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6.2 Characteristic Equation . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6.3 Exergy Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6.4 Methodology for Numerical Computation for Uneven GiSPVT Greenhouse . . . . . . . . . . . . . . . . . . 8.6.5 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6.6 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.7 Design of Earth Air Heat Exchanger (EAHE) . . . . . . . . . . . . . . . 8.7.1 Optimization of Length of EAHE . . . . . . . . . . . . . . . . . 8.7.2 Validation of Experimental Results . . . . . . . . . . . . . . . . 8.7.3 Optimization of Number of Risers and Headers for a Given Number of Air Exchange . . . . . . . . . . . . . . 8.7.4 Final Design of EAHE Integration with Quonset Greenhouse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.7.5 Final Recommendations . . . . . . . . . . . . . . . . . . . . . . . . .

xxiii

170 170 174 175 177 178 178 182 183 185

187 187 189

192 193 193 194 197 198 199 200 202 207 208 215 218 220 224 226 227 227 228 229 231 232

xxiv

Contents

8.8

Thermal Modeling of an Integration of EAHE with Room Air of GiSPVT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 9

Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2 Classification of Solar Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2.1 Open Solar (Sun) Drying . . . . . . . . . . . . . . . . . . . . . . . . 9.2.2 Controlled Environment Solar Drying System . . . . . . 9.3 Working Principle of Various Design of Solar Dryers . . . . . . . . . 9.3.1 Solar Cabinet Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3.2 Greenhouse Integrated Semitransparent PV Thermal (GiSPVT) Dryer . . . . . . . . . . . . . . . . . . . . . . . . 9.3.3 Active Indirect Solar Dryer . . . . . . . . . . . . . . . . . . . . . . 9.4 Heat and Mass Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4.1 Convective Heat Transfer Coefficient . . . . . . . . . . . . . . 9.4.2 Evaporative Heat Transfer Coefficient . . . . . . . . . . . . . 9.4.3 Evaluation of C and N Under Forced Mode of Operation for Indoor Simulation . . . . . . . . . . . . . . . . 9.5 Thermal Modeling of Single-Slope Fully Covered GiSPVT Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10 Thermal Modeling of Greenhouse Integrated Semi-transparent Photo-Voltaic Thermal (GiSPVT) System: A Periodic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1.1 Steady-State Thermal Analysis . . . . . . . . . . . . . . . . . . . 10.1.2 Transient Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1.3 Quasi-steady-State Condition . . . . . . . . . . . . . . . . . . . . . 10.1.4 Periodic Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3 Design of Uneven GiSPVT with Partition with Porous Green Jute Net . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4 Periodic Thermal Mathematical Modeling of GiSPVT . . . . . . . . 10.4.1 Time-Independent Matrix . . . . . . . . . . . . . . . . . . . . . . . . 10.4.2 Time-Dependent Matrix . . . . . . . . . . . . . . . . . . . . . . . . . 10.4.3 An Overall Exergy of GiSPVT . . . . . . . . . . . . . . . . . . . 10.4.4 Thermal Load Leveling . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4.5 Decrement Factor (DF) . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4.6 Computational Methodology . . . . . . . . . . . . . . . . . . . . . 10.5 Numerical Results and Discussions . . . . . . . . . . . . . . . . . . . . . . . . 10.6 Conclusions and Recommendations . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

245 245 247 248 248 250 252 252 264 265 265 268 269 274 280

283 283 283 284 285 285 287 289 290 296 297 299 299 299 300 300 306 309

Contents

xxv

11 Application of Photovoltaic Thermal (PVT) Technology . . . . . . . . . . . 11.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Aquaculture and Hydroponics/Aquaponics . . . . . . . . . . . . . . . . . . 11.2.1 The Freshwater Aquaculture Systems . . . . . . . . . . . . . . 11.2.2 The Brackish Water Aquaculture System . . . . . . . . . . . 11.2.3 The Marine Aquaculture System . . . . . . . . . . . . . . . . . . 11.2.4 Advantages and Disadvantages of Aquaculture . . . . . . 11.2.5 Experimental GiSPVT Water Pond . . . . . . . . . . . . . . . . 11.3 Thermal Modeling of Aquaculture Water Pond . . . . . . . . . . . . . . 11.3.1 Analytical Expressions for Water Pond Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3.2 Electrical Power of GiSPVT . . . . . . . . . . . . . . . . . . . . . 11.3.3 Monthly Average Electrical Output . . . . . . . . . . . . . . . . 11.3.4 The Yearly Electrical Output . . . . . . . . . . . . . . . . . . . . . 11.3.5 Thermal Energy of GiSPVT . . . . . . . . . . . . . . . . . . . . . . 11.3.6 Energy Matrices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3.7 Methodology for Computation . . . . . . . . . . . . . . . . . . . . 11.3.8 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 11.4 The BiSPVT Passive Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.5 PVT Water Collectors Connected in Series . . . . . . . . . . . . . . . . . . 11.5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.5.2 System Description of N-PVT-CPC . . . . . . . . . . . . . . . 11.5.3 Analytical Expression . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.6 SPVT Air Collectors Connected in Series . . . . . . . . . . . . . . . . . . . 11.6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.6.2 Working Principle of SPVT Air Collector . . . . . . . . . . 11.6.3 Thermal Modeling of SPVT Air Collector, Tiwari et al. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.6.4 New Mass Flow Rate Factor at nth SPVT Air Collector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.6.5 Expression for the Rate of Thermal Energy of N-SPVT Air Collector Connected in Series . . . . . . 11.6.6 Electrical Efficiency of nth SPVT Air Collector . . . . . 11.6.7 Methodology for Numerical Computation . . . . . . . . . . 11.6.8 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 11.7 The PVT Air Collector for Room Air/Space Heating of Building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.8 PVT Water Heating System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.9 The PVT Integrated Biogas Plant . . . . . . . . . . . . . . . . . . . . . . . . . . 11.10 PVT Integrated Swimming Pool . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.10.1 Methodology to Evaluate the Variation of m ˙f with Time and Electrical Power . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

313 315 316 318 318 318 319 320 322 322 325 326 326 326 327 329 330 337 337 337 340 341 353 353 355 357 359 360 361 363 364 368 372 375 375 379 383

xxvi

Contents

Appendix A: Conversion of Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387 Appendix B: Specification of Solar Cell Materials . . . . . . . . . . . . . . . . . . . . 393 Appendix C: Physical Properties of Some Materials . . . . . . . . . . . . . . . . . . 397 Appendix D: Program of Calculation of Solar Radiation and Solair Temperatures on Building Surfaces . . . . . . . . . . . . . . . . . . . . . 403 Appendix E: Fourier Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 Appendix F: Matlab Code for Evaluating Fourier Coefficients . . . . . . . . . 417 Appendix G: Matrix Inversion Code for Real and Complex . . . . . . . . . . . 419 Appendix H: Steam Table for Saturation Vapor Pressure . . . . . . . . . . . . . . 421

About the Author

Prof. Gopal Nath Tiwari hails from Sagarpali, Ballia, in the state of Uttar Pradesh, India. After completing his basic primary education from Ballia, he moved to Varanasi for higher education and completed his studies from Banaras Hindu University (BHU). Later, he joined IIT Delhi in the year 1977 under the mentorship of Padma Shri Prof. Mahendra Singh Sodha, who introduced Prof. Tiwari to solar energy research. Professor Tiwari was superannuated in June 2016. To his credit, he has published more than 700 research papers with h-index of 100 and supervised more than 100 Ph.D. students. After superannuation, he moved back to his hometown Ballia to implement the work done at IIT Delhi and provide basic education to nearby children through BERS Public School. He has also established a “Sodha Energy Research Park” at Margupur in Ballia (UP), to impart energy education to locals.

xxvii

Nomenclature with Units and Notation

Aam AC Arm Aac Arc b bo CdTe CE c-Si Cf DF DC DO EAHE g F' FR FF GiSPVT GHG h hi hi ' ho hpf Ib I(t)

Aperture area of SPV-CPC module (m2 ) Alternative current Receiver/absorber area of PV module (m2 ) Aperture area of collector (m2 ) Receiver area of collector (m2 ) Breadth of receiver (m) Breadth of aperture area (m) Cadmium telluride Controlled environment Crystalline silicon Specific heat of fluid (J/kg K) Decrement factor Direct current Dissolved oxygen Earth air heat exchanger Acceleration due to gravity, 9.8 m/s2 Collector efficiency factor Flow rate factor Fill factor of PV module Greenhouse integrated semitransparent photovoltaic thermal Greenhouse gases Heat transfer coefficient (W/m2 K) Heat transfer coefficient for space between the glazing and absorber plate (W/m2 K) Heat transfer coefficient from bottom of PVT to ambient air (W/m2 K) Heat transfer coefficient from top of glass cover (W/m2 K) Heat transfer coefficient from absorber plate to working fluid (W/m2 K) Solar beam radiation (W/m2 ) Total solar radiation (W/m2 ) xxix

xxx

Kg Ki Kp Lg Lrm Lam Li Lp m˙ f N PF PF1 PF2 pH P(T) PV PVT q˙ Q˙ Q˙ uth N th R RCC Per unit Kelvin (K) Ta Tc Tf Tfi Tfo TfoN U UA Tp T0 TLL UL,m UL,c Utc,a Utc,p , Utc,f

Nomenclature with Units and Notation

Thermal conductivity of glass (W/m K) Thermal conductivity of insulation (W/mK) Thermal conductivity of absorber plate (W/mK) Thickness of glass cover (m) Length of receiver of PV module (m) Length of aperture of PV module (m) Thickness of insulation (m) Thickness of absorber plate (m) Mass flow rate of working fluid (kg/m2 ) Number of SPVT collectors Packing factor of PV module Penalty factor due to glass covers of SPV module Penalty factor due to absorber plate below PV module Potential of Hydrogen Partial vapor pressure at temperature, T·N/m2 Photovoltaic Photovoltaic thermal The rate of heat transfer per m2 , W/m2 The rate of heat transfer, W The rate of useful thermal energy (W) Conversion factor for solar radiation Re-enforced concrete cement Per unit degree Celsius (K−1 or °C−1 ) Ambient air temperature (°C) Solar cell temperature (°C) Working fluid temperature (°C) Working fluid inlet temperature (°C) Working fluid outlet temperature (°C) Fluid outlet temperature at the end of Nth PVT-CPC collector (°C) An overall heat transfer coefficient, (W/m2 K) The rate of hear transfer W/K Absorber plate temperature (°C) Reference cell temperature for optimum cell efficiency, i.e., 25 °C Thermal load leveling Overall heat loss coefficient from PV module to ambient air (W/m2 K) Overall heat loss coefficient from glazing to ambient air (W/ m2 K) Overall heat loss coefficient from cell to ambient air (W/ m2 K) Overall heat loss coefficient from cell to plate/absorber (W/ m2 K)

Nomenclature with Units and Notation

Utp,a

Overall heat loss coefficient from absorber plate to ambient air (W/m2 K) Air/wind velocity (m/s) World war

V WW

Greek Letters α βc β0 ε γ ρ σ τ ηc ηm ηi (ατ )eff μm ν λ

Absorptivity Packing factor Temperature coefficient of electrical efficiency Emissivity of the surface Relative humidity, % Reflectivity Stefan’s Boltzmann constant Transmittivity of glass cover Electrical efficiency of solar cell Electrical efficiency of PV module Instantaneous thermal efficiency Product of effective absorptivity and transmittivity Micrometer Frequency Wavelength

Subscripts a b c d eff en ex ext ew f fi fo g i k

xxxi

Ambient air Beam radiation Solar cell/collector Diffuse radiation Effective Energy Exergy Extraterrestrial Evaporation from free water surface Working fluid Inlet working fluid Outlet working fluid Glass cover Instantaneous Conduction

xxxii

m ov p r sc T

Nomenclature with Units and Notation

PV module Overall Absorber plate Reflected radiation Solar constant Total

Chapter 1

General Introduction

1.1 Greenhouse Effect We know that Earth is moving around Sun in elliptical path. Further, Earth also rotates along its axis. Since the observers (human being) are located on the Earth and hence the observers feel that the Sun is moving around Earth (us), day and night are observed. The Earth consists of tectonic plates. Tectonic plates are pieces of Earth’s crust and uppermost mantle. The tectonic plates are around 100 km thick, and it consists of two principal types of material: oceanic crust (3/4 of earth) and continental crust (1/4 of earth). It is believed that the ocean crust and continental crust were in the form of ice and desert land. The tectonic plates were supposed to be broken and moving with respect to each other’s, and between two plates, there is crack for escaping of the various natural gases [methane (CH4 ), carbon dioxide (CO2 ), carbon monoxide (CO), oxygen (O2 ) https://en.wikipedia.orgwiki/Nitrogen nitrogen (N2 ), hydrogen sulfide (H2 S), ozone (O3 ), water vapor (H2 O), and helium] available beneath the Earth. These gases being light weight moved toward Sun and became stagnate between Sun and Earth, Fig. 1.1. These gases form a layer between Sun and Earth, and it may be due to gravitational forces. Solar scientists probably refer this layer of gases as an Atmosphere for its own purposes, Tiwari et al. [1]. It is also a porous media. The Sun, a perfect sphere of hot plasma, is located at the center of the Solar System. The Sun is source of all renewable energy directly and non-renewable energy (fossil fuel) indirectly. It is responsible for all living organism on the planet Earth including human being. The diameter and the mass of Sun are 109 and 330,000 times higher than that of Earth. It accounts for about 99.86% of the total mass of the Solar System. It consists of about 73% and 25% hydrogen and helium respectively, and the rest is heavy gases, namely oxygen, carbon, neon, and iron. The energy from the Sun in the form of heat (electromagnetic waves) and light (photons) energy comes from a nuclear fusion reaction at temperature of about 1.5 × 107 K (15 million Kelvin) which is happening inside the core of the Sun. The 99% of this energy is generated at core of SUN. During nuclear fusion at high pressure and temperature in the sun’s core © Bag Energy Research Society 2023 G. N. Tiwari, Advance Solar Photovoltaic Thermal Energy Technologies, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4993-9_1

1

2

1 General Introduction

Reflected short wave length radiation

SUN

CO

CO2

Atmosphere

CH4

Extraterrestrial O3

O2

H2O

Earth

Terrestrial

Reflected long wave length radiation

a

Solar radiation, hᵞ

(H2O)

C6H12O6 (CO2)

(H2)

b Fig. 1.1 a Basic working principle of global greenhouse effect. b Photosynthesis process between plant and photon of solar radiation

cause nuclei of 4-Hydrogen atom (4.03130 AMU) to separate to form one helium atom (4.00268 AMU) which mass are less than two hydrogen molecules/ 4-hydrogen atom (1 Atomic Mass Unit (AMU) equals 1.67 × 10−27 kgs). The remaining mass is converted into energy as E = mc2 = (2.8 × 10–6 kgs) × (3 × 108 m/s)2 = 2.6 × 1011 J (Einstein’s theory). The Sun acts as a black body at temperature of about 6000 K, and it radiates energy in the form of electromagnetic (e/m) waves as well as photon (E = hν) ranging wavelength of 0 to ∞ μm as Solar Energy/radiation, Tiwari [2]. Electromagnetic wave and photon of solar energy provide us thermal energy as well responsible for photosynthesis to the living organism including plants. Atmosphere which consists of natural gases as mentioned above has very unique two properties namely.

1.1 Greenhouse Effect

3

(i) It transmits only short wavelength radiation coming from Sun between 0.3 μm and 3 μm and (ii) It behaves as an opaque for the rest of radiation having wavelength either below 0.3 μm and above 3 μm. Sometimes, atmosphere is also referred as filter of required solar radiation coming from Sun for living organism. The atmosphere can also be referred as transparent layer to short wavelength of solar radiation and opaque to long wavelength radiation. The regions between the Sun and the atmosphere and between the atmosphere and the planet Earth are referred as extraterrestrial and terrestrial region respectively.

1.1.1 Global Greenhouse Effect There is strong relation between the Sun, the Atmosphere and the planet Earth for survival of all living organism on the planet Earth. For example, the short wavelength radiation coming from the Sun is partially reflected, absorbed, and transmitted through atmosphere and reaches the Earth as shown in Fig. 1.1. The Earth absorbed a part of short wavelength radiation after reflection from the Earth and then Earth’s temperature increases and then Earth emits long wavelength radiation due to Wien’s displacement law (λT = 3000 μm.K). This long wavelength radiation (thermal energy) emitted from the Earth is blocked by atmosphere due to its second property as mentioned above. Hence, the air in terrestrial region is heated fast due to its low heat capacity and the temperature of air rises. Now, if the temperature above ice of oceanic continent rises, the ice starts melting and formed the water which is in steady state. Now, we also consider the radiation coming from Sun in the form of photon (E = hν) contains energy much higher than the binding energy of H2 O. If the photon strikes H2 O, then hydrogen (H2 ) and oxygen (O2 ) are separated. After that oxygen (O2 ) is released to environment to sustain clean environment (209.46 ppm, Table 1.1) which is the basic need of human being for survival. Further, the hydrogen (H2 ) reacts with carbon dioxide (CO2 ) of environment, (412 ppm, Table 1.1), to make it hydrocarbon (mass) in the form of algae (biomass). So, the algae are the first living organism taken birth on the planet earth. This reduces the level of carbon dioxide (CO2 ) in environment. This process provides additional O2 and reduces CO2 in environment to sustain it. The green plant which contains maximum H2 O consumes CO2 released either by human being/ industries/environment and the plant release O2 for living organism including human being for good health as shown in Fig. 1.1b. This also helps to clean environment, and process is known as photosynthesis. Since the color of algae is green and atmosphere and earth under consideration acts as roof and floor hence this phenomenon is known as global greenhouse effect. From algae formation to human being, it might have taken many million years. It is a history, Tiwari [3]. The chemical reaction of photosynthesis between plant and photon of solar radiation is given by

4

1 General Introduction

Table 1.1 Major constituents of dry air, by mole fraction [8] Mole fraction(A)

Gas Name

Formula

In ppm(B)

In %

Nitrogen

N2

780,84

78.084

Oxygen

O2

209,46

20.946

Argon

Ar

9,340

0.9340

Carbon dioxide (August,

2021)(C)

CO2

416

0.0416

Neon

[12]

Ne

18.18

0.001818

Helium

He

5.24

0.000524

Methane

CH4

1.87

0.000187

Krypton

Kr

1.14

0.000114

H2 O

0–30,000(D)

0–3%(E)

Not included in above dry atmosphere Water vapor(D)

Notes (A) Mole fraction is sometimes referred to as volume fraction; these are identical for an ideal gas only (B) ppm: parts per million by molecular count (C) The concentration of CO has been increasing in recent decades 2 (D) Water vapor is about 0.25% by mass over full atmosphere (E) s

6CO2 + 6H2 O + solar radiation(Photon, h ν) → C6 H12 O6 + 6O2 .

(1.1a)

1.1.2 Ecological Balance Ecology, a branch of biology, is considered to have interactions among all living organisms including human being and their biophysical environment. Till World War I and II, there are eco-balance between biophysical environment and human being (one of living organism). Broadly, to maintain clean environment, one must have at least about 30% forestation. However, we, all human being, are responsible to disturb eco-system to fulfill our greed through fast growth of industrialization and population after World War II.

1.3 Solar Radiation

5

1.2 Microclimate Similar to two properties of atmosphere, most of transparent materials including UV-polythene and glass cover also behave as a transparent to short wavelength and opaque to long wavelength radiation. A house of any shape is constructed with transparent cover material; it is referred as greenhouse/glass house to maintain microclimate which affects inside (i) air temperature, (ii) relative humidity and (iii) plant leaf temperature by the solar energy transmission from the transparent cover material. Further, microclimate of greenhouse can be controlled to an optimum level by using either additional heating/cooling throughout the cultivation period to increase the productivity by several times per unit area.

1.3 Solar Radiation The basic source of solar radiation is Sun. It has a diameter (D = 2R) of 1.39 × 109 m and located at an average distance of 1.5 × 1011 m from the Earth. It is well known that 99% of the sun’s energy is created in spherical region between 0 and 0.23R at center with the temperature (T) of about (8 − 40) × 106 K. Energy generated at center core of Sun is due to fusion reactions as given below, Tiwari et al. [1]: H2 + H2

1.5×107 K Θ

=

He + 2.6 × 1011 (Joules)

(1.1b)

( ) The produced energy E = mc2 at core of center is transferred to the outer surface by convection. Solar radiation coming from the Sun is classified as a heat (thermal energy) in the form of electromagnetic waves as well as light/photons (E = hν) respectively. The average wavelength of radiation emitted by any hot surface is governed by Wein’s displacement law as λmax .T = 2897.8 ≈ (3000)μm K

(1.2)

The derivation of Eq. (1.2) can be seen in the book by Tiwari [2]. Example 1.1 Evaluate the wavelength radiation emitted from greenhouse floor at temperature of 288 K(15 ◦ C). Solution From Eq. (1.2), one gets, λ = 2897.8/288 = 10.06 μm. This wavelength radiation will be blocked by greenhouse canopy cover due to second properties of transparent cover.

6

1 General Introduction

1.3.1 Solar Constant The solar constant (Isc ) is defined as the solar radiation/flux measured per unit area (W/m2 ) normal to surface in extraterrestrial region at mean Sun–Earth distance. Its numerical value is 1367 W/m2 . Since, the Earth moves around the Sun in elliptical orbit around the year with variation of 1.7% in distance between Sun and Earth. The solar intensity/radiation/ irradiance in extraterrestrial region variation with nth day of year is expressed as, Duffie and Beckmann [4] Iext = Isc [1.0 + 0.033 cos(360n/365)]

(1.3a)

where the value n should be counted from January 1 of the year. Example 1.2 Evaluate extraterrestrial solar radiation for value of solar constant = 1367 W/m2 on June 22 and December 21, 2020, respectively. Solution From Eq. 1.3, one has For June 22, 2020, n = 173, Iext = 1367[1.0 + 0.033 cos(360 × 173/365)] = 1322.49 W/m2 For December 21, 2020, n = 355, Iext = 1367[1.0 + 0.033 cos(360 × 355/365)] = 1411.43 W/m2 One can see that the extraterrestrial radiation in June is more than winter due to closeness between Sun and earth. In extraterrestrial region, all solar radiation is direct/beam radiation and in terrestrial region, some of solar radiation has no direction due to its scattering from bottom of atmosphere by aerosols and other particulates present in atmosphere and hence it has two components, namely. Direct/Beam radiation (Ib ): It is normal component of the solar radiation incident on horizontal surface,W/m2 . Diffuse radiation (Id ): It is scattered solar radiation without any direction incident on horizontal surface,W/m2 . The total/global radiation (I): It is the sum of the direct/ beam and diffuse radiation on horizontal surface, W/m2 . It is measured by any pyranometer on horizontal surface. The total radiation is also known as global radiation/insolation. The diffuse radiation is also measured by same instrument with help of shading ring. The difference between total and diffuse radiation is a direct/beam radiation. A direct/beam radiation can be evaluated as follows:

1.4 Earth-Sun Angles and Conversion Factors

Ib = I − Id

7

(1.3b)

1.4 Earth-Sun Angles and Conversion Factors Greenhouse has many shapes with transparent material including transparent plastic, semi-transparent photo-voltaic module (SVPM) or combination of both. In order to obtain solar radiation on any inclined greenhouse cover with any orientedon, there are many methods available, Tiwari and Mishra [5], Tiwari et al. [1]. However, we will discuss one of the simplest methods, for known hourly variation of direct/beam (Ib ) and diffuse (Id ) radiation on horizontal surface, known as Liu and Jordon formula [6]. They have developed a following relation between incident angle (θi ) of direct/ beam radiation in terms of earth-sun angles as cos θi = (cos ϕ cos β + sin ϕ sin β cos γ ) cos δ cos ω + cos δ sin ω sin β sin + sin δ(sin ϕ cos β − cos ϕ sin β cos γ

(1.4)

where θ i is unknown incidence angle between incident radiation and normal to the inclined surface with any orientation, Duffie and Beckman (1991). This incidence angle depends on earth-sun angles which will be discussed in next section.

1.4.1 Earth-Sun Angles Followings are Earth-Sun angles: Latitude angle: φ is the latitude angle of a location of greenhouse on Earth’s surface. Inclination angle: β is an inclination angle of inclined surface with any orientation receiving solar radiation. Surface azimuth angle: γ is surface azimuth angle which shows the orientation of surface. It is an angle made between the line due south (Northern Hemisphere) and projection of normal to the inclined surface on the horizontal plane. In Northern Hemisphere, γ is negative for the projections in east of south and positive for the projections falling in west of south and vice versa in Southern Hemisphere. The values of γ for Northern Hemisphere with some orientations are given in Table 1.2. Declination angle: δ is declination angle and its expression for nth day of year is expressed as

8

1 General Introduction

Table 1.2 Surface azimuth angle (γ ) for various orientations in Northern Hemisphere

Surface orientation

γ

Sloped toward south

0◦

Sloped toward north

180◦

Sloped toward east

−90◦

Sloped toward west

+90◦

Sloped toward southeast

−45◦

Sloped toward southwest

+45◦

[ δ = 23.45 sin

360 (284 + n) 365

] (1.5)

Example 1.3 Calculate declination angle for Example 1.2. Solution From Eq. 1.5, one has For June 22, 2020, n = 173, [ δ = 23.45 sin

] 360 (284 + 173) = 23.4480 365

For December 21, 2020, n = 355, ] 360 δ = 23.45 sin (284 + 355) = −23.44980 365 [

This shows that declination angle varies between +23.4480 and −23.44980 over the year. Hour angle: ω is hour angle between (i) projections of Sun’s rays (solar meridian) and line south–north through center and (ii) the angular displacement of Sun from local meridian. South–north line is also referred as line due south. Hour angle corresponding to one hour is 15◦ , and developed relation is given by ω = (ST − 12)15◦

(1.6)

where ST is local solar time. The total hour angle from sunrise to sunset is (2ωs ). The ±ωs corresponds to hour angle with reference to sunrise and sunset respectively. The values of hour angle, ω based on Eq. 1.6 in Northern Hemisphere, are listed in Table 1.3. Zenith angle: θz is zenith angle between Sun’s rays and line perpendicular to horizontal plane. In Eq. 1.4, when β = γ = 0, then θi = z . . From Eq. 1.4, one can have

1.4 Earth-Sun Angles and Conversion Factors

9

Table 1.3 Value of hour angle with time of the day (For Northern Hemisphere) Time of the day (hours)

6

7

8

9

10

11

12

Hour angle (degree)

−90◦

−75◦

−60◦

−45◦

−30◦

−15◦

0◦

Time of the day (hours)

12

13

14

15

16

17

18

Hour angle (degree)

0◦

+15◦

+30◦

+45◦

+60◦

+75◦

+90◦

cos θz = sin δ sin ϕ + cos δ cos ϕ cos ω

(1.7)

Example 1.4 Determine total hour angle from sun rise and noon (ω S ). Solution Since zenith angle (θz ) at noon will be 90 ° and hence the total hour angle from sun rise and noon (ω S ) can be evaluated from Eq. 1.7 by substituting θz = 90 ° , Then 0 = sin δ sin ϕ + cos δ cos ϕ cos ω S or, ω S = cos−1 (− tan ϕ tan δ) Similarly, the total sun rise hour from noon to sunset will be same. So the total sun shine hours between sun rise and sun set will be 2 ω S . Example 1.5 Evaluate total sun shine hour angle for Example 1.2 at latitude of New Delhi (30 ° ). Solution From Examples 1.2 and 1.3, one has For June 22, 2020, n = 173 and δ = 23.448◦ , so 2ω S = 2 cos−1 (− tan ϕ tan δ) = 2 cos−1 (− tan 30 × tan 23.448) = 2 cos−1 (−0.577 × 0.4337) = 2 cos−1 (−0.2502) = 104.48◦ For December 21, 2020, n = 355, δ = −23.4498◦ 2ω S = 2 cos−1 (− tan 30 × tan(−23.4498)) = 2 cos−1 (−0.577 × −0.4338) = 151.009◦ Altitude angle: α is an altitude or solar altitude angle between horizontal plane and sun’s rays. Also α = 90 − θ Z . Numerical value is considered positive and negative for slope toward south and north respectively.

10

1 General Introduction

Sunshine hour (N): The total duration in hours of sun’s movement from sunrise to sunset is given as N=

2 2ω S = cos−1 (− tan ϕ tan δ) (Example 1.4) 15 15

(1.8)

Here 1 hour = 150 [Appendi x − A] and ωs = cos−1 (− tan ϕ tan δ) can be obtained by using the condition of β = γ = 0, then θi = z = 90 in Eq. 1.4. Example 1.6 Evaluate total sunshine hours (N) for Example 1.5. Solution From Example 1.5, we have For June 22, 2020, n = 173, δ = 23.448◦ and 2ω S = 2 cos−1 (−0.2502) = 104.48◦ . By using Eq. 1.8, the total sunshine hours will be N=

2ω S 104.48◦ = = 6.96 hours 15 15

For December 21, 2020, n = 355, δ = 2 cos−1 (−0.577 × −0.4338) = 151.009◦ By using Eq. 1.8, the total sunshine hours will be N=

−23.4498◦ and 2ω S

=

151.009◦ 2ω S = = 10.07 hours 15 15

This shows that sunshine hour in summer is much more than winter condition. This significantly depends upon latitude of place.

1.4.2 Conversion Factors For any inclined surface with any orientation, there will be three type of solar radiation, namely (i) beam, (ii) diffuse, and (iii) reflected from horizontal surface and surrounding. Therefore, there are three conversion factors namely, beam conversion factor (Rb ), diffuse conversion factor (Rd ), and reflected conversion factor (Rr ) for solar radiations from horizontal surface to an inclined surface. These conversion factors will convert the beam and diffuse radiations from horizontal surface to an inclined surface. These are as follows: For beam radiation: The conversion factor for beam radiation (Rb ) is defined ( as ) the ratio of beam radiation incident on an inclined surface with any orientation Ib' , W/m2 to that on a horizontal surface W/m2 .

1.4 Earth-Sun Angles and Conversion Factors

11

The flux of beam radiation incident on horizontal (Ib ) and an inclined surface (Ib' ) is given by Ib = I N cos θ Z

(1.9a)

Ib' = I N cos θi

(1.9b)

and,

where θz and θi are the angles of incidence on the horizontal and inclined surfaces respectively and I N is the intensity of normal irradiance/solar radiation incidence to the inclined surface given by I N = Iext exp[−(m.ε.TR + α)] with m(air mass)

(1.9c)

[ ]−1 m = cos θ Z + 0.15 × (93.885 − θ Z )−1.253 , ε. = 0.9 (emissivity), the values of TR and α are given in Table 1.4 for northern part of India for different month and weather condition, Singh and Tiwari [7], Ahmed and Tiwari [8]. The diffuse radiation can be obtained as Id =

1 (Iex − I N ) cos θ Z 3

(1.9c)

From Eq. 1.9, one can define conversion factor (Rb ) for beam radiation as, Rb =

Ib' cos θi = Ib cos θz

(1.10)

Depending on the orientation of inclined surface, the expression for cos θi and cos θz can be obtained from Eqs. (1.4) and (1.7) respectively. For diffuse radiation: The conversion factor for diffuse radiation (Rd ) is defined as the ratio of diffuse radiation incident on an inclined surface, W/m2 to that on a horizontal surface, W/m2 . Lack of any established method for finding the distribution of diffuse radiation over the sky makes its estimation very difficult. But it can be estimated by considering the sky as the isotropic source of diffuse radiation. For a tilted surface at an angle β from the horizontal surface, the conversion factor for diffuse radiation is expressed as follows: Rd =

1 + cos β 2

(1.11)

Here it clears that (i) for β = 0, Rd = 1, means all diffuse radiation falls on horizontal surface which is directly exposed to sky and (ii) for β = 90◦ , vertical surface, Rd = 21 means both surface receiving equal diffuse radiation

D Hazy condition

C Cloudy condition

B Partially cloud Y

A Clear day

Type of day

7.47

0.96

α

0.27

TR

5.88

α

0.15

α

TR

2.28

0.07

α

TR

2.25

January

TR

Parameters▼

Month►

1.04

8.97

0.37

6.36

0.13

2.78

0.10

2.79

February

0.24

10.77

0.37

6.11

0.14

2.89

0.17

2.85

March

0.07

11.18

0.31

7.77

0.17

3.15

0.23

2.72

April

0.07

13.69

0.07

9.20

0.16

5.44

0.16

3.54

May

0.61

12.47

0.06

10.54

0.20

4.72

0.28

2.47

June

1.26

8.21

0.41

7.13

0.24

5.58

0.37

2.73

July

1.10

8.58

0.51

7.97

0.18

5.43

0.41

2.58

August

0.84

9.40

0.49

5.51

0.31

3.23

0.29

2.53

September

1.29

7.24

1.26

5.01

0.22

4.56

0.47

1.38

October

1.43

4.30

1.06

4.93

1.14

0.19

0.59

0.62

November

1.70

4.02

0.64

3.23

0.42

1.83

0.54

0.72

December

Table 1.4 Approximate numerical value of turbidity factor, TR and attenuation, α in Eq. 1.9c for northern part of India, Singh and Tiwari [7], Ahmed and Tiwari [8]

12 1 General Introduction

1.4 Earth-Sun Angles and Conversion Factors

13

For reflected solar radiation: The reflected solar radiations are the radiations reflected from ground and other objects near surface of interest. Assuming reflected radiations to be diffuse and isotropic, the conversion factor for reflected solar radiation (Rr ) is expressed by: Rr =

1 − cos β 2

(1.12)

Here too it clears that (i) for β = 0, Rr = 0, means there is no reflected radiation on horizontal surface as expected which is directly exposed to sky and (ii) for β = 90◦ , vertical surface, Rr = 21 means both surface receiving equal reflected radiation. It may be mentioned here that both the beam and diffuse components of solar radiation undergo reflection from the ground and the surroundings. Example 1.7 Determine the angle of incidence, θi for direct irradiance/solar radia◦ ◦ tion on an inclined surface, β = 45 from the horizontal with orientation, γ = 30 west of south and located at New Delhi at 1:30 (solar time) on February 16, 2019. Solution ◦

◦

Known parameters, the value of n = 47 and δ = −13.0 (Eq. (1.5)); ω = +22.5 (Eq. (1.6)); ◦ ◦ ◦ γ = 30 ; β = 45 ; ϕ = +28.58 (New Delhi). From Eq. 1.4, we have an expression for the angle of incidence of direct irradiance/ solar radiation on an inclined surface as ( ( ◦) ( ◦) ◦) cos θi = sin −13 sin 28.58 cos 45 ( ( ◦) ( ◦) ( ◦) ◦) − sin −13 cos 28.58 sin 45 cos 30 ( ( ◦) ( ( ◦) ◦) ◦) + cos −13 cos 28.58 cos 45 cos 22.5 ( ( ◦) ( ◦) ( ( ◦) ◦) ◦) + cos −13 sin 28.58 sin 45 cos 30 cos 22.5 ( ◦) ( ◦) ( ( ◦) ◦) + cos −13 sin 45 sin 30 sin 22.5 = 0.999 From above, we get. ◦ θi = cos−1 (0.999) = 2.56 , Example 1.8 Find out the number of sunshine hours (N) for New Delhi on December 22 and June 22, 2019, respectively. Solution For the present case, one has ◦

ϕ = 28.58 (New Delhi); for Dec. 22, 2013,n = 356, and δ = −23.44o From Eq. (1.5), one gets, N=

[ ( ( 2 ◦) ◦ )] cos−1 − tan −23.44 tan 28.58 15

14

1 General Introduction

2 cos−1 [(0.434)(0.545)] 15 2 cos−1 [0.237] = 10.18 hours = 15 =

◦

Similarly, for June 22, 2013, n = 173; δ = 23.45 (Eq. (1.5)). From Eq. (1.8), ( we have ◦ ◦) 2 N = 15 cos−1 − tan 23.45 tan 28.58 = 13.82 hours, Example 1.9 Find out the zenith angle of the sun, θ Z at New Delhi at 2.30 PM on February 20, 2019. Solution ◦

◦

For present case, n = 51; ϕ = 28.58 (New Delhi); δ = −11.58 (Eq. (1.5)); ◦ ω = 37.5 (Eq. (1.6)). From Eq. (1.7), we have ( ( ◦ ◦) ◦) cos θ Z = cos(28.58 ) cos −11.58 cos 37.5 ( ( ◦) ◦) + sin −11.58 sin 28.58 = 0.587 ◦

θz = cos−1 (0.587) = 54.03

Example 1.10 Evaluate the conversion factor for the beam radiation for the inclined surface for time specified in Example 1.7. Solution For horizontal surface, cos θz = sin δ × sin ϕ + cos δ × cos ϕ × cos ω (Eq. (1.7)) is given by ( ( ( ( ( ◦) ◦) ◦) ◦) ◦) cos θz = sin −13 × sin 28.58 + cos −13 × cos 28.58 × cos 22.5 = 0.683 From Example 1.1, cos θi is given by cos θi = 0.999 Further from Eq. (1.10), Rb is given by Rb = cos θi / cos θz = 1.463 ◦

This shows that beam radiation on inclined surface at β = 45 in winter condition ◦ will be more than horizontal surface (β = 0 ) as expected.

1.4 Earth-Sun Angles and Conversion Factors

15

1.4.3 Total Solar Radiation on Inclined/Tilted Surface with Any Orientation For any inclined and oriented surface, Liu and Jordan (1962) have obtained an expression for getting total solar radiation as IT = Ib Rb + Id Rd + ρ Rr (Ib + Id )

(1.13)

where Ib is calculated using Eq. (1.9) and Id = 13 (I N − Ib ), approximately, Rb , Rd , and Rr are estimated using Eqs. (1.10–1.12). Value of reflection coefficient ρ for ordinary and snow covered ground surface can be considered as 0.2 and 0.6, respectively. Equation (1.13) can only be used for known measured data of hourly beam and diffuse solar radiation. For unknown hourly beam and diffuse solar radiation, the following expression is used to evaluate total radiation on an inclined/tilted surface with any orientated surface. It is given by IT = I N cos θi + Id Rd + ρ Rr (I N cos θ Z + Id )

(1.14)

where an expression for hourly variation of I N and Id are known, Eqs. (1.9) and (1.13), respectively. Also, the hourly values of cos θi and cos θ Z can be evaluated from Eqs. (1.4) and (1.7), respectively.

1.4.3.1

Solair Temperature (Tsa )

It is an effective air temperature which includes the effect of solar radiation, ambient air and surface temperature, surface convective and radiative heat transfer coefficient along with long wavelength radiation exchange between surface to sky condition. For example, an energy balance equation in terms of W/m2 (a) For glazed horizontal surface The rate of heat gain/loss through horizontal glazed roof q˙u to room air (Tr ) can be written as q˙u = U L (Tsa − Tr )

(1.15)

where

]−1 [ U L = h10 + h1i , an overall heat transfer coefficient from room air (Tr ) to ambient air (Ta ) which includes the effect of outside (h 0 = 5.7 + ◦ 3, 8 V, V is the wind velocity) and inside (h i = 2.8 W/m2 C) convective het transfer τ2

coefficient and vice versa and Tsa = UgL I (t) + Ta − ∈ΔR , a solar temperature for UL double-glazed horizontal surface; τg , transmissivity of glass; ∈, emissivity of glass

16

1 General Introduction

surface, and ΔR = 60 W/m2 , long wavelength radiation between ambient air and sky. (b) For glazed vertical surface Equation (1.15) remains the same with change in solar temperature. In this case, solar temperature becomes Tsa =

τg2 UL

I (t) + Ta

with ΔR = 0 for vertical glazed wall The programming of calculating solar radiation on all surfaces and corresponding its solar temperature is given in Appendix IV. Problems 1.1 Find out temperature of sun for different months for the following data; Solar Constant = 1367 W/m2 , Sun Diameter(2R S ) = 1.39 × 109 m Sun − Earth distance(L se ) = 1.5 × 1011 m Hint:

( ) ( ) Iext = σ TS4 4π Rs2 / 4π L 2se and Eq. 1.3 σ = Stefan − Boltzmann constant = 5.67 × 10−8 W/m2 K4

1.2 Find Out Declination Angle (δ) for March 31, 2014. Hint: Follow Eq. (1.5). 1.3 Find out hour angle (ω) at 2.30 p.m. Hint: Follow Eq. (1.6). 1.4 Calculate the daily variation of the extraterrestrial solar intensity (Iext ) and the declination angle (δ) for the month of June, 2014. Hint: Follow Eqs. (1.3) and (1.5) respectively. 1.5 Evaluate the hourly beam radiation (Ib ) on (i) horizontal surface and (ii) on inclined surface of 15° inclination on January 15, 2020, in terrestrial region Hint: Follow α = 90 − θz ; for horizontal surface, Ib = I N cos θz ; for / inclined surface, Ib = I N cos θi . 1.6 Evaluate the conversion factor for beam (Rb ), diffuse radiation (Rd ), and ◦ reflected radiation (Rr ) for New Delhi (Table 1.1) at 12:00 noon, for an 15 inclined surface facing east-south on February 16, 2020. Hint: Follow Eqs. (1.10–1.11) 1.7 Find out the average wavelength of the solar radiation received on the earth. Hint: Follow Eq. 1.2.

1.4 Earth-Sun Angles and Conversion Factors

17

1.8 Find out the average wavelength of radiation emitted by the earth. Hint: Follow Eq. 1.2 1.9 Prove that cos θz = sin α Hint: Use θz = 90 − α. 1.10 Calculate the solar altitude angle (α) for different hour angles for New Delhi for January 1, 2020 Hint: See Problem 1.9. 1.12 Calculate the beam and diffuse radiation on horizontal surface for December 21, March 21, and June 21, 2020, for New Delhi Hint: Follow Eq. 1.9 Objective Questions 1.1 The diffuse radiation in the extraterrestrial region is (a) Minimum (b) Maximum (c) Zero (d) None of these. Answer: (c). 1.2 The solar constant is measured (a) Near sun (b) Near earth (c) Terrestrial region (d) Extraterrestrial region. Answer: (d). 1.3 The short wavelength radiation in terrestrial region is (a) Between 0.03–0.30 μm (b) Between 3 and 30 μm (c) Between 0.3 and 3 μm (d) None of these. Answer: (c) 1.4 The annual value of solar radiation is maximum on the surface having inclination equal to (a) Zero (b) Latitude (c) 450 (d) 900 Answer: (b). 1.5 The earth emits (a) Infrared radiation (b) Short wavelength radiation (c) Ultraviolet radiation (d) Long wavelength radiation. Answer: (d). 1.6 The atmosphere reflects (a) Long wavelength radiation (b) Short wavelength radiation (c) All radiation (d) None of above Answer: (a). 1.7 The sunshine hour (N) at equator of earth (a) varies with ‘n’ (b) is constant (c) is zero (d) is 24 h. Answer: (b). 1.8 The relation between Zenith, θz and solar altitude (α) angles is given by (a) θz + α = 600 (b) θz + α = 900 (c) θz + α = −900 (d) θz + α = 00 Answer: (b).

18

1 General Introduction

1.9 The energy generated at core of sun is due to (a) Fission reaction process (b) Conduction process (c) Fusion reaction process (d) Radiation process. Answer: (c). 1.10 The wavelength range of infrared region in solar spectrum is (a) 7-∞ μm (b) 0.7–3 μm (c) 70-∞ μm (d) None of these. Answer: (b). 1.11 In Wein’s displacement law I.E. λT = C, the values of C is (a) 30 μm.K (b) 300 μm.K (c) 3000 μm.K (d) None of these. Answer: (c). 1.12 Air-mass at early morning and late evening is (a) Zero (b) Minimum (c) Maximum (d) None. Answer: (c). 1.13 The sunshine hour (N) in the Northern Hemisphere of Earth on December 21 is (a) Maximum (b) Minimum (c) Zero (d) None. Answer: (a). 1.14 The solar radiation is measured in (a) Extraterrestrial region (b) Terrestrial region (c) On earth (d) On mountain. Answer: (c) and (d). 1.15 The latitude angle at equator of earth is (a) ± 900 (b) ± 450 (c) ± 300 (d) zero. Answer: (d). 1.16 The diffuse radiation in comparison with beam radiation during clear days in terrestrial region is (a) Minimum (b) Equal (c) Zero (d) Maximum Answer: (a) 1.17 The diffuse radiation in comparison with beam radiation during clear days in extraterrestrial region is (a) Minimum (b) Equal (c) Zero (d) Maximum Answer: (c) 1.18 Reflection from any horizontal surface takes place only by (a) Diffuse radiation (b) beam radiation (c) both beam and diffuse radiation and (d) all of them Answer: (b) 1.19 Reflection from any inclined surface takes place only by (a) Diffuse radiation (b) Beam radiation (c) Both beam and diffuse radiation and (d) All of them Answer: (d) 1.20 Diffuse radiation from any horizontal surface is (a) Minimum (b) Equal (c) Zero and (d) Maximum Answer: (a)

References

19

1.21 Sunshine hours in summer in comparison with winter in Northern Hemisphere is (a) Equal (b) Less (c) More (d) None Answer: (c) 1.22 The declination angle will be zero for value of n equal to (a) 360 (b) 365 (c) 284 (d) 81 Answer: (d) 1.23 The relation between zenith and altitude angle is given by (a) α = 900 − θ Z (b) α = 900 + θ Z (c) α = θ Z (d) α = 1800 − θ Z Answer: (a). 1.24 The conversion factor (Rb ) for beam radiation for clear days is (a) Less than one (b) More than one (c) Equal to one and (d) Zero Answer: (b) 1.25 The expression for beam radiation is given by (a) Ib = IT − Id (b) Ib = IT + Id (c) Ib = IT and (d) Ib = Id Answer: (a)

References 1. Tiwari GN, Tiwari A, Shyam (2016) Handbook of solar energy, Springer 2. Tiwari GN (2002) Solar energy: fundamental, design, modelling and applications. Narosa Publishing House, New Delhi and CRC Press, New York 3. Tiwari GN (2020) Ecology, environment and human being. Ecol Conserv Sci 1(3):ECOA.MS.ID.555565. https://doi.org/10.19080/ECOA.2020.01.555565 4. Duffie JA, Beckmann WA (1991) Solar engineering of thermal processes. Wiley, New York 5. Tiwari GN, Mishra RK (2012) Advance renewable energy sources. RSC publishing, UK 6. Liu BYH, Jordan RC (1960) Sol Energy 4:1–19 7. Singh HN, Tiwari GN (2005) Energy 30:1589 8. Ahmad MJ, Tiwari GN (2008) CIGR Ejournal 10:1

Recommended Additional References for Further Studies 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

Kasten F, Young AT (1989) Appl Optics 28:4735 Perez R, Ineichen P, Maxwell E, Seals R, Zelenka A (1992) ASHRAE Trans 98:3578 Orgill JF, Hollands KGT (1977) Sol Energy 19:357 Collares-Perira M, Rabl A (1979) Sol Energy 22:155 Gopinathan KK (1988) Sol Energy 41:379 Liu BYH, Jordan RC (1961) ASHRAE J 3(10):53 Hottel HC, Whiller A (1958) Transactions of the conference on use of solar energy. The Sci Basis II(I):74, Section A. University of Arizona Press. Kasten F, Young AT (1989) Appl Opt 28:4735 Perez R, Ineichen P, Maxwell E, Seals R, Zelenka A (1990) ASHRAE Trans 98:354 Machler MA, Iqbal M (1985) ASHRAE Trans 91(1a):106 Muneer T, Hawas MM, Sahili K (1984) Energy Convers Manage 24(4):265

20

1 General Introduction

20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32.

Lam JC, Li DHW (1996) Build Environ 31(6):527 Boland J, Scott L, Luther M (2001) Environmetrics 12:103 Miguel A, Bilbao J, Aguiar R, Kambezidis H, Negro E (2001) Sol Energy 70:143 Whillier A (1956) Arch Meteorol Geophys Bioclimatol B8:197 Collares-Pereira M, Rabl A (1979) Sol Energy 22:155 Newell TA (1983) Sol Energy 31:339 Gueymard (1986) J Solar Energy Eng Trans ASME 108:320 Baig A, Akhter P, Mufti A (1991) Renew Energy 1:119 Law EW, Prasad AA, Kay M, Taylor RA (2014) Sol Energy 108:287 Besharat F, Dehghan AA, Faghih AR (2013) Renew Sustain Energy Rev 21:798 Ali NC, Muneer T (2013) Energy Convers Manage 67:117 Bakirci K (2009) Renew Sustain Energy Rev 13(9):2580 Bansal NK, Minke G (1988) Climatic zones and rural housing in India. Part 1 of the IndoGerman project on passive space conditioning Klein SA (1977) Sol Energy 19(4):325 Thekaekara MP (1977) Solar irradiance, total and spectral. Chapter III in solar engineering, Sayigh AAM (ed). Academic Press, Inc. New York Tiwari GN, Dubey S (2010) Fundamentals of photovoltaic modules and their applications. RSC publishing, UK Trace Gases, Ace.mmu.ac.uk. Archived from the original on 9 October 2010. Retrieved 2010– 10–16

33. 34. 35. 36.

Chapter 2

Water Quality

2.1 Introduction As mentioned in Chap. 1, the survival of living organism including human being on the planet earth depends on good environment (Table 1.1) which consists of many gases including O2 and CO2. The level of CO2 has increased significantly from 270 to 412 ppm (1 mg/L = 1.0011423 part per million (ppm)) since World War II due to fast growth of industrialization. In addition to good environment, good quality of water is basic need of human being in different ways including agriculture. Table 2.1 [1] indicates that freshwater availability on planet earth in liquid form is 0.3% out of 2.5% being freshwater. Due to growth of population along with industrialization as mentioned above, the percentage of water in liquid form is being polluted globally. There is a third parameter, namely good quality of food, which comes from agriculture/aquaculture/aquaponics (hydroponics), etc. required by human being for good health. Further, there is strong need of large good quality of water in this sector. For each sector, one needs different parameters (indicator) of water quality. So basically, followings are main indicators of water quality: (a) Dissolved oxygen, (b) Turbidity, (c) Bioindicators, (d) Nitrates, (e) pH scale, and (f) Water temperature. So, in the following section, we will discuss this parameters/indicator for each sector.

© Bag Energy Research Society 2023 G. N. Tiwari, Advance Solar Photovoltaic Thermal Energy Technologies, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4993-9_2

21

2 

22

Water Quality

Table 2.1  Distribution of saline and freshwater Source of water

Volume of water in km3 (cu mi)

% total water

% salt water

(A) Oceans

1,338,000,000 (321,000,000) 24,364,000 (5,845,000)

96.5

99.0

% freshwater

1.762

69.6

24,064,000 (5,773,000) 300,000 (72,000)

1.74

68.7

(C) Groundwater

23,400,000 (5,600,000)

1.6912

(a) Saline groundwater

12,870,000 (3,090,000)

0.93

(b) Fresh groundwater

10,530,000 (2,530,000)

0.76

( C) Soil moisture

16,500 (4,000)

0.0012

(B) Ice and snow (a) Glaciers (b) Ground ice and permafrost

0.022

% liquid surface freshwater

0.86

0.95 30.1 0.047

(D) Lakes

176,400 (42,300)

0.013

(a) Saline lakes

85,400 (20,500)

0.0062

0.0063

(b) Caspian Sea

78,200 (18,800)

0.0056

0.0058

(c) Other saline lakes

7,200 (1,700)

0.00052

0.00053

(E) Freshwater lakes

91,000 (22,000)

0.0066

0.26

87.0

(a)African Great Lakes

30,070 (7,210)

0.0022

0.086

28.8

(b)Lake Baikal

23,615 (5,666)

0.0017

0.067

22.6

(c) North American Great Lakes

22,115 (5,306)

0.0016

0.063

21.1

(d) Other freshwater lakes

15,200 (3,600)

0.0011

0.043

14.5

(F) Atmosphere

12,900 (3,100)

0.00093

0.037

(a)Swamps

11,470 (2,750)

0.00083

0.033

(c) Rivers

2,120 (510)

0.00015

0.0061

(G) Biological water

1,120 (270)

0.000081

0.0032

11.0 2.03

The total volume of water on Earth is estimated at 1.386 billion km3 (333 million cubic miles), with 97.5% being salt water and 2.5% being freshwater. Of the freshwater, only 0.3% is in liquid form on the surface Because the oceans that cover roughly 71% of the area of Earth reflect blue light, Earth appears blue from space and is often referred to as the blue planet and the Pale Blue Dot. Liquid freshwater like lakes and rivers covers about 1% of Earth’s surface [5] and altogether with Earth’s ice cover. Earth's surface is 75% water by area [6]

2.2  Water Quality for Human Consumption

23

2.2 Water Quality for Human Consumption Water is very important and basic need for body of human being. Water propagates throughout the body which carries nutrients, oxygen, and wastes to and from your cells and organs. Water keeps your body cools at level of 37 ℃ temperature with regulating system. Water cushions your joints. It protects your tissues and organs from shock and damage. The clean water crisis is also an emerging global crisis after World War II. This affects approximately seven hundred eighty five (785) million people around the world. Further, one thousand one hundred million (1.1 billion) people lack access to water, two thousand seven hundred million (2.7 billion) experience water scarcity at least one month in a year, and two thousand four hundred million (2.4 billion) people suffer from the contamination of water with poor sanitation. Most water in Earth’s atmosphere and crust comes from saline seawater covering about 75% area of earth through water cycle (H2O). The freshwater accounts for nearly 1% of the total (Fig. 2.1). The vast bulk of the water on Earth is saline/ salt water. Its average salinity is about 35–45‰. It means 3.5% roughly equivalent to 34 g of salts in 1 kg of seawater. This can further vary slightly according to the amount of runoff received from surrounding land. Overall saline water is over

Fig. 2.1  Graphical representation of Table 2.1 regarding water distribution on the planet earth

2 

24

Water Quality

97% on Earth from oceans and marginal seas, saline groundwater and water from saline closed lakes, Fig. 2.1 [1] and Table 2.1 [1]. Selected physical and chemical properties of water and nutrients of drinking water have been summarized in Tables 2.2 and 2.3, respectively. Further, the optimum value of pH for each item for human consumption including drinking water has also been given in Table 2.4. One can conclude from these tables that optimum value of sodium and pH value recommended by WHO are 200 mg/kg and seven respectively. Most of underground water on the Earth and sea water are 10,000 ppm and 30,000–45,000 ppm respectively. Due to rising problem of drinking water in developed, developing, and underdeveloped countries, WHO set a norms of drinking water according to salt content for supply and use to the people. Table 2.5a, b show broad classification of water available on planet earth. There are various conventional and renewable (non-conventional) methods to purify sea water and underground hard/saline water to be used for drinking purposes. These methods are as follows: (a) Conventional method: The traditional process of desalination is distillation, i.e., boiling and recondensation of seawater to leave salt and impurities behind, Table 2.6 [5]. (b) Renewable (Non-conventional) method: In this category, rain harvesting and solar distillation [6, 7] by using solar energy

2.3 Water Quality for Agriculture [8] The water quality for irrigation determines for the higher yield with quality along with maintenance of soil productivity and protection of the environment. The concentration (ppm) and composition of soluble salts (NaCl) in water determines its quality for irrigation for open field as well pot cultivation through drip irrigation. There are basically four basic criteria for evaluating water quality for irrigation purposes. These are as follows: (a) Water salinity/Electrical Conductivity (EC)/Total Dissolved Solids (TDS) (b) Sodium hazard (sodium adsorption ratio-SAR), (c) Residual sodium carbonates (RSC) and (d) Turbidity (e) pH value (f) Color (g) Alkalinity, and (h) Ion toxicity.

2.3 Water Quality for Agriculture

25

Table 2.2  a Selected properties of water [Horvath (1975); Perry (1985)] [2, 3] H2O 18.0148 373.91 ℃ 22.05 MPa 315.0 kg/m3 0.01 ℃ 615.066 Pa 100.0 °C 0.0 ℃ 918.0 kg/m3 999.973 kg/m3 0.889 mN s/m2 72 mN/m 4.1796 kJ/kg.K 2257.7 kJ/kg 333.8 kJ/kg 1.403 km/s 78.40 8 μS/m 1.333 480. × 10−12 m2/N 256.32 × 10−6K−1 0.608 W/m.K

Chemical formula Molecular weight Critical temperature Critical pressure Critical density Triple point temperature Triple point pressure Normal boiling point Normal freezing point Density or ice at normal melting point Maximum density, 3.98 ℃ Viscosity, 25 ℃ Surface tension, 25 ℃ Heal Capacity, 25 ℃ Enthalpy of vaporization, 100 ℃ Enthalpy of fusion, 0 ℃ Velocity of sound, 0 ℃ Dielectric constant, 25 ℃ Electrical conductivity, 25 ℃ Refractive index, 25 ℃ Liquid compressibility, 10 ℃ Coefficient of thermal expansion, 25 ℃ Thermal Conductivity, 25 ℃ b. Water properties as a function of temperature TK

Temperature, celsius

Pr

Cp, kJ/ kg.K

σ mN/m

ρ tonne/m3

273.15 280 2K5 295 305 315 325 335 345 355 365 373. L5

0 6.85 11*5 21,85 31.85 41.85 51. B5 61.85 71.85 81 JB5 91,85 100

12.99 10.26 8.81 6.62 5.02 4.16 3.42 2.88 2.45 2.14 1.91 1.76

4.217 4.198 4.189 4.181 4.178 4.179 4.182 4.186 4.191 4.199 4.209 4.217

75.5 74.8 74.3 72.7 70.9 69.2 67.4 65.8 64.1 62.3 60.5 58.9

0.999839 0.999908 0.999515 0.997804 0.995074 0.991495 0.96719 0.982234 0.976706 0.970638 0.96407 0.958365

Η mNS/ m2 1.75 1.422 1.225 0.959 0.769 0.631 0.528 0.453 0.389 0.343 0.306 0.279

λ W/m.K 0.569 0.582 0.59 0.606 0.62 0.634 0.645 0.656 0.668 0.671 0.677 0.68

2 

26 Table 2.3  WHO Guidelines ((mg/L)) for drinking water (a Levels likely to give rise to consumer complaints, b Guideline value, N/A = not available)

S. No. 1 2 3 4 5 6 7 8 9 10 11

Nutrients Iron Zinc Copper Fluoride Sodium Chloride TDS Iodine, calcium, phosphorus Magnesium, potassium Ammonia Manganese

Water Quality

Numerical values 0.3a 3.0a 2.0b 1.5b 200a 250a 1000 N/A N/A 1.5a 0.1a

Table 2.4  Optimum value of pH for drinking water

2.3.1 Electrical Conductivity (EC) Electrical conductivity (EC) of water is known as the capacity of water to flow the electric current through liquid water. EC depends on the dissolved ions (DI) in the water and their moving charge (movement). It is a good solvent; the water dissolved mineral salts in the form of ions. It keeps the electric current due to ionic

2.3 Water Quality for Agriculture

27

Table 2.5  a Drinking water norms set by World Health Organization (WHO) and different countries. Category of nation 1 2 3

Salt concentration in ppm (1 mg/L = 1.0011423 Developed nations Developing nations Underdeveloped

Part per million (ppm)) 500 1500 2000

b Water classification as per dissolved salt content [ppt (parts per thousand):1 ppt =1 gram/ liter=1111mg/liter=1000ppm] Total dissolved solids (ppm) Water type   30,000 Sea water

Table 2.6  Conventional method for purification of sea/saline water [5]

conduction. For larger EC of water, there is high concentration of ions and temperature in the liquid water. The electrical conductivity (EC) of water also affects the plant growth either open field or inside greenhouse. The measurement of EC at 25 °C water temperature is considered as optimum.

2 

28

Water Quality

2.3.2 Water Salinity The salinity behavior of liquid water is also known as total dissolved solids (TDS). It contains the negatively change ions (anions) and +ve changes ions (cations). The total dissolved solids (TDS) change the color and chemical properties of liquid water. There is a relationship between (i) the total dissolved solids (TDS) and (ii) electrical conductivity (EC) as follows:

TDS(mg/L) = EC(dS/m) × K(1)

(2.1)

where (i) K = 640 in most cases (for EC: 0.5−5 dS/m: Decisiemens per meter), (ii) K = 735 for mixed waters, and (iii) K = 800 for EC >5 dS/m Equation (2.1) is applied for EC ranging from 0.5 to 5 dS/m. It is not applicable for wastewater. The TDS is a measure of the amount of material dissolved in water. This includes (i) bicarbonate, (ii) carbonate, (iii) calcium, (iv) chloride, (v) magnesium, (vi) nitrate, (vii) organic ions, (viii) phosphate, (ix) sodium, (x) sulfate, etc. (Table 2.3). The density (ρ) of the water increases with increase of total dissolved solids (TDS) concentrations which can be harmful. It determines the flow of water into and out of an organism's cell along with reduction in water clarity/transparency. It is responsible to a decrease in photosynthesis process and leads to an increase in water temperature.

2.3.3 Sodium Adsorption Ratio (SAR) The sodium adsorption ratio (SAR ) is measured as a property of liquid water. This gives an information on the comparative concentrations of (i) sodium, (ii) calcium, and (iii) magnesium ions. The sodium adsorption ratio (SAR ) can be calculated from a formula given below:

SAR = [Na+ ]/ Ca2+ + Mg2+ /21/2

(2.2)

where [Na + ], [Ca2+], and [Mg2+] are the concentrations in meq/L (Milliequivalents per liter) of (i) sodium, (ii) calcium, and (iii) magnesium ions. A high sodium ion concentration affects the hydraulic conductivity /permeability of the soil. It creates water infiltration problems in irrigation of water in either open filed or inside greenhouse. For higher value of sodium adsorption ratio (SAR ), the soil becomes hard and compact when dry and finally reduces the infiltration rates of water and air into the soil of cultivated land. This problem is also related to several factors such as (i) the salinity rate and (ii) type of soil. For example, sandy soils may not get damage as easily as other heavier soils if it is irrigated with high SAR water.

2.3 Water Quality for Agriculture

29

2.3.4 Residual Sodium Carbonates (RSC) The residual sodium carbonate (RSC) is used to predict the additional sodium hazard associated with CaCO3. Its precipitation involves in calculation of the residual sodium carbonate. It is an alternative measure of the sodium (Na) content in relation with calcium and magnesium. The residual sodium carbonates (RSCs) can be evaluated as follows: − 2+ + Mg+2 RSC = CO2− 3 + HCO3 − Ca

(2.3)

where all concentration numerical value is in meq/L.

2.3.5 Turbidity The turbidity is defined as an amount of cloudiness in the liquid water. It is created by dissolved or total suspended solids materials which is invisible most of the time by the naked eye as smoke in air. The turbidity can be caused by (i) silt, sand, and mud; (ii) bacteria and germ, and (iii) chemical precipitates. The turbidity is measured in Nephelometric Turbidity Units (NTUs). It is the values of light absorbing or light scattering property of liquid water. High level of turbidity can have the following risk/problem: (a) In drinking water to the people for developing gastrointestinal diseases. (b) Affects (i) light penetration and productivity, (ii) recreational values, and (iii) habitat quality and (c)  The life of fish and other aquatics animal can be in danger due to increased sedimentation and siltation.

2.3.6 The pH of Water The pH value of liquid water is the concentration of hydrogen ions (H+) and hydroxyl ions (OH−) in it. It is generally used to calculate the acidic, basic, or neutral behaviors of liquid water. The pH values range from 1 to 14 (Table 2.4). The pH value is selected in the following manner: (i) If pH of water  7, it is called the basic nature water. The pH of liquid water and soil could not harm the plant growth directly.

30

2 

Water Quality

2.3.7 The Color of Water The color of water is also an important indicator to define water pollutants source. It represents the type of any solid material dissolved in liquid water. Water color can be known as follows: (a) The transparent water has blue color with low level of dissolved solids in the water. (b) The yellow or brown color is due to the dissolved organic matter in the water. (c) The apparent blue color of water bodies is due to selective absorption and scattering of solar light/ artificial light spectrum. (d) Reddish/ deep/ green yellow waters is due to algae formation (Chap, global greenhouse effect). True color can be measured by filtering the water after removing all suspended material.

2.3.8 Alkalinity The ability of water to neutralize the added acids is known as alkalinity. The most important factor determines root media pH (Table 2.4). Over the long time, the pH is adversely affected by the water having high alkalinity. It can be assessed with the measure level of calcium bicarbonate/carbonate. Undesirably, acid is injecting into the liquid water to neutralize the level of high level of bicarbonate in fertilizers.

2.3.9 Ion Toxicity The high concentration of ion toxic elements in liquid water can reduce crop growth with low level of crop production. The primary ionic constituents are (i) boron, (ii) sodium, and (iii) chloride. Even small amount of ionic constituents in the water can cause the damage of crop either in open field or inside greenhouse cultivation. The water infiltration and salinity problems can also be due to toxicity. During transpiration process (evaporation of water content in leaves) from surface of leaves, the dissolved ions in water move and accumulated on its surface of the leaves. It reduces the transpiration (evaporation) process. It adversely affects the plant growth. Toxicity from sodium and chloride or from any one is danger to sensitive crop.

2.4 Water Quality for Aquaculture

31

2.4 Water Quality for Aquaculture [9] Water quality is a critical factor for culturing any aquatic organism. It varies by species wise, and it must be supervised to ensure growth and survival. It is important to note that farmers should pay attention to chemical and physical properties of the water. The quality of the water can significantly affect the organism’s health in the production. The overall cost associated with getting a final product to the market is an important issue. Water quality parameters which are required in the aquaculture industry are as follows: (i) Total alkalinity (ii) Ammonia (iii) Dissolved oxygen (DO) (iv) Hardness, (v) Nitrites (vi) Temperature, and (vii) The pH value In addition to above parameters, other required parameters are as follows: (i) Carbon dioxide (CO2), (ii) Chlorine, (iii) Salinity (NaCl), and (iv) Hydrogen sulfide. Parameters such as alkalinity and hardness are fairly stable. However, but others parameters namely dissolved oxygen (DO) and pH value vary on the daily.

2.4.1 Total Alkalinity Total alkalinity is the sum of the carbonate and bicarbonate alkalinities. The total alkalinity plays a very important role for aquaculture especially for shrimp farming water quality conditions. In simple way, the total alkalinity of the water is absorbed cations (hydrogen ions H+) to maintain the pH value (pH) of the same capacity. It is usually preferred to have alkalinity and hardness concentrations above 50 mg/l for fish and 80 mg/l for crustaceans in aquaculture ponds, Crustaceans such as crabs, lobsters, and shrimps (झींगा) have a soft body in several sections and covered with a hard outer shell. Figure 2.2 shows that moderate alkalinity has lower pH value during daytime with photosynthesis/respiration [10]. This also shows that photosynthesis/ in aqua water pond always happens only during daytime. This means the importance of solar radiation for survival of any fish. For lower value of the total alkalinity, water may suddenly change, then farmed fish prone to strong stress response which results in disease-prone.

32

2 

Water Quality

Fig. 2.2  Variation of pH with time for low and moderate alkalinity [10]

2.4.2 Ammonia The most harmful inorganic nitrogen compounds are ammonia (NH3) for fish or shrimp in aquaculture. Another is nitrite whose accumulation in water pond may deteriorate water quality, and finally it will reduce growth and increase oxygen consumption. Ammonia in aqua water pond can be measured as Total Ammonia Nitrogen (TAN). The TAN is both ionized (NH4+ = NH3 + H+) and unionized (NH3) ammonia. Unionized ammonia (NH3) is the number one killer of aquatic invisible animals. Aquaculture production should control the concentration of NH3 ≤ 0.015 ppm. For higher concentration of NH3 (≥ 0.02 ppm) in aqua water pond water, death fish will occur. The accumulated ammonia concentration up to a very high level of 10.81 mg/L and with an average value of 6.35 mg/L leads to a mortality rate as high as 70% [11]. Figure 2.3 shows the variation of NH4+ and NH3 in percentage with pH under 25 °C. Following conclusions from Fig. 2.3 can be made: (i) There is almost no ammonia (NH3) in water for pH  7.0, the value of NH3 increases exponentially along with the toxicity of TAN. (iii) The pH affects the toxicity of NH3. if pH  8.5% it severe toxicity. For crab, shrimp nursery, NH3 should be controlled at 0.01 ppm; if less than 0.01 ppm, it will cause death.

2.4 Water Quality for Aquaculture

33

Fig. 2.3  Variation of NH4+ and NH3 in percentage with pH under 25 °C [11]

2.4.3 Dissolved Oxygen (DO) [12] Dissolved oxygen (DO) is the most important parameters/indicator of aquaculture water pond quality. Dissolved oxygen (DO) concentration below 3 mg/L is frustrating (stressful) to shrimp (झींगा) and most frustrating to warm water fishes. This results in lower survival and production of fishes. DO concentrations below 1.0– 1.5 mg/L (1 mg/L = 1.0011423 part/million (ppm)) for a few hours can kill warm water animals? There are some reasons for decrease/sudden depletion of dissolved oxygen (DO) in fishery ponds. These are as follows: (i) Due to insufficient level of solar radiation (sunlight) particularity cloudy/ hazy condition. It is generally happened during monsoon/winter days. (ii) High stocking density with respect to the volume of water in pond. This results in the shortage of dissolved oxygen (DO) for the biomass in a water pond. (iii) Unwanted accumulation of a large amount of fish unconsumed feed, inorganic or organic and other organic wastes fertilizers, etc. (iv) Production of toxic gases due to death of fishes and its decomposition due to excessive or poor quality of food or chemical supplements. (v) Excessive growth of aquatic plants covering the water surface/pond margin. (vi) Accumulation of polluted matters from outside the water pond due to rainfall, inundation, or flood, etc. Followings are majors to be taken (i)

Use of lime periodically is a prerequisite from initial stage as a prophylactic measure. Also keep the pond free from unwanted substances

34

2 

Water Quality

(ii)

Incorporate an air supply/wind circulation system in the pond from environment. The use of aerator is more effective device in this case. (iii) Drain out water from the bottom surface of water pond (preferably) and refill it with freshwater at top of water pond. (iv) Allow ducks to swim water pond top surface with help of a bamboo pole to feed free oxygen from air to inside water pond. (v) If possible and easy, paddle a boat with oars from one end to other end to aerate water in a large pond. (vi) Remove aquatic plants and vegetation to facilitate solar radiation (sunlight) inside the water pond. (vii) Stop feeding and using fertilizers temporarily until the situation improves. (viii) If there is a large number of fish in the pond, a partial harvest is necessary to reduce the stocking density.

2.4.4 Hardness [13] Optimum hardness and alkalinity levels of water for aquaculture are in the range of 50–300 ppm CaCO3. It provides a good stabilizing effect to pH swings. The sample is determined with standard test kits. The values of 50–100 mg/l range are generally considered as a moderate for freshwater farming. Variation of mole fraction (inorganic compound) (HCO3−, CO3 2−, and CO2) with pH value of water has been shown in Fig. 2.4. Following conclusions can be inferred as follows:

Fig. 2.4  Variation of mole fraction (inorganic compound) (HCO3−, CO3 2−, and CO2) with pH value of water

2.4 Water Quality for Aquaculture

35

(i) HCO3− increases with decrease of CO2 with increase of pH value after pH > 4.5 till pH = 8. (ii) CO2 is practically nil at 8.3 and (iii) For pH > 8.5, the variation behavior of HCO3− and CO3 2− with pH value is reversed. (iv) At 10.33, concentration of HCO3− and CO3 2− becomes equal.

2.4.5 Nitrite The amount of nitrates should not exceed 1–2 mg/L. The increase in the content of them, especially of organic origin, affects the state of the fish—lowers the body's resistance. It has been reported in the literature that the desired nitrate concentration for aquaculture water pond is 0.2 to 10 mg/l. Nitrate is not toxic. Nitrite is the source of aquatic animal pathogenic which destroys the red blood cells. Nitrification consumes dissolved oxygen (DO) in water pond, and it can be a major source of acidity to neutralize alkalinity. Nitrification can contribute 30–40 percent of the oxygen demand. Fertilizer manufacturers have reported the acidity of ammonium fertilizers as calcium carbonate required for its neutralization as given in Table 2.7. A typical application rate for urea in ponds is 50–100 kg/ha/crop. These rates could produce acidity equal to 80.5–160.0 kg calcium carbonate/ha/crop. This amount of acidity can be a serious problem in water with total alkalinity concentrations below 20 mg per liter. Periodic liming is necessary to avoid low alkalinity in some fertilized ponds. Some other important points should be noted: (i) Higher water hardness will directly affect the toxicity of nitrite in water quality which reduces nitrite toxicity.

Table 2.7  Nitrogen concentration and potential acidity of common fertilizers. [14] Fertilizer

Nitrogen (%)

Urea Ammonium nitrate Ammonium sulfate Diammonium phosphate Ammonium polyphosphate Monoammonium phosphate

45 34 20 18 13 11

Potential Acidity (kg calcium carbonate/100 kg fertilizer) 161 118 151 97 72 79

36

2 

Water Quality

(ii) Aquaculture water nitrite chlorine should be controlled  14;    (b);    (c) < 7 and    (d) > 7 Answer: (d) 2.6 What is the optimum temperature for growth of fish farm (aquaculture water pond)? (a) 20 – 300C;    (b) ≫ 300C;    (c) = 300C and    (d) Type of species

Answer: (d) 2.7 What is percentage of freshwater available for living organism on the earth? (a) 26%;    (b) 2.6%;    (c) 0.26%    (d) None of them Answer: (c). 2.8 What is norm set by WHO for drinking water in ppm for developed countries? (a) 1000 ppm;    (b) 50 ppm;    (c) 1500 ppm    (d) 500 ppm Answer: (d) 2.9 What is the salinity of sea water in ppm? (a) > 30000 ppm;     (b) > 40000 ppm;     (c) > 45000 ppm and all of them Answer: (d). 2.10 Basic parameters required for high yield of fish from aquaculture water pond are as follows: (a) Temperature;    (b) pH value;    (c) Dissolved oxygen (DO)     (d) All of them Answer: (d). 2.11 Electricity conducted in water via (a) Dissolved ion of NaCl;    (b) Dissolved ion of oxygen (DO);    (c) Dissolved ion of CuO    (d) None of them Answer: (a)

48

2 

Water Quality

References 1. Water distribution on Earth—Wikipedia, https://en.wikipedia.org › wiki › 2. Horvath AL (1975) Physical properties of inorganic compounds, Arnold 3. Perry RH, Green D (ed) (1985) Perry’s chemical engineers’ handbook, 6th edn., McGraw-Hill 4. Manuel Olivares, Chile Ricardo Uau ,Essential Nutrients In Drinking Water( Chapter 4): 5. Nutrients in Drinking Water - WHO | World Health Organization. https://www.who.int › water_sanitation_health › dwq 6. Shatat M, Riffat SB (2014) Water desalination technologies utilizing conventional and renewable energy sources. Int J Low-Carbon Technol 9(1):1–19. https://doi.org/10.1093/ ijlct/cts025 7. Malik MAS, Tiwari GN, Kumar A, Sodha MS (1982) Solar distillation. Pergamon Press Ltd., U.K. 8. Tiwari GN, Sahota L (2017) Advanced solar distillation systems: basic principles. Thermal Modeling and Its Application, Springer 9. Arshad M, Shakoor A, Irrigation Water Quality, https://www.researchgate.net › publication › 320531819_ 10. Indicators of Aquaculture Water Quality – PANGOO. https://www.pangoogroup.com › 8-indicators-of-aquac 11. Boyd CE, Tucker CS, Somridhivej B (2016) Alkalinity and Hardness: critical but elusive concepts in aquaculture. J World Aquacult Soc. https://doi.org/10.1111/jwas.12241 12. Huang HH (2019) Biofloc technology (BFT) for Ammonia assimilation and reuse in aquaculture. Emerg Technol Environ Res Sustain Aquacult. https://doi.org/10.5772/ intechopen.88993 13. Importance of Dissolved Oxygen Level in Aquaculture and Fish Biodiversity. https://blog. mygov.in › importance-of-dissolved-oxyge 14. Boyd CE, Tucker CS, Somridhivej B (2016) Alkalinity and Hardness: critical but elusive concepts in aquaculture. J World Aquacult Soc 47(1). First published: 27 January 2016, https://doi.org/10.1111/jwas.12241 15. Nitrification an important process in aquaculture https://www.globalseafood.org 16. Boyd CE (2018) Water temperature in aquaculture—global seafood alliance. https://www. globalseafood.org 17. Boyd CE (2008) Carbon dioxide: waste, nutrient—global seafood alliance. https://www.globalseafood.org 18. Boyd CE (2017) Electrical conductivity of water, part 1—global seafood alliance. https:// www.globalseafood.org › Advocate

Chapter 3

Solar Cell and Photo-Voltaic Effect

3.1 Introduction On the basis of electrical conduction, solid/material can be classified as (a) conductors, (b) semiconductors, and (c) insulators. These can be explained on the concept of energy band gap between valence and conduction band. The energy band gap for these is as follows: (a) Conductors E g ≈ 0 : There is no forbidden gap between valence and conduction band, and hence, electron can easily move from valance to the conduction band. (b) Semi-conductor E g < hυ : The energy band gap is lesser than that of insulator energy band gap. Hence, valence electron can cross easily energy band gap on acquiring thermal /light energy from solar radiation falling on junction. (c) Insulators (E g > hυ): In this case, energy band gap is very large. Therefore, electrons in valence band cannot cross energy band gap from valance band to the conduction band which results no conduction of current. Here, h and υ are the Planck’s constant and the frequency of photon, respectively. The temperature-dependent energy band gap can be expressed as E g (T ) = E g (0) −

aT 2 T +b

(3.1)

where the value of a and b for different materials can be obtained Table 3.1. For T = 0, E g (T ) = E g (0), this indicates that the materials behaves as an insulator. Example 3.1 Find out the energy band gap in a silicon crystal material at 50 °C. Solution After substituting the appropriate values of a and b from Table 3.1 in Eq. 3.1, one gets

© Bag Energy Research Society 2023 G. N. Tiwari, Advance Solar Photovoltaic Thermal Energy Technologies, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4993-9_3

49

50

3 Solar Cell and Photo-Voltaic Effect

Table 3.1 Numerical values of constants ‘a’ and ‘b’ for different solar cell materials Material

E g (0)

a

b

Silicon (Si)

1.166 eV

7 × 10−4 eVK−1

636 K

Gallium arsenide (GaAs)

1.519 eV

5.8 × 10−4 eVK−1

204 K

Germanium (Ge)

0.7437 eV

4.77 × 10−4 eVK−1

235 K

E g (T ) = 1.16 −

7 × 10−4 × (323)2 = 1.11 eV 323 + 1100

This shows that E g (T ) < E g (0). Thus, silicon crystal behaves as semi-conductor.

3.2 Basics of Semiconductor and Solar Cells The basics of semiconductor and solar cell will be discussed in this section. A semiconductor material has an electrical conductivity value falling between a conductor (metallic copper) and an insulator (glass). Its conducting properties may be changed by introducing impurities (doping) namely with Group V elements like phosphorus (P) and arsenic (As) having valence electrons five into the crystal structure, namely silicon, germanium, and gallium arsenide which all has four valence electrons (Fig. 3.1a).

3.2.1 Doping There are two types of semiconductor, namely intrinsic and extrinsic semiconductor. Intrinsic (pure) semi-conductors have Fermi level in the middle of the conduction and valence band. If the electrical conductivity of the intrinsic semiconductor is increased by adding the controlled amount of specific impurity ions, then the doped semiconductors are referred as extrinsic semiconductors. Further, extrinsic semiconductor is classified as. (a) n-type Material An n-type semiconductor is an intrinsic semiconductor. In this case, pure silicon is doped with Group V elements like phosphorus (P) and arsenic (As) (valence electrons=5). The compound is to be an electrically conductive n-type semiconductor with extra valence electrons. Since it donates electrons, it is also referred as donors as well as emitters There is an excess of one electron in outermost orbit of n-type semiconductor.

3.2 Basics of Semiconductor and Solar Cells

51

a ATOMIC STRUCTURE of Silicon

Number of electron in nth orbit of atom = 2n2 •

• For silicon, valence electron is 4 (outermost orbit) •

b Depletion or p Electrons

n

EC

E1

EF E2 Holes

EV

Fig. 3.1 a Atomic structure of silicon. b Energy band levels for a p–n junction of solar cell [From Tiwari and Mishra, 2012]

(b) p-type material: It is also an intrinsic semiconductor (a single crystal of silicon) doped with Group III element like boron (B) or indium (In). This results holes in compound that lack electrons. Every element in the boron group has three electrons in its outermost shell (so-called valence electrons). There is deficiency of one electron in outer most orbit p-type semiconductor named as hole. In p-type material, an energy level is near to valence band in forbidden energy band. These materials has characteristic of positively charged states known as holes. Such a material is known as p-type material, having holes (n h ) as majority carriers. It is important to mention here that in p-type material holes are in majority and electrons are in minority and vice versa in n-type materials. For intrinsic semi-conductor, ne = nh = ni

(3.2)

52 Table 3.2 Numerical value of Boltzmann constant, k in different units

3 Solar Cell and Photo-Voltaic Effect

Value of k

Units

1.38 × 10−23

JK−1

8.62 × 10−5

eVK−1

1.38 × 10−16

ergK−1

3.2.2 Fermi Level (E F ) The Fermi level (E F ) is the energy level which is in between the valance and conduction band of an extrinsic semiconductor. For a given temperature, the probability for the majority charge carriers to be excited for conduction of current varies as exp[−eϕ/kT], where e is the electronic charge, and ϕ is the electrical potential difference between the Fermi level and the valence or conduction band, k is the Boltzmann constant, Table 3.2. For details, see Chap. 4 of Tiwari et al. [1].

3.2.3 The p–n Junction The electronic asymmetry is the essential requirement for the conversion of solar energy (photon) into the electricity. The electronic asymmetry is created by joining the p-type and n-type semiconductors together (perfect contact). At the junction between p-type and n-type semiconductors, the majority charge carriers electron flow from n-type semiconductor to p-type semiconductor and majority charge carriers holes flow from p-type semiconductor to n-type semiconductor, creating a positive charge in n-region and negative charge in p-region. During the flow of charge carriers, the recombination process results a region having no mobile charges known as depletion region. Due to flow of holes (positive carriers) from p-type material to n-type material, the direction of current is from p material to n-type material across depletion region. This current can be referred as internal current/dark current. In other words, the flow of current is in opposite direction to flow of electrons (negative charge carriers) from n-type material to p-type materials. So, p- and n-type materials are considered as positive and negative terminals. The steady state is achieved when the built in potential across the junction opposes the flow of charge from either sides as shown in Fig. 3.1b. The p–n junction is connected to any external batteries either in forward or in reverse bias as per the required application. In forward bias condition, the direction of internal/dark current across depletion region and external current are in same direction. In this case, terminal at p and n material of semiconductor is connected to positive and negative terminal of external battery, then the charge carrier face reduced band potential difference. In reverse bias condition, the charge carriers have to overcome band potential difference due to reverse connection between p-n junctions unlike forward bias.

3.2 Basics of Semiconductor and Solar Cells

53

3.2.4 The p–n Junction Characteristics The p–n junction connection in reverse and forward connection has been shown in Fig. 3.2a. Further, the characteristic curve has been given in Fig. 3.2b in absence of external bias (V = 0) for reverse and forward conditions. As shown in Fig. 3.2a, one can get current (I) with change in external voltage (V ) for reverse and forward bias by changing the resistance in closed loop. The results indicates that there is a large variation of current in forward bias as direction of current across junction is increased due to same direction unlike reverse bias as shown in Fig. 3.2b. Since n-type semiconductor is more conducting in nature in comparison with ptype semiconductor due to excess of electron, and hence, the n-type semiconductor

a Depletion region is more p

n

p

n

R

R

V

V

Reverse Biased

Forward Biased

b I

Forward Biased Region

-V

V

Reverse Biased Region -I

Fig. 3.2 a Reverse and forward bias connection between p–n junction and external battery without illumination. b I-V characteristic of p–n junction without illumination

54

3 Solar Cell and Photo-Voltaic Effect

a

e-

hυ Depletion Region

n p

h+

b

Io IL

I

I V

V

I Fig. 3.3 a P–n junction with photon illumination. b I-V characteristic of p–n junction with illumination with photon of solar energy

is exposed to photon as shown in Fig. 3.3a. Further, the thickness of n-type semiconductor is in μm to have low thermal resistance to photon for easy excess to depletion region. In other words, photon is easily transmitted to depletion region to isolate neutralized electrons and holes because photon energy (hυ) is much more than binding energy of electron–hole combination. Due to small thermal resistance (0.1–0.5 μm) of n-type semiconductor in comparison with 0.20–0.5 mm thickness of p-type semiconductor, it is easy for new created electron to move through n-type semiconductor. Hence, the motion of electron movement in presence of illumination is always in opposite to direction of movement of electron without illumination. So, in I-V characteristic curve with illumination, one gets negative current value as shown in Fig. 3.3b.

3.2.5 Photovoltaic Effect As explained in Sect. 3.2.4, the electron–hole pairs in the depletion region due to the absorption of photon (solar radiation) are driven by the internal electric fields producing a photocurrent (I L ). The direction of the photocurrent is in a direction

3.2 Basics of Semiconductor and Solar Cells

55

opposite to the forward dark current as shown in Fig. 3.3b. This photocurrent flows continuously even in the absence of external applied voltage as short-circuit current (ISC ). Absorption of more light produces more electron–hole pairs; hence, this current depends linearly on the light intensity. This effect is known as photovoltaic effect. The p–n junction with this effect is referred as solar cell/photo cell.

3.2.6 Solar Cell (Photovoltaic) Materials, Tiwari and Mishra [2] The solar cells are consists of various materials with different structure to reduce the initial cost and achieve maximum electrical efficiency. There are various types of solar cell material, namely (a) the single crystal, (b) polycrystalline, (c) amorphous silicon, (d) compound thin-film material, and other semi conductor absorbing layer which give highly electrical efficient solar cells for specialized applications. Crystalline silicon (c-Si) cells are more expensive but most popular due to easily availability throughout world and high stability with maximum life. The amorphous silicon (a-Si) thin-film solar cells are less expensive and stability. The amorphous silicon layer is used with both hydrogen and fluorine incorporated in the structure. The electrical efficiency of a-Si module lies between 6 and 8%. Thin-film solar cells can be manufactured by using a variety of compound semiconductor. These compound semiconductor materials are cadmium sulfide (CdS), cadmium telluride (CdTe), copper–indium selenide (CuInSe2 ), copper sulfide (Cu2 S), and indium phosphate (InP). The copper–indium selenide (CuInSe2 ) solar cell stability appears to be excellent. The combinations of different band gap material in the tandem configurations lead to photovoltaic generator of higher efficiencies. Here, we will only discuss the material easily available for manufacturing of solar cells. Silicon (Si) Crystalline silicon (c-Si) is most extensively used bulk material for manufacturing of solar cells. Bulk silicon can be processed to obtain monocrystalline silicon, polycrystalline silicon, or ribbon silicon using advanced processing technologies. (i) Monocrystalline silicon (c-Si): Monocrystalline silicon is cut from the cylindrical ingots made from Czochralski process. The solar cells are cut in pseudosquare shape to minimize the wastage of processed monocrystalline silicon in comparison with cylindrical shape of solar cell. Hence, photo-voltaic (PV) module is prepared by using monocrystalline silicon, some portion/area is uncovered from the solar cell. So, packing factor is always less than 1. (ii) Poly- or multi-crystalline silicon (poly-Si or mc-Si): In poly- or multicrystalline silicon, the crystal structure is not same throughout. Polycrystalline silica is made from square ingots, and hence, photo-voltaic (PV) module prepared by poly or multi-crystalline silicon has packing factor 1 without

56

3 Solar Cell and Photo-Voltaic Effect

wastage of any materials. Because of that, it is most popular nowadays. The ingots are made by cooling and solidifying the molten silicon in controlled environment. The wafers (of thickness ~ 180–350 μm) are cut from the square ingots, and it is used for manufacturing polycrystalline solar cells. It is less expensive compared to monocrystalline solar cells. Polycrystalline solar cells have lower electrical efficiency due to grain boundaries present in solar cells. (iii) Ribbon silicon: Ribbon silicon is the thin film made from the molten silicon. These are polycrystalline in nature. In processing of ribbon silicon, there is no waste of processed silicon as well as no sawing is required; therefore, solar cell manufactured from ribbon silicon is further less expensive than polycrystalline solar cells. Thin-film solar cells with transparent top and bottom cover can be potentially used in building and greenhouse integrated photovoltaic thermal systems to produce both electrical and thermal power. In spite of all the present technologies (generations of solar cells), the first-generation solar cells abundantly cover the photovoltaic market; hence, efforts are being made to achieve lowest cost per watt solar cell. The total series resistance of the solar cell can be expressed as: Rs = Rcp + Rbp + Rcn + Rbn

(3.3)

where Rcp , the metal contact to p-type semiconductor resistance; Rbp , the bulk ptype resistance; Rcn , the contact to n-type semiconductor resistance, and Rbn , the bulk n-type resistance. In thermal modeling, an electrical losses due to Rs is always neglected for its small value. The idealized junction current is given as, I = I0 exp

e(V − IRs ) kT

−1

(3.4a)

If Rs is neglected, then Eq. 3.4a becomes diode current as I D = I0 exp

eV kT

−1

(3.4b)

In addition, a shunt path may exist for current flow across the junction due to surface effect or poor junction region. This alternate path for current constitutes a shunt resistance R p across the junction. Then, I = I L − I0 exp

e(V − IRs ) AkT

−1 −

V − IRs Rp

where A is an empirical non-idealist factor and is usually 1.

(3.5)

3.3 Basic Parameters of Solar Cell

57

(i) Organic/polymer Solar Cells Organic solar cell is a thin-film polymer solar cell. The polymer solar cell made of using organic semiconducting materials like copper phthalocyanine, polyphenylene vinylene, and carbon fullerenes, Gautam and Kaushik [3]. These solar cells are less costly and have high optical absorption coefficient, and the energy band gap can be tailored by changing the chain length of polymer. The energy conversion efficiency of organic solar cells is low in comparison to inorganic solar cells. The lower stability, smaller life, and degradation are the major limitations of organic solar cells. But it is easy to install as greenhouse cover material due to it flexible in nature. It has same life as greenhouse transparent PVC covers.

3.3 Basic Parameters of Solar Cell In this section, some basic parameters essential for understanding of characteristics curve of solar cell (Fig. 3.2b) will be discussed. Figure 3.2b shows negative current. This gives the direction of current because negative current has no meaning. Hence, Fig. 3.2b can be redrawn as shown in Fig. 3.4a. Further, Fig. 3.4b shows electrical power curve integrated with I-V curve. This is useful to determine the maximum power at maximum voltage and correspondingly maximum current can be obtained. Followings are basic parameters of solar cells:

3.3.1 Overall Current (I ) An overall current (I ) flowing through solar cell is given by I = ID − IL

(3.6a)

eV kT

(3.6b)

From Eq. 3.4b, one has I = I0 exp

− 1 − IL

where I L and I0 are light induced and leakage current, respectively. If leakage current (I0 ) is very small in comparison with light-induced current (I L ), then Eq. 2.6b will be negative as shown in Fig. 3.3b. It is due to fact that light-induced current (I L ) varies according to variation of solar radiation.

58

3 Solar Cell and Photo-Voltaic Effect

a

b

Im

Electrical power curve Vm

Fig. 3.4 a Modified I-V characteristic curve of solar cell. b Variation of electrical power and current with voltage curve

3.3.2 Short-Circuit Current (I SC ) Short-circuit current, ISC is the light-induced current (I L ) when load in the circuit is zero, i.e., both the terminals (positive and negative) of solar cell are connected together (V = 0), Fig. 3.4a.

3.3.3 Open-Circuit Voltage (Voc ) Open-circuit voltage is the voltage across the solar cell when there is no current flowing in the circuit. This means I = 0 in Eq. 3.6b (Fig. 3.4a). There is infinite

3.3 Basic Parameters of Solar Cell

59

resistance between the terminals of solar cell. It can be found from Eq. (3.6) by substituting I = 0, and it can be expressed as follows: Voc =

IL kT ln +1 e I0

(3.7)

The open-circuit voltage is the voltage for maximum load in the circuit. The I-V characteristics curve with illumination and without illumination has been shown in Figs. 3.3b and 3.4, respectively. The I-V curve for both cases has been −IRs ) − 1 [4]. For ideal solar cell, series resistance plotted using I = I0 exp e(V kT must be zero as explained earlier and shunt resistance must be infinite. For better performance of solar cell, the series resistance must be kept as minimum as possible and the shunt resistance must be as large as possible. In commercial solar cell, the shunt resistance is very large and is neglected in comparison to the forward resistance of diode.

3.3.4 Maximum Power Referring to Fig. 3.4b, the maximum power, Pmax from solar cell will be Pmax = V P max I P max

(3.8a)

where V P max and I P max can be obtained from power and voltage curve derived from Fig. 2.4b. Corresponding to maximum power, there will be maximum power resistance given below R P max =

V P max I p max

(3.8b)

The electrical efficiency of solar cell is also defined as, η=

P I T × Ac

(3.9)

where P = V × I and IT × Ac are the power delivered by solar cell and the solar radiation, IT falling on solar cell of area Ac .

60

3 Solar Cell and Photo-Voltaic Effect

3.3.5 Fill Factor (FF) The fill factor (FF) gives an idea about the maximum power output withdrawn from the solar cell for given Voc and Isc . In another words, FF determines the sharpness of I-V curve. Mathematically, it is expressed as ratio of maximum power to maximum power derived under short-circuit current and open-circuit voltage. It is expressed as follows: FF =

Pmax Imax × Vmax = Voc × Isc Voc × Isc

(3.10)

The value of FF in ideal condition is unity. Deviation from the ideal value is due to the defects and contact resistance in solar cell mentioned in Eq. 3.3. Lower the value of the FF less sharp will be the I-V curve as shown in Fig. 3.4b. For c-Si solar cell, the maximum value of fill factor (FF) is 0.88. Numerical value of fill factor (FF) is provided by manufacturer of solar cell. So, the maximum power can also be obtained for known FF as Pmax = Vmax × Imax

(3.11a)

Similarly, the power can be also evaluated from known current and voltage as shown in Fig. 3.4a. The output power from solar cell is obtained by multiplying the output voltage and output current as given below: Pout = Vout × Iout

(3.11b)

3.3.6 Solar Cell Electrical Efficiency ηec The solar cell electrical power conversion efficiency can be expressed as, ηec =

Voc × Isc × FF Pmax Vmax × Imax = = Pin Incident solar radiation × Area of solar cell I (t) × Ac (3.12)

where Imax and Vmax are corresponding to given I (t) The typical characteristic of c-Si solar cell under standard test condition is given in Table 3.3. Further, it is important to note that there is basic difference between standard test condition and real open door condition which has been briefly summarized in Table 3.4. The specification of different solar cells has been given in Appendix-B.

3.3 Basic Parameters of Solar Cell Table 3.3 Characteristic of c-Si solar cell under STC

61

S.No Characteristic

Value

1

Thickness of emitter (Tc )

2μm

2

Thickness of base (Tb )

250 μm

3

Concentrated sunlight(C)

1

4

Total short-circuit current (I sc )

40.01mA/cm2

5

Total open-circuit voltage (V oc )

630.56mV

6

Maximum total current (I m )

38.21mA/cm2

7

Maximum total voltage (V m )

550.42mV

8

Fill factor (FF)

0.8335 (83.35%)

9

Conversion electrical efficiency (ηc ) 0.2103 (21.03%)

Table 3.4 Difference between standard test condition (STC) and real condition S.No

Type of condition

Standard test condition (STC)

Real condition (open field)

1

Incidence angle of solar radiation

Zero

Latitude ± 15 [+ refer winter and –ve refer summer]

2

Solar irradiation

1000 W/m2

It depends on time, date and latitude

3

Ambient air temperature

25 °C

It depends on time, date, latitude and weather condition, season as well

4

Air mass coefficient (AM)

1.5

It depends on time, date and latitude

5

System losses (T&D)

Assumed to be zero

It depends on location of PV panel, inverter and grid meter and users

◦

Example 3.2 Evaluate fill factor (FF) for a solar cell for the following parameters: VOC = 0.2V , ISC = −5.5 mA, Vmax = 0.125V , Imax = −3 mA Solution Substituting the appropriate values in Eq. (3.10), we get, Fill factor, FF =

Vmax × Imax 0.125 × 3 = 0.34 = Voc × Isc 0.2 × 5.5

Example 3.3 Evaluate the maximum power (Pmax ) and solar cell electrical efficiency (ηec ) of the solar cell at an intensity of 200 W/m2 . Other given parameters:VOC = 0.24 V, ISC = −9 mA, Vmax = 0.14 V, Imax = −6 mA, AC = 4 cm2 . Solution From Eq. (3.11), one gets Pmax = Vmax × Imax = 0.14 × (−6) = −0.84 mW

62

3 Solar Cell and Photo-Voltaic Effect

Since electric power is never negative and hence Pmax = 0.84 mW. Negative sign in current only shows the direction of current. From Eq. (3.12), one has the following, 0.14×6×10−3 Solar cell electrical efficiency (ηec ) = output = ( 200×4×10−4 ) = 0.0105 = 1.05% input ( )

3.4 Effect of Solar Cell Temperature (Tc ) on Its Electrical Efficiency A fraction of incident solar radiation produces electricity by solar cell as mentioned earlier. The remaining solar radiation is converted into thermal energy which raises its temperature after thermal loss from top and bottom. Due to increased temperature of solar cell, electrons in depletion region starts colliding each other more frequently, then its direction of movement is disturbed and it affects the current and hence power. The temperature of solar cell deteriorates the electrical performance of the solar cell. For unit area of solar cell, the energy balance can be written as follow: αc I (t) = ηc I (t) + U L (Tc − Ta )

(3.13)

where αc is the absorptivity of the solar cell, ηc is the electrical efficiency of the solar cell, and U L is the overall loss coefficient from top loss as well bottom of solar cell; the top and bottom loss coefficient is determined by taking into account of convection and radiation both. From Eq. (3.13), solar cell temperature, Tc can be obtained as Tc = Ta +

ηc αc 1− I (t) UL αc

(3.14)

The electrical efficiency (ηec ), as a function of temperature, is given by [5, 6] ηc = η0 [1 − β0 [Tc − T0 ]]

(3.15)

where η0 is electrical efficiency of solar cell at standard test condition (STC) [solar ◦ flux of 1000 W/m2 and surrounding temperature of T0 = 25 C]; β0 c-Si silicon efficiency temperature coefficient 0.0045 K−1 or 0.0064 K−1 and Tc is solar cell temperature (K ). Solar cells are tested for their efficiency at 25 °C, and that is why this is used as the reference point. Most solar cells have a temperature coefficient of around − 0.3%/°C to–0.5%/°C. For example, Sun power’s solar cell all has a temperature coefficient of − 0.37%/°C From Eqs. 3.14 and 3.15, one can get an analytical expression for solar cell temperature as

3.4 Effect of Solar Cell Temperature (Tc ) on Its Electrical Efficiency

Tc =

Ta +

αc UL

1− 1−

η0 (1+β0 T0 ) αc

63

I (t) (3.16)

η0 β0 I (t) UL

It is important to note that an analytical expression for solar cell temperature (Tc ) given by Eq. 3.16 is a function of design and climatic parameters and can be evaluated. After knowing the numerical value of solar cell temperature (Tc ), one can get electrical efficiency of solar cell from Eq. 3.15. Electrical power obtained by solar cell can be written as E˙ el = ηc I (t) Ac

(3.17)

where Ac is an area of solar cell Example 3.4 Determine solar cell temperature for the following parameters: ◦ ◦ Ta = 30 C, T0 = 25 C, η0 = 0.15, β0 = 0.0045 K−1 , αc = 0.9, U L = ◦ 6 W/m2 C, and I(t) = 200 W/m2 . Solution From Eq. 3.16, we get

Tc = =

Ta +

αc UL

1− 1−

η0 (1+β0 T0 ) αc

η0 β0 I (t) UL

I (t)

=

30 + 0.15 1 − 1−

0.1668 0.9

0.135 6

30 + 0.8147 ◦ = 31.52 C 0.9775

So, one can see that solar cell temperature is increased by 1.52 °C due to incident solar radiation on it. Example 3.5 Calculate solar cell electrical efficiency for Example 3.4 Solution From Eq. 3.15, one has ηc = η0 [1 − β0 [Tc − T0 ]] = 0.15[1 − 0.0045(31.52 − 25)] = 0.15[1 − 0.02934] = 0.15 × 0.97066 = 0.1456 This indicates that solar cell electrical efficiency is decreased due to increase in solar cell temperature. This is responsible for creating collision between electrons in depletion region. Example 3.6 Calculate solar cell temperature for Examples 2.4 and 2.5 Solution By using Eq. 3.14, one gets

64

3 Solar Cell and Photo-Voltaic Effect

Tc = Ta +

ηc αc ◦ 1− I (t) = 30 + 0.15(1 − 0.16667) = 30.15 C UL αc

This indicates that real numerical value of solar cell is further reduced in comparison with results reported in Example 3.4 and solar cell electrical efficiency will be as follows: ηc = η0 [1 − β0 [Tc − T0 ]] = 0.15[1 − 0.0045(30.15 − 25)] = 0.1465 This iteration process should continue till electrical efficiency becomes constant.

3.5 Generation of Solar Cell (Photovoltaic) Materials Photovoltaic (PV) cells (solar cells) are basically classified (grouped) into four generations, namely first-generation, second-generation, third-generation, and fourth (4th)-generation cells. Different components and materials of c-Si solar cell (first generation) have been shown in Fig. 3.5. One can see that there is first silicon nitride anti-reflection material to avoid reflection from solar cell exposed surface to have maximum solar radiation as a input. Further, one can observe that thickness of phosphorous emitters (n-type) material is less than p-type material due to its large value of electrical conductivity and transparent to photon of solar radiation. A doped p-type square wafer [10] having thickness around 300 μm with an effective area of 10 × 10 cm2 or 12.5 × 12.5 cm2 . At end there is Al base (rear contact) to support solar cell. These are based on the materials used for manufacturing of solar cells. Figure 3.6 shows different stages for manufacturing of solar cell. Followings are the brief about different generation of solar cell materials. Fig. 3.5 Different components of c-Si solar cell

3.5 Generation of Solar Cell (Photovoltaic) Materials

65

Fig. 3.6 Different stages of manufacturing of solar cell

Different generations of solar cells First Generation Single crystal silicon wafers (c-Si) (24.7 %)

Second Generation Amorphous silicon (a-Si) (12.1 ) Polycrystalline silicon (poly-Si) (20.5 ) Cadmium telluride (CdTe) (16.5 ) Copper indium gallium diselenide (CIGS) (19.5 )

Third Generation Polymer solar cells (> 8 ) Dye sensitized solar cell (DSSC) (11.1 )

Fourth Generation Organic-inorganic hybrid solar cells (~ 3 )

As can be seen from above that solar cell technologies are categorized into four generations. These generations are classified according to the time of evolution of respective technology. Presently, research and development activities for the efficiency improvement along with reduction in production cost and stability for each generation of solar cell are being continued in various research groups globally. About 85% of the solar cell market is dominated by first- and second-generation solar cells, Pierce (2008).

66

3 Solar Cell and Photo-Voltaic Effect

3.5.1 First Generation of Solar Cell First-generation solar cells are based on Si wafer technology which includes monocrystalline and polycrystalline silicon solar cells. These solar cells are single junction solar cell with 33% theoretical electrical efficiency, Hence [7]. The processing technology involved for manufacturing of first-generation solar cell requires high energy and labor investment. Energy conversion efficiency of first generation solar cell is 15–20%. These solar cells are widely used among all the generation of solar cells.

3.5.2 Second Generation of Solar Cell Second-generation solar cells include the amorphous solar cells. The efficiency of these solar cells is low in comparison to first-generation solar cells, but the production cost is low. This solar cell technology does not require high-temperature processing unlike first-generation solar cell. The second-generation solar cell materials include CdTe, CIGS, a-Si and micro-amorphous silicon. The second-generation solar cells are manufactured by depositing the thin film of above materials on the substrates (Si, glass or ceramics) using chemical vapor deposition technique or molecular beam epitaxial technique or spin coating technique.

3.5.3 Third Generation of Solar Cell Third-generation technologies mainly focus on the improvement of energy conversion efficiency and light absorption coefficient of second-generation solar cells while keeping the production cost near to the production cost of second-generation solar cells. The enhancement in efficiency can be achieved by manufacturing multijunction solar cells, improving the light absorption coefficients (concentrating solar cells) and by using techniques to increase the carrier collection, Soto et al. [8].

3.5.4 Fourth Generation of Solar Cell The 4rth (fourth-generation) solar cell technology is also referred to as the 4G solar cell technology. This technology makes use of the combination of inorganic and organic materials, as a means to boost the electrical efficiency with cost-effectiveness and stability of solar cells. The 4G solar cells are engineered at solar scale in comparison with first generation. It is characterized by the flexibility of conducting polymer

3.6 Applications of Solar Cells [9]

67

Fig. 3.7 Solar cell efficiency of different generation (Appendix-B)

films (the organic materials), and the stable nanostructures (inorganic materials), and hence, it also called hybrid solar cell. In the fourth-generation solar cells, the commonly used material is transparent tindoped indium oxide. However, new alternatives have made use of graphene, metal nanowires, and metal grid structures. The essence of the nanomaterials in these solar cells enables large volume of surrounding the nanomaterial to be filled using a conductor, such as a polymer. The main advantage of fourth-generation solar cell is the combination of organic and inorganic substrates that improve the harvesting of solar energy to ensure better electrical efficiency to maintain also meaningful cost savings. The National Renewable Energy Laboratory (NREL) [11] provided an electrical efficiency of different generation of solar cell as given in Fig. 3.7. Here it is important to mention that only higher electrical efficiency is not enough to select the type of solar cell, but its stability and life are also important and hence considering all three parameters, c-Si solar cell is preferred which captures most of markets at present. Further, Eq. 3.15 indicates that electrical efficiency decreases with increase of solar cell temperature as shown in Fig. 3.8 for all types of solar cell.

3.6 Applications of Solar Cells [9] There are many applications of solar cell which will be discussed in coming chapters which include as follows:

68

3 Solar Cell and Photo-Voltaic Effect

Fig. 3.8 Variation of electrical efficiency of various solar cells with temperature

(a) (b) (c) (d) (e)

Photo-voltaic thermal system (water/air collectors) Building/greenhouse integrated system Street light/charging of batteries Water pumping/irrigation and Roof top integration/stand-alone system for power generation, etc.

Problems 3.1 Find out the energy band gap in different solar cell materials (Table 2.1) at Hint: Example 3.1 3.2 Find out different fill factor (FF) for a solar cell for the following parameters VOC = (0.2 − 0.4)V , ISC = −(5.5 − 8)mA, Vmax = 0.125V, Imax = −3mA Hint: Example 3.2 3.3 Evaluate the maximum power (Pmax ) and solar cell electrical efficiency (ηec ) of the solar cell at an intensity of 200 W/m2 . Other given parameters: VOC = 0.2 V, ISC = −5.5 mA, Vmax = 0.14 V, Imax = −6 mA, AC = 4 cm2 . Hint: Example 3.3 3.4 Find out variation of solar cell temperature for the following parameters ◦ ◦ Ta = 30 C, T0 = 25 C, η0 = 0.15, β0 = 0.0045 K−1 , αc = 0.9, U L = ◦ 6 W/m2 C, and I(t) = 200 − 400 W/m2 . Hint: Eq. 3.16 3.5 Evaluate electrical efficiency of solar cell for Problem 2.4 Hint: Eq. 3.15 3.6 Draw I-V curve in forward case without illumination. Hint: See Fig. 3.2b. 3.7 Draw I-V curve in reverse case without illumination. Hint: See Fig. 3.2b.

3.6 Applications of Solar Cells [9]

69

3.8 Draw I-V curve in forward case with illumination. Hint: See Fig. 3.3b and 3.4a. 3.9 Draw I-V curve in reverse case with illumination. Hint: See Fig. 3.3b. 3.10 Draw the variation of an electrical efficiency of solar cell with its temperature for given following parameters ◦ ◦ η0 = 0.15, β0 = 0.0045/0 C, T0 = 25 C, and Tc = 25 − 50 C, Hint: Use Eq. 3.15. 3.11 Draw the power curve with solar intensity for Example 3.4 of an area of solar cell ( Ac = 0.60 m2 ) Hint: Use Example 3.4 and Eq. 3.17. Objective Questions 3.1 Solar energy can be used for (a) Thermal energy (b) Electrical energy (c) Mechanical energy (d) All of them. Answer: (a) and (b) 3.2 The common material used for making solar cell is (a) Silver (b) Iron (c) Aluminum (d) Silicon Answer: (d) 3.3 The electrical output of a solar cell mainly depends on (a) Solar radiation (b) Heat component of solar radiation (c) Ultraviolet radiation (d) Infrared radiation Answer: (a) 3.4 Solar photo-voltaic (PV) cells convert solar radiation directly into (a) Mechanical energy (b) Heat energy (c) Electricity (d) Transport energy Answer: (c) 3.5 The SPVT stands for (a) Solar photo-voltaic thermal (b) Solar plate-voltaic thermal (c) Solar plate-voids thermal (d) None of the above Answer: (a) 3.6 Solar photo-voltaic (solar cell) technology is used for (a) Solar air heater (b) Biogas plant (c) Solar water heater (c) Solar lantern Answer: (d) 3.7 The highest reported electrical efficiency of solar cell is (a) Amorphous silicon (b) Single crystal silicon (c) Polycrystalline silicon (d) Thin-film silicon Answer: (b) 3.8 The maximum electrical efficiency of a commercial solar cell is (a) 3% (b) 12%-30% (c) 50%-65% (d) 65%-70% Answer: (b)

70

3 Solar Cell and Photo-Voltaic Effect

3.9 The world’s largest solar power plant exists at (a) Germany (b) USA (c) India (d) UK Answer: (b) 3.10 Which of the following materials has the lowest solar cell electrical efficiency? (a) Amorphous silicon (b) Gallium arsenide (c) Polycrystalline silicon (d) Single crystal silicon Answer: (b) 3.11 PV (solar cell) system provides (a) Clean power (b) Good environment (c) Sustainable climate (d) All of them Answer: (d) 3.12 Fill factor (FF) of solar cell is (a) Less than 1 (b) More than one (c) Zero and (d) Equal to one Answer: (a) 3.13 The solar cell produces (a) Direct current (DC) (b) Alternate current (AC) (c) indirect current (d) None of them Answer: (a) 3.14 The thickness of n material in solar cell is in (a) Micrometer (b) Millimeter (c) Centimeter (d) Meter Answer: (a) 3.15 The thickness of p material in solar cell is in (a) Micrometer (μm) (b) Millimeter (mm) (c) Centimeter (d) Meter Answer: (b) 3.16 Thickness of n material in comparison with p material is (a) More (b) Less (c) Equal (d) Negligible Answer: (b) 3.17 Which material of solar cell is exposed to solar radiation (a) n-material (b) p-material (c) Both and (d) None 3.18 Energy band gap between n and p material in solar cell is (a) Infinity (b) Large (c) Very large and (d) Zero Answer: (d) 3.19 The electrical efficiency of solar cell depends on (a) Temperature (b) Solar radiation (c) Wind velocity and (d) All of them Answer: (d) 3.20 The electrical efficiency of solar cell can be increased by (a) Increasing its temperature (b) Decreasing its temperature (c) Increasing solar radiation and (d) Increasing wind velocity Answer: (b) and (d) 3.21 The electrical efficiency of solar cell is maximum at. (a) 25°C (b) Ambient air temperature, T a (c) 100°C and (d) 0 °C Answer: (a)

References

71

References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Tiwari GN, Tiwari A, Shyam (2016) Handbook of solar energy, Springer Tiwari GN, Mishra RK (2012) Adv Renew Energy Sources, RSC publishing UK Gautam NK, Kaushik ND (2002) Energy 27:347 Tsalides P, Thanailakis A (1985) Solar Cells 14:83 Kern J, Harris I (1975) Sol Energy 17(2):97 Pierce B, Very high efficient solar cells, http://www.arpa.mil/sto/smallunitops/vhesc.html. Accessed 25 Jul 2008 Hance J, Breakthrough in solar energy, http://news.mongabay.com/2008/0710-hance_solar. html. Accessed 18 Aug 2008 Soto WD, Klein SA, Beckman WA (2006) Sol Energy 80:78 Tiwari GN, Dubey S (2010) Fundamentals of Photovoltaic modules and their applications. RSC publishing, UK Semiconductor Materials for Solar Cells, https://ocw.tudelft.nl › wp-content › uploads › Sol... Best Research-Cell Efficiency Chart—NREL, https://www.nrel.gov › cell-efficiency

Recommended additional references for further studies 11. Fortman M, Zhou T, Malone C, Gunes M, Wronski R (1990) Deposition conditions, hydrogen content and the Staebler-Wronski effect in amorphous silicon. In: Conference record of the 21st photovoltaic specialist conference, 1648–1652 12. Green AM (1998) Solar cells operating principles technology and system application, 1st edn. University of New South Wales, New South Wales 13. Roedern BV, Ullal HS (2008) The role of polycrystalline thin film PV technologies in competitive PV module markets. In: 33rd IEEE photovoltaic specialists conference proceedings, 1–4 14. Schock H (2007) Chalcopyrite (CIGS) based solar cells and production in Europe. In: Technical digest 17th international photovoltaic science and engineering conference (PVSEC-17), 40–43 15. Fraunhofer ISE (2009) World Record: 41.1% efficiency reached for multi-junction solar cells at Fraunhofer ISE; press release 16. O’Regan B, Gratzel M (1991) Nature 353:737 17. Tiwari A, Sodha MS (2006) Renew Energy 31(15):2460 18. Evans DL (1981) Sol Energy 27:555 19. Barra L, Coiante D (1993) Sol Energy 51:383 20. Prakash J (1994) Energy Convers Manage 35:967 21. Yamawaki T, Mizukami S, Masui T, Takahashi H (2001) Sol Energy Mater Sol Cells 67:369 22. Nagano K, Mochida T, Shimakura K, Murashita K, Takeda S (2003) Sol Energy Mater Sol Cells 77:265 23. Singh GK (2013) Analysis of environmental impacts on the performance of PV modules, Ph.D. Thesis, I.I.T. Delhi, New Delhi, India 24. Agrawal B, Tiwari GN (2010) Building Integrated photovoltaic thermal systems. RSC publishing, UK 25. Agrawal B, Tiwari GN, Developments in Environmental durability for photovoltaics. Pira International Ltd., UK

Chapter 4

Photovoltaic (PV) Module and Its Panel and Array

4.1 Introduction In Chap. 3, the solar cells convert visible solar radiation into direct current (DC) and voltage to produce electrical power by the photovoltaic effect. Single solar cell cannot generate enough electrical power due to low voltage (mV) for many of the practical applications. Therefore, solar cells are connected in series to increase voltage and hence DC electrical power as per requirement. It is referred as photo-voltaic (PV) module.

4.1.1 Photo-Voltaic (PV) Module The solar cells connected in series, Fig. 4.1a, are sandwiched between top toughen transparent glass and bottom opaque/transparent cover with the help of ethyl vinyl acetate (EVA) to protect it from adverse weather conditions for its longer life as shown in Fig. 4.1b. The photo-voltaic (PV) modules are available in different size and shape depending on the required electrical output power. In Fig. 4.1a thirty-six (36) cSi base solar cells are connected in series to produce 18 V with electrical power of about 75 Wp . The number and size of series connected solar cells decide the electrical output of the PV module from a particular material (wafer-based c-Si, or a thin-film CdTe, or crystalline silicon) primarily. The electrical interconnections and weather and climatic conditions are some other factors which affect electrical output of the PV module. Globally, opaque PV modules, Fig. 4.1b, made of different materials are easily available in the market and it widely used. But semi-transparent (glass to glass) PV modules, Fig. 4.1c, are available with specific order. In this type of PV module, the series connected cells are sandwiched between top glass cover and Tedlar/glass and sealed with metal frame. Most of the c-Si base PV modules are rigid, but thin-film solar cell-based modules are flexible (curved toughen glass–glass © Bag Energy Research Society 2023 G. N. Tiwari, Advance Solar Photovoltaic Thermal Energy Technologies, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4993-9_4

73

74

4 Photovoltaic (PV) Module and Its Panel and Array

(a) Top View Toughen

Tedlar (b) Cross-sectional view

(c ) Semi-transparent PV module

(d) Aluminium base flexible PV module

(d) Thin film flexible PV module Fig. 4.1 Opaque and semi-transparent PV module

4.1 Introduction

75

PV module, Fig. 4.1c). Figure 4.1c, d shows the aluminum (Al) base flexible and thin-film PV modules. Here it is important to mention that thin-film PV module is more flexible than Al base PV module. The positive and negative terminals for interconnections are provided on the backside of PV module through junction box (Fig. 4.1a). All PV modules are rated in watt peak (W p ) under STC; it is the power produced at 1000 W/m2 and surrounding air temperature of 250 C (Table 3.4). A typical panel with 40 W p rating may produce energy between 100 Wh and 200 Wh per day depending upon sunshine hours with clear weather condition. Table 4.1a, b shows the technical and physical parameters of a typical 75Wp PV module under STC condition. Example 4.1a Calculate conductive heat transfer coefficient (h k ) for EVA and Tedlar. Solution: An expression for conductive heat transfer coefficient is given by So, for EVA by using data of Table 4.1 hk =

Thermal conductivity of material Thickness

hk =

0.26 = 260 W/m2 ◦ C 0.001

Table 4.1 Parameters of a typical 75Wp PV module under STC condition [Appendix-B] S.No.

Variable

Rating

1

Current

4.4 Amp

2

Voltage

18 V

3

Constant solar radiation

1000 W/m2

4

Area of solar cell

0.605m2

5

Packing factor

0.89

6

Electrical efficiency

12% (0.12 in fraction)

7

Number of solar cell in one PV module

36

Physical of glass material and solar cell Physical properties

Glass

c-Si solar cell

Tedlar

EVA

Thermal conductivity (W/mK)

0.78

1300

0.1583

0.26

Specific heat (kJ/kgK)

0.84

0.7

–

–

Diffusivity (m2 /s)

3.44 ×10−4

0.8 ×10−4

–

–

Density

(kg/m3 )

2700

2330

–

–

Transmittance

0.90–0.95

0

0 or 0.94

> 0.9

Thickness (m)

0.003

0.0001

0.00035

0.001

76

4 Photovoltaic (PV) Module and Its Panel and Array

For Tedlar hk =

0.1583 = 452 W/m2 ◦ C. 0.00035

Other main components of PV modules are as follows: (a) Junction box: A junction box has bypass diodes that keep power flowing in one direction and prevent it from feeding back to the PV module. • It is pre-installed on the backside of a solar PV module with help of silicon adhesive. • It is often an overlooked piece of the PV module but protective from an environment (b) Charge controller: Solar charge controller is an electronic device that manages the DC power from PV panel/arrays going into the battery bank from the solar array. • It ensures that the deep cycle batteries are not overcharged during the day. • The power does not run backward to the solar panels overnight and drain the batteries. • Its design depends on rated current available from PV panel/arrays and hence its cost/ (c) Solar batteries: The charge controller is connected to battery for charging by DC current. There are four main types of battery technologies: • Lead acid battery: Lead acid batteries (flooded lead acid batteries and sealed lead acid batteries) are the tried and true technology of the solar battery world. It is the cheapest energy storage option and the most cost effective. It is also reliable. It can be easily disposed of and recycled. It needs ventilation. It can be used for emergency backup storage in case of a power outage. It requires regular maintenance. • Lithium ion battery: It quickly became one of the most widely used solar battery banks for e-rickshaw/residential solar installations. It requires almost no regular maintenance. It can hold more energy in a smaller space than a lead acid battery. It has a longer life cycle, or lifespan, as well most have a guaranteed warranty of at least 10 years. It is more expensive than other energy storage technologies. • Nickel cadmium battery: A nickel cadmium battery converts chemical energy to electrical energy upon discharge and converts electrical energy back to chemical energy upon recharge. It is not useful for PV systems. The electrolyte is a solution of potassium hydroxide (KOH) with a small addition of lithium hydrate which increases the capacity and life of the battery. It is not recommended for solar charging. • Flow battery: It is also not suitable for PV system.

4.1 Introduction

77

(d) Inverters: The inverter is a static device. An inverter refers to a power electronic device that converts power in DC form (PV-SYSTEM) to AC form at the required frequency and voltage output. The voltage source inverter has stiff DC source voltage that is the DC voltage has limited or zero impedance at the inverter input terminals. Example 4.1b Calculate number of c-Si solar cell with open-circuit voltage of about 0.5 V with 0.08 V drops at more than 25 °C operating temperature for 15 V opencircuit voltage of PV module. Solution At normal operating temperature, the voltage available across the terminals of each crystalline solar cell is 0.5–0.08 = 0.42 V. 15 Hence, the required number of solar cells to construct such solar module = 0.42 = 36. Hence, 36 numbers of crystalline solar cells are required to build a standard solar module of 15 V. Hence, number of solar cell can be calculated for any required open-circuit voltage of PV module.

4.1.2 Photo-Voltaic (PV) Panel and Array First, PV module, Fig. 4.1, with rated power is prepared by connecting solar cells in series with fixed voltage. In this case, current varies with solar intensity. After those, PV modules can be connected in series further to increase required voltage, say three PV modules, Fig. 4.2a, and then it is referred as PV panel. A photovoltaic (PV) array consists of PV panels which can be connected either in series (S-series array) to increase voltage or parallel (P-parallel array) to increase current or both (S-P array) as shown in Fig. 4.2b. Further, total cross-tied (TCT) PV array is connected using TCT configuration including sensors to measure voltage with shading effect. The performance of honeycomb (HC) configuration is superior than series (S), series– parallel (SP), and bridge-link (BL) PV array configurations under partial shading condition (PSC). Size of the PV array depends on the electrical power requirement. The DC power produced from the PV array is converted into the AC power through an inverter cum charge controller, and then, it is fed to the different AC electrical loads. The PV modules are connected in series to achieve the desired voltage; then such series connected strings are connected in parallel to enhance the current and hence power output from the array. The size of the PV array decides the capacity of such array; it may be in watts, kilowatts, or megawatts. The electrical output of the PV module depends on solar irradiance, solar cell temperature, electrical efficiency of solar cell, and load resistance. For a given generation of solar cell, current increases with increasing solar radiation and marginally affected (decrease) due to temperature rise. But higher solar cell temperature decreases the voltage output of solar cell due to collisions of electrons in depletion region which in turn decreases the electrical efficiency and power output. The

78

4 Photovoltaic (PV) Module and Its Panel and Array

(a) PV string

(b) PV arrays Fig. 4.2 Array connection of PV module

load resistance is decided by the operating point of module at peak power point. The solar cell electrical efficiency is governed by manufacturing process and solar cell material, and it varies from 9 to 20%. Therefore for better performance, the PV module in an array must operate at peak power point. The array must be installed at open place (no shading), and PV module must be kept cool as maximum as possible. Example 4.2 Calculate an electrical power for three PV modules connected in series as shown in Fig. 4.2a for data of Table 4.1 under STC. Solution: Since PV modules are connected in series and hence its voltage will added, it becomes 18 + 18 + 18 = 54 V. By connecting PV module in series, the currents will remain the same, i.e., 4.4 A (Table 4.1). Now, an electrical power for three PV modules (P) = I ×V = 54×4.4 = 273.6W p under STC.

4.2 Materials of PV Module

79

Example 4.3 Calculate an electrical power for three PV panels (each consists of four PV modules) connected in series as shown in Fig. 4.2b for data of Table 4.1 under STC. Solution: By using Example 4.2, the total voltage of one panel consists of four PV modules connected in series = 18 + 18 + 18 + 18 = 72 V. Now, the total voltage of one array consists of three PV panels connected in series = 72 + 72 + 72 = 216 V. So, an electrical power from one PV array (Fig. 4.2b) (three PV panels) = 216 × 4.4 = 950 W p under STC. Example 4.4 Calculate an electrical power for four PV panels (each consists of four PV modules connected in series) connected in parallel as shown in Fig. 4.2b for data of Table 4.1 under STC. Answer: From Example 4.3, the voltage of one panel consists of four PV modules connected in series = 72 V. Since four panels are connected in parallel, its current 4.4 A will be added for same voltage of 72 V = 4.4 + 4.4 + 4.4 + 4.4 = 17.6 A. So, an electrical power from one PV array (Fig. 4.2b) (4 × 4) = 72 × 17.6 = 1267.2 W p under STC.

4.2 Materials of PV Module Following material-based PV modules are available in the market:

4.2.1 Single Crystal Silicon (c-Si) Solar Cells Module Single crystal silicon (c-Si) PV module deploys the series connected crystalline solar cell which is sandwiched between transparent top glass cover (with high transmittivity, low iron content glass), encapsulate (100% transparent ethylene vinyl acetate (EVA)), and back cover (Tedlar, Fig. 4.1b/Mylar/glass, Fig. 4.1c). The crystalline PV modules are divided into two categories, namely (a) opaque PV module (Fig. 4.1b) if the back cover of the PV module is opaque and (b) semitransparent PV module if back cover is also transparent. Since an electrical efficiency of semitransparent PV module (with packing factor less than one) is always higher than an electrical efficiency of opaque PV module due to its low operating temperature. Further, semi-transparent PV module has many applications in building and agricultural greenhouse, Fig. 4.3. Semi-transparent PV module with different packing factor with rating power has been shown in Fig. 4.4 manufactured by central electronics (CEL), Ghaziabad (U.P.), India. The amount of light transmitted depends on the packing factor of semitransparent

80

4 Photovoltaic (PV) Module and Its Panel and Array

PV module. Lower the packing factor, Fig. 4.4c, lower is the area covered by solar cell. Therefore for electrical/thermal/daylighting/photosynthesis application packing factor of the semitransparent PV module can be optimized as per the requirement.

Fig. 4.3 Uneven span greenhouse integrated semitransparent photovoltaic thermal system

C

(a) 80 Wp PV module

(b) 50 Wp PV module

(c) 25 Wp PV module

Fig. 4.4 Semitransparent PV module with different packing factor and electrical power

4.2 Materials of PV Module

81

Daily average electrical efficiency With water flow = 7.36 % Without water flow = 6.85 % Fig. 4.5 Photo of thin-film PV module

4.2.2 Thin-Film PV Modules The thin-film PV modules are made of thin-film solar cells. The thin-film solar cells are manufactured at lower temperature; hence, these technologies are less energyintensive with low cost production. Further the thin-films solar cell can be easily deposited on different substrates such as (a) transparent glass and (b) conducting metal and flexible plastic. The flexibility leads to the use of greater interest in the area having non-smooth surface (different structures) such as greenhouse canopy roof area as shown in Fig. 4.5. The major drawback of this technology is low energy conversion efficiency and degradation on exposure to the adverse weather condition. The major challenge for this technology is improvement of conversion efficiency of commercially made thin-film PV modules (Fortman et al [1]). The other materials used for thin-film solar cell technology for manufacturing thinfilm PV modules are copper–indium–diselenide (CIS), copper–gallium–diselenide (CGS), copper–indium–gallium–diselenide (CIGS), and cadmium telluride (CdTe). The energy conversion efficiency achieved by these thin-film technologies is up to about 20%.

4.2.3 Single and Multi-Junction PV Modules The multi-junction solar cells PV module utilizes wider range of solar spectrum for electricity generation. In multi-junction solar cells, different solar cells placed in tandem arrangement have different band gaps. Therefore, a multi-junction solar cell utilizes different range of spectrum for electricity generation which reduces the absorption losses and has improved efficiency. The thermodynamic performance

82

4 Photovoltaic (PV) Module and Its Panel and Array

limit of multi-junction solar cells is 68% which is further improved to 85% for concentrating multi-junction solar cells. The PV module manufactured from multi-junction solar cell is very lightweight panels and used particularly in space applications. The tandem arrangement can be made by mechanical stacking or by monolithic technique or by both. Most commonly used dual-junction solar cell is gallium-arsenide (GaAs) with efficiency up to 30%.

4.2.4 Emerging and New Organic PV Module This category of PV modules uses the recent and emerging technology of solar cells, namely organic solar cells (OSC), dye sensitized solar cells (DSSC), quantum well solar cells (QWSC), etc. The major issues are center of recent research and development activities worldwide reduction in cost production and enhancement in energy conversion efficiency. PV modules utilizing new and emerging solar cell technology are categorized on the basis of light absorbing capacity and electricity generation mechanism. The solar cell which contains only organic polymers is termed as organic solar cell; if it includes some inorganic material, then it is known as hybrid organic solar cells. The dye sensitized solar cells contain porous nanoparticles titanium dioxide which enhances the light gathering capacity of the solar cell and hence the electrical efficiency. Properties of different solar cell materials at standard test condition are given in Table 4.2.

4.3 Design Parameters of PV Module Following basic parameters are important in design of PV system: Table 4.2 Specifications of solar cell material (at solar intensity 1000 W/m2 and cell temperature 25 °C) and cost (From Tiwari and Mishra [2]) Solar cell technology

Electrical efficiency (%)

Fill Aperture Life Manufacturing Selling factor area time* cost ($/kWp in price (FF) (10–4 × (years) 2007) ($/kWp in m2 ) 2007)

Monocrystalline silicon

24.7 ± 0.5 0.828 4.0

30

2.5

3.7

Multi-crystalline silicon

19.8 ± 0.5 0.795 1.09

30

2.4

3.5

5

1.5

2.5

Copper–indium–diselenide 18.4 ± 0.5 0.77 (CIS/CIGS)

1.04

Thin silicon cell

16.6 ± 0.4 0.782 4.02

25

2.0

3.3

Cadmium telluride (CdTe)

16.5 ± 0.5 0.755 1.03

15

1.5

2.5

Amorphous silicon (a-si)

10.1 ± 0.2 0.766 1.2

20

1.5

2.5

4.3 Design Parameters of PV Module

83

4.3.1 Packing Factor β c of PV Module It is defined as the ratio of total number of solar cell area to the total PV module area, and it can be expressed as: area of one solar cells × number of solr cell in PV module area of PV module Area of total solar cell = . Area of PV module

βc =

(4.1a)

It is clear that βc is always less than unity in pseudo-solar cell PV module, Fig. 3.1b, and it has maximum value of one when all area is covered by solar cell (rectangular solar cell). So, the total solar cell area in one PV module = βc × Area of PV module.

(4.1b)

Then, the total area of non − packing factor = (1 − βc ) × Area of PV module. (4.1c)

4.3.2 Electrical Efficiency of PV Module The electrical efficiency of PV module in percentage can be expressed as: ηm = τ g × ηc .

(4.2a)

This shows that the electrical efficiency of PV module (ηm ) is less than electrical efficiency of solar cell (ηc ) due to the presence of glass over solar cell. It can also be expressed in terms of fill factor (FF), short-circuit current (I SC ), and open-circuit voltage (V OC ) as: ηem =

FF × Isc × Voc , Am × I

(4.2b)

where Am and I are area and incident solar intensity on PV module. The maximum value of fill factor (FF) of PV module based on Si is one. The temperature dependent electrical efficiency of PV module can be expressed as ηm = ηmo 1 − βr e f Tc − Tr e f

(4.2c)

84

4 Photovoltaic (PV) Module and Its Panel and Array

where ηmo is electrical efficiency of PV module, ηmo = τg ηref is the module’s elec◦ trical efficiency at the reference temperature, and Tref = 25 C and at solar radiation of 2 1000 W/m . βref is the temperature coefficient under standard test condition (STC). The values of ηmo and βref are given in Table 4.2. Here it is important to mention that ηref is always same for either individual solar cell or solar cell of PV module.

4.3.3 Electrical Load Efficiency The electrical load efficiency of PV array may be expressed as: I L × VL . Am × I p

ηload =

(4.2d)

Example 4.5 Evaluate packing factor (PF) of photo-voltaic (PV) module having 36 solar cells with area of 0.605 m2 , and each pseudo-solar cell has an effective area of 0.015 m2 . Solution As we know the packing factor, βc =

area of solar cells area of PV module

=

36×0.015 0.605

=

0.54 0.605

= 0.89.

Example 4.6 Find out the electrical efficiency of PV module at an intensity of 400 W/m2 . Given: FF = 0.8, ISC = 3.2 A, VOC = 16 V , I L = 1 A, VL = 14 V , area of module = 1m2 . Solution From Eq. (4.2b), we have ηem =

FF × Isc × Voc Am × I

=

0.8 × 3.2 × 16 × 100 = 10.24%. 400 × 1

Example 4.7 Using Example 4.6, find out load efficiency of PV module having I L = 1 A, VL = 14 V Solution: As we know load power, PL = I L × VL = 1 × 14 W, Eq. 3.2d. Further, ηem =

PL 1 × 14 × 100 = 3.5%. = I × Am 400 × 1

Example 4.8 Evaluate the number of PV module for greenhouse requirement of 40 Wp PV panels for the following load: (a) Four 40W lamps in night for photosynthesis and one 15W fan used 4 h per day (b) Two 35W fans used 6 h per day (c) One 60W cooling system used 12 h.

4.4 Energy Balance Equations for PV Modules

85

Solution Daily load for each items will be as follows: (a) Four 40W lamps and one 15W fan used 4 h per day = (40 × 4 + 15) × 4 = 700 Wh (b) Two 35W fans used 6 h per day = 35 × 2 × 6 = 420 Wh (c) One 60W :Cooling system for 12 h = 60 × 12 = 720 Wh. Total daily load for greenhouse = 1840 Wh. For 150 Wh per day energy production per 40 Wp PV module, then number of PV module required (in parallel connection) = 1840 Wh/150 Wh = 12.3. Therefore, a 12 V system needs 13 PV modules connected in parallel.

4.4 Energy Balance Equations for PV Modules In this section, we will discuss the energy balance of single PV module with following assumptions: (i) (ii) (iii) (iv)

One-dimensional heat conduction. The system is in quasi-steady state. The ohmic losses between solar cells in PV module are negligible. Heat capacity of transparent glass, Tedlar, and ethyl vinyl acetate (EVA) are negligible.

4.4.1 For Opaque (Glass to Tedlar) PV Module (Fig. 4.1a), Tiwari and Sodha [16] In this case, solar radiation, I (t), after transmission from glass cover τg I (t) is absorbed by solar cell with area Am and packing factor, βc is τg αc βc I (t)Am . The remaining solar radiation τg (1 − βc )I (t) is absorbed by Tedlar (αT ) on nonpacking area of PV module which is τg αT (1 − βc )I (t)Am . The temperature of solar cell increases. Therefore, there will be (a) upward rate of overall heat loss Ut,ca (Tc − Ta ) Am from solar cell to ambient air through top glass cover and (b) bottom rate of overall heat loss Ub,ca (Tc − Ta )Am from solar cell to ambient air through Tedlar in addition to electrical power generation of τg ηc βc I (t)Am . The thermal circuit diagram corresponding to Fig. 3.1a in terms of various heat losses and gain is shown in Fig. 4.6a. Referring to Fig. 4.6a, an energy balance equation for opaque PV module can be mathematically summarized as follows: τg [αc βc I (t) + (1 − βc )αT I (t)] = Utc,a (Tc − Ta ) + Ubc,a (Tc − Ta ) + τg ηc βc I (t).

(4.3a)

86

4 Photovoltaic (PV) Module and Its Panel and Array

a

b

Fig. 4.6 a Thermal circuit diagram of opaque PV module shown in Fig. 3.1a. b Thermal circuit diagram of semitransparent PV module shown in Fig. 4.1b

4.4 Energy Balance Equations for PV Modules

87

The numerical values of constants in Eq. 4.3a are given in Table 4.4. The above equation can be re-arranged as τg [αc βc I (t) + (1 − βc )αT I (t)] = ULm (Tc − Ta ) + ηm I (t),

(4.3b)

where ULm = (Utc,a + Ubc,a ) and ηm = τg ηc . From Eq. (4.3b), one can get Tc − Tref = (Ta − Tref ) +

τg {αc βc + (1 − βc )αT − ηc βc } I (t) . ULm

(4.4)

With the help of Eq. 4.2c and above equation, one gets

ηc =

τ {α β +(1−β )α } I (t) ηref 1 − βref (Ta − Tref ) + [ g c c ULm c T ]

1−

ηref βref τg βc ULm

I (t)

.

(4.5a)

After knowing electrical efficiency of solar cell by Eq. (4.5a), one can get electrical efficiency of PV module as ηm = τ g ηc .

(4.5b)

The threshold intensity I (t)th can be obtained by putting denominator of Eq. (4.5a) greater than zero (positive) and is given as follows: I (t)th >

ULm . ηref βref τg βc

(4.6)

Example 4.9 Evaluate an electrical efficiency of opaque c-Si PV module for I(t) = 500 W/m2 and Ta = 45 °C by using the data of Table 4.4. Solution: Known parameters from Table 4.4 are as follows: τg = 0.95, αc = 0.9, ◦ βc = 0.5 assumed, ∝T = 0.5, Ut,ca = 9.1794 ∼ = 9.2 W/m2 C, Ub,ca = 5.6789 ∼ = ◦ ◦ 5.68 W/m2 C, Tref = 25 C (Eq. 4.2c), βref = 0.0062/0 C (Table 4.3a) and ηref = 0.15. ◦ First calculate ULm = (Utc,a + Ubc,a ) = 9.2 + 5.68 = 14.88 W/m2 C From Eq. 4.5a, one has

ηc =

τ {α β +(1−β )α } I (t) ηref 1 − βref (Ta − Tref ) + [ g c c ULm c T ]

1−

ηref βref τg βc ULm

I (t)

.

Substitute the appropriate known values in the above equation, one gets

88

4 Photovoltaic (PV) Module and Its Panel and Array

Table 4.3 a. Specifications for various silicon and non-silicon-based PV modules Different Solar cell Types (n)

Module efficiency ïo (%)

Expected life nPV (Yrs)

Specific energy content Ein (kWh m−2 )

(Ein ) for A = Temp. 1.21 m2 coefficient (kWh m−2 ) β (o C−1 )

References for β (o C−1 )

c-Si

16

30

1190

1439.9

0.0062

Durisch et al. [20]

mc-Si

14

30

910

1101.1

0.0049

-Do-

nc-Si*

12

25

610

738.1

0.0036

Assumed

a-Si

6

20

378

457.3

0.001

Durisch et al. [20]

CdTe

8

15

266

321.8

0.002

Assumed

CIGS

10

5

24.5

29.6

0.0031

Durisch et al. [20]

b Values of PV and PVT module electrical efficiencies and temperature coefficients [2] Tref (◦C)

ηmo

βref

Comments

References

25

0.15

0.0041

Mono-Si

Evans [3]

28

0.117 (average)

0.0038 (average)

Average of Sandia and commercial cells

OTA [4]

25

0.11

0.003

Mono-Si

Truncellito and Sattolo [5]

25

0.13

0.0041

PVT system

Mertens [6]

20

0.10

0.004

PVT system

Prakash [8]

25

0.10

0.0041

PVT system

Garg and Agarwal [9]

20

0.125

0.004

PVT system

Hegazy [10]

0.0026

a-Si

Yamawaki et al. [11]

0.13

0.004

Mono-Si

RETScreen [12]

0.11

0.004

Poly-Si

0.05

0.0011

a-Si

25

0.178

0.00375

PVT system

Nagano et al. [13]

25

0.12

0.0045

Mono-Si

Chow [14]

25

0.097

0.0045

PVT system

Zondag et al. [15]

25

0.09

0.0045

PVT system

Tiwari and Sodha [16]

0.005

25 25

Barra and Coiante [7]

0.12

0.0045

PVT system

25

0.12

0.0045

PVT system

Assoa et al. [17]

25

0.127

0.0063

PVT system

0.127 unglazed

0.006

PVT system

Tonui and Tripanagnostopoulos [18]

0.117 glazed

0.0054

PVT system

Othman et al. [19]

4.4 Energy Balance Equations for PV Modules Table 4.4 Design parameters of PV module

ηc =

89

Parameters

Numerical values

τg

0.95

αc

0.9

βc

0.22–0.8

∝T

0.5

Ut,ca

9.1794 W/m2 °C

Ub,ca

5.6789 W/m2 °C

ηref

0.16

0.16 1 − 0.0062 (45 − 25) +

[0.95{0.9×0.5+(1−0.5)0.5}]500 14.88

1 − 0.16×0.0062×0.95×0.5 × 500 14.88 0.16[1 − 0.0062{15 + 23.27}] 0.12 = = = 0.1239. 1 − 0.01583 0.9842

So, an electrical efficiency of c-Si opaque PV module = τg ×ηc = 0.95×0.1239 = 0.1177. Example 4.10 Calculate solar cell temperature of opaque PV module for data of Example 4.9. Solution: From Eq. 4.4, one has. τ {α β +(1−βc )αT −ηc βc }] I (t) Tc = Ta + [ g c c . U Lm Substitute the required numerical value of each parameter from Example 4.9 in the above equation, one gets as τg {αc βc + (1 − βc )αT − ηc βc } I (t) U Lm [0.95{0.9 × 0.5 + (1 − 0.5) × 0.5 − 0.1239 × 0.5} × 500] = 25 + 14.88 [0.95{0.45 + 0.475 − .06195} × 500] ◦ = 25 + 27.55 = 52.55 C. = 25 + 14.88

Tc = Ta +

4.4.2 For Semitransparent (Glass to Glass) PV Module (Fig. 4.1b) In case too, thermal circuit diagram of semi-transparent PV module indicating various ther ate of heat loss/gain is shown in Fig. 4.6b. Same assumptions have also been made as in Sect. 4.4.1. Solar radiation received on non-packing area of opaque PV module will be further transmitted by glass in

90

4 Photovoltaic (PV) Module and Its Panel and Array

case of semi-transparent PV module as τg2 (1 − βc )I (t)Am . For semi-transparent PV module, Fig. 4.1b, energy balance equation can be written as αc τg βc I (t) = Utc,a (Tc − Ta ) + Ubc,a (Tc − Ta ) + τg ηc βc I (t).

(4.7a)

Equation 4.7 can be re-arranged as αc τg βc I (t) = U Lm (Tc − Ta ) + ηm I (t),

(4.7b)

where ULm = Utc,a + Ubc,a and ηm = τg ηc . From Eq. (4.7b), we can have Tc − Tref = (Ta − Tref ) +

αc τg − ηc βc I (t) ULm

(4.8)

With the help of Eq. 4.8, Eq. (4.2c) becomes ηc = ηref 1 − βref (Ta − Tref ) +

αc τg βc − ηc τg βc I (t) ULm

.

The above equation reduces to

ηc =

ηref 1 − βref (Ta − Tref ) + 1−

ηref βref τg βc ULm

αc τg βc ULm

I (t)

I (t)

.

(4.9a)

After knowing electrical efficiency of solar cell by Eq. (4.9a), one can get electrical efficiency of PV module as ηm = ηc τ g .

(4.9b)

Similarly in this case also, the threshold intensity I (t)th is given as follows: I (t)th >

ULm . ηref βref τg βc

(4.10)

Hourly variation of solar cell temperature and electrical efficiency is shown in Fig. 4.7a. This reveals that solar cell electrical efficiency decreases with increase of solar cell temperature which is in accordance with the studies concluded by Evans [3]. Further, Fig. 4.7b shows the comparison of electrical efficiency of solar cell of semitransparent (glass to glass) and opaque (glass to Tedlar) PV module. From this figure, one can see that solar cell electrical efficiency in glass to glass (semi-transparent) PV module is more due to its low temperature. In this case, the part of solar radiation [τg (1 − βc )αT I (t)] available in non-packing area of opaque PV module in Eq. 4.3a

4.4 Energy Balance Equations for PV Modules

91

is further transmitted by back glass of semi-transparent PV module, and hence, its temperature is lower than temperature of opaque PV module. Example 4.11 Evaluate an electrical efficiency of semi-transparent c-Si PV module for I(t) = 500 W/m2 and Ta = 45 °C by using the data’s of Table 4.4. Solution: Known parameters from Table 4.4 are as follows: τg = 0.95, αc = ◦ 0.9, βc = 0.5 assumed, Ut,ca = 9.1794 ∼ = 9.2 W/m2 C, Ub,ca = 5.6789 ∼ = ◦ ◦ 5.68 W/m2 C, Tref = 25 C (Eq. 4.2c), βr e f = 0.0062/0 C (Table 4.3a) and ◦ ηref = 0.15. From Example 4.9 ULm = 14.88 W/m2 C. From Eq. 4.9a, one has

a

Cell Temperature

16

60

15

50

Cell Temperature (oC)

Electrical Efficiency (%)

Electrical Efficiency

40

14

30 13

20

12

10

11

0 08:0009:0010:0011:0012:0013:0014:0015:0016:0017:00 Time (Hours)

b

Glass to glass

Glass to tedlar

Electrical efficiency, %

12.0

11.0

10.0

9.0

8.0 09:00

10:00

11:00

12:00

13:00

14:00

15:00

16:00

Time (Hours)

Fig. 4.7 a Hourly variation of cell temperature and cell efficiency for a typical day of summer. b Comparison of electrical efficiency of solar cell for opaque and semi-transparent PV module, Tiwari and Mishra [2]

92

4 Photovoltaic (PV) Module and Its Panel and Array

ηc =

ηref 1 − βref (Ta − Tref ) + 1−

ηref βref τg βc ULm

αc τg βc ULm

I (t)

I (t)

.

Substitute the appropriate known values in the above equation, one gets. ηc =

0.16 1 − 0.0062 (45 − 25) +

[0.95×0.9×0.5]500 14.88 0.16×0.0062×0.95×0.5 × 500 14.88

1− 0.13 0.16[1 − 0.0062{15 + 14.36}] = = 0.1329 = 0.9842 0.9842

Example 4.12 Calculate solar cell temperature of semi-transparent PV module for data of Example 4.9. Solution: From Eq. 4.8, one has α τ −ηc )βc I (t) Tc = Ta + ( c g U Lm . Substitute the required numerical value of each parameter from Example 4.9 in the above equation, one gets as αc τg − ηc βc I (t) [0.5 × {0.9 × 0.95 − 0.1329} × 500] = 25 + U Lm 14.88 [0.5 × 0.855 × 500] ◦ = 25 + 14.37 = 39.36 C. = 25 + 14.88

Tc = Ta +

From Exampled 4.9 and 4.10, one can infer that an electrical efficiency of semitransparent PV module is more than an electrical efficiency of opaque PV module due to its lower solar cell temperature (Examples 4.10 and 12).

4.4.3 Series and Parallel Combination of PV Modules The PV modules can be connected either in (a) series to increase the current or (b) parallel to increase in the voltage as mentioned earlier. It is referred as panel. Further, PV modules are also connected in both series and parallel to have the maximum power production at same current/voltage as per requirement; then it is referred as array. Solar panel is a group of several modules connected in series–parallel combination in a frame that can be mounted as roof structure of greenhouse, then the whole system will be referred as greenhouse integrated semi-transparent photo-voltaic thermal (GiSPVT) system as shown in Fig. 4.8a. Series and parallel connection of PV modules in an array is shown in Fig. 4.8b. In parallel connection, blocking diodes are connected in series with each series string of modules, so that if any string should fail, the power output of the remaining series string will not be affected by the failed string. Also bypass diodes are installed across each module, so that if one

4.4 Energy Balance Equations for PV Modules

93

a

b Blocking diode

Module

Bypass diode

Fig. 4.8 a Photo of a typical greenhouse integrated semi-transparent photo-voltaic thermal (GiSPVT) system for vegetable cultivation. b Series and parallel connection of modules in a panel (From Tiwari and Mishra [2])

module should fail, the power output of the remaining modules in a string will bypass the failed module. Some modern PV modules come with such internally embedded bypass diodes. The large number of interconnected solar panels is known as solar PV array as explained before. Problems 4.1 Calculate voltage of the following two PV modules with open-circuit voltage of each one is about 0.5 V.

94

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

4 Photovoltaic (PV) Module and Its Panel and Array

Hint: Total voltage = open-circuit voltage of one solar cell × number of solar cell. Calculate number of c-Si solar cell with open-circuit voltage of about 0.5 V with and without 0.08 V drops at more than 25 °C operating temperature for 72 and 30 V open-circuit voltage of PV module. Hint: Example 4.1 Evaluate packing factor (PF) of photo-voltaic (PV) module for Problem 4.1. Each Pseudo-solar cell have an effective area of 0.015 m2 . Hint: Example 4.5 Find out packing factor (PF) of photo-voltaic (PV) module having 36, 72, and 108 solar cells with area of 0.605 m2 , 1.5 m2 , and 2.5 m2 , and each pseudo-solar cell has an effective area of 0.015 m2a . Hint: Example 4.5 Find out the electrical efficiency of photo-voltaic (PV) Module at an intensity of 400, 800, and 1000 W/m2 . Given: FF = 0.8, ISC = 3.2 A, VOC = 16 V, I L = 1 A, VL = 14 V, area of module = 2 m2 . Hint: Example 4.6 Find Out Variation of Load Efficiency of PV Module Having I L = 1 − 6 A,VL = 14 − 25 V. Hint: Example 4.7 Evaluate the Number of PV Module for Greenhouse Requirement of 40 − 120 Wp PV Panels for the Following Load for Parameters Given in Example 3.4. Hint: Example 4.8 Evaluate an electrical efficiency and solar cell temperature of opaque c-Si PV module for I(t) = 500 W/m2 and Ta = 45 °C by using the data of Table 4.4 for different packing factor (0.2 to 1). Hint: Example 4.9 Evaluate an electrical efficiency and solar cell temperature of semi-transparent c-Si PV module for I(t) = 500 W/m2 and Ta = 45 °C by using the data of Table 4.4 for same packing factor of Problem 4.8. Hint: Example 4.11.

4.4 Energy Balance Equations for PV Modules

95

4.10 Compare the results of an electrical efficiency and solar cell temperature of problems 4.8 and 4.9 and give your comments. Objective Questions 4.1 Energy Payback time (EPBT) should be (a) More than life of PV system (b) Equal to life of PV system relation (d) Less than life of PV system

(c) No

Answer: (d). 4.2 Photo-voltaic (PV) system is (a) Non-renewable source of energy (b) Renewable source of energy (c) Finite source (d) All of them. Answer: (b). 4.3 Photo-voltaic (PV) system provides (a) Clean power (b) Good environment (c) Sustainable climate (d) All of them Answer: (d). 4.4 Electrical efficiency of semi-transparent PV module is (a) More than opaque PV module (b) Equal to opaque PV module (c) Less than opaque PV module (d) None of them. Answer: (a). 4.5 Solar cell in PV module is connected in (a) Parallel (b) Series (c) Series and parallel (d) None of them. Answer: (b). 4.6 The PV modules are connected in series to increase (a) Voltage (b) Voltage and current (c) Current (d) Power Answer: (c) and (d) 4.7 The PV modules are connected in parrel to increase (a) Voltage (b) Voltage and current (c) Current (d) Power Answer: (a) and (d). 4.8 The electrical efficiency of PV module increases with (a) Increase of packing factor (b) With decrease of packing factor (c) With zero packing factor (d) None of them. Answer: (b). 4.9 The electrical efficiency of PV Module increases with (a) Decrease of solar cell temperature (b) With flow of air over it (c) With flow of water over it (d) All of them. Answer: (d). 4.10 The electrical efficiency of semi-transparent PV module in Comparison with opaque PV module is (a) More (b) Less (c) Equal (d) None. Answer: (a).

96

4 Photovoltaic (PV) Module and Its Panel and Array

4.11 The temperature of semi-transparent PV Module in comparison with opaque PV module is (a) More (b) Less (c) Equal (d) None. Answer: (b). 4.12 The PV module gives maximum electrical power in (a) Visible wavelength region (b) Infrared region (c) Far infrared (d) Ultraviolet region. Answer: (a). 4.12 The electrical efficiency of PV module in comparison with solar cell is (a) More (b) Less (c) Equal (d) None. Answer: (b). 4.14 The semi-transparent PV Module in comparison with opaque PV module Has (a) More applications (b) Less applications (c) Equal applications (d) None. Answer: (a). 4.15 The electrical efficiency of PV module increases with decrease of its temperature (a) False (b) Correct (c) Never possible (d) Always true. Answer: (b) and (d).

References 1. Fortman M, Zhou T, Malone C, Gunes M, Wronski R (1990) Deposition conditions, hydrogen content and the Staebler-Wronski effect in amorphous silicon. In: Conference record of the 21st photovoltaic specialist conference, 1648–1652 2. Tiwari GN, Mishra RK (2012) Advanced renewable energy sources. RSC publishing UK 3. Evans DL (1981) Sol Energy 27:555 4. OTA—Office of Technology Assessment (1978) Application of solar technology to today’s energy needs, energy conversion with photovoltaic. Princeton, 10:406 5. Truncellito NT, Sattolo AJ (1979) General electric advanced energy department 6. Mertens R (1979) In Proceedings of UK-ISES conference on C21 Photovoltaic solar energy conversion, 65 7. Barra L, Coiante D (1993) Sol Energy 51:383 8. Prakash J (1994) Energy Convers Manage 35:967 9. Garg HP, Agarwal RK (1995) Energy Convers Manage 36(2):87 10. Hegazy AA (2000) Energy Convers Manage 41:861 11. Yamawaki T, Mizukami S, Masui T, Takahashi H (2001) Sol Energy Mater Sol Cells 67:369 12. RET Screen International, Photovoltaic Project Analysis (2001) PV 22 13. Nagano K, Mochida T, Shimakura K, Murashita K, Takeda S (2003) Sol Energy Mater Sol Cells 77:265 14. Chow TT (2003) Sol Energy 75(2):143 15. Zondag HA, de Vries DW, van Helden WGJ, van Zolingen RJC (2003) Sol Energy 74(3):253 16. Tiwari A, Sodha MS (2006) Renew Energy 31(15):2460 17. Assoa YB, Menezo C, Fraisse G, Yezou R, Brau J (2007) Sol Energy 81:1132 18. Tonui JK, Tripanagnostopoulos Y (2007) Renew Energy 32:623 19. Othman MY, Yatim B, Sopian K, Abu Bakar MN (2007) Desalination 209:43 20. Durisch W, Bitnar B, Mayor JC, Kiess H, Lam K, Close J (2007) Solar Energy Mater Solar Cells 91:79–84

References

97

Recommended Additional References for further Studies 21. Shyam GN, Tiwari IM, Al-Helal (2015) Solar Energy 114:61 22. Singh GK (2013) Analysis of environmental impacts on the performance of PV modules, Ph.D. Thesis, I.I.T. Delhi, New Delhi, India 23. Duffie JA, Beckman W (1991) Solar engineering of thermal processes. Wiley, New York 24. Tiwari GN, Mishra RK, Solanki SC (2011) Appl Energy 88:2287 25. Dupeyrat P, Ménézo C, Fortuin S (2014) Energy Build 68:751 26. Makki A, Omer S, Sabir H (2014) Renew Sustain Energy Rev 41:658 27. Asim N, Sopian K, Ahmadi S, Saeedfar K, Alghoul MA, Saadatian O, Zaidi SH (2012) Renew Sustain Energy Rev 16(8):5834 28. Agrawal B, Tiwari GN (2010) Building Integrated photovoltaic thermal systems. RSC publishing, UK 29. Agrawal B, Tiwari GN (2008) Developments in Environmental durability for photovoltaics. Pira International Ltd, UK

Chapter 5

Concepts of Greenhouse and Its Application

5.1 Introduction As explained in Chap. 1, global greenhouse effect is responsible for living organism on the planet earth. It was only possible after formation of atmosphere between the Sun and Earth with its two unique properties, namely (i) transmission of short wavelength of solar radiation and (ii) behaves as opaque for long wavelength emitted from surface of earth. Till now, about 92% of agricultural product/plants are grown in the open field due to photosynthesis by using photon of solar energy for a growing climatic conditions provided by nature due to global greenhouse effect. In some of the climatic condition (temperate)/regions, none of crops can grow due to extremely adverse condition. Human being has developed technological methods to grow some high-value crops in the excessive cold climate condition by providing house made by transparent glass/ plastic. In such house, glass behaves as an atmosphere with similar properties with respect to solar radiation. This technological development by human being is known as greenhouse technology, Tiwari [1]. Greenhouse technology can create favorable environment also known as built environment, DMGH [2]. Greenhouse technology can also be used for solar dryer, Tiwari and Barnwal [3]. “Greenhouse Technology is the science to provide favorable environment conditions to grow the plants in off-seasons”.

5.1.1 Classification of Greenhouse 5.1.1.1

Based on Shape

There are many ways to classify the greenhouse structure. One of the simplest ways is to classify on the basis of shape. The most popular greenhouses are as follows:

© Bag Energy Research Society 2023 G. N. Tiwari, Advance Solar Photovoltaic Thermal Energy Technologies, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4993-9_5

99

100 Fig. 5.1 Photo of even type plastic greenhouse

5 Concepts of Greenhouse and Its Application

The Greenhouse with roof vent

• Even span type greenhouse: The even span greenhouse is similar to a conventional common house with same inclination and area of inclined roof. There is overlapping pan which increases the chance of leakage as shown in Fig. 5.1 • Ground to ground greenhouse: The ground to ground greenhouse is generally built with short sidewalls with dome shape with different covering materials. It can also be designed with environmental controls. Sometimes, it can be referred as tunnel greenhouse. • Lean to type greenhouse: In this case, greenhouse is attached to sides of house facing solar radiation at entrance easier access of utilities including electricity and water supply. This allows for better monitoring of your plants in greenhouse. • Quonset greenhouse: A Quonset greenhouse is dome shaped with vertical walls with suitable height mostly on hillsides for maximum heating by solar energy due to minimum heat loss from cover. Quonset greenhouses have ventilation systems, heating systems, circulation fans, and better environmental control. It is expensive which needs more support due to many uneven structure as shown in Fig. 5.2.

Fig. 5.2 Quonset plastic greenhouse

5.1 Introduction

101

Fig. 5.3 Design of uneven greenhouse [W1 < W2 ]

• Ridge and furrow type: The ridge and furrow greenhouse is a jointed even/ uneven span/Quonset greenhouse to allow for an increased indoor space with sunlight. In this case, supporting gutters structure could prohibit solar radiation inside greenhouse. • Uneven span type greenhouse: In this case, both inclined roof inclination and area are different unlike even span greenhouse as shown in Fig. 5.3. The steeper angle and long roof face the south direction to receive the solar radiation in northern hemisphere. 5.1.1.2

Based on Technology/cost

Further, there are three categories of greenhouse based on investment to assist the users in selecting the appropriate investment for their requirement and budget. These are as follows: (a) Low technology/cost greenhouses: In this case, tunnel/ground to ground greenhouse shape up to height of 3 m without vertical wall is preferred due to significant crop production over field production with environmental limitations. The structure of such house can be locally available bamboo which is cost effective. This can be installed over ground tunnel preferable in harsh cold climatic condition such as in Leh, India. In this case, greenhouse inside environment is heated with solar energy as well as ground thermal energy with minimum heat loss from canopy cover due to least cover area. If shape of greenhouse is circular dome type, then it is referred as igloos greenhouse. This type of structure is relatively inexpensive and easy to erect without any automation. The life of structure and canopy cover is more or less which can survives up to 3–5 years depending upon quality of bamboo and canopy cover. (b) Medium technology greenhouses: In the case of medium technology greenhouses, Quonset/even/uneven shape is preferred which offers a compromise between cost and productivity. Medium level greenhouses have vertical wall between 2 and 4 m and a central height less than 5 m with provision of ventilation through roof/walls. Such greenhouse structure is preferably made from rigid material (metallic pipes) other than bamboo to have longer life in comparison

102

5 Concepts of Greenhouse and Its Application

with low technology/cost greenhouses. The canopy cover may be usually clad with either single or double skin plastic film or glass. It uses varying degrees of automation like forced mode ventilation/fan-pad cooling/misting/drip irrigation, etc. Crop production in medium level greenhouses can be more efficient than low cost greenhouse as well open field production due to increase of the efficiency of water use. There is greater opportunity to use non-chemical pest and disease management strategies. Life of structure of medium technology greenhouses may be more than 30 years depending upon maintenance of structure. (c) High technology greenhouses: In the case of high technological greenhouse, the ridge and furrow type greenhouse is preferred with vertical height of 4 m and central height of up to 8 m from ground level for multi-tier cultivation. In this case, structures of greenhouse may be reinforce cement concrete (RCC) with expected life of 100 years. These structures offer enormous opportunities for economic and environmental sustainability. The greenhouse may have all provision of forced mode ventilation/fan-pad cooling/misting/drip irrigation, etc., as in the case of medium technological greenhouse. In this case too, cladding may be plastic film (single or double), polycarbonate sheeting or glass for crop favorable environment control which offer superior crop and environmental performance. Use of pesticides can be significantly reduced. High technological greenhouse provides a shelter in which a suitable environment is maintained for plants with help of solar energy from the sun to provide sunlight for photosynthesis and some heat to maintain greenhouse air temperature, to regulate the environment in such greenhouse. An automatic automation is done for heating, air circulation/ventilation, cooling, watering, CO2 , light, etc.

5.2 Applications The greenhouse technology has the following main applications as far as concern of food security:

5.2.1 Crop (Vegetables/flowers) Production The plant needs the following basic parameters for optimum growth: (i) (ii) (iii) (iv)

Solar intensity I(t) Temperature (T) Carbon dioxide (CO2 ) Relative humidity (γ ).

The utilization of solar energy, I(t), in the form of photon for crop production is a process of photosynthesis. In this case, the photon of solar energy has an energy

5.2 Applications

103

content of E = hν; h = 6.62607015 × 10−34 J second, being Planck’s constant and ν, the frequency of photon. The incident photon in visible range on the green plant separates hydrogen (H2 ) and oxygen (O2 ) due to its strong energy content in comparison with lose binding energy in water molecules. The oxygen is released to atmosphere, and hydrogen reacts with CO2 of atmosphere to make hydrocarbon and hence growth of plants. Most of the living organisms on planet earth ultimately depend upon solar (light) energy. So, visible light of solar energy constitutes a source of energy for all plants in agricultural sector. Light energy, carbon dioxide (CO2 ), and water all enter into the process of photosynthesis through which carbohydrate is formed as explained earlier. The process results in growth of the plant, which can be visualized as an increase in dry matter. When all the factors such as (i) carbon dioxide, CO2 , (ii) temperature, (iii) relative humidity, (iv) composition of root media, and (v) watering are optimized for photosynthesis, an optimum solar radiation/light intensity can be determined. Variation in any one of the mentioned parameters adversely affects the growth of the plant, and hence, growth of plant is very sensitive to climatic condition. For open field cultivation, none of the above parameters are under control (Fig. 5.4a). Plants growth is subjected to variations in ambient air temperature and solar radiation, variable wind velocity, untimely rain, etc. The role of greenhouse effect due to transparent atmosphere for survival of all living organism on the planet earth (Chap. 1) can be made similar to a transparent house around the crop where a favorable microclimate inside the greenhouse can be created with passive/active different heating and cooling concepts to cultivate the specific crop in any season of the year (Fig. 5.4b).

5.2.2 Aquaculture (Fish Production) Fish farming (pisciculture) involves raising of commercially fish either in tanks or fish ponds as food for preferable human being. It is the principal form of aquaculture. Other methods may fall under mariculture. Globally, the most important fish species produced in fish farming are carp, tilapia, salmon, and catfish. Due to population growth and shortage of food, the demand is increasing, which has resulted in widespread overfishing in wild fisheries. China provides 62% of fish as a protein is increasing very fast throughout the world. As of now, more than 50% of seafood was produced by aquaculture. Farming carnivorous fish (salmon) does not always reduce pressure on wild fisheries but are usually fed fishmeal and oil extracted from wild forage fish. The 2008 global returns for fish farming recorded by the FAO totaled 33.8 million tons worth about $US 60 billion [4]. Table 5.1 provides the information about most 15 cultured fish species by weight and earned money (FAO 2013) [5] The water acts a root media of fish production, and hence, its temperature plays an important role. However, it is very difficult to control the temperature. It depends on weather/climatic condition, solar energy, ambient air temperatures, wind velocity, relative humidity, etc. Temperature is an important factor affecting the growth and

104 Fig. 5.4 a Open field cultivation and b greenhouse controlled environment cultivation

5 Concepts of Greenhouse and Its Application The Conventional Surface Cultivation: Open field Irrigation

(a)

Pot and Field Cultivation inside Greenhouse

(b)

survival of all living organisms on planet earth. Cold water and warm water species (fish culture) will not tolerate water temperatures > 20–25 °C and < 20 °C respectively. Tropical species will die at temperatures of 10 to 20°C and most do not grow at temperatures < 25 °C as shown in Fig. 5.5 Water temperature ranges described above are very general, and each species, whether cold water, warm water, or tropical, has its characteristic temperature requirements. There is a low temperature below which fish die, at slightly higher temperature, fish live, but they do grow very slowly. At a certain temperature, growth will increase rapidly with increasing temperature until the optimum temperature is reached. As temperature rises beyond the optimum temperature, growth will slow, cease, and fish will die if the increase continues after optimum value as mentioned in Fig. 5.5. Based on the above observation, the following basic parameters are required for fish production/growth in open water pond:

5.2 Applications

105

Table 5.1 Top fifteen cultured fish species by weight, FAO statistics, 2013 [5] S.No. Species

Environment

Tonnage (millions) Value (UD$ billions)

1

Atlantic salmon

Marine

2.07

(10.10)

2

Amur catfish

Freshwater

0.41

(0.55)

3

Bighead carp

Freshwater

2.90

(3.72)

4

Black carp

Freshwater

0.50

(1.15)

5

Catla (Indian carp)

Freshwater

2.76

(5.49)

6

Common carp

Freshwater

3.76

(5.19)

7

Crucian carp

Freshwater

2.45

( 2.67)

8

Grass carp

Freshwater

5.23

( 6.69)

9

Milkfish

Marine

0.94

(1.71)

10

Nile tilapia

Freshwater

3.26

(5.39)

11

Northern snakehead Freshwater

0.48

(0.59)

12

Rainbow trout

Freshwater/brackish/ 0.88 marine

(3.80)

13

Roho labeo

Freshwater

1.57

(2.54)

14

Silver carp

Freshwater

4.59

(6.13)

15

Wuchang bream

Freshwater

0.71

(1.16)

Fig. 5.5 Growth rate of fish with temperature [6]

106

5 Concepts of Greenhouse and Its Application

Fig. 5.6 Open and controlled even type greenhouse integrated with water pond for fish culture

(i) (ii) (iii) (v) (vi)

The Open pond and Greenhouse pond fish culture for comparison

Solar intensity I(t) Temperature (T) Oxygen (O2 ) Relative humidity (γ ) Salinity.

In recent years, the freshwater prawn farming has been taken up in northern Indian states in shallow water pond. An ambient air temperature in northern India and hilly areas falls below 10 °C during the winter season from December to January. Due to very lower temperature of the pond water as shown in Fig. 5.5, the fish mortality increases and fish production is reduced significantly. For good health of fish and high production rate, the optimum temperature of water pond should be maintained. Thus, for complete survival of fish and getting the maximum production, it is necessary to maintain the temperature between 25 and 35 °C of the water pond in the winter, especially for prawn farming [6]. The temperature of water pond below 14 and above 35 °C is dangerous for prawn farming. For achieving the proposed optimum temperature between 25 and 35 °C, a greenhouse should be integrated to water pond as shown in Fig. 5.6. Effect of salinity in water pond for fish growth is given in Table 5.2. It can be seen that fish growth decreases with increase of salinity for prawn fish.

5.2.3 Aquaponics [7] Aquaponics consists of main two parts, namely (i) the aquaculture part to raise aquatic animals (fishes) and (ii) the hydroponics part for growing plants. In aquaculture, aquatic effluents accumulate in water pond due to the closed recirculation of most aquaculture systems which results from uneaten feed. The effluent-rich water becomes high concentrations toxic to the aquatic animal (fish). But effluent-rich

5.2 Applications Table 5.2 Effect of salinity on fish growth [6]

107

Salinity (ppt)

Food energy recovered as fish growth (%)

0.5

33.4

2.5

31.8

4.5

22.2

6.5

20.1

8.5

10.4

10.5

−1.0

water with high concentrations toxic contains nutrients which are essential for plant growth. In hydroponics systems, the roots of plants are immersed in the nutrient-rich effluent water available from aquaculture to. After the water has passed through the hydroponic subsystem, it is cleaned and oxygenated and can return to the aquaculture vessels. This cycle is continuous as shown in Fig. 5.7. Aquaponics systems are usually grouped into several components/subsystems which are responsible for the effective removal of solid wastes available in water pond either to add bases to neutralize acids, or to maintain water oxygenation. Typical components include. (a) Rearing tank: the tanks to raise and to feed the fish (b) Settling basin: a unit to catch uneaten food and detached biofilms and for settling out fine particulates (c) Biofilter: a place where the nitrification bacteria can grow and convert ammonia into nitrates, which can be used by the plants [14] (d) Hydroponics subsystem: the portion of the system where plants are grown by absorbing excess nutrients from the water (e) Sump: the lowest point in the system where the water flows to and from which it is pumped back to the rearing tanks.

Fig. 5.7 Integration of aquaculture and hydroponics as aquaponics [7]

108

5 Concepts of Greenhouse and Its Application

Fig. 5.8 Photo of greenhouse integrated aquaponics

The water temperature is an important parameter for bacteria growth for aquaponics in general. The ideal temperature range for bacteria growth and productivity is 17–34 °C similar to aquaculture as shown in Fig. 5.7. So it becomes economical to integrate aquaculture and hydroponics in single unit into greenhouse to achieve the desired temperature during winter month by suing solar energy as shown in Fig. 5.8.

5.2.4 Solarization [8] Soil solarization is a technique which is friendly with an environment and climate. Solariztion has been practiced in many developed countries since 1970. In this case, transparent flexible sheet is used to cover soil after pacing seeds inside soil. Solar radiation is used to heat soil through plastic cover to control pests such as bacteria, insects, and weeds in the soil. The solar radiation warms up the soil to temperatures that kill bacteria, fungi, insects, mites, nematodes, weeds, and weed seeds. During solarization, short wavelength solar radiation (0.3–3.0 µm) is transmitted through transparent plastic and absorbed by soil to be solarized, and soil temperature starts increasing and emits long wavelength as explained earlier in Chapter 1. The transparent plastic does not allow long wavelength radiation to escape; hence, air temperature above soil is also heated which helps soil to retain its temperature. If black plastic is used in place of transparent plastic, it is known as tarping. During tarping, solar energy is absorbed by the black plastic, some heat is transferred into the soil by convection, and rest is lost back into the surrounding air by convection and radiation. In this case, soil is heated indirectly and temperature is lower than direct gain by transparent plastic as shown in Fig. 5.9. Use of a double layer of transparent plastic, or on top of black cover, can further increase temperatures of soil

5.2 Applications

109

with effectiveness. Thermal killing due to heat buildup from the solar radiation has been considered the primary way of solarization and tarping work. Solarization technique can be also used for seedling for pre- and post-harvesting of crop before transplantation. Many studies have found that solarization under the right conditions provides excellent weed control. Marenco and Lustosa [9] have observed that three weeks of solarization in Brazil controlled more than 50% of weed species and doubled carrot yield. Doing solarization for seedling in small land can create a job opportunity in rural area for other farmers with increased yield. It is a very simple device as can be seen in Fig. 5.10.

Fig. 5.9 Average soil temperatures at 2'' depth during two weeks of solarization, tarping, and uncovered control treatment in Old Town, ME. (https://eorganic.org/node/25440) [8] Fig. 5.10 Photo of soil solarization

110

5 Concepts of Greenhouse and Its Application

5.2.5 Transparent Plastic mulching [10] Mulching is a protective covering of soil by colored plastic, Fig. 5.11, sawdust, compost, or paper, etc., to minimize the evaporation, maintain soil temperature, prevent erosion, control weeds, enrich the soil, or keep clean fruit. Following are the advantages by using plastic mulches along with the use of drip irrigation: (a) Soil temperature: The use of plastic mulch changes the soil temperature. For example, white plastic mulches, Fig. 5.11a, having low and high value of transmissivity and reflectivity reduce the soil temperature in summer helping to establish plants in mid-summer when cooler soil might be required. The black plastic mulches, Fig. 5.11b with high absorptivity applied to over the soil, intercept solar radiation to warm up the soil due to greenhouse effect to allow earlier plantation as well as encouraging faster growth in the growing season in winter month. It is only due to microclimate greenhouse effect. Soil temperature with black plastic mulch will be higher than white mulch (more reflection) of solar radiation from white surface of plastic mulch in for the same climatic condition. In black mulch, solar radiation is absorbed by black surface and the heat from black surface is transferred to soil surface by convection and radiation, and hence, soil temperature is significantly more than white mulch soil surface. (b) Soil moisture retention: Plastic mulches reduce the evaporative heat loss from soil surface to environment air to conserve the water required for irrigation. Plastic mulches also help in uniformly distributing moisture to the soil to reduce plant stress. (c) Weed management: Plastic mulches prevent direct solar radiation to reach the soil. Clear plastics prevent weed growth due to high reflection losses of solar radiation. Holes in the mulch for plants tend to be the only pathway for weeds to grow due to photosynthesis as shown in Fig. 5.11.

(a) Fig. 5.11 Covering of soil by a black and b white plastic sheet [10]

(b)

5.2 Applications

111

(d) Reduction in the leaching of fertilizer: The use of drip irrigation in plastic mulch allows one to reduce loss of fertilizers. With the help of drip irrigation, one can eliminate the loss of nitrogen and other nutrients to depths below the root media zone. Drip irrigation requires lower amounts of water with fertilizers for injection of fertilizers to the root zone as per requirement for adequate plant growth. (e) Improved crop quality: Plastic mulches keep ripening (mature stage) fruits off of the soil to keep the fruit and vegetables clean. The plastic mulch covering the soil decreases the crusting effect of rain and sunlight to keep the soil loose and well aerated underneath the plastic mulch. This increases the amount of oxygen (O2 ) in the soil for microbial activity and also creates a practically weed-free area around the plant. In such case, root damage is therefore eliminated which can lead to an improvement in the overall growth of the plant.

5.2.6 Solar Greenhouse Drying Adopted from [Post-harvest food losses estimation—Food and Agriculture ...www. fao.org › ess › Final_PHLs_Estimation_6-13-13]. Present world human population is expected to reach about 10.5 billion by 2050 (UN March, 2013). This may raise additional global food security concerns. In order to meet the food demand in 2050 by us, required food production in agricultural sector would need to be increased by 60% (Alexandratos and Bruinsma [11]). This demand can be met either by (i) increasing food production, (ii) improving distribution, or (iii) reducing the post-harvest losses. Thus, reducing the post-harvest food losses is a very important parameter to ensure future global food security. According to Food and Agriculture Organization (FAO) of U.N., about 1.3 billion tons of food are globally wasted/lost per year (Gustavasson et al. [12]). Reduction in these food losses can increase the availability of food for human consumption and increase global food security. Food production is currently being challenged by limited agricultural land, water, and weather variability due to increase in pollution in environment as well as climate change. Further, to achieve the goals of food security globally, food availability needs to be also increased along with reductions in the post-harvest process at farm, retail, and consumer levels. This will also increase income as well as employment to farmers. Food losses [12] have been shown in Fig. 5.12 in every sector including vegetables/food and fisheries. In order to reduce post-harvest losses, solar drying is essential to sustain environment and climate change. Following are classifications of solar drying: (a) Open sun drying Open sun drying is a traditional drying method in Asian countries. It reduces the moisture content of paddy under sun. The solar radiation warms up the grains spread over porous net after absorption and evaporation of water took place by heat transfer

112

5 Concepts of Greenhouse and Its Application

Fig. 5.12 Food losses for commodity vary across global region [12]

from surface of paddy to ambient air. The rate of water evaporating from the grains depends on local climatic condition. It is economical and easily maintained without disturbing environment. It needs little investment and is environmentally friendly since it uses the sun as the heat source and therefore produces no CO2 . In this case, temperature control is difficult, grain is directly exposed to sun, and quality particularly color of grain diminishes. It is also not possible to open sun drying during the raining season. The working principle is explained in Fig. 5.13a. Open sun drying can be preferable recommended for vegetables/medicinal plant/fish, etc. It is not hygienic due to exposure of crops to environment. (b) Greenhouse dryer Actually, the greenhouse dryer works under greenhouse effect to create favorable microclimate inside the drying chamber which is made up of transparent plastic/glass as a material. There are many dryers based on this concept, namely cabinet dryer, conventional dryer, and mixed mode dryer working under natural mode of operation. These dryers have low capacity and are used at domestic level for small products with low moisture content. But commercial purposes, greenhouse dryer under natural/ forced mode of operation is found to be best for high moisture content crops; crops dried in the greenhouse dryer are of a superior quality and color as compared to open sun drying. In this case, short wavelength radiation is transmitted by transparent roof/walls of greenhouse, it is absorbed by crop surface, and its temperature starts increasing. The cool air coming from below of crop through vents provided at lower part of greenhouse is heated by hot crop, and moisture is thus taken by cooled air and thrown out by either natural mode or forced mode as shown in Fig. 5.13b. In this

5.3 Greenhouse Integrated Photo-Voltaic Thermal (GiSPVT) System

113

(a)

(b) Fig. 5.13 a Open sun drying of crop. b Ground to ground greenhouse solar dryer under forced mode of operation

case, greenhouse dryer can be designed for a given capacity and type of crop to be dried.

5.3 Greenhouse Integrated Photo-Voltaic Thermal (GiSPVT) System As can be seen from previous section, high technological greenhouse is fossil fuelbased energy-intensive electrical power due to automation of greenhouse for maintaining favorable crop environment inside greenhouse for good quality of crop. In

114

5 Concepts of Greenhouse and Its Application

such greenhouse, high-value crop/flowers should be grown for high return during off-season, pre-and post-harvesting due to large sum of investment in the project. It is also a well-known fact that fossil fuel-based electrical power is one of the parameters responsible for creating environment degradation and damage to climate. This makes for survival of human being very difficult on the planet earth. Hence, there is strong need to develop sustainable greenhouse system which may be friendly with environment and climate. In order to achieve this goal, roof of greenhouse prepared by plastic film (single or double), polycarbonate sheeting, or glass in both medium/ high technological greenhouses should be replaced by semitransparent photo-voltaic module as explained in Chap. 4. In this case, one can choose either crystalline silicon (c-Si) or organic thin-film PV base module depending upon shape of canopy cover and GiSPVT life expectancy. Integration of crystalline silicon (c-Si) PV module with roof of the ground to ground type greenhouse is shown in Fig. 5.14 for aquaponics, and life of the structure depends on material of structure and can be expected much more than 30–40 years. The semitransparent organic PV module is based on curved canopy cover based on plastic film (single or double), polycarbonate sheet due to its flexibility in nature as shown in Fig. 5.15 for crop production with life expectancy of maximum 10–15 years. In both cases, solar radiation is transmitted (i) through non-packing area of semitransparent PV module, Figs. 5.14 and 5.15 through plastic film (single or double), polycarbonate sheet, and organic PV film inside greenhouse, and it is utilized to heat greenhouse air for creating favorable environment for crop production. In addition to thermal energy, system also provides electrical power to be used for automation of control systems. The GiSPVT system has many applications including crop production, aquaculture, aquaponics, and drying along with following advantages: 1. It is a self-sustained system. 2. It works in the rural area without grid power backup. 3. The crop is protected from harsh weather condition. Fig. 5.14 Photo of c-Si PV module integration with roof of ground to ground type greenhouse with glass wall

5.3 Greenhouse Integrated Photo-Voltaic Thermal (GiSPVT) System

(b)

115

(a)

Fig. 5.15 Photo of Quonset plastic greenhouse with and without organic PV film integration with roof

4. The generated and stored electrical power can be used for photosynthesis in night under continuous cloudy/hazy condition in a day. 5. Both channel/pot cultivation of vegetables/flower can be carried out. 6. It can be used for off-season and pre- and post-harvest of crop for high return. 7. Such system also provided cooling effect during daytime due to shading through packed solar cell. 8. It also reduced heat loss during night hours due to double glazing of semitransparent PV module in roof of greenhouse. 9. It is used for direct as well as indirect heating. Indirect heating through solar cell can be optimized as per requirement. However, there is very little work done on greenhouse integrated semitransparent photo-voltaic thermal (GiSPVT) integrated water pond for aquaculture and aquaponics. Problems 5.1 Plot the curve between salinity and fish growth. Hint: Use Table 5.2. 5.2 Develop Liner equation between fish growth (Y) and salinity (X) by using the data of Table 5.1. Hint: Apply linear regression analysis. Objective Questions 5.1 The root media of crop is (a) Soil (b) Water (c) Salty water Answer: (a)

(d) All of them

116

5 Concepts of Greenhouse and Its Application

5.2 The root media of fish production is (a) Soil (b) Water (c) Salty water (d) All of them Answer: (b) and (c) 5.3 The root media of aquaponics (hydroponics) is (a) Soil (b) Water (c) Salty water (d) All of them Answer: (b) 5.4 The optimum temperature range for fish growth is (a) 30–32 O C (b) 15–30 O C (c) > 30 °C (d) All of them Answer: (a) 5.5 The production of fish is reduced in winter due to (a) Increased water pond temperature (b) Decreased water pond temperature (c) Freezing water pond temperature (d) None of them Answer: (b) and (c) 5.6 The wastewater in aquaculture pond can be reused (a) Fertilizer in agriculture production (b) Aquaponics (hydroponics) (c) Aquaculture (d) All of them Answer: (a) and (b) 5.7 Due to solarization in winter month, the temperature of root media of the plant is (a) Unaffected (b) Decreased (c) Increased (d) None Answer: (c) 5.8 Due to mulching in summer month, the temperature of root media of the plant is (a) Unaffected (b) Decreased (c) Increased (d) None Answer: (b) 5.9 Inside greenhouse, the temperature is increased due to following (a) Trapping of long wavelength radiation (b) Trapping of ultra-violet radiation (c) Trapping of infrared (d) Trapping of short wavelength radiation Answer: (d) 5.10 What should be orientation of uneven greenhouse in northern hemisphere? (a) South direction (b) North and south directions (c) East–West direction (d) East–south direction Answer: (a) and (b) 5.11 What should be orientation of Quonset type greenhouse in northern hemisphere? (a) South direction (b) North and south directions (c) East–west direction (d) East–south direction Answer: (c) 5.12 What should be orientation of even greenhouse in northern hemisphere? (a) South direction (b) North and south directions (c) East–West direction (d) East–south direction Answer: (c) 5.13 Semi-transparent roof of greenhouse in summer provides (a) Heating effect (b) Cooling effect (c) Heating/cooling effect (d) None Answer: (b)

References

117

5.14 Semi-transparent roof of greenhouse in winter provides (a) Heating effect (b) Cooling effect (c) Heating/cooling effect (d) None Answer: (b) 5.15 The most economical shape of greenhouse for cold climatic condition is (a) Even shape (b) Uneven (c) Quonset (d) tunnel Answer: (c) and (d) 5.16 Fish growth is maximum in (a) High salinity (b) Zero salinity (c) Medium salinity (d) Lowest salinity Answer: (d)

References 1. Tiwari GN (2003) Greenhouse Technology for controlled environment, alpha science. (UK) also published by Narosa Publishing House, New Delhi 2. DMGH: Lesson 1 History and Types of Greenhouse (ecoursesonline.iasri.res.in › mod › page › view) 3. Tiwari GN, Barnwal P (2008) Fundamentals of solar dryers. Anamaya Publisher, New Delhi 4. Fishery and Aquaculture Statistics: Aquaculture Production 2008 FAO Yearbook, Rome 5. World aquaculture production of fish, crustaceans, molluscs, etc., by principal species in 2013. FAO Yearbook of Fisheries Statistics 2014 6. Water temperature in aquaculture (https://www.aquaculturealliance.org/advocate/water-tem perature-in-aquaculture/) 7. Aquaponics, (https://en.wikipedia.org/wiki/Aquaponics) 8. Solarization and Tarping for Weed Management on Organic ... . (https://eorganic.org/node/ 25440) 9. Marenco RA, Lustosa DC (2000) Soil solarization for weed control in carrot. Pesquisa Agropecuária Brasileira 35:2025–2032. https://doi.org/10.1590/S0100-204X20000 01000014 (verified 27 Aug 2018). 10. Plastic-mulch-wikipedia (https://en.wikipedia.org/wiki/Fish_farming) 11. Alexandratos N, Bruinsma J (2012) World agriculture towards 2030/2050: the saving water. From Field to Fork-Curbing Losses and Wastage in the Food Chain 2012 revision. Working paper: FAO: ESA No. 12–03, 4 12. Gustavsson J, Cederberg C, Sonesson U, van Otterdijk R, Meybeck A (2011) Global Food losses and food waste: extent causes and prevention. Food and Agriculture Organization (FAO) of the United Nations, Rome

Recommended additional reference for further studies 13. Classification of Greenhouses - Garden and Farms (gardenreboot.blogspot.com › 2013/10 › classification-o) 14. 4 Frame Material Options for a Greenhouse—The Spruce(www.thespruce.com › Gardening > Outdoor Rooms) 15. How To Build A Greenhouse In 10 Easy Steps | Rimol. (www.rimolgreenhouses.com › learningcenter › 10-step.)

118

5 Concepts of Greenhouse and Its Application

16. Advantages and Disadvantages of Greenhouses—Get Revising(getrevising.co.uk › GCSE › Biology) 17. Summer Greenhouse Maintenance Checklist - Gothic Arch. (www.gothicarchgreenhouses. com › blog › summer-green.) 18. Build A Greenhouses | Gothic Arch Greenhouses. www.gothicarchgreenhouses.com. (builda-greenhouses) 19. Fish farming—Wikipedia. https://en.wikipedia.org.wiki. Fish_farming

Chapter 6

Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic Thermal System (GiSPVT)

6.1 Introduction Greenhouse technology (GT) is the technique to create an ideal microclimate around the plants to protect nit from the adverse climatic conditions, namely cold, diseases, excessive solar radiation, extreme temperature, insects, large-scale precipitation (rail fall), and wind. This is only possible by erecting a greenhouse/glass house as explained in Chap. 4. Greenhouse technology is a framed or inflated bamboo/ steel/RCC structure covered with transparent material to grow crops under partial or fully controlled microclimate to get optimum growth and productivity. Followings are the advantages of greenhouse: (i) The crop yield may be 10–12 times higher in comparison with outdoor cultivation. It depends on the type of greenhouse, crop, and microclimate control facilities. (ii) Reliability of year round greenhouse cultivation increases for vegetables and flower crops. (iii) Pre- and post-harvest along with off-season production of vegetable and fruit crops. (iv) Superior transplants of grown seeds can be produced continuously. (v) Efficient utilization of chemicals and pesticides to control pest and diseases. (vi) Water conservation due to minimum water loss. (vii) Hardening of tissue cultured plants. (viii) Production of quality produce. (ix) Easy monitoring and controlling the instability of various ecological system. (x) Modern techniques of aeroponics, aquaculture, hydroponic (soil less culture), and nutrient film techniques are only possible inside greenhouse cultivation. The construction of greenhouse is influenced by structural and covering materials. For higher span, material should be stronger. For smaller spans, simple designs like hoops can be followed. Following materials are generally used for construction of structure: © Bag Energy Research Society 2023 G. N. Tiwari, Advance Solar Photovoltaic Thermal Energy Technologies, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4993-9_6

119

120

(a) (b) (c) (d)

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

Wooden/bamboo/flexible framed structure Galvanized/PVC pipe framed structure Truss framed structure Re-enforced cement and concrete (RCC).

Transparent covering materials are the important components of the greenhouse structure due to transmission of solar radiation inside greenhouse to control the required greenhouse air temperature. The types of frames and method of fixing of covering materials also vary with covering material. The recommended transparent covering materials are as follows: (a) (b) (c) (d) (e) (f)

Glass glazing Fiber glass-reinforced plastic (FRP) glazing Plain/corrugated/plastic film sheet UV stabilized LDPE film Silpaulin type sheet Net house.

Suitable site selection and orientation of greenhouse can make a difference in the functional and environmental operations of greenhouse. It is a very important parameter for success of greenhouse technology (GT). Before installation of greenhouse, one should note the following parameters into consideration: 1. A short access of greenhouse site to main connectivity and market will facilitate for handling of materials/crop product to avoid cost of construction. One of the important factors is the supply of good quality water available near the site. 2. Greenhouse should be located away from shading like buildings and trees to avoid obstruction of solar radiation/sunlight. 3. An east–west-oriented greenhouse maintains better in winter season compared to north–south oriented with respect to solar radiation/sunlight. 4. Greenhouse orientation has to be decided at specific latitude by considering wind direction, available wind break as well as availability of sunlight throughout the year. The structural requirements of greenhouse and the cost per unit area for different models greenhouses for cultivation of vegetables/flowers are briefly given in following sections with diagrams. This will enable an interested entrepreneur to construct a greenhouse on his own accord. However, the local weather conditions and the individual requirement will play a major role in the selection of the greenhouse model.

6.2 Low Technology/Low Cost Greenhouses

121

6.2 Low Technology/Low Cost Greenhouses In this case, materials requirement are as follows: (1) Wooden/bamboo/PVC poles: Selection of the materials plays an important role in structural strength. (2) Galvanized iron (GI) wire: Generally 4-mm-diameter G.I. wires are used to fasten the bamboo sticks to the mainframe structures. (3) Nails: Long wire nails are used for fixing the wooden poles with supporting poles and nails required. (4) UV stabilized transparent film: Low density polyethylene (LDPE) film is the most commonly used for greenhouses due to less expensive and easy to install. Tunnel houses or “igloos” are low cost greenhouses with total height of less than 3 m. These are the most common type greenhouses without vertical walls and ventilation. The structure of low cost greenhouse is relatively inexpensive and easy to erect without automation. Low technology greenhouses have significant production and environmental limitations with cost effectiveness.

6.2.1 Wooden/Bamboo Base Greenhouse In this case, it is easy to have foundation/footing of bamboo with the help of brick and cement inside ground as shown in Fig. 6.1a, b. Further, it is easy to have any shape of greenhouse mentioned in Chap. 4 due to flexibility of bamboo. In strong windy area, it is not advisable to have bamboo structure. Further, transparent single-layer plastic sheet is used to cover the structure with help of screws/nuts/bolts and gasket for proper fittings between structure and plastic sheet. The life of such greenhouse depends upon quality of bamboo and plastic. It can have maximum life of 5 years. Size of such greenhouse can be very small suitable domestic purpose and can be installed in lawn of house.

6.2.2 PVC Pipe Structure Greenhouse As shown in Fig. 6.1c, flexible PVC pipe has been used for domestic drying of medicinal plants/jiggery/spices to store in the form of powder for off-season uses. PVC greenhouse is lightweight, and it can be transported from exposed solar radiation area to unexposed area. It can be used as per requirement to avoid deterioration of plastic due to unnecessary exposure to solar radiation, and its life can be extended. There is also provision of a fan at top end to remove moist air for faster drying. It needs small grid power.

122

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

The Classification of a Greenhouse Low cost bamboo/cane Greenhouse can be constructed using the local materials for villagers

a

b

The greenhouse drying of jaggery in forced mode

c Fig. 6.1 a East–west-oriented wood-based bamboo Quonset greenhouse constructed at IIT Delhi, 2005 b Locally available bamboo Quonset type greenhouse under construction c Cylindrical flexible PVC pipe Quonset type domestic greenhouse

6.3 Medium Technology Greenhouses

123

6.3 Medium Technology Greenhouses Medium technological greenhouses are characterized by vertical walls (2–3 m) more than low cost greenhouse. They may have provision of ventilation either through roof or side wall or both. The covering materials of medium level greenhouses are either single or double skin plastic film or glass with varying degrees of automation. Medium level greenhouses offer a compromise between cost and crop productivity. It represents a reasonable balance between economic and environmental aspects for the industry. Crop production in medium level greenhouses can be more efficient than open field/low cost greenhouse production. Hydroponic systems increase the efficiency of water use. Since long time back, farmers are using various coverings materials to physically protect crops from harsh weather inconsistencies. Frequent weather changes (freezes, droughts, floods) are risky for high-value vegetable crops in open condition. The life of medium technological greenhouse depends on structural materials (galvanized pipe) and its maintenance.

6.3.1 Quonset Greenhouse Figure 6.2a, b shows line diagram and photograph of galvanized iron (G.I.) Quonset type greenhouse constructed at IIT Delhi, Tiwari and Sharma [5] with effective area of 5 × 4 m with central height of 2 m. The low density polyethylene (LDPE) film has been fixed with the help of nuts and bolts with washer to avoid cracking in film. Provision of door on east side has also been given. Such greenhouse is most suitable for cold climatic/weather and hilly condition as mentioned earlier. In this case, transparent cover area is less than even type greenhouse, and hence, the night losses are minimum. Cooling pad-fan arrangement has also been incorporated in the design for forced mode of operation as shown in figure. It is not feasible and practical to have roof vent arrangement to avoid hot air leakage from inside greenhouse. On east side, there is provision of exhaust fan and west side, and cooling pad arrangement has been made. Solar radiation is trapped inside enclosure of greenhouse and retains the thermal energy to raise greenhouse inside temperature in winter due to greenhouse effect. If needed to lower the temperature inside greenhouse, first fan is used, and then if required, cooling pad-fan is used in case of more heat to be thrown outside. Further, flexible covering insulating material to reduce night heat loss is used as shown in Fig. 6.2c in harsh cold climatic condition. These are passive arrangements to create proper microclimate inside greenhouse. It is an economical option for farmers to have such greenhouse to increase their crop production during off-season. The cucumber cultivation with vertical growth of the plants has been studied in winter [5].

124

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

Fig. 6.2 a Line diagram of Quonset greenhouse b Galvanized iron (G.I.) pipe structure: Quonset type greenhouse constructed at IIT Delhi c Use of movable insulation over cover of Quonset type greenhouse

a

The Classification of a Greenhouse Contd… An arch type greenhouse for vertical growth of the plant

b

The movable curtain is used to cut-off solar radiation to reduce the cooling load

c

6.3 Medium Technology Greenhouses

125

6.3.2 Even Type Greenhouse Figure 6.3a and b shows the structure of even type greenhouse made by galvanized iron (G.I.) pipe (1/2 inch diameter) and prefabricated material with coating to avoid corrosion. The use of prefabricated structure is expensive but has more life, and also, it is easy to cover it by single/double cover transparent materials with suitable nails/nuts/bolts with rubber gasket. Even type greenhouse is generally recommended for composite climatic condition which requires both heating (winter months) and cooling (summer months) arrangement. Further, different level of either heating or cooling of greenhouse is required for weather changing from either winter to summer or vice versa. (a) Heating arrangements: In this case, one can have as many as roof vents as per requirements depending upon local weather condition as shown in Fig. 6.3c and d. During winter months, roof vent is always closed for thermal heating. Further, brick wall on north side of greenhouse, Fig. 6.3c, has been made to reflect incident solar radiation on north wall. It is required to avoid further loss of transmitted solar radiation inside greenhouse through north transparent wall. If north wall is opaque, then this direct loss will be reduced to increase the greenhouse room air temperature. It is required if width of greenhouse is less than length of greenhouse. In ridge and furrow type greenhouse, north wall is not required due to large area. In this case too, an arrangement of movable insulation can be made as shown in Fig. 6.3e to cover it during night in winter condition to retain the trapped thermal energy. Even this can be used if solar gain is less than heat loss from inside greenhouse. Another arrangement of heating of greenhouse air is an integration of ground air collector, Ghosal et al. [2], Fig. 6.3f and earth air heat exchanger, Fig. 6.3g, Ghosal et al. [1, 3], to greenhouse air. It is very simple to construct and integrate with greenhouse. It is economical as well. However, it should be used during nighttime at very low outside ambient air temperature. During daytime instead of heating, it starts cooling greenhouse air due to high greenhouse air temperature and more upward heat loss during daytime from glazed plastic cover. (b) Cooling arrangement: The roof vent is used for natural cooling for hot air removal from inside greenhouse to outside due to the presence of hot air near the roof. The opening depends upon the level of cooling requirement. For example if weather is changing from winter to summer, then opening of roof vent should be done during peak sunshine hours to maintain the required greenhouse room air temperature. Further, weather condition is shifting toward summer; then roof vent is not sufficient; then forced mode of operation should be done to fast removal of hot air from inside greenhouse. With start of summer condition with survival of plants in post-harvest condition, cooling pad-fan arrangement should be used as shown in Fig. 6.3h. Area of cooling pad and capacity of fan depend on volume of greenhouse air. Effect of water flow over canopy cover of greenhouse has also been studied by Ghosal et al. [4]. Further, cooling pad and fan arrangement also increases inside relative humidity which also helps in

126

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

Fig. 6.3 a Galvanized iron (G.I.) pipe structure even type greenhouse under construction b Prefabricated structure of even type greenhouse c North brick wall with roof vent provision in even type greenhouse at IIT Delhi d Complete view from south side with roof vents and force mode of operation e View of south direction of even type greenhouse covering with movable insulation f Even type greenhouse integrated with ground air collector g View of earth air heat exchanger (EAHE) integrated with even type greenhouse h View of fan-cooling pad arrangement in west side of even type greenhouse i View of inside thermal curtain integrated with even type greenhouse

Construction of Greenhouse at IIT Delhi

a

b The north wall for thermal heating inside the greenhouse under construction……

c

6.3 Medium Technology Greenhouses Fig. 6.3 (continued)

127

The Greenhouse with roof vent

d

The manual covering of a greenhouse

e The complete view of a ground air collector

f

128

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

g

The evaporative cooling system supplied by the Ambassador cooler company

h

i Fig. 6.3 (continued)

6.3 Medium Technology Greenhouses

129

cooling for plants. The cooling pad and fan arrangement becomes more effective if internal thermal curtains are used inside greenhouse as shown in Fig. 6.3i. In this case, volume of greenhouse air is reduced for cooling due to partition of volume of greenhouse.

6.3.3 Ridge and Furrow Type Greenhouse As mentioned earlier in Chap. 5, ridge and furrow type greenhouse is nothing but jointed Quonset/even and uneven type/other design of greenhouse installed for larger area for commercial agricultural crop production. In this case, mild steel/galvanized pipe structure with rigid strength should be prepared with respect to strong wind condition in the area of installation of greenhouse. The greenhouse should be multipurpose greenhouse including solarization of seeds, various off, and pre- and postharvest cultivation for vegetables/fruits for commercial application to have high return annually. In this case, most of low energy-intensive heating/cooling arrangements mentioned earlier should be integrated depending upon local climatic/weather condition. Figure 6.4 shows the ridge and furrow Quonset, Fig. 6.4a, and even type greenhouse, Fig. 6.4b, having cooling pad-fan arrangement. Fig. 6.4 a Ridge and furrow type Quonset type greenhouse. b Ridge and furrow type even type greenhouse

a

b

130

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

6.4 High Technology (Hi-Tech) Greenhouses High level greenhouses have a wall height of at least 4 m for vertical cultivation. The central height from ground may be about 8 m above ground level with multitier cultivation if required with high resistance with strong wind. These structured greenhouses offer superior quality of crop/vegetables/flowers/fruits under good environmental conditions. High technology (Hi-Tech) structured greenhouses will have roof/sides wall advance ventilation and evaporative cooling, inside green net, misting, latest micro-irrigation, and relative humidity along with sensor of each cooling and heating arrangement. If required, high energy-intensive heating/cooling arrangement for shorter period under worst weather condition to save plant inside greenhouse has also been provided. Cover cladding may be plastic film (single or double), polycarbonate sheeting, or glass. Environmental controls are almost always automated. High-tech structures also offer enormous sustainability opportunities for economic growth and environmental including climate controlled and photosynthetic active radiation (PAR), lighting facility, screening systems, plant trellising (bamboo/steel rod to support climbing plant), and fertigation (injection of fertilizers to irrigation system) systems. Use of pesticides is significantly minimized due to high temperature inside greenhouse in comparison with outside ambient air temperature. High technology structures provide an internationally agribusiness opportunities. Hi-Tech greenhouses can be of any shape depending upon local climatic and weather condition. These are expensive greenhouse, Fig. 6.5, in comparison with low and medium technological greenhouse. However, it offers a highly quality productive, sustainable microenvironmental condition inside greenhouse for an advanced fresh produce industry. Fig. 6.5 Glimpse of high-tech greenhouse

6.5 Greenhouse Integrated Semi-transparent Photo-Voltaic Thermal …

131

6.5 Greenhouse Integrated Semi-transparent Photo-Voltaic Thermal (GiSPVT) System As mentioned in Sect. 6.4, Hi-Tech greenhouse required almost automated system for advance ventilation and evaporative cooling, misting, latest micro-irrigation, relative humidity, and cooling and heating arrangement. Greenhouse automated system is fossil fuel-based grid energy-intensive which is not friendly with environment and climate. Hence, researchers in the past have drawn an attention to develop greenhouse integrated semi-transparent photo-voltaic thermal (GiSPVT) system for agriculture application, namely crop production, aquaculture, aquaponics, solarization, soil mulching, etc. (Chap. 5). The GiSPVT system can provide thermal energy, solar radiation for photosynthesis, and electrical energy. This will also protect the agricultural produces from worst weather condition just like Hi-Tech greenhouse. In this case, instead of cover cladding like plastic film (single or double), polycarbonate sheeting or glass, cover cladding is either semitransparent photo-voltaic (PV) module or combination of semitransparent photo-voltaic (PV) module, and transparent glass. So, a suitable microenvironmental condition inside the greenhouse for production of agriculture produces becomes self-sustained automated. The greenhouse integrated semi-transparent photo-voltaic thermal (GiSPVT) system will be more expensive in comparison with Hi-Tech greenhouse (Sect. 5.4), but it will self-sustain. Further, the life of covering material in GiSPVT will be around 30 years along with extra power production which will be used for other domestic application. The GiSPVT can be associated with grid connection if grid power is available round the year continuously. So an extra land is not required for installation of GiSPVT like stand-alone system. An overall cost evaluation of GiSPVT system depends upon use of GiSPVT for highvalue off-season crops, pre- and post-harvesting along with solarization of seeds for other farmers, etc. Structural construction of Hi-Tech greenhouse and GiSPVT are same except cladding of cover materials. Further, choice of semi-transparent PV module will depend on shape of roof as mentioned in Sect. 5.3.

6.5.1 Working Principle of GiSPVT Figure 6.6 shows the cross-sectional view of uneven type of GiSPVT oriented north– south direction in northern hemisphere to receive maximum annual solar radiation. Inclination of south roof depends on grid and off-grid connection. In grid connection, an inclination should be at an angle equal to latitude of place; otherwise, it should be as per requirement of crop production. For example, electrical power is needed more in summer condition due to cooling arrangement for sustainable microclimate inside the greenhouse, and hence, inclination should be latitude minus fifteen in off-grid connection with inverter and batteries. In this case, there is direct gain of solar radiation through non-packing area and glazed walls like Hi-Tech greenhouse and indirect gain from back of solar cell by convection inside greenhouse to heat

132

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

Greenhouse integrated Semitransparent Photovoltaic Thermal (GiSPVT) System Parameters to optimize

Pot position

Packing factor of PV module

with sown seeds

80 Wp module

as crop grows

50 Wp module

25 Wp module

Fig. 6.6 Cross-sectional view of GiSPVT (Give dimensions as mentioned in Sect. 5.3.3)

the inside air. Another advantage of c-Si-based GiSPVT system is it reduced an overall heat loss coefficient from inside greenhouse to outside ambient air due to double glazing of PV module which reduces night heat loss through roof in cold climatic condition. So greenhouse air is heated in cold climatic condition to create microclimate of summer condition for off-season crop production. There can be an arrangement for roof vent as well as sliding door for extraction of excess heat by natural mode from inside greenhouse to outside.

6.5.2 Layout Plan of GiSPVT The floor plan of GiSPVT with an effective area of 24.4 × 36.6 is 893.04 m2 . The floor plan has been divided into six equal zones with each area of 12.2 × 12.2 m. Zones-1 and -2 in north side have 10 kWp roof top with packing factor of 80% (Fig. 4.4a) and 40% (Fig. 4.4b), respectively, and zones-5 and -6 in south side have 10 kWp with packing factor of 22% (Fig. 4.4c). In zones-3 and -4 in middle, mixed combination of simple glass window and 22% packing factor has been used as roof top. The uneven type GiSPVT as shown in Fig. 6.6 has been facing south direction.

6.5 Greenhouse Integrated Semi-transparent Photo-Voltaic Thermal …

133

6.5.3 Foundation for GiSPVT System Concrete is a proper mixing of coarse aggregate, fine aggregate, cement in ratio of 3:3:1, and water. It is also referred as footing of the re-enforced cement concrete (RCC) structure required for larger area like in the case of Hi-Tech, Fig. 6.5, and ridge and furrow type, Fig. 6.6, greenhouses. In this case, RCC structure is in contact with ground and distributing load over a larger area. RCC footings are done in loadbearing structures. The cement hydrates form a binder with the water. The result is a hardened mass with “filler” and pores. There are various types of cement for low heat, rapid set, and other properties. Footing plays a very critical role in overall structure stability of a greenhouse. It is easy to construct such foundation with local mason and available materials, and it is economical. Foundation work is same for both Hi-Tech greenhouse and GiSPVT. In this case, a structure of steel bar/bamboo (iron rod) is prepared as shown in right of Fig. 6.7a and placed in prepared pit of 0.91 m inside the ground. Further mixer of coarse aggregate, fine aggregate, cement in ratio of 3:3:1, and water is placed over it with boundary of wooden plate as per specification. It is left over the one week, and water is sprayed over it continuously for good strength. Final prepared footing is shown in left of Fig. 6.7a. Further, the number of foundation depends upon the built-up area of greenhouse and its design. Figure 6.7b shows the foundation work along with brick wall from foundation as per design. Further, a north brick wall arrangement as shown in Fig. 6.7c should also be made. This solves two problems, namely it does not allow strong wind in harsh weather condition to pass through greenhouse to save canopy cover and also block solar radiation passing through north canopy cover. It is important in winter regional area. Figures 5.7b and c show photo of the all erected RCC pillar from north and south ends with cross section of 0.23 × 0.23 m with brick boundary (0.10 m) of all around up to height of about 1.82 m from footing (Fig. 6.7a) with tie beam to give strength to boundary. The brick boundary wall area with an effective area of 222.97 m2 is used to avoid any external water leakage coming from outside due to heavy rain and flood in worst weather condition. The central and lowest heights of uneven type GiSPVT of each zone are about 3.66 m and 1.83 m, respectively. An inclination of south and north roof from horizontal is 10 and 37, respectively, as shown in Fig. 6.6. The distance between central pillar and lowest pillar from north and south direction is 2.44 m and 9.75 m, respectively (Fig. 6.6). Also, there is brick wall in north side (Fig. 6.7c) for reflection of solar radiation from inner wall to greenhouse floor if any, and it also reduced heat loss from north wall. There are 15 RCC pillars of height of 3.66 m and 2.74 m, respectively, and 20 RCC pillars of height of 1.83 from tie beam as shown in Fig. 6.7c.

134

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

Fig. 6.7 a Foundation work for GiSPVT b Views of constructed pillars from south direction c Views of constructed pillars from north direction with brick north wall with provision of entry to GiSPVT

a

b

c

6.5 Greenhouse Integrated Semi-transparent Photo-Voltaic Thermal …

135

6.5.4 Semi-transparent PV Module South Roof As mentioned earlier, the roof of GiSPVT system will be ccovered by semitranspaprent PV module with packing factor of 80%, 40%, and 22% in following manner: (a) Roof of zone-1 (Fig. 6.8a) will be covered by 80 Wp semi-transpaprent PV module with packing factor of 80%. (b) Roof of zone-2 (Fig. 6.8b) will be covered by 50 Wp semi-transpaprent PV module with packing factor of 40%, Fig. 5.8b. (c) Zones-3 and -4 (Fig. 6.8c) will be covered by combination of transprent window glass and 50 Wp and 25 Wp semi-transpaprent PV module with packing factor of 40%and 22%, respectively. (d) Zones-5 and -6 (Fig. 6.8d) will be covered by 25 Wp semi-transpaprent PV module with packing factor of 22%. The fixing of mettal circular plates over RCC pillar for leveling of first and second layer by weilding is shown in Fig. 6.9a. The fixing of first layer mild steel beam over circular plate fixed at top of RRC pillar plate at top of pillar for uniform leveling is shown in Fig. 6.9b. Figure 6.9c shows a complete view of first and second layer mild steel beam fixed over plate at top of pillar for uniform leveling. Figure 6.9d gives a complete view of first and second layer mild steel beam fixed over plate with green paint to avoid corrosion with water in contact if any. Figure 6.10a and b shows the external view of fixing of semi-transparent PV module with packing factor of 80% on mild steel roof struture with the help of alluminium frame in zone-1. The spacing if left between two PV modules is filled with white flexible rasin to avoid any leakage during either roof cleaning with water or rain. The roof surface with an effective area of about 120.8 m2 for each zone has been covered with semi-transparent PV module of 10 kWp. Further, Fig. 6.10c also shows the inner view during fixation of PV module with 40% packing factor in zone-2. In order to avoid the leakage of water at lower end of south roof between two rows, a provison of rain water harvesting has also been made as shown in Fig. 6.10c. Exit of rain water harvsting through PVC pipe has been provided for each water harvesting. On top of rain water harvesting, a strong peddlar has also been made to walk over it for leaning north and south roof with the help of stair provided in north roof for each zone. Further, at top of each zone, water spray with the help of plastic pipe with proper hole on both sides is also given for cleaning of roof as per requirement. The inlet is connected with underground boring with pump to boost the water in the pipes. Provision of rain harvesting from east and west roof is shown in Fig. 6.10d and e, respectively.

136

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

a

b

c Fig. 6.8 a Inside view of zone-1 b Inside view of zone-2 c Inside view of zones-3 and -4 d Inside view of zones-5 and -6

6.5 Greenhouse Integrated Semi-transparent Photo-Voltaic Thermal …

137

d Fig. 6.8 (continued)

6.5.5 Medium Tech GiSPVT Further, complete view of 30kWp GiSPVT from north side is shown in Fig. 6.11a which is medium technology greenhouse integrated photo-voltaic thermal (GiSPVT) system. The north roof of each zone has an effective area of 37.12 m2 , and it is covered by window glass of 5 mm with provision of roof vent as shown in same figure to allow excess of inside hot air to escape to outside by natural mode of operation. The rate of escape can be determined by opening area from time to time as per requirement. Also east and west walls have also been made of window glass of the same thickness with sliding door as shown in Fig. 6.11b. The east and west window glass wall area is equal, and each one has an effective area of 167.23 m2 . The south window wall area is 44.59 m2 . The purpose of sliding door is same as of roof vents. In winter season, roof vents as well sliding doors are always closed for maximum thermal heating, and roof vents and sliding doors are opened if needed for inside thermal energy removal. The roof vents and sliding doors can be referred as one of the passive cooling methods. Such greenhouse is most suitable for cold climatic region of any part of world. In this case, one can use fans provided vertical glass wall preferable in east and west sides for further cooling. Also, photo of ridge and furrow type GiSPVT even type greenhouse in Spain is shown in Fig. 6.12. Further, high-tech greenhouse integrated semi-transparent photo-voltaic thermal (GiSPVT) can also be based as mentioned in Sect. 6.4.

138

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

Fig. 6.9 a View of fixing plate at top of pillar for uniform support to mild steel beam with wielding b View of fixing of first layer mild steel beam over plate at top of pillar for uniform leveling c Complete view of first and second layers mild steel beam fixed over plate at top of pillar for uniform leveling d Complete view of first and second layers mild steel beam fixed over plate with green paint

a

b

c

6.6 Photo-Voltaic System

139

Fig. 6.9 (continued)

d

6.6 Photo-Voltaic System 6.6.1 Background A photo-voltaic (PV) system is a distributed power generation system that produces electrical power by harnessing solar energy and converts it into electricity. Solar power generation plant comes under the category of renewable energy sources (RES) as they do not involve fossil fuel such as coal, petroleum, and natural gas sources for power generation. Solar PV plants are classified broadly based on their location. In this section, we will discuss installation of 30 kWp (equivalent to 116 kWp), installation of three types of semitransparent PV panels, namely (a) 80 Wp, (b) 50 Wp, and (c) 25 Wp with different packing factors (PF) mentioned in Sect. 5.5.4 for allowing different solar radiation for each block with water proofing and panel cleaning arrangement. The entire greenhouse is divided into two sections: One is south side and another is north side. The south side is facing due to south as shown in Fig. 6.13. South side is categorized as semi-transparent PV panels side, and north side is categorized as transparent window glass with open roof window for hot air circulation from inside to outside. South roof semi-transparent PV module is divided into six zones as follows: 1

Zone-1

80 Wp module with maximum packing factor (PF) of 80%

2

Zone-2

50 Wp module with packing factor (PF) of 40%

3

Zone-3

50 Wp module with packing factor (PF) of 40% and 6 mm window glass

4

Zone-4

25 Wp module with packing factor (PF) of 22% and 6 mm window glass

5

Zone-5

25 Wp module with packing factor (PF) of 22%

6

Zone-6

25 Wp module with packing factor (PF) of 22%

140

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

Fig. 6.10 a Top view of fixing of semi-transparent photo-voltaic module on roof structure b Inside view of fixed semi-transparent photo-voltaic module on roof structure c Inside view of fixed semi-transparent photo-voltaic module on roof structure with different packing factor d Provision of collecting wastage water during cleaning and rain water from roof top

a

b

c

6.6 Photo-Voltaic System

141

Fig. 6.10 (continued)

d

6.6.2 Description Specifications of Each Component The sketch/line diagram of SPV of each 10 kWp with different PV module along with each component has been reported in Table 6.1. Central electronic limited (CEL), Sahibabad, Ghaizabad (UP), India, has compared the solar module technology and recommended the crystalline technology based on the Indian environment, electrical efficiency, and Indian market share considerations. The type of PV modules used for this greenhouse integrated semitransparent photo-voltaic thermal (GiSPVT) system project is unique and customized for special use of greenhouse. The brief details are given in Tables 6.2 and 6.3, respectively. Solar PV modules are rated under industrial Standards Test Conditions (STC) of solar irradiation of 1000 W/m2 with zero angle of incidence, solar spectrum of 1.5 air mass, and 25 °C surrounding temperature and also at nominal operating cell temperature (NOCT) (Chap. 2) when operating under 800 W/m2 irradiance, 20 °C ambient air temperature, and wind speed of 1 m/s. Solar PV module is generally operated in the open field even at higher temperature. This higher operating temperature of PV module results in the losses due to the temperature coefficient, Eq. (4.2c). In the PV module, the temperature coefficient is −0.0004383/ rise in temperature of solar cell.

6.6.3 Description of Solar Power Plant Generation System The rate of solar radiation varies with time and day of the year as mentioned in Chap. 1, and hence, the electrical power output of the PV system varies directly proportional to the level of solar radiation incident on the PV module surface. The power output of PV array (Chap. 3) too varies throughout the day. As a result, the

142

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

(i)

(ii)

Top view

a

North view

Without glazed wall

With glazed wall

b Fig. 6.11 A Complete over view ridge and furrow type of 30 kWp GiSPVT system with provision of north roof vent b View of glazed west wall with sliding window

6.6 Photo-Voltaic System

143

GiSPVT system located at Derio, Biscay, Spain •

ULMA Agrícola and Tecnalia installed PV modules on one of its two glass greenhouse units measuring approximately 400 m2 in Derio, Biscay, Spain

Fig. 6.12 Photo of ridge and furrow type GiSPVT even type greenhouse in Spain

Fig. 6.13 View of GiSPVT after fitting of semi-transparent PV module in south side

inverter continuously matches the output of the PV array with a reference power source to maximize the PV array output (Fig. 6.14). Based on this reference power source, PV systems are classified as: 1. Off-grid systems: In this case, the system comprises a battery bank that functions as the reference power source as well as a storage mechanism which can supply power at day and night as per requirement even in the absence of the Sun. For GiSPVT, we have considered off-grid system due to non-availability of power throughout day/night. 2. Grid-connected systems: In this case, the solar power system is coupled with the grid which provides the reference power source and is also an unlimited storage option which can supply electrical power whenever solar radiation is not available. This is valid if grid system has continuous power for 24 h.

144

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

Table 6.1 Brief detail of each components used in roof top PV system Sr. No.

Description

Remarks

1

Sketch/line diagram of SPV complete system with details

Figure 6.14

2

Capacity and power of each module

80 Wp 50 Wp 25 Wp

3

Number of PV modules

792

4

Solar cell technology

Polycrystalline

5

Inclination of PV module

Fixed tilt at 10°

6

PCU/inverter capacity with detail specification

Nexn15KVA/240 V, single phase, smart MPPT

7

Type of inverter and inverter efficiency

Off-grid 98%

8

No. of inverter/PCU

03 (15 KVA/240 V)

9

DC bus voltage

1100 V

10

Capacity of battery bank (current, voltage and Ah)

12 V/150 Ah

11

Type of battery being used (lead acid tubular/li-ion/SMF, etc.)

Amaron SMF, VRLA

12

Details of protections are deployed PV array and AC output side

SPD, DC isolator, DC MCB, AC MCB, fuses, over current relay

13

Details of metering, data logging operation

The DATA logger takes care of data monitoring and SPV system

14

Details of PV module roof mounting system

Roof mounted system with fabricated primary, secondary, and tertiary structures

A brief description of each of the components is presented below: 3. PV Modules: The PV modules are the devices that actually convert solar energy to electricity. The PV modules are made from solar/PV cells, which are most commonly manufactured using silicon as mentioned in Chap. 2. Generally, silicon-based solar cells provide higher electrical efficiency (15–20%) but are relatively costly to manufacture, whereas thin-film solar cells are cheaper but less efficient (5–10%). Since different types of PV modules have different characteristics (in terms of electrical efficiency, cost, performance in low solar radiation levels, degradation rate), no single type is preferable for all projects. Good quality PV modules generally have a useful life of 25 to 30 years. It is important to assess the quality of PV modules for use in projects. 4. Inverter: The inverter converts the DC power produced by the PV modules into AC power. The AC power is then either injected into the grid or consumed on-site. For grid-connected rooftop solar applications, inverters come in standard sizes ranging from a few hundred watts to hundreds of kilowatts depending on system

6.6 Photo-Voltaic System

145

(a)

(b) Fig. 6.14 a Electrical connection of 80 Wp PV panel system, b electrical connection of 50 Wp PV panel system, and c electrical connection of 25 Wp PV panel system

146

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

(c) Fig. 6.14 (continued) Table 6.2 Specification of PV module

(a) Type of PV module (i) PV module type

Multi-crystalline make CEL

(ii) Semi-transparent

Each one

(iii) PV module wattage (Wp )

80, 50 and 25

(iv) Rated power (Pmax )

82.05, 52.08 and 29.28

(v) Rated current (I m )

4.36, 2.84, 1.51

(vi) Rated voltage (V m )

18.85, 18.84 and 19.14

(vii) Open-circuit voltage (V oc )

22.81, 22.66 and 22.73

(viii) Short-circuit current (I sc )

4.85, 3.08 and 1.67

(ix) Number of PV module

168, 208 and 390

(b) Physical dimensions (i) Length

1063 mm

(ii) Width

667 mm

(iii) Thickness

12 mm

(iv) Weight

16 kg

6.7 Junction Box Table 6.3 Electrical parameters at standard test condition (STC) at 1000 W/ m2 and 25 °C

147

80 W

50 W

25 W

Rated power (Pmax )

82.05

52.08

29.28

Rated voltage (V mp )

18.85

18.84

19.14

Rated current (I mp )

4.36

2.84

1.51

Open-circuit voltage (V oc )

22.81

22.66

22.73

Short-circuit current (I sc )

4.85

3.08

1.67

size. These inverters are usually string inverters, which have smaller capacities (typically 300 kW) and are generally used in MW-scale solar PV projects. There are many different types of inverters in the market; selection of an inverter for a project depends on a number of factors, including application, size, cost, function, usage, etc. Inverters also perform energy monitoring functions. From the technology perspective, inverters have matured to a large degree and opportunities of cost reduction through technology innovation are not expected in the market. Top-of-the-line inverters offer efficiencies in the range of 97–99% (Table 5.1). 5. Module Mounting Structure: The mounting structure, or racking system, is the support structure that holds the PV panels. PV modules are generally mounted on support structures in order to more efficiently capture solar radiation, increase generation, and have a stable structural support. Mounting structures can be either fixed or tracking. Fixed tilt mounting systems are simpler, low maintenance, and cheaper than tracking systems. Due to these reasons, fixed tilt mounting structures are the norm in India. Mounting structure designs are highly specific to the site and over time have seen improvement in durability and reduction in costs. Cost reduction is mostly achieved through designs that use less material (mostly steel or aluminum). Mounting structures for rooftop solar PV installations also require compliance with regulations or guidelines associated with the structural aspects of the roof, such as load-bearing capacity and wind loading. 6. Balance of System: Balance of system (BOS) consists of cables, switchboards, junction boxes, meters, etc. Electricity meters record the amount of electricity consumed and/or produced (in kWh and kVAh) by a customer within a premises.

6.7 Junction Box Junction boxes are made of thick (suitable thickness) PVC plastic, suitable for outdoor application. This will be suitable for mounting on glass. Terminal block of 16A rating with disconnecting links will be present inside the junction boxes. Earthing connection mounts will be provided in the junction boxes. The junction boxes will have suitable arrangement for the following: • Combine groups of PV modules into independent charging subarrays that will be wired into the controller.

148

• • • •

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

Provide arrangement for distribution of each of the groups. Provide a test point for each subgroup for quick fault location. Provide group array isolation. The current carrying ratings of the junction boxes will be suitable with adequate safety factor to interconnect the solar PV array.

6.8 AC Distribution Box The AC distribution box (ACDB) is provided between this PCU, and this main LT distribution panel provides suitable protection insulation and change over between the load and the power output of the PCU. Standard industrial make ACDB is used at project site. Typically, the ACDB is manufactured from powder coated metal enclosures and houses the suitably rated MCB, isolators, and manual change over switches. The ACDB consists of distribution feeder that is used to cater the existing loads of the facility with solar generated electrical power.

6.9 Cabling Cables used are extremely robust and resist high mechanical load and abrasion. Good temperature resistance and excellent weather proofing characteristics also provide long services life to the cables used. The connectors used have high current capacity and are easy to use. (a) LT Cables 1.1. KV grades, copper conductor XLPE cables of suitable diameter are used as the power cable for connection between the solar PV modules, strings to junction boxes, and from junction boxes to inverter. The LT cables are used as conduit pipes of adequate strength. The cables are terminated using copper lugs of adequate cross-section area. (b) Control Cables 1.1. KV grade, Cu conductor, XLPE flexible cables are used for all control cables required for the solar power plant. These cables are laid on structural support and use conduit pipe of adequate strength. The cable will be terminated using Cu lugs of adequate cross-section area. The terminal ends of the cables and wires are fitted with good quality letter and number ferrules of proper sizes so that the cables can be identified easily. (c) Earthing System The earthing for the power plant equipment is made as per provisions of IS: 3043. Earthing system is made with copper bonded 3 meter long and 17.2 mm diameter with chemical compound. Necessary provisions are made for bolted

6.11 Data Logger

149

isolating joints of each earthing pit for periodic checking of earth resistance. The complete earthing system is mechanically and electrically connected to provide independent return to earth. In compliance with ruled 33 and 61 of Indian electricity act 1956 (as amended up to date), all non-current carrying metal parts are earthed with two separate and distinct earth continuity connectors to efficient earth electrode. (d) Protection Relays The SPV system and the associated power evacuation system are protected as per Indian standards. Over current replays, reverse power relays, and earth faults relays are the minimum requirements.

6.10 Fire-Fighting System The fire-fighting systems design shall be confirmed to TAC/NFPA norms. The type of fire protection systems for complete plant shall be including portable fire extinguishers.

6.11 Data Logger The data logger takes care of data monitoring and regular data logging of the SPV system. The data logger used is of track, so make which is a GSM-based system needs to recharge on periodic intervals. The data logger also allows user to perform monitoring and logging of each PCUs. The system is configured, and real-time data can be obtained. Following data from the system are logged and displayed: • DC voltage • DC current • DC power.

6.11.1 Erection and Commissioning Phase For proper commissioning phase of GiSPVT, design, erection, and quality assurance expertise are put to test. As discussed in the earlier section, staff identified to operate the plant has been involved. After complete construction of GiSPVT, the checklist designed to ensure that the plant has been properly installed with appropriate safety measures. The plant shall be subjected to a performance test, after the successful completion of the performance test of the GiSPVT plant; the plant will be taken over by the consumer.

150

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

As per the time frame provided by the customer, this project got delayed due to heavy rains and flood at project site, Jawahar Nagar (Mrgupur), Ballia. For this kind of erection, soil condition should not be slippery. But due to flood site, soil became against material handling equipment like cranes and tractors. Erection of building integrated greenhouse solar power plant is further divided into two parts: • South side—PV panels side • North side—float glass side. Components of south side: • • • •

Primary structure—mild steel Secondary structure—mild steel Tertiary structure—aluminum Float glass and accessories. Components of north side:

• Primary structure—mild steel • Secondary structure—aluminum • Float glass and accessories. Structure Details: Module mounting structure (MMS) and its accessories play an important role for the performance of the solar plant, and in the case of greenhouse selection becomes more sensitive as humidity level is very high. After considering all these parameters structure design done and fitted as per drawing, Zero Leveling of entire structure along with solar panels is being executed. For Zero Leveling, a BASE PLATE of 16 mm thickness (9 inch × 8 inch) placed over concert column is shown in Fig. 6.9a. The material specification of GiSPVT is given in Table 6.4. Objective Questions 6.1. The preferred glazing material for low cost greenhouse is (a) (b) (c) (d)

Plain/corrugated/plastic film sheet UV stabilized LDPE film Silpaulin type sheet Net house

Answer: (b) 6.2. The preferred glazing material for medium/high-tech greenhouse is (a) (b) (c) (d)

Plain/corrugated/plastic film sheet UV stabilized LDPE film Silpaulin type sheet Window glass

Answer: Window glass

6.11 Data Logger

151

Table 6.4 Material specification Sr. No.

Description

Dimension

Qty

Unit weight (kg)

Total weight (kg)

Primary structure components 1

Base plate for zero leveling

228.6 × 203.2 × 16 (mm)

50

18

900

2

MS tube painted for south side

203.2 × 203.2 × 6 (mm)

20

193

3860

3

MS tube painted for north side

96 × 48 × 2.2 (mm)

15

193

2895

4

MS tube painted for support (north and south sides)

100 × 50 × 2 (mm)

65

28.4

1846

22

5280

36

22

792

Secondary structure components 180 × 75 × 15 × 240 2 (mm)

5

MS painted purlin C channel type (south side)

6

MS tube painted for 50 × 50 × 2 purlin (north side) (mm)

Tertiary structure components 7

Aluminum tube (south side)

50 × 25 (mm)

114

3.5

399

8

Aluminum tube (north side)

50 × 50 (mm)

165

3.5

577.5

9

Aluminum U channel for PV panels and float glass

14 × 14 × 14 (mm)

92

1.5

138

10

Aluminum glazing strip for PV panels and float glass

50 × 3 (mm)

200

1.5

120

11

Float glass (South Block-3 and Block-4)

1063 × 667 × 6 ( mm)

Triangle frame with glass components

6.3. The preferred structural material for construction of low cost greenhouse is (a) (b) (c) (d)

Wooden/bamboo greenhouse PVC pipe Galvanized iron (G.I.) pipe Reinforced concrete and cement (RCC)

Answer: (a) and (b) 6.4. The preferred structural material for construction of for medium/high-tech greenhouse greenhouse is

152

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

(a) (b) (c) (d)

Wooden/bamboo greenhouse PVC pipe Galvanized iron (G.I.) pipe Reinforced concrete and cement (RCC)

Answer: (c) and (d) 6.5. Low cost greenhouse is most suitable for (a) (b) (c) (d)

Hot climatic condition Composite climatic condition Partial cloudy condition Cloudy condition

Answer: (d) 6.6. Low cost greenhouse may need additional (a) (b) (c) (d)

Needs heating arrangement Cooling arrangement Heating and cooling both Partial cooling arrangement

Answer: (d) 6.7. Medium tech greenhouse may need automation arrangement (a) (b) (c) (d)

For heating application For cooling arrangement For heating and cooling None of them

Answer: (d) 6.8. Self-sustain greenhouse is (a) (b) (c) (d)

Low cost greenhouse Medium tech greenhouse High-tech greenhouse GiSPVT

Answer: (a) and (d) 6.9. Maximum life of greenhouse is (a) (b) (c) (d)

For high-tech greenhouse Low cost greenhouse GiSPVT None of them

Answer: (a) and (c) 6.10. Solarization of seeds can be achieved (a) Due to greenhouse effect

6.11 Data Logger

153

(b) In exposed solar radiation (c) In off sunshine hours (d) In all condition Answer: (a) 6.11. Mulching in root media provides (a) (b) (c) (d)

Cooling effect Heating effect Heating and cooling None

Answer: (a) 6.12. For large-scale cultivation inside greenhouse, one of the following shape is preferred (a) (b) (c) (d)

Quonset Even Uneven Ridge and furrow

Answer: (d) 6.13. The preferred PV module used for greenhouse is (a) (b) (c) (d)

Opaque Semitransparent c-Si Semitransparent thin film All of them

Answer: (b) and (c) 6.14. Semi-transparent PV modules provide (a) (b) (c) (d)

Electrical power Thermal energy Lighting All of them

Answer: (d) 6.15. Medium Tech greenhouse can be economical in (a) (b) (c) (d)

Moderate climatic condition Composite climatic condition Cold and climatic condition Harsh hot condition

Answer: (a) and (c)

154

6 Construction of Greenhouse Integrated Semi-transparent Photo-Voltaic …

References 1. Ghosal MK, Tiwari GN (2006) Modeling and parametric studies for thermal performance of an earth to air heat exchanger integrated with a greenhouse. 47(13–14):1779–1798. https://doi.org/ 10.1016/j.enconman.2005.10.001 2. Ghosal MK, Tiwari GN, Das DK, Pandey KP (2005) Modeling and comparative thermal performance of ground air collector and earth air heat exchanger for heating of greenhouse. 37(6):613–621. https://doi.org/10.1016/j.enbuild.2004.09.004 3. Ghosal MK, Tiwari GN, Srivastava NSL (2004) Thermal modeling of a greenhouse with an integrated earth to air heat exchanger: an experimental validation. 36(3):219–227. https://doi. org/10.1016/j.enbuild.2003.10.006 4. Ghosal MK, Tiwari GN, Srivastava NSL (2003) Modeling and experimental validation of a greenhouse with evaporative cooling by moving water film over external shade cloth. 35(8):843– 850. https://doi.org/10.1016/s0378-7788(02)00242-6 5. Tiwari GN, Sharma PK (1999) Off-season cultivation of cucumbers in a solar greenhouse. Energy 24(2):151–156. https://doi.org/10.1016/s0360-5442(98)00083-8

Recommended Additional References for Studies 6. Ghosal MK, Tiwari GN (2004) Mathematical modeling for greenhouse heating by using thermal curtain and geothermal energy. 76(5):603–613. https://doi.org/10.1016/j.solener.2003.12.004 7. How to build a low-cost greenhouse with PVC pipes dengarden.com › landscaping 8. Greenhouse technology indiaeng.com › Kaveripakkam › 04-Greenhouse techn

Chapter 7

Cultivation of Vegetables in Winter

7.1 Introduction In this chapter, we have made an attempt to cultivate vegetables along with power generation in desert (unfertilized) land available in my home land, Ballia, under photo-voltaic-based greenhouse [1]. It is an attempt based on my forty years’ experience in the area of greenhouse vegetables cultivation in field and pot at Indian Institute of Technology Delhi under mentorship of Padmashree Prof. M.S. Sodha. The project is also funded by Department of Science and Technology, Government of India, under Mission Innovation for rural development. Generally, vegetables can be classified as (a) summer season and (b) winter season crops [2–4]. Summer and winter season crops are typically fruits and root crops salad greens respectively. Winter and summer vegetables, Maynard and Hochmuth [5] crops are as follows: (a) Summer season vegetables: • • • • • • • • • • • • • • •

Arugula (rocket) Basil Beans Bottle gourd (Lauki) Capsicum Celery (cold climates) Corn Cowpea Cucumbers Edamame Eggplant Herbs (annual) Muskmelons Okra Peppers

© Bag Energy Research Society 2023 G. N. Tiwari, Advance Solar Photovoltaic Thermal Energy Technologies, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4993-9_7

155

156

7 Cultivation of Vegetables in Winter

• • • • • • •

Pumpkins Squash Sweet potato Tomatillo Tomato Watermelon and Zucchini, etc.

(b) Winter season vegetables: • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Arugula (rocket) Beets Broccoli Brussels sprouts Cabbage Cardoon Carrots Cauliflower Celery (Jimikand) Chard Collards Coriander (Dhania) Cress (Sarso) Daikon (Muli) Garlic, Fennel Kale Kohlrabi (Band-gobhi) Lettuce Mizuna Mustard greens Onions (bulbing) Onions (bunching–standard onions harvested before they form bulbs). Pak choi (Bok choy) Peas Potatoes Radishes Shallot (chhote pyaaz) Spinach and Watercress (Jalkumbhi), etc.

Winter season crops are planted in soils to germinate with temperature of 4.4– 7.2 °C at depth below 3 cm inside root media. They generally thrive at temperatures of −17 °C lower than that required by warm season crops. They prefer the temperature to stay below 21 °C.

7.2 Basic Parameters of Summer and Winter Vegetables Crop

157

As mentioned in Chap. 5, each vegetable plant needs the main parameters which constitute root media composition and climatic controlled condition for maximum fruiting.

7.1.1 Root Media Root media (soil chemistry) nutrients are very important for vegetable plant growth along with harvesting. It includes the release of dissolved mineral nutrients in soil moisture. The optimum soil temperature for planting and growing of most vegetables varies between 18 and 24 °C. This optimum temperature helps to germinate during seedling.

7.1.2 Climatic Controlled Condition There are basically following four climatic parameters required for proper growth of vegetables due to photosynthesis process: (i) (ii) (iii) (iv)

Solar intensity, I(t) Environment air temperature (T ) Carbon dioxide (CO2 ) Relative humidity (γ ).

For present book, we have considered only six vegetables which include five summer vegetable crops and one winter crop. In northern part of India, maximum number of days falls under summer condition, and hence, if summer vegetable crops can grow in winter, then availability of summer crop can be met throughout year.

7.2 Basic Parameters of Summer and Winter Vegetables Crop 7.2.1 Bottle Gourd (Lauki) Bottle gourd is generally known as Calabash, Lagenaria siceraria, and it belongs to Cucumber family and it is popularly known as Lauki in India. It is widely cultivated as a fruiting vegetable in Indian subcontinent and around the world during summer and monsoon period. It is a climber plant with spring like tendrils. The bottle gourd has following basic requirements/qualities:

158

7 Cultivation of Vegetables in Winter

(i) The seedling should be done in a big container at least 14 inch depth. (ii) There should be good-quality potting mixture in the container before planting seeds, and organic veggie mix is one of the best growing media. Sandy loam soil is most suitable for its cultivation. (iii) It should be grown either one seed per container or at interval of 2–3 feet which germinate in 7–8 days. It is very fast growing and quickly form the habit of a climber either on strong poles or roof of the house. It requires plenty of watering and abundant moisture all the time. (iv) The harvesting season begins after 2–3 months of seed sowing, and it goes up to 6–8 weeks. It should be grown in open climate with sunny locations. (v) It has many shape and sizes like cylindrical and short round. (vi) It has best low-calorie health food loaded with vitamins, minerals, and plenty of water. It is cooked as a vegetable through chopping and making Koftas and Halwa in India (vii) It is also used in many string instruments as a resonator like Sitar, Veena, etc. at the end of the strings. (viii) The optimum temperature during night and day are 18–22 °C and 30–35 °C respectively.

7.2.2 French Beans French beans are a major export crop. It is known as snap/green beans. The interest in farming of French beans is fast-growing for both fresh consumption and processing (mainly canning and freezing). It has following basic characteristic/along with climate control: (i) It contains calcium, fat, iron, phosphorus, protein, starch, and vitamins A, B, D. (ii) It can be grown in different soil types, ranging from sandy, loam to clay, silty loam to heavy clay soils. (iii) Seedlings will not tolerate temperature below 10 °C. (iv) The optimum temperature for growth/production is 20–25 °C and can survive up to temperature of 32 °C. (v) The optimum soil pH is 6.5 to 7.5 and (vi) the spacing should be single rows of 30 × 15 cm, and it is separated by a path of about 50 cm. (vii) Climbing varieties of French beans grow up to about 1.8 m high which need to be supported. (viii) The main diseases during farming include rust, angular leaf spot, root rots, bacterial blights, etc. To control these diseases, farmers are advised to use crop rotation, tolerant varieties, field hygiene, health certified seeds, and use of recommended insecticides and fungicides.

7.2 Basic Parameters of Summer and Winter Vegetables Crop

159

(ix) Harvesting should be done twice a week for the fine beans and three times a week for the extra fine beans. This continues for around three weeks. (x) Picking should be done at regular intervals depending on buyer specifications.

7.2.3 Tomato Tomato is practically considered as a fruit as well as vegetables. Daily consumption of tomatoes provides a great boost to health which also gives in improving the flavor of food. Globally, it is used in different foods like pasta, pizzas, ketchup, and various beverages. They are relatively easy to cultivate and grow very quickly. Hence, it makes a great food source for many nations; tomatoes have following benefits along with climate control, root media, and container: (i) Tomatoes are a good source of vitamin C and potassium, minerals, good source of fiber, reduce UV damage to skin and lower the risk of sunburn. (ii) It helps control blood pressure; prevent atherosclerosis; lower LDL cholesterol and triglycerides (iii) It is a warm-season crop and is usually grown as summer annuals. (iv) Its seeds germinate best at constant soil temperatures of around 21–27 °C at depth of at least 3 inches. (v) The use garden soil and homemade compost as a starting mix with some sand after pasteurization of the soil and compost. (vi) Germination takes place between 10 and 15 days and after that transplantation should be done after germination. (vii) Seeds are usually germinated indoors preferably inside greenhouses. Starting tomato seeds successfully requires (a) the tomato seeds, (b) containers to plant the seeds, (c) soil for germination of the seeds, (d) water and natural light. (viii) The use of tomatoes as a food benefits health which include eye care, good stomach health, reduced blood pressure, diabetes, skin problems, urinary tract infections. improve digestion, stimulate blood circulation, reduce cholesterol levels, improve fluid balance, protect the kidneys, detoxify the body, prevent premature aging, and reduce inflammation. (ix) Greenhouse cultivation is best option for tomatoes production.

7.2.4 Capsicum Capsicum is also known as (a) sweet pepper, (b) bell pepper or Shimla Mirch. It is one of the popular vegetables grown throughout India and has rich in Vitamin A and C and minerals like calcium, magnesium, phosphorus, potassium, etc. Capsicum can be grown around the year using protected structure, namely greenhouse where temperature (day of 25–30 °C and night of 18–20 °C) and relative humidity (RH) 50–60% can be maintained. If maximum temperature exceeds 35 °C or minimum

160

7 Cultivation of Vegetables in Winter

falls below 12 °C, fruiting is affected. Capsicum has different varieties, namely green, yellow, red, white, and even orange and purple. The red-colored capsicum is known as Bombay, while the yellow and the green are known as Orobelle and Indra, respectively. It adds its unique taste to the prepare chilly paneer or the pizza. Following parameters should be taken care of: (i) Well-drained sandy loam soils with pH of 6–7 and having good percolation are most suitable to grow capsicum. (ii) Cost-effective poly-house and net house structures are most commonly used to grow capsicum throughout year. (iii) Places/location/sites having high rainfall, high wind velocity, and humidity are not suitable for cultivation of capsicum (iv) Good-quality seeds are required for producing better seedlings. Seeds are sown at a depth of ½ cm in sterilized coco peat (root media, mixture of coconut power and compost) placed in container/pots and covered with the same media. (v) The pot should be covered with plastic sheets (mulching, Chap. 4) till germination of seeds. Seeds germinate in about a week’s time after sowing. (vi) Biodegradable Neem cake powder should be used in root media at proper interval to avoid any diseases. (vii) Seedlings of 30–35 days old are used for transplanting after watering the root media at a depth of 5 cm. (viii) The pruning should be done after 30 days of transplanting at an interval of 8 to 10 days to have more branches. (ix) It has relatively long duration (9–10 months) crop in poly-house.

7.2.5 Cucumber Cucumber comes under category of vegetable that loves full sun and water. It grows quickly in loamy soil during summer as long as they receive consistent watering [2]. It should be plugged before it becomes too large due to bitterness. Cucumber has been classified as vining cucumbers and bush cucumbers. • Vining cucumbers: It grows on vigorous vines shaded by large leaves. The growth of these plants is fast, and the crop yield is abundant if you care for them properly. It produces more fruit, but requires a larger space than bush varieties. • Bush cucumbers: It is nicely suited to containers with minimum 18-inch-diameter/ small gardens. Here we will only discuss bush cucumber which requires the following basic parameters and surrounding climatic condition: (i) Root media is prepared with proper mixing of soil with pH of around 6.5–7.0, compost and vermiculite, sand, a mineral that helps retain moisture.

7.2 Basic Parameters of Summer and Winter Vegetables Crop

161

(ii) Plant 3–5 seeds at 1 inch deep in the middle of each container and seedling becomes 4 inches tall, them retain one seedling per container. (iii) Cucumbers growth season is short, lasting 55–60 days for field-grown varieties, and over 70 days for greenhouse varieties. Pollinated seeds should be used in greenhouse. (iv) Minimum soil temperatures should be at least 15 °C. (v) Optimum temperatures for proper growth vary between 18 and 28 °C with high light/solar intensity. (vi) Watering at early morning avoid diseases in leafs. (vii) It contains 90% water and used as a salad, mixed with raita, wrapped in sandwiches, pickled. (viii) It is recommended for skin benefits, weight loss, hydration during summer, cancer prevention, vitamin K to bone health, reduced risk for many health conditions, such as heart disease, diabetes, stroke and obesity, comforting soups, helps eyes in treating dark circles, beauty packs and face masks, etc. (ix) Cucumbers have naturally low in calories, carbohydrates, sodium, fat, and cholesterol for good health.

7.2.6 Broccoli Broccoli is known to be a hearty and tasty vegetable for good health of human being. It is rich in dozens of nutrients. It is known to be pack the most nutritional punch of any vegetable. It comes from the cabbage family, and broccoli can be categorized as an edible green plant. Broccoli needs following basic parameters of root media and climatic condition to grow in pot as well field condition along with health benefits: (i) (ii) (iii) (iv) (v) (vi) (vii)

(viii)

(ix)

Broccoli cultivars are cool-season crops. It needs an average daily temperature between 18 and 23 °C. It should be harvested before the flowers on the head bloom bright yellow. Its seeds are capable of germinating in soil temperatures at 4 °C, but warmer soil is preferred. The root media consists of soil, soil sand, manure, and fertium with good pasteurization. Raw broccoli contains almost 90% water, 7% carbs, 3% protein with almost no fat with very low calories (only 31 cal per cup (91 g), sugar, fibre, fat. It is a particularly rich source of vitamin C and K1, B9 and has a contents of sulfur-containing glucosinolate compounds, isothiocyanates and sulforaphane, But some contents are diminished by boiling potassium, iron, and manganese, etc. It prevents cancer, reduces cholesterol and allergic reaction and is powerful antioxidant heart health, diet aid, skin and eye care, anti-aging and bone health etc. It can be used as salad, pizza topping, fresh pesto.

162

7 Cultivation of Vegetables in Winter

7.3 Root Media for Planting Vegetables and Temperature of Soil, Inside Medium Tech Greenhouse Room Air The medium tech greenhouse integrated semi-transparent photo-voltaic thermal (GiSPVT) system has been construction on unfertilizer (desert) land in Jawahar nagar (Margupur), Chikhar-22 17 01, Ballia (UP), India, Fig. 7.1 for the following advantages: (a) It provides off-grid power generation. (b) The desert land can be used for channel as well as pot cultivation during offseason. (c) The growing crop will be protected from harsh weather condition for a given climatic condition of local area. For cultivation of above-mentioned summer vegetables, two types of container have been adopted due to unfertilized land for winter season cultivation by adopting manual operation to reduce the cost of production by minimum utilization energy input: (i) Brick Channel In order to have channel cultivation 20 brick channel measuring 15feet × 1.5feet × 2feet for each zone, namely 80 Wp (zone-I), 50 Wp (zone-II), 50 Wp (zone-III) and 6 mm glass and 25 Wp (equal area), (zone-V) has been constructed. Figures 7.2a show the view of constructed channel in each zone. Root media generally known as farmyard manure (FYM) is prepared for channels and pots. Between two channels, there is a gap of 0.3 m to minimize root medium interaction. (ii) Re-Enforced Concrete Cement (RCC) Pot The pots having dimension (diameter) of 16, 14, and 12 inches with same root medium have also been prepared and placed in each zone for comparison of cultivation between brick channel and pot. Fig. 7.1 View of desert/ unfertilized land inside GiSPVT system

7.3 Root Media for Planting Vegetables and Temperature of Soil, Inside …

163

Fig. 7.2 a View of brick channel inside GiSPVT system b Prepared root media for all Group-I and II vegetables

a

b

7.3.1 Root Media Farmyard manure (FYM) is one of the more valuable organic fertilizers maintaining soil fertility in the systems of alternative agriculture. Further, root medium was prepared in ration of 40:40:20 with soil, sand, and organic fertilizer (prepared by dung). Following steps have been adopted for growing above mentioned vegetables inside greenhouse integrated semitransparent photo-voltaic thermal (GiSPVT) system (Chap. 6): (i) Root media consist of 40% soil, 40% sand soil, 20% dung manure which has been mixed and pasteurized to become steady state in couple of months (ii) The proper mixing of soil, sand, and organic fertilizer has been carried out at interval of one week with help of water to have best root condition for seeding and transplantation. (iii) The pasteurized root media was used to fill pots and brick channel, and watering was done till seedling. (iv) Seedling of most vegetables was done at depth of 1 inch and below it.

164

7 Cultivation of Vegetables in Winter

(v) Germination of different vegetable takes place at different time. (vi) After two weeks of germination, transplantation was done except few. (vii) Transplantation of bottle gourd was done at distance of 3 m in brick channel, and other five were done at distance of 0.3 m. (viii) Transplantation has also been done in pot under similar condition. The photograph of prepared root media for all vegetables has been shown in Fig. 7.2b.

7.3.2 Soil Temperature The temperature range for seedling and germination of most of winter and summer season vegetables is: (a) Minimum soil temperatures: It should be between 1.6 and 15.5 °C (b) Soil temperature required for 70% germination: It should be between 7 and 24 °C (c) Optimal soil temperature range for 100% germination: It should be between 18 and 35 °C. The soil temperature can be measured by soil thermometer/thermocouple/mercury thermometers, etc. after couple of minutes after insertion inside root media. The measurement should continue at least three–four consecutive days in month time. One should follow following precautions: (i) It should be measured between 1 and 3 inches deep inside root media. (ii) The soil temperature for transplants should be taken at 4 to 6 inches deep inside root media. (iii) There are two types of sowing, namely direct sow (tomatoes, broccoli and transplant out bottle gourd, French beans, cucumber).

7.3.3 Greenhouse Room Air Temperature The six calibrated mercury thermometers were suspended inside greenhouse in six zone, and one thermometer was suspended in shade to measure ambient air temperature under dry condition. The measurement was taken once in a week.

7.3.4 Solar Radiation The solar radiation in each zone inside GiSPVT and outside and ambient air temperature in shaded condition was also measured along with inside room air temperature by using solar measuring instrument as shown in Fig. 7.3.

7.3 Root Media for Planting Vegetables and Temperature of Soil, Inside …

165

Fig. 7.3 Measuring instrument for solar radiation

Fig. 7.4 Measuring instrument for relative humidity

7.3.5 Relative Humidity The relative humidity in each zone inside GiSPVT and outside was also measured by using hygrometer instrument (Fig. 7.4).

7.3.6 Electronic Weighing Machine Electronics weighing machine with least count of 1 gm has been used to measure yield of each vegetables from each zone to see the effect of packing factor of semitransparent photovoltaic module integrated in roof (Fig. 7.5).

166

7 Cultivation of Vegetables in Winter

Fig. 7.5 Photograph during weighing of cucumber after first harvest (Group-I)

7.3.7 Harvesting of Vegetables Harvesting at interval of 15 days was carried out in each zone after complete growth of each vegetable. The weight of vegetable cultivated in each zone was measured for comparison of results.

7.4 Cultivation of Vegetables For cultivation of vegetables, bottle gourd, French beans, tomato, capsicum, cucumber, and broccoli have been selected to grow inside greenhouse integrated semi-transparent photo-voltaic thermal (GiSPVT) system. We have divided vegetables in two groups, namely Group-I (bottle gourd, French beans, tomato) and GroupII (capsicum, cucumber, and broccoli), Fig. 7.6 due avoid mixing of activities of each group.

7.4.1 Sowing of Seeds The sowing of seed of Group-I vegetables (bottle gourd, French beans, tomato) was done on October 17 and 18, 2020, in pots placed in four row at about 1 inch deep, Fig. 7.7a and in brick channel inside greenhouse. The germination of each vegetable was observed between October 21 and 24 in all cases inside and outside. However, the germination of tomatoes starts first. The germinated plants were ready for transplantation of first sowing after 10–12 days. The sowing of second group seed (capsicum, cucumber, and broccoli) was done on November 1–2, 2020, inside GiSPVT in brick channel, Fig. 7.7b. It has been observed

7.4 Cultivation of Vegetables

167

(a)

(b) Fig. 7.6 View of arrangement of Group-I and II vegetables in pots in zone-3

that germination and growth of plant were better inside GiSPVT in comparison with outside, Fig. 7.8. It may be due to high greenhouse air temperature and relative humidity inside GiSPVT. The period of germination was same as in the case of first sowing. The plants in second sowing become ready for transplantation earlier than first sowing.

7.4.2 Transplantation The transplantation of first and second sowing was done on October 25 and November 15, 2020, respectively. Figure 7.9 shows the photograph after transplantation inside

168

7 Cultivation of Vegetables in Winter

Fig. 7.7 a View of first sowing of Group-I vegetables outside GiSPVT on October 17, 2020 b View of second sowing of Group-II vegetables on November 1, 2020

a

b Fig. 7.8 Photograph of germination of seed inside GiSPVT after second sowing

7.4 Cultivation of Vegetables

169

Fig. 7.9 Photograph after transplantation in to brick channel and pots inside GiSPVT after second sowing

greenhouse integration semi-transparent PV thermal system (GiSPVT) system in brick channel as well as in pots in different zone.

7.4.3 Growing of Various Planted Vegetables After transplantation of Group-I and II vegetables, there were better growth inside GiSPVT in comparison with outside particularly in the month of October/November due to optimum temperature inside GiSPVT, and it continues till fruiting takes place. Figure 7.10 shows growth of cucumber in pot inside GiSPVT. Fig. 7.10 View of growing of capsicum in pot

170

7 Cultivation of Vegetables in Winter

7.4.4 Maintenance of Inside Greenhouse Following steps were taken for maintenance of root media and inside climatic condition as follows: (i) The manual watering was done regularly to avoid dryness to root media. Bottle gourd and cucumber need more watering in comparison with others. (ii) To maintain CO2 level after full growth, biomass was burnt inside GiSPVT during 10am in the morning. This was done intermittently during yellowing of leafs particularly bottle gourds and cucumber. It was required during low level of solar radiation. During high level of solar radiation (blue sky condition), sliding windows in east and west sides were open to reduce the greenhouse air temperature as well as mixing of air between greenhouse and ambient air to maintain CO2 level inside. (iii) Roof of greenhouse integrated semi-transparent photo-voltaic thermal (GiSPVT) system was cleaned with flowing water to provide sufficient daylighting for photosynthesis and to maintain greenhouse room air temperature to maintain its transmissivity. It was mandatory to do due to dust deposition due to burning of unused dry plants in agricultural field. (iv) The side glass wall is also cleaned manually at regular interval. (v) The required pesticides were spray over the plant to avoid any diseases occurring in the leaf particularly bottle gourd and cucumber.

7.4.5 Cultivation of Vegetables Flowering were noticed first in French beans on November 26 and then started for other later on up to December 04, 2020. The view of flowering of French beans, tomatoes in brick channel and cucumber in pot in Zone-III has been shown in Fig. 7.11.

7.4.6 Fruiting of Vegetables We have first harvested French beans as shown in Fig. 7.12a on January 25, 2021, in each zone with weight of 120 gm, (pot), 150 gm (pot), 320 gm (pot), and 40 gm (pot) in zones I, II, III, and IV respectively. It has been found that the yield is maximum in Zone-III due to maximum solar radiation availability with highest nonpacking factor. However, Zone-IV gives minimum value due to excess value of organic root media in channel. The root media has played an important role. The first cultivation of other vegetables namely cucumber, Fig. 7.12b; bottle gourd (Lauki), Fig. 7.12c; broccoli, Fig. 7.12d; tomatoes, Fig. 7.12e and capsicum, Fig. 7.12f have been carried out between January 25 and February 09, 2021. It has been also observed

7.4 Cultivation of Vegetables

171

a

b Fig. 7.11 a View of flowering of French beans in pot (Group-I) in zone-III b View of flowering of tomatoes in brick channel and cucumber in pot in zone-III

that maximum and minimum weight of cucumber have been observed as 330 gm and 210 gm respectively while in the case of bottle gourd (Lauki) it is 1200 and 75 gm respectively. Here it important to note that bottle gourd and cucumber have given more yield in brick channel due to its large root while French beans, broccoli, tomatoes, and capsicum gives maximum yield in pot due to small root. Further, bottle gourd and cucumber should not be grown nearby because of domination of growth of bottle gourd over cucumber. The healthiest weight of tomato is about 90 gm. Based on experimental observations, we have observed the followings: (i) The root media for Group-I and II vegetables should be prepared at least six months in advance so that root media becomes in a steady state condition. During these periods, the watering to root media and its mixing should be carried out at interval of 15 days. It is valid for both brick channel and pot.

172 Fig. 7.12 a First cultivation of French beans dated December 25, 2020, in pot b View of cucumber in brick channel before first harvesting on January 11, 2021 c First cultivation of bottle gourd (Lauki) on January 25, 2021 d First cultivation of Broccoli dated February 9, 2021 e View of fruiting of tomatoes in brick channel of Group-I dated February 09, 2021 f View of fruiting of capsicum in pot dated February 09, 2021

7 Cultivation of Vegetables in Winter

a

b

c

7.4 Cultivation of Vegetables

173

Fig. 7.12 (continued)

d

e

f

174

7 Cultivation of Vegetables in Winter

(ii) Sowing of seeds should be at different depth in moist root media, for example, seed of bottle gourd should be at least ½ inch below root media top surface while tomatoes seeds should be just below. (iii) In the proposed GiSPVT root media is automatically warmer due to greenhouse effect and hence no need of polarization. (iv) Transplantation should be carried out with growth of plant at least 2–3 inch height. (v) Regular watering should be done in root media due to fast evaporation of moisture from root media surface. (vi) The vegetables requiring more root propagation along with branches, like bottle gourd and cucumber, should be planted in either brick channel with distance of at least 2.5–3feet or in bigger 16 inch pot with diameter of 3 feet. Other vegetables with smaller height like French beans, broccoli, capsicum, and tomatoes can be grown in even smaller pot. (vii) The bottle gourd and cucumber needs more solar radiation for proper photosynthesis and hence it has given maximum yields in zone II and IV [3]. (viii) During complete cloudy condition which happened during January 15 to February 4, 2021, cow dung of 5 kg was burned for thermal heating of greenhouse air and to maintain CO2 level. The rest thermal energy was available from beneath ground surface by convection.

7.5 Measurements of Climatic Parameters (i) The hourly variation of solar intensity, greenhouse room air temperature, relative humidity inside and outside were measured with a solarimeter, hygrometer, and calibrated thermometers. The thermometers were suspended in the central position of each zone inside GiSPVT, and one thermometer was suspended in shade to obtained ambient air temperature. The soil temperature has also been measured with a calibrated thermometer during sowing and transplantation. During sowing and transplantation, the temperature of the soil is about 1.6– 2.5 °C higher than greenhouse air temperature which is a basic requirement for fast germination. It may be due to the direct absorption of solar radiation on the surface of the container of root media. (ii) The hourly measured data for the typical day of the month from December to March is given in Fig. 7.13. Table 7.1 shows the number of clear days, partially cloudy days and diffuse days for each month. (iii) Electronics weighing machine with a least count of 1 gm has been used to measure the yield of each vegetable from each zone to see the effect of the packing factor of a semi-transparent photovoltaic module integrated into the roof as shown in Fig. 7.14.

7.6 Harvesting of Vegetables

175

7.6 Harvesting of Vegetables Harvesting at an interval of 15 days was carried out in each zone after the complete growth of each vegetable. The weight of vegetables cultivated in each zone was measured for comparison of results.

(a)

(b) Fig. 7.13 Hourly variation of some climatic parameters for typical days during cultivation of vegetables

176

7 Cultivation of Vegetables in Winter

(c)

(d) Fig. 7.13 (continued)

7.7 Electrical Output (Generation Off-Grid)

177

(e)

(f) Fig. 7.13 (continued)

7.7 Electrical Output (Generation Off-Grid) The GiSPVT system produced 30482.94 kWh of electricity during the July 2020 to June 2021. The system produced lowest electrical energy of 1062 kWh during the January 2021 due to the less solar radiation reaching the solar panel as the weather condition was cloudy and foggy for most part of the month (24 days). The maximum electrical energy of 3254 and 3278 kWh was produced in the months of October 2020 and April 2021 as the weather condition was sunny for 25 and 28 days respectively.

178

7 Cultivation of Vegetables in Winter

Table 7.1 Number and types of days in each month Month

Weather condition Clear

Partially cloudy

Remark Diffuse/Hazy

Number of days in month

Jun-20

15

10

5

Cloudy

30

Jul-20

7

15

8

Cloudy

31

Aug-20

8

17

6

Cloudy

31

Sep-20

16

8

6

Scattered radiation

30

Oct-20

25

3

3

Sky blue

31

Nov-20

24

6

0

Sky blue

30

Dec-20

20

3

8

Sky blue

31

Jan-21

2

5

24

Scattered radiation

31

Feb-21

26

2

0

Sky blue

28

Mar-21

31

0

0

Sky blue

31

Apr-21

28

2

0

Sky blue

30

May-21

6

5

20

Scattered radiation

31

208

76

80

Total number of days

365

The monthly average electrical energy produced was 2540.40 kWh, and the daily average was 83.51 kWh. Table 7.2 shows the average monthly and daily electrical energy produced in each zone. The overall electrical energy produced by the system for the period July 2020 to June 2021 was for 208 clear days. The electrical energy produced would be significantly high (~38000 kWhr) if the average clear sunny days in India are considered which is about 300 days which would lead to better economics of the system.

7.8 Conclusions and Recommendations On the basis of results and experience observed during cultivation of vegetables, following conclusions and recommendations have been made.

7.8.1 Conclusions (i) Desert/unfertilized land can be used for cultivation through container made up of brick channel and RCC pot having 18 inch diameter and 2 feet depth as

7.8 Conclusions and Recommendations

French beans

e guard

Brocoli

179

Cucumber

Tomatoes

Capsicum

Fig. 7.14 Weighing of various vegetables produced inside GiSPVT

Jun-20

Jul-20

Aug-20

Sep-20

Oct-20

Nov-20

Dec-20

Jan-21

Feb-21

Mar-21

Apr-21

May-21

1

2

3

4

5

6

7

8

9

10

11

12

Annual Avg. daily (kWh)

Avg. monthly (kWh)

Total annual (kWh)

Month

S. No.

27.50

836.52

10,038.29

984.31

1079.57

962.44

493.92

349.98

721.83

952.56

1071.81

592.70

909.94

929.63

989.60

Zone 1 (10 kWp )

27.96

850.47

10,205.59

1000.72

1097.56

978.48

502.15

355.81

733.86

968.44

1089.67

602.58

925.11

945.12

1006.10

Zone 2 (10 kWp )

Monthly power generation

28.05

853.25

10,239.05

1004.00

1101.16

981.69

503.80

356.98

736.27

971.61

1093.24

604.56

928.14

948.22

1009.40

Zone ¾ (10 kWp )

Table 7.2 Electrical energy produced in each month and in each zone

83.51

2540.24

30,482.94

2989.03

3278.29

2922.60

1499.87

1062.77

2191.95

2892.61

3254.72

1799.84

2763.19

2822.97

3005.10

Total monthly generation (kWh)

300

425

400

250

160

300

375

350

175

260

250

275

Avg intensity (w/m2 )

22

30

23

17

14.5

20

23

25

28

29

29

30

Avg ambient temp, (°C)

7.5

6

5.5

5

5

5.5

6

7

8

8

8.5

8.5

Sunshine (hr)

75

65

75

95

80

65

90

85

95

80

85

85

Avg. relative humidity, %

180 7 Cultivation of Vegetables in Winter

7.8 Conclusions and Recommendations

(ii)

(iii)

(iv)

(v)

(vi)

(vii)

(viii)

(ix) (x) (xi)

181

well as solar power generation with protection from harsh weather condition due to greenhouse effect. Root media of each vegetable should contain soil, sand soil, and manure in ratio of 40:40:20 with proper mixing with pasteurization at least six month prior to seedling. Root media took time to become in a steady state with watering at regularity and mixing should be done before/after watering. Sowing should be done at least one inch deep in root media with planning for maximum utilization of greenhouse area to make system economical. It is better to do sowing inside greenhouse integrated semi-transparent photo-voltaic thermal (GiSPVT) system to avoid damage due to insect, birds, diseases and intermittent harsh weather condition, etc. Transplantation should be done after sufficient germination with height of at least 2–3 inches per pot/at sufficient distant in brick channel. In such cases, survival rate is more otherwise one has to keep extra plant for further transplantation. The level of CO2 inside GiSPVT may be sufficient during seedling/ transplantation but not sufficient at full growth of plants; hence, an arrangement should be made either burning biomass at proper interval inside GiSPVT or to opening of sliding window during peak sunshine hours. It is needed if leaf of plant starts yellowing. It has been observed that there should be arrangement of sufficient solar light/ light by self-solar power inside GiSPVT, and hence, such system is selfsustain. For uniform availability of light intensity, two 100 W light arrangement has been made in north wall to keep uniform photosynthesis in north side (Zones 1 and 2) Inside greenhouse air temperature is always higher by 5–6 °C till morning in comparison with outside ambient air temperature. In noon time, it goes up to 35–36 °C when outside temperature is about 20 °C for clear sunny condition. Even in very cloudy condition inside greenhouse temperature is always 5– 6 °C higher due to release of thermal energy from ground surface and brick channel. Relative humidity inside GiSPVT system is maximum (about 90%) in early morning and late evening in comparison with noon time (75%) which help in cooling the plant as per requirement. The maximum yield has been observed in Zone-III and IV (25 Wp ) respectively due to sufficient sun lighting for proper photosynthesis. The bottle gourd (Lauki) and cucumber give higher yield in brick channel when planted separately proper distance of 3 feet. Based on average production of different vegetables, the yield per on Beegha (2700 square feet) between October, 2020 to February, 2021, Fig. 7.14, are as follows: (a) French beans = 708 kg; (b) Bottle gourd (Lauki) = 1.8 tons; (c) Tomatoes = 4.8 tones (d) Broccoli = 2.15 tones; (e) Capsicum = 2.6 tones; and (f) Cucumber = 700 kg.

182

7 Cultivation of Vegetables in Winter

Fig. 7.15 Effect of packing factor on daily overall exergy

(xii) GiSPVT greenhouse room air temperature is always higher by 4–5 °C in comparison with outside ambient air temperature during harsh winter condition with completely cloudy condition between January 1 and February 2, 2021 due to emission of radiation from floor. The temperature inside greenhouse has been recorded by calibrated thermometer in each zone. The average daily outside ambient air temperature has been recorded as 16 °C. (xiii) There is variation of solar intensity between 108 and 318 W/m2 from Zone-I to Zone-IV for clear sky condition with outside solar intensity of 640 W/m2 in month of December. During cloudy period in the month of January only diffuse radiation of level 10–40 W/m2 was observed. (xiv) An average relative humidity during day has been reported as 77–80% in comparison with outside as 70%. During late night times, it becomes about 95% due to less respiration from the plant. (xv) The ground floor temperature was always higher by 5 °C due to less loss of thermal energy to outside. In this, the roof vent and sliding doors are always closed to keep higher temperature inside. (xvi) An overall exergy decreases with increase of packing factor as shown in Fig. 7.15. In this case, as direct gain decreases with an increase of packing factor.

7.8.2 Recommendations (i) A proper planning including the size of container and quality of seeds with respect to climatic condition for individual vegetable is required for sowing of each vegetable due to its different qualities and behavior. It is due to fact

7.8 Conclusions and Recommendations

(ii)

(iii)

(iv)

(v) (vi) (vii)

(viii)

(a) (b) (c) (d)

183

that roots should not interact with root of same vegetation so that each plant grows independently and gives maximum yield/production. The roof vents and sliding doors operation should be used in the case of excess heat trapped inside GiSPVT. In the case of excess heat, inside air temperature heats up. Further opening of at least sliding door helps in mixing of greenhouse room air and outside air due to movement to keep required CO2 level uniform. If leafs starts yellowing, it means CO2 level inside greenhouse is not sufficient for photosynthesis. So one should inject at least burning of biomass inside greenhouse to certain period during noon time. If growth and flowering is not sufficient then one should take advice from local expert to use pesticide for better yield. It should be sprayed over plant at regular interval as per advice. The watering is needed at regular interval at least of vegetables having water content of 90% for example bottle gourd. One crop should be grown at a time because it is easier to prepare root media, sowing, transplanting, pruning and maintaining. One should use pollinated seeds for greenhouse application. Unpollinated seed should be only used in open field cultivation. In this case, male and female interact due to wind in open field. There is need of spraying medicine over the plant in full growth condition regularly but spaying period varies from winter to summer condition as follows: Preparation of medicine in fifteen litter of water by proper mixing two spoon vigor (vitamin) and three cup killer insecticide. In summer, the spraying of mixture should be done interval of 20 days. In winter, the spraying of mixture should be done interval of 10 days. In foggy condition, spraying should be done at interval of seven days.

7.8.3 Suggestions to Farmers In unfertilized land, small farmers are advised to adopt low cost Quonset greenhouse with pot cultivation with appropriate size. The size of pot depends upon the type of vegetables. For example for growth of bottle gourd and cucumber, one should have locally available bigger size pot due to larger spread of root and its branches in vertical growth. For smaller growth of vegetables, one can have smaller pot. The constructed poly-greenhouse can be used also for solarization during germination for pre/post-harvesting of vegetables. Objective Questions 7.1. The root media preparation for soil, sand, and organic fertilizer should be in proportion of (a) 60:20:20, (b)40:40:20; (c) 20:40:40 and (d) none Answer: (b)

184

7 Cultivation of Vegetables in Winter

7.2. Root media for bottle gourd will be sufficient (a) In brick channel; (b) In small pot; (c) In larger pot and (d) none Answer: (a) and (c) 7.3. The branch propagation of bottle gourd and cucumber needs (a) Vertical growth; (b) Horizontal growth; (c) Vertical and horizontal growth and (d) All of then Answer: (c) 7.4. The French beans, broccoli, capsicum and tomatoes can be grown in (a) Brick channel; (b) Pot; (c) Open filled and (d) All of them Answer: (d) 7.5. All vegetables can be grown for maximum yield (a) Zone-I (80 Wp ); (b) Zone-II (40 Wp ); (c) Zone-III (20 Wp ) and (d) Zone-IV (20Wp and glass) Answer: (c) and (d) 7.6. Solar radiation inside GiSPVT is maximum in (a) Zone-I (80 Wp ); (b) Zone-II (40 Wp ); (c) Zone-III (20 Wp ) and (d) Zone-IV (20 Wp and glass) Answer: (d) 7.7. The dung cake should be burnt around in full growth for producing CO2 inside GiSPVT at (a) 12 noon; (b) 4 pm; (c) 10am and Night hours Answer: (c) 7.8. The watering of full growth plant in GiSPVT should be done in (a) Daily; (b) Weekly; (c) Quarterly and (d) Monthly Answer: (b) and (c) 7.9. The spray of medicine should done during (a) Yellowing leafs; (b) Start of damage of fruiting; (c) Full-grown vegetables and any time Answer: (b) 7.10. The burning of dung cake helps in addition to feed CO2 inside GiSPVT for (a) Cooling; (b) Heating; (c) Cooling/heating and (d) None of them Answer: (b) 7.11. For withdrawal of heat inside GiSPVT sliding window should be open during temperature. (a) More than 50 °C; (b) More than 30 °C; (c) Less then 30 °C and (d) 100 °C Answer: (b) Acknowledgements We appreciate the kind visit of Shri Hari Pratap Sahi, DM, Ballia (Fig. 7.16a) and Prof. Kalplata Pandey, VC, JNCU, Ballia (Fig. 7.16b) during operation of Mission Innovation project funded by Department of Technology (DST), Government of India and getting attention of vegetable growth and power generation in desert area of Ballia district.

References

185

Fig. 7.16 a Photograph during visit of Shri Hari Pratap Sahi, DM, Ballia, dated January 31, 2020 b Photograph during inauguration of SODHA ENERGY RESEARCH PARK (SERP) on February 08, 2021

a

b

References 1. Tiwari GN (2003) Greenhouse technology for controlled environment, alpha science (UK) also published by Narosa Publishing House, New Delhi 2. Tiwari GN, Sharma PK (1999) Off-season cultivation of cucumbers in a solar greenhouse 24(2):151–156. https://doi.org/10.1016/s0360-5442(98)00083-8 3. Cossu M, Yano A, Solinas S, Deligios PA, Tiloca MT, Cossu A, Ledda L (2020) Agricultural sustainability estimation of the European photovoltaic greenhouses. Eur J Agron 118:126074. https://doi.org/10.1016/j.eja.2020.126074

Recommended Reference 4. Vegetable planting and soil temperature—harvest to table (harvesttotable.com › vegetableplanting-and-soil-tempe) 5. Maynard DN, Hochmuth G (1997) Knott’s handbook for vegetable growers, 4th edn. Wiley, New York 6. Prodhan AZMS, Islam MS, Islam MM et al (2018) Effect of soil and environment on winter vegetables production. MOJ Food Process Technol 6(4):384–389. https://doi.org/10.15406/ mojfpt.2018.06.00192 7. Smith P (1999) HGIC 1301 Broccoli. Clemson University. Retrieved 25 Aug, 2009 8. Branham SE, Stansell ZJ, Couillard DM, Farnham MW (2017) Quantitative trait loci mapping of heat tolerance in broccoli (Brassica oleracea var. italica) using genotyping-by-sequencing.

186

9. 10.

11. 12. 13. 14. 15. 16. 17. 18.

7 Cultivation of Vegetables in Winter Theor Appl Genet 130(3):529–538. https://doi.org/10.1007/s00122-016-2832-x. ISSN 14322242. PMID 27900399. S2CID 2361874 Broccoli—Wikipedia (en.wikipedia.org› wiki › Broccoli) Lopes JC, Mauri J, Ferreira A, Alexandre RS, de Freitas AR (2012) Broccoli production depending on the seed production system and organic and mineral fertilizer. Hortic Bras 30(1):143–150. https://doi.org/10.1590/s0102-05362012000100024 Best way to grow capsicum in home|India gardening tips (acegardener.com› vegetablegardening › growing-cap...) Nutrition facts for tomatoes, raw, orange, recommended daily (www.nutritionvalue.org › Tomatoes,_raw,_orange_nutr...) Tomatoes, raw, orange contains 16 calories per 100 g serving. One serving contains 0.2 g of fat, 1.2 g of protein and 3.2 g of carbohydrate. The latter is g sugar... 7 Health benefits of tomatoes—tomato nutrition facts (www.goodhousekeeping.com› health › diet-nutrition) Nutrition facts for tomatoes, raw, orange, recommended daily .(www.nutritionvalue.org› Tomatoes,_raw,_orange_nutr...) Cucumbers: planting, growing, and harvesting cucumbers (www.almanac.com› gardening › growing guides) Broccoli health benefits: 11 health benefits of broccoli|What (timesofindia.indiatimes.com ›) Broccoli 101: nutrition facts and health benefits—healthline (www.healthline.com › nutrition › foods › broccoli)

Chapter 8

Thermal Modeling of Greenhouse Integrated Semi-transparent Photo-Voltaic Thermal (GiSPVT) System: Quasi-Steady-State Analysis

8.1 Introduction In Chap. 4, the greenhouse has been first classified on the basis of its shape and then on the basis of technology cum cost consideration. Further, it is important to note that researchers in the area of greenhouse have classified greenhouse on the basis of climatic condition. Greenhouse technology is also referred as controlled environment (CE) greenhouse (CE-greenhouse). On the basis of climate, it is broadly classified as (i) Winter CE-greenhouse: In winter greenhouse, one needs heating of inside enclosed air by greenhouse effects as mentioned in Chap. 1. It is also established that thermal energy required for thermal heating is mostly met by glazed roof and wall by using solar energy. It can be known as passive heating. If additional heating is required for harsh climatic condition, then it is referred as active heating of greenhouse. In this case, the heat loss from inside greenhouse air to ambient air should be minimized particularly during off-sunshine hours. There are many methods of active heating of controlled environment (CE) greenhouse. The winter greenhouse is most successful because most of required thermal energy is met by solar energy including photosynthesis. Further, an energy required for thermal heating is much less than thermal cooling. In winter greenhouse, any shape and technology as mentioned in Chap. 4 can be adopted as per requirement of farmers [1–11]. (ii) Summer CE-greenhouse: The summer greenhouse needs thermal cooling particularly in harsh warm condition. If passive cooling is integrated with summer CE-greenhouse, it is worth and economical. However, in the case of active heating, one needs control system for many parameters like temperature, relative humidity, CO2 , light for photosynthesis, etc., and cooling of CEgreenhouse becomes high-grade energy-intensive, and hence, it is much more expensive in comparison with winter greenhouse. Because of this, greenhouse is referred as Hi-Tech greenhouse. So, in this case, high-value crop should be grown to make summer greenhouse economically feasible/viable [4–7, 12–18]. © Bag Energy Research Society 2023 G. N. Tiwari, Advance Solar Photovoltaic Thermal Energy Technologies, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4993-9_8

187

188

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

In winter EC-greenhouse, there is some times requirement of thermal heating, and hence there is no exchange air between greenhouse room air and outside ambient air (no ventilation). In such cases, the level of CO2 inside greenhouse depends upon leaf area index (LAI) which is 3 for fully developed crop. Sanchez-Guerrero et al. [11] have studied the effects enrichment of CO2 on production of cucumber crop inside greenhouse, and compared to the results with un-enriched winter conditions, they observed that (i) in the un-enriched greenhouse, CO2 depletion was substantial without ventilation, and (ii) the variable CO2 enrichment results in a significant increase in yield along with biomass. Chen et al. [6] have developed a mathematical model to optimize shape of greenhouse to capture maximum solar radiation for winter condition for thermal heating and concluded that sawtooth shape equivalent to Quonset/gothic/modified arch shape captures maximum solar radiation for clod climatic condition of China. Chen et al. [10] have used the phase change material (PCM) in plastic greenhouse for night heating of winter greenhouse. Jana et al. [7] have studied effect of greenhouse to increase the growth of some tropical fishes in winter condition. Paparozzi et al. [8] have grown strawberry with increase in productivity, sugars, and phytonutrient content during the winter month. Cervantes et al. [9] have studied the effect of cleanup winter greenhouse on survival of Cabbage looper, Trichoplusia ni, (T.ni) inside and outside and found that pupae placed inside the greenhouses were survived unlike outside for survival of vegetables in southwestern British Columbia. Mesmoudi et al. [5] have developed a thermal model for an unheated glasshouse without crop in the region of Batna, Algeria, and performed an experiment during January to March: (i) cloudy night, (ii) windy night, and (iii) cloudless night. They have found that the ground surface inside greenhouse is compensating the various energy losses through the walls during the night. In summer EC-greenhouse, Sun et al. [13] have studied best management practice (BMP) to keep greenhouse vegetable yield stable, improving nitrogen use efficiency (NUE) in root media and reducing the nitrogen pollution level in environment. Murakami et al. [14] have developed a net placed below roof of a summer greenhouse to (i) have high visible light (VL) transmittance and (ii) strong absorption in the near-infrared ray (NIR) region (700–2500 nm) during sunshine hours. This newly developed net improves the sweetness of melon fruits harvested in mid-summer. This also provides cooling effect to greenhouse air. Perigees et al. [19] have studied the effect of ten combinations of five cooling techniques, namely roof ventilation, shading screen, fogging under and above screen, and fogging without shade screen during the summer periods of 2002 and 2003 in a 132 m2 greenhouse located in Madrid, Spain. The greenhouse has a steel structure and a single-layer methacrylate cover. They have concluded that the combination of a shade screen and above and below screen fogging gives same results with lower relative humidity for above fogging with reduced water consumption by 8–15% as expected. Çakir et al. [16] have designed the semicircular-shaped greenhouse with side wall ventilation with 75% green-colored shading net for cutting the inside solar radiation for cooling with minimum irrigated water. With this design, they found that cucumber yields were increased with averages of 128.2 and 126.5 ton/ha with four days irrigation per week.

8.2 Earth Air Heat Exchanger for Thermal Heating/Cooling

189

Bazgaou et al. [20] have studied the effect of thermal storage to store surplus air thermal energy (SATE) in greenhouses during all the year for heating and cooling to minimize the cost production. They have considered that storage system consists of a quartzitic sandstone, thermal storage blocks, and pipes with fans to circulate hot/cool air to improve greenhouse microclimate located in the Souss-Massa region, Morocco, to increase tomato yield. The solar heating and cooling system (SHCS) varied between 15.68 and 140 MJ/day during day, and 65% of this heat recovered at night in plastic greenhouse with an area of 165 m2 . Recently, Friman-Peretz et al. [17] have conducted an experiment in two greenhouse tunnel with a tomato crop by using: (i) in first tunnel greenhouse, a flexible and semi-transparent organic photovoltaic (OPV) modules covering 37% of the roof area which results 23% roof shading, and (ii) in second tunnel greenhouse, a 25% black shading screen was used. After two-year experiments, they concluded that leaf area index (LAI), cumulative yield, and average fruit the semi-transparent organic photovoltaic (OPV) modules-covered greenhouse mass were higher. Similar study has been carried out by Ezzaeria et al. [4]. In this case too, 40% roof area of the greenhouse is covered with integration of flexible organic solar panels. This also provides shading effect to produce tomato during summer/winter condition in the south Mediterranean region. There are some more studies in the same area that have been carried out by Yano et al. [21], Hassanien et al. [22], Zisis et al. [23], Ravishankar et al. [24], and Moretti and Marucci [25].

8.2 Earth Air Heat Exchanger for Thermal Heating/ Cooling In addition to the above-mentioned passive heating/cooling arrangement for greenhouse room air, there is another concept used for both heating/cooling throughout the year known as earth air heat exchanger (EAHE). In this case, preferably a conductive pipe is buried underground at depth depending upon requirement as shown in Table 8.1. Vidhi [45] has studied effect of depth on underground soil temperature, and he found that there is significant variation of ground temperature with depth against ambient air temperature ranging from 0 to 40 °C. As depth increases, the fluctuation decreases, and it becomes 5 °C at 4 m depth for a dry-arid location (Las Vegas). One can see from Table 8.1 that the underground temperature varies with depth from the ground surface. This depth mostly depends on physical properties of soil, location, and climatic condition. As per requirement, the pipes are buried at optimum depth either below heating/cooling space or nearby. When the hot/cool air is passed through buried pipes, then heat is transferred either from flowing hot/cool air to the ground or vice-versa. If flowing air is hot, then it is cooled and reverse is trend for flowing cooled air.

190

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

Table 8.1 Ground temperatures for various surface conditions Surface condition

Depth (m)

Ground air temperature (o C)

Daily average (a) Winter months

0.18

17.84

(b) Summer months, Bhardwaj and Bansal [44]

0.18

32.87

Annual average (a) Vidhi [45]

4

23.45

(b) Díaz-Hernández et al. [32]

2.5

27–28

(c) Hermes et al. [40]

2 4

18.7 20

(d) Bisoniya [46, 47]

2

25

(e) Bhardwaj and Bansal [44]

4

29 (exposed surface) 19 (wetted surface) 17 (wetted and shaded surface)

(f) Zang et al. [48]

5

17.6

(g) Ozgener et al. [29, 39], Turkey

3

34

(g) KSU, Saudi Arabia, experimental

2.5 to 3

28–29

(h) BERS, Ballia, India, experimental

2.5 to 3

26–27

Classification of earth air heat exchanger (EAHE) is as follows: (i) Closed-loop earth air heat exchanger: In this case, inlet as well as outlet of an earth air heat exchanger (EAHE) is connected with greenhouse room air. This is most suitable for winter greenhouse. The use of EAHE is preferably required during off-sunshine hour due to sudden drop in outside ambient air temperature, Tiwari et al. [26], Chel and Tiwari [27, 28], Ozgener et al. [29, 30], Bisoniya et al. [31], Díaz-Hernández et al. [32], Barbares et al. [33], Ghosal et al. [34], and Hepbasli [35]. (ii) Open-loop earth air heat exchanger: In this case, fresh ambient air is connected to inlet of an earth air heat exchanger (EAHE), and the outlet of an earth air heat exchanger (EAHE) is connected with greenhouse room to lower. Here, an earth air heat exchanger is preferable used during daytime. So in this case, grid power is required during sunshine hours, Li et al. [36–38], Yang et al. [39], Hermes et al. [40], Peretti et al. [41], Rosa et al. [42], and Amanowicz and Wojtkowiak [43]. An earth air tunnel exploits the constant ground temperature 4 m below the ground surface, where it remains constant throughout the year (Table 8.1). The air passing through a tunnel or a buried pipe gets cooled in summers and heated in winters. Parameters like surface area of pipe, length and depth of the tunnel below ground, dampness of the earth, humidity of inlet air, and its velocity affect the exchange of heat between air and the underground surrounding soil. The heating/cooling is not limited to only greenhouse, but it can be extended to space heating/cooling in the

8.2 Earth Air Heat Exchanger for Thermal Heating/Cooling

191

building design to make heating/cooling economical with coefficient of performance more than one. Li et al. [36, 37] have studied an open-loop double-layer earth air heat exchanger (EAHE) with an average heating potential of 4665 W with power consumption of 130 W. This gives an average heating coefficient of performance (COP) of 29.7. Rosa et al. [42] have found that results also showed that the performance of EAHE remains the same if spacing between two pipes is reduced from 1.0 to 0.5 m for given air velocity and pipe diameter. In this case, required land area for EAHE is reduced to half. They have considered open-loop earth air heat exchangers (EAHE) as a passive heating/cooling contribution to reduce the energy demand in building. Amanowicz and Wojtkowiak [43] have used CFD software to analyze the flow characteristics of multi-pipe earth air heat exchangers (EAHEs). The design of EAHE is similar to conventional flat plate collector (two headers and multiple risers combinations) to reduce the energy consumed (low-pressure loss) in flow of air thorough pipes for low energy building. An experimental horizontal earth air heat exchanger (EAHE) (0.102 m diameter of 6 m length PVC pipes) placed at 2.5 m beneath the ground under a warm humid weather conditions of Mexico was considered by Díaz-Hernández et al. [32]. They reported that earth air heat exchanger (EAHE) acts as a cooler and heater during the day and night, respectively, with temperature difference of 5.5 °C. Li et al. [36] have concluded based on his studies about EAHE that the heating and sensible cooling capacity have the strongest correlation with inlet air temperature and the moisture content inside room. The average annual COP and payback period of EAHE are 8.5 and 2.38 years, respectively. Further, EAHE provides an 82.5% reduction in greenhouse gas emissions for open-loop configuration. An overall energy and exergy efficiency of closed-loop EAHE was studied Hepbasli [35] with respect to different reference temperatures of 0 °C and 18 °C, respectively. They observed an overall energy and exergy efficiency of 72.1% and 19.8%, respectively, at reference temperature of 0 °C. However, it drops significantly with sudden increase of reference temperature up to 18 °C. Ozgener et al. [29, 30] have also studied a U-bend galvanized earth air heat exchanger (EAHE) with length of 47 m and diameter of 0.47 m in terms of its total thermal resistance. They have estimated total heat exchanger thermal resistance as a 0.021 K-m/W under steady-state condition. Bisoniya et al. [31, 46] have studied the both open and closed earth air heat exchanger by considering different materials, air flow velocity, and length. They found that there is temperature rise of 4.1 to 4.81 °C for the pipe of 23.42 m length with 0.15 m diameter with air flow velocity ranging from 2 to 5 m/s. The hourly thermal heat gain was found to be in the range of 423.36–846.72 kWh. They reported that temperature of ground at 1.5 to 2 m is almost constant throughout the year. Further, they also found that there is not much difference in performance between steel and PVC pipe earth air heat exchanger. They have also discussed the energy metrics for Indian hot and dry climatic conditions. Peretti et al. [41] have also considered the similar design of earth air heat exchanger (EAHE) as proposed by Amanowicz and Wojtkowiak [43]. However, Peretti et al. [41] have explored the possibility of integration of EAHE with HVAC system for residential coupling. Hermes et al. [40] have found the optimum depth of heat exchanger at 2 m

192

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

beneath ground in the summer and winter seasons due to the water tables close to the surface in the studied regions of Brazil. Nayak and Tiwari [49, 50] have carried out performance and energy metrics analysis of EAHE and photo-voltaic integrated greenhouse system for composite climate of New Delhi. The analysis was based on work carried out by Ghosal and Tiwari [51], Ghosal et al. [34, 55] without PV integrated. In this chapter, a thermal modeling will be developed for Quonset/uneven shape of CE-greenhouse integrated semi-transparent photo-voltaic thermal (CE-GiSPVT) system. (i) Without EAHE (ii) With EAHE [39]. The proposed thermal modeling can be used for any other shape as a special case.

8.3 Working Principle of Greenhouse Integrated Semi-transparent Photo-Voltaic Thermal (GiSPVT) System In Chap. 5, Fig. 5.1 shows a cross-sectional view of experimental controlled environmental (CE) greenhouse without integration of semi-transparent photovoltaic roof for application in agriculture sector, namely crop production/aquaculture/aquaponics. The number of flexible organic/c-Si semi-transparent photovoltaic module (PV) if integrated with roof as shown in Fig. 8.1a depends upon the required load to the system, Friman-Peretz et al. [17]. The packing factor will depend upon the number of flexible organic/c-Si semi-transparent photovoltaic module used for integration to roof of CE-greenhouse. This is also treated as shading device to minimize the direct gain for one of cooling concepts. For further cooling, one can use green shade with below/above fogging arrangement, Perigees et al. [19] and Ezzaeria et al. [4]. The CE-greenhouse is having an orientation of east–west direction. It can be observed from figure that there is direct as well as indirect gain through non-packing and packing area of east and west roof. The glazed four walls can transmit all solar radiation incidents on it. The east and west walls will receive maximum solar radiation early morning and late evening respectively due to motion of Sun from east to west due south. The CE-greenhouse can also receive additional thermal energy if it is integrated with earth air heat exchanger/ground collector/grid power devices depending upon additional heat requirement. An earth air heat exchanger (EAHE) integration if placed below CE-greenhouse at appropriate depth to save additional land requirement will be most economical. The design of an earth air heat exchanger depends upon the local climatic condition as well as cooling/heating load, i.e., either open or closed loop as mentioned earlier. It is generally economical to design heat exchanger made up of PVE pipes.

8.4 Basic Heat Transfer

193 (b)

(a)

S

W

E C-Si Semi Transparent PV Module

N

i=3

i=3

i=2 i=2

i=1 i=1

(c)

Fig. 8.1 a Cross-sectional view of controlled environment (EC) greenhouse with integration of semitransparent flexible organic/c-Si photovoltaic (OPV) modules (GiSPVT) system b Crosssectional view of Quonset-type c-Si semi-transparent integrated greenhouse c Quonset greenhouse with flexible organic photo-voltaic thermal (OPVT) over the roof (GiSPVT)

8.4 Basic Heat Transfer [53] As we know that there are three types of heat transfer, namely conduction, convection, and radiation. It is also known that these heat transfers depend on temperature difference, but only one heat transfer plays an important role at a time in comparison with others. For example, conduction has major role in solid in comparison with convection and radiation. Similarly, convection and radiation play an important role in fluid and air/vacuum. Further, there is another heat transfer related to convection known as mass transfer from working fluid/wetted surface/green plant surface. Heat transfers are very complex phenomenon. However in this section, a brief discussion will be done to analyze GiSPVT system for thermal modeling.

8.4.1 Conduction Conduction takes place in any solid material. Based on Fourier’s law of heat conduction, one can write the rate of heat transfer per m2 (q˙k ) by conduction as

194

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

q˙k = h k (T1 − T2 ) W/m2 ,

(8.1)

where h k = KL , conductive heat transfer coefficient, a ratio of thermal conductivity [Appendix-C] and thickness of solid material, and T1 and T2 are hot and cold surface of solid material. The unit of heat transfer coefficient can be considered as either W/m2 K or W/m2 ◦ C.

8.4.2 Convection Convection generally takes place from solid surface to working fluid surface/wetted surface/air either in natural mode or in forced mode. (a) from Solid Surface to Air In this case, there is empirical relation which is widely used. Here, one can write an expression for the rate of heat transfer by convection (q˙c ) as q˙c = h c (T1 − T2 ) W/m2 ,

(8.2)

where h c , W/m2 °C is convective heat transfer coefficient, a ratio of the rate of heat transfer by convection per m2 to temperature difference. There are many empirical expressions for convective heat transfer coefficient, h c from solid to air. But two are mostly used as empirical expressions as follows: h c = 5.7 + 3.8V

(8.3a)

where h c , W/m2 °C is considered as forced convective and radiative heat transfer coefficient and V, the wind velocity and h c = 2.8 + 3V

(8.3b)

where h c is considered as forced convective heat transfer coefficient. However, in natural mode, V = 0. (b) from Solid to Working Fluid In natural mode, an expression for h c can be written by using the dimensionless number and can be expressed as Nusselt number, Nu =

hc L = C(GrPr)n K

or hc =

K C(GrPr)n L

(8.3c)

8.4 Basic Heat Transfer

where Grashof number, Gr =

195 μC gβ ' ρ 2 X3 ∆T μ/ρ , Prandtl number, Pr = K/ρC = K p , and μ2 p β ' = T1 are thermal conductivity, density, specific

K, ρ, Cp , μ, g, X = L, and heat, viscosity, acceleration due to gravity, characteristic dimension, and thermal expansion coefficient, respectively. Further, in forced mode, an expression for h c can be written by using the dimensionless number and can be expressed as Nusselt number, Nu =

hc L = C(RePr)n K

(8.3d)

with following Reynolds number Reynolds number, Re =

ρu0 X u0 X ρμ20 = = μu0 /X μ ν

The Gr, Pr, and Re depend on physical properties of working fluid (water/air), Table 8.2 and Appendix-C. The X is a characteristic dimension which can be considered as average value of length and breadth of rectangular surface. Example 8.1 Evaluate convective heat transfer coefficient (h c ) for a horizontal rectangular surface (1.0 × 1 m) maintained at 134 ◦ C exposed to water/air at 20 ◦ C. Solution: The average temperature, T f = (134 + 20)/2 = 77 ◦ C and the characteristic = 1 m. dimension (L = X ) = 1+1 2 (a) Surrounding water For the water thermal properties, Table 8.2a at T f = 77 ◦ C is = 3.72×10−4 kg/ms, K = 0.668 W/m.K, = 973.7 kg/m3 , Pr = 2.33, and β' = 1/(77 + 273) = 2.857 × 10−3 K−1 . The Grashof number, Eq. (7.3c), can be calculated as Gr L =

gβ ' ρ 2 (∆T )X 3 9.8 × 2.857 × 10−3 (973.7)2 × 114 × (1)3 = = 1.594 × 1013 ( )2 2 −4 μ 3.72 × 10

This is a turbulent flow, and for heated plate facing upward, the values are C = 0.14 and n = 1/3. Now, a convective heat transfer coefficient, h c , can be calculated as hc =

)1/3 ( 0.668 K = 3467 W/m2 K (0.14)(Gr L Pr)1/3 = (0.14) 1.594 × 1013 × 2.33 L 0.9

Here, one can observe that convective heat transfer coefficient is very large, and its value is four digit. It mainly depends on physical properties of water. For normal operating temperature of GiSPVT, the value is h c ≥ 100 W/m2 K.

196

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

Table 8.2 a Temperature dependent physical properties of water (saturated liquid) b Properties of air at atmospheric pressure (the value of μ, K, C p , and Pr is not strongly pressure-dependent and may be used over a fairly wide range of pressures) a Temperature °C

Specific heat (Cp ) (kJ/kg)

Density(ρ) (kg/m3 )

Viscosity (μk ) (kg/m s)

Thermal conductivity (K) (W/mK)

Prandtl number (Pr)

°F 32

0.00

4.225

999.8

1.79 × 103

0.566

13.25

40

4.44

4.208

999.8

1.55

0.575

11.35

50

10.00

4.195

999.2

1.31

0.585

9.40

60

15.56

4.186

998.6

1.12

0.595

7.88

70

21.11

4.179

997.4

9.8 × 104

0.604

6.78

80

26.67

4.179

995.8

8.6

0.614

5.85

90

32.22

4.174

994.9

7.65

0.623

5.12

100

37.78

4.174

993.0

6.82

0.630

4.53

110

43.33

4.174

990.6

6.16

0.637

4.04

120

48.89

4.174

988.8

5.62

0.644

3.64

130

54.44

4.179

985.7

5.13

0.649

3.30

140

60.00

4.179

983.3

4.71

0.654

3.01

150

65.55

4.183

980.3

4.3

0.659

2.73

160

71.11

4.186

977.3

4.01

0.665

2.53

170

76.67

4.191

973.7

3.72

0.668

2.33

180

82.22

4.195

970.2

3.47

0.673

2.16

190

87.78

4.199

966.7

3.27

0.675

2.03

200

93.33

4.204

963.2

3.06

0.678

1.90

210

104.40

4.216

955.1

2.67

0.684

1.66

ρ (kg/m3 )

C p (kJ/ kgK)

μ (kg/m-s) × 10–5

v (m2 /s) × 10–6

K (W/m2 K) × 10–3

α (m2 /s) × 10–5

b T (K)

Pr

100

3.6010

1.0259

0.6924

1.923

9.239

0.2501

0.770

150

2.3675

1.0092

1.0283

4.343

13.726

0.5745

0.753

200

1.7684

1.0054

1.3289

7.490

18.074

1.017

0.739

250

1.4128

1.0046

1.488

9.49

22.26

1.3161

0.722

300

1.1774

1.0050

1.983

15.68

26.22

2.216

0.708

350

0.9980

1.0083

2.075

20.76

30.00

2.983

0.697

400

0.8826

1.0134

2.286

25.90

33.62

3.760

0.689

(b) For surrounding air By using the physical properties of air, Table 8.2b at T f = 77 ◦ C and L = 1 m Gr L .Pr =

(9.8) × (134 − 20) × (1)3 × (0.697) = 4.51 × 109 )2 ( −5 (293) × 2.08 × 10

8.4 Basic Heat Transfer

197

For hot surface facing upward and turbulent flow condition, the heat transfer coefficient can be calculated as ) ( ) ( ( )0.333 K 0.03 × 0.14 × (Gr L Pr)0.333 = × (0.14) × 4.91 × 109 hc = L 0.9 = 2.83 W/m2 ◦ C It is important to note that the convective heat transfer coefficient for air surrounding is same as given in Eq. (6.3b) for v = 0. Further, its value changes from 3467 to 2.83 W/m2 ◦ C with change of fluid from water to air for given same other parametetrs.

8.4.3 Radiative Heat Transfer In this case, net radiation exchange per m2 between two parallel horizontal surface (T1 ) with surface having emittance (ε) and sky temperature,Tsky , can be written as [ ( )4 ] q˙r = εσ (T1 + 273)4 − Tsky + 273

(8.4a)

where Tsky is sky temperature, generally less than ambient air temperature, and its expression is given by Tsky = Ta − 12

(8.4b)

The above equation may be rewritten as, ( ) ( ) 4 q˙r = εσ T14 − Ta4 + εσ Ta4 − Tsky or ) ( q˙r = εσ T14 − Ta4 + ε∆R

(8.4c)

[ ( )4 ] = 60 W/m2 is the difference where ∆R = σ (Ta + 273)4 − Tsky + 273 between the long wavelength radiation exchange between the horizontal surface at temperature Ta and the sky temperature at Tsky . Since Ta and Tsky are at low temperature and hence according to Wein’s displacement law, Eq. (8.4c), the emitted radiation will be long wavelength radiation which is blocked by atmosphere. The ε and σ = 5.6 × 10−8 W/m2 K4 are emissivity of surface and Stefan Boltzmann constant, respectively. Further, after linearization of first term of Eq. (8.4c), one can have

198

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

q˙r = h r (T1 − Ta ) + ε∆R where ) ( )3 ( h r = εσ T12 + T22 (T1 + T2 ) = ε 4σ T for T 1 ∼ = T2

(8.4d)

It is necessary to discuss here that the numerical value of ∆R becomes zero for the surfaces not directly exposed to sky condition. Example 8.2 Determine the radiative heat transfer coefficient between the surface at 25 ◦ C and greenhouse room air temperature at Ta = 24 ◦ C. Solution: Since the temperatures are approximately same, hence from Eq. (8.4d), we have, h r = 4εσ T 3 = 4 × 5.64 × 10−8 × (25 + 273)3 = 6 W/m2 ◦ C

8.4.4 Mass Transfer [54] The mass transfer generally takes place from free water/wetted/plant surface to surrounding. The mass transfer is sometimes referred as evaporation/respiration depending upon the situation. In the present case, we will refer respiration from the green plants. The green plant contains almost about 90% water content, so it can be treated as wetted surface. There is strong relation between convective heat transfer coefficient and mass transfer by Lewis relation, Tiwari et al. [53]. The relation for respiration from green plant to surrounding can be expressed as follows: [ ] q˙ew = 0.016 × h c Pw − γ Ps

(8.5a)

where Pw and Ps are partial vapor pressure at water (plant surface) to surrounding temperature. The surrounding temperature can be ambient air/greenhouse room air temperature. An expression for P(T ) can be determined from ( P(T ) = exp 25.713 −

5144 T + 273

)

Since the low operating temperature range of greenhouse plant and room air temperature, Eq. (6.4e) can be liberalized as [ q˙ew = 0.016 × h c

Pw − γ Ps Tw − Ts

] (Tw − Ts ) = h ew (Tw − Ts )

(8.5b)

8.4 Basic Heat Transfer

199

with [ h ew = 0.016 × h c

Pw − γ Ps Tw − Ts

] ,

(8.6)

an evaporative/respiration heat transfer coefficient and can be evaluated for average value of Tw and Ts over 24-h cycle. It is important to mention here that evaporation/respiration cannot happen without convection, while convection can happen without evaporation/respiration. Example 8.3 Determine the rate of respiration/evaporative heat transfer coefficient in W/m2 ◦ C from average wetted/plant surface (35 ◦ C) to an average ambient air temperature (15 ◦ C) with a relative humidity, γ , of 50%. Solution: Thus, the vapor pressures at wetted, Appendix-H and ambient air temperatures can be calculated, Eq. (8.5a), as, ( Pw = exp 25.317 −

5144 273 + 35

) = 5517.6 N/m2

and ( Pa = exp 25.317 −

5144 273 + 15

) = 1730 N/m2

For h c = 2.8 W/m2 ◦ C [Eq. (8.3b) for V = 0 inside greenhouse] and using Eq. (8.5a), one gets the rate of evaporation as: q˙ew = 16.273 × 10−3 × 2.8 × (5517.6 − 0.5 × 1730) = 211.99 W/m2 The evaporative/respiration heat transfer coefficient, h ew , can be obtained, Eq. (8.6), as h ew =

211.99 q˙ew = 10.60 W/m2 ◦ C = 35 − 15 (Tw − Ta )

8.4.5 Total Heat Transfer [53] The total heat transfer coefficient will be sum of Eqs. (8.1), (8.2), (8.4d), and (8.6), and it is expressed as.

200

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

q˙ = h 1 (T1 − T2 ), W/m2

(8.7)

where h 1 = h k + h c + h r + h ew and h 1 = h k + h c + h r , with and without (empty) evaporation/respiration inside the greenhouse, respectively. In both cases, h c = 2.8 W/m2 ◦ C. If convection and radiation are considered together, it is advisable to consider h c + h r = 5.7 + 3.8V , W/m2 ◦ C. For air surrounding either inside or outside greenhouse, conductive heat transfer coefficient is neglected and hence. h 1 = h c + h r + h ew = 5.7 + 10.60 W/m2 ◦ C inside greenhouse, Example 8.3 (8.7a)

8.4.6 An Overall Heat Transfer Coefficient [53] In this case, it is defined as inverse of total thermal resistance from inside greenhouse to an ambient air as follows: [ U=

∑ Li 1 1 + + ho Ki hi i

]−1 (8.8)

The expression for h o = h c is given by (8.3). Example 8.4 Determine an overall heat transfer coefficient from (i) Inside greenhouse to ambient air through glass walls (ii) Solid surface to ambient through top glazed surface and bottom glazed of semi-transparent PV roof module greenhouse room air (iii) Greenhouse floor surface to inside ground. Given: L g,wall = 0.005 m, L s,solar cell = 0.003 m, K g,wall = K g,solar cell = 0.96 W/m/◦ C, and V = 1 m/s. Solution: (i) From Eq. (8.8), one has the following expression for an overall heat transfer coefficient from inside greenhouse to an ambient air through glass wall as: [

Ui,wall

0.005 1 1 ++ + = 9.6 0.96. 2.8

]−1

= [0.10416 + 0.0052 + 0.357]−1

= [0.446]−1 = 2.14 W/m2 ◦ C Further, same calculation for an overall heat transfer coefficient from inside greenhouse to an ambient air through glass roof with organic solar cell on its top can be

8.4 Basic Heat Transfer

201

considered. In this case, one can neglect the conductive heat transfer coefficient through organic solar cell due to its small thickness in comparison with c-Si solar cell. It can be seen that wind velocity (V) plays an important role in Ui,wall value, while window glass role is insignificant. (ii) (a) From solar cell surface to ambient air through top glass cover for c-Si semitransparent PV module, Ut,ca , as [ Ut,ca =

Lg 1 + Kg ho

]−1

[

1 0.003 + = 0.96 9.5

]−1

= [0.003125 + 0.10416]−1

= [0.144]−1 = 6.94 W/m2 ◦ C (b) From bottom solar cell surface to greenhouse room air through glass cover for c-Si semitransparent PV module, Ub,cr , Eq. (8.3b), as [ Ub,cr =

Lg 1 + Kg hi

]−1

[ =

1 0.003 + 0.96 2.8

]−1

= [0.003125 + 0.3571]−1

= [0.3602]−1 = 2.78 W/m2 ◦ C Here, h i is convective heat transfer coefficient from inner glass to greenhouse room air with V = 0. One has to note that an overall top heat transfer coefficient, Ut,ca , from solar cell to ambient is more than bottom overall heat transfer coefficient, Ub,cr , as expected. (c) An expression for an overall heat transfer coefficient from greenhouse room air to an ambient through semitransparent PV module can be written as ]−1

]−1 [ 0.0001 + 0.3602 = 0.114 + Ut,ca 1300 [ ]−1 −8 = 0.114 + 7.69 × 10 + 0.3602 = 2.1088 W/m2 ◦ C [

Ura1 =

1

+

L sc 1 + K sc Ub,cr

So one can see that solar cell material does not have much effect in this case, and hence, its effect is always neglected. (iii) From greenhouse floor surface to inside ground at depth of 3 m as [ Ugo =

L g0 1 + hg K g0

]−1

[ =

3 1 + 2.8 0.69

]−1

[ =

3 1 + 2.8 0.69

]−1

= [0.3571 + 4.3478]−1 = [4.7049]−1 = 0.21 W/m2 ◦ C

202

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

One can also see that underground depth plays an important role. For side losses in aqua water pond, an overall side heat transfer coefficient, Uso , can be evaluated as [ Ugo =

L g0 1 + hs K g0

]−1

[ =

1 0.60 + 100 0.69

]−1

≈ 1 W/m2 ◦ C

Here, h s is convective heat transfer coefficient between water and vertical wall of pond, and side thickness of ground has been considered as 0.60 m. (iv) From semitransparent organic solar cell surface of PV module to ambient air, Eq. (8.3a) should be used by considering appropriate value of wind velocity, i.e., h o = 5.7 + 3.8V , W/m2 K/W/m2 ◦ C (v) From semitransparent organic solar cell surface of PV module to greenhouse room air, Eq. 8.3 should be used by considering zero value of wind velocity, i.e., h i = 2.8 W/m2 K/2.8 W/m2 ◦ C

8.5 General Thermal Modeling of Quonset GiSPVT In order to write an energy balance equation of greenhouse integrated (c-Si/flexible organic) semi-transparent photo-voltaic thermal (even type GiSPVT), Fig. 8.1b, one has the following assumptions: (i) (ii) (iii) (iv) (v) (vi) (vii) (viii) (ix) (x) (xi)

The greenhouse is east–west oriented. The GiSPVT system is in quasi-steady state. No temperature gradient along thickness of individual component. Heat capacity of insulating materials is neglected. The temperature of plants is uniform. The heat capacity of plants is equivalent to water mass due to high content of water in the plant. The greenhouse floor area and surface plant area with full growth is supposed to be approximately same at initial stage. The electrical losses between two solar cells are negligible. Ethyl-vinyl acetate (EVA) has 100% transmittivity. Temperature beneath and around of water pond, T00 , has been assumed to be equal to an average ambient temperature. The floor and the plants temperatures are same.

The physical properties of window glass, c-Si, and thin-film solar cell are given in Table 8.3.

8.5 General Thermal Modeling of Quonset GiSPVT

203

Table 8.3 Physical properties of glass material, c-Si and thin-film solar cell Physical properties

Glass

c-Si solar cell

Thin film

Thermal conductivity (W/mK)

0.78

1300

884–1260

Specific heat (kJ/kgK)

0.84

0.7

Diffusivity (m2 /s)

3.44 × 10-4

0.8 × 10-4

Density (kg/m3 )

2700

2330

Transmittance

0.90–0.95

0

0.4–0.95

Absorptivity

0.05

0.93

0.74–0.84

Thickness (m)

0.003

0.0001

10−6

(a) For c-Si semi-transparent PV east roof, Fig. 8.1b: αc τg β

i=3 ∑

Ai Ii = Ut,ca (Tci − Ta )

i=1

i=3 ∑

Ai + Ub,cr (Tci − Tr )

i=3 ∑

i=1

+ η0 τ g β

i=3 ∑

Ai

i=1

A i Ii

(8.9a)

i=1

where αc ,η0 , τg ,β, Ut,ca , Ub,cr , Tci , Ta , and Tr are absorptivity and electrical efficiency and transmittivity of solar cell under standard test condition (STC), an overall heat transfer coefficient from solar cell to an ambient and greenhouse room air, solar cell of east PV module, ∑ and an ambient air and greenhouse room air temperatures, respectively. Further, i=3 i=1 Ai = A E = A W , total east facing roof area, i stands for 1st, 2nd, and 3rd section of east roof. For organic solar cell (OPV) module, Eq. (8.9a) becomes αc τg β

i=3 ∑

Ai Ii = h o (Tci − Ta )

i=1

i=3 ∑

Ai + h i (Tci − Tr )

i=1

i=3 ∑

A i + η0 τ g β

i=1

i=3 ∑

A i Ii

i=1

(8.9b) where design parameters of OPV module as mentioned in Eq. (8.9a) will be different, and expression for h o and h i is given in Example 8.4. From Eq. (8.9a), one has the following: Tci =

τg β(αc − η0 )

∑i=3

Ai Ii + Ut,ca A E Ta + Ub,cr A E Tr Ub,cr A E + Ut,ca A E i=1

By using above equation, one can get

204

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

Ub,cr (Tc − Tr )A E = P F1 τg β(αc − η0 )

i=3 ∑

Ai Ii − Ura1 A E (Tr − Ta )

(8.9c)

i=1 b,cr whereP F1 = Ub,crU+U , penalty factor due to indirect gain to greenhouse room air t,ca for c-Si semitransparent PV module i = h oh+h , penalty factor due to indirect gain to greenhouse room air for OPV i semi-transparent PV module b,cr Ut,ca , an overall heat transfer coefficient from greenhouse room and Ura1 = UUb,cr +Ut,ca air to ambient through c-Si semi-transparent PV roof of greenhouse ho = hhoi+h , an overall heat transfer coefficient from greenhouse room air to ambient i through OPV semi-transparent roof of greenhouse.

Example 8.5a Calculate penalty factor (P F1 ) for (i) c-Si semitransparent and (ii) organic PV module. Solution: (i) From Example 8.4 and Eq. (8.9c), Ut,ca = 6.94 W/m2 2.78 W/m2 ◦ C, then

◦

C and Ub,cr =

For c-Si semi-transparent PV module, P F1 =

Ub,cr 2.78 = 0.286 = Ub,cr + Ut,ca 6.94 + 2.78

and for an organic PV module,h i = 2.8 W/m2 °C and h o = 9.5 W/m2 °C for V = 1 m/s P F1 =

2.8 hi = 0.325 = ho + hi 9.5 + 2.8

This indicates that the penalty factor (P F1 ) for c-Si semi-transparent PV module is less than an organic semi-transparent PV module; hence, c-Si PV module should be preferred in comparison with an organic PV module. Example 8.5b Calculate an overall heat transfer coefficient from greenhouse room air to an ambient (Ura1 ) through (i) c-Si semi-transparent and (ii) OPV semi-transparent roof of greenhouse. Solution: By using Example 8.5a and Eq. (8.9c). (i) An overall heat transfer coefficient from greenhouse room air to ambient air through c-Si semi-transparent PV roof of greenhouse is given by Ura1 =

2.78 × 6.94 Ub,cr Ut,ca W = = 1.985 2 ◦ . Ub,cr + Ut,ca 6.94 + 2.78 m C

8.5 General Thermal Modeling of Quonset GiSPVT

205

(ii) An overall heat transfer coefficient from greenhouse room air to ambient air through OPV semi-transparent roof of greenhouse is given by Ura1 =

hi ho h o +h i

=

2.8×9.5 9.5+2.8

= 3.088 mW 2◦C .

In this case too, an overall heat transfer coefficient from greenhouse room air to ambient air through c-Si semi-transparent PV roof is less than an organic semitransparent PV module; hence, c-Si PV module should be preferred in comparison with an organic PV module on both reasons. (b) For semi-transparent PV west roof, Tcj : αc τg β

j=3 ∑

)∑ j=3

(

A j I j = Ut,ca Tcj − Ta

j=1

(

A j + Ub,cr Tcj − Tr

)∑

j=1

+ η0 τ g β

j=3 ∑

j=3

Aj

j=1

Aj Ij

(8.10a)

j=1

∑ j=3 Here, j=1 A j = A W , total west facing roof area equal to east facing roof area ( A E ), j stands for 1st, 2nd, and 3rd section of west roof. Further, an expression for west roof solar cell temperature, Tcj , can be obtained from Eq. (8.10a), as Tcj =

τg β(αc − η0 )

∑ j=3 j=1

A j I j + Ut,ca A W Ta + Ub,cr A W Tr

Ub,cr A W + Ut,ca A W

From above equation, it gives the following: ∑ ( ) Ub,cr Tcj − Tr A W = P F1 τg β(αc − η0 ) A j I j − Ura1 A W (Tr − Ta ) j=3

(8.10b)

j=1

Here, P F1 and Ura1 are same as in Eq. (8.9c) (see Example 8.5). For greenhouse room air, Tr : ( ) Q˙ ex + Ub,cr (Tci − Tr )A E + Ub,cr Tcj − Tr A W (

)

+ h 1 T p − Tr A p =

k=4 ∑ k=1

Ak Uk (Tr − Ta )

(8.11)

206

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

where k stands for 1st (east wall), 2nd (west wall), 3rd (north wall), and 4th (south wall). The Tcj , Tr , T p , A E , A W , and A p are west solar cell, greenhouse room air, plant temperatures, east roof, west roof, and plant surface area, respectively. The Q˙ ex is the rate of heated/cooled air available from earth air heat exchanger (EAHE). This is a practical approach for plant cultivation during summer/winter(months. ) The modeling of EAHE for evaluating the rate of thermal energy available Q˙ ex will be discussed in Sect. 8.6. (c) For greenhouse cultivated plant: U00

(

⎤ ⎡ j=3 i=3 k=4 ∑ ∑ ∑ T00 − T p A f + Fs τg2 (1 − β)⎣ A i Ii + A j I j ⎦ + τg A k Ik )

i=1

j=1

( ) dT p + h 1 T p − Tr A p = MpC p dt

k=1

(8.12)

Here, w0 (t)−γ Pr 0 (t)} , Eq. (8.7a) Tiwari et al. [53], Pw0 (t) and Pr 0 (t) h 1 = 5.7 + 0.016×2.8{P Tw0 −Tr o are partial vapor pressure at plant and room air temperatures, and γ is relative humidity of greenhouse air depending upon fogging, misting, irrigation, etc. The Fs is fraction of direct radiation blocked by green shade inside greenhouse, and it is always less than one and equal to one without shading. The T00 , M p , C p , and t are underground temperature, mass and specific heat of plants, and time of the day, respectively. Example 8.6 Evaluate total heat transfer coefficient from plant to greenhouse room air for parameters of Example 8.3 Solution: An expression for total heat transfer coefficient from plant to greenhouse room air is given by h 1 = 5.7 +

0.016 × 2.8{Pw0 (t) − γ Pr 0 (t)} Tw0 − Tr o

Substituting appropriate value from Example 8.3, one has h 1 = 5.7 + 10.60 = 16.3 W/m2 ◦ C

8.6 Thermal Modeling of the Uneven GiSPVT

207

8.6 Thermal Modeling of the Uneven GiSPVT Equations (8.9) to (8.12) are general energy balance. It can be applicable to any orientation, shape, and dimensions of greenhouse integrated semi-transparent photovoltaic thermal (GiSPVT) systems. For example, Eqs. (8.9) to (8.12) can be reduced to uneven GiSPVT system, and Fig. 6.6 for north–south orientation. In this case, there will be minimum incident solar radiation on north roof unlike southern roof, so we can neglect it. In the present analysis, heat exchanger effect has not been considered. The following are energy balance equations of each component of uneven GiSPVT, Fig. 6.6 with same assumptions mentioned in earlier section: (a) Energy balance equation for c-Si semi-transparent PV south roof: In semitransparent PV module, the rate of solar radiation absorbed by solar cell having temperature, Tc , must be equal to the sum of rate of thermal energy lost from solar cell to ambient air through glass top as well as to room air through bottom glass and the rate of electrical energy produced by solar cell. This can be written as, αc τg β A R S I (t) = Ut,ca (Tc − Ta )A R S + Ub,cr (Tc − Tr )A R S + η0 τg β A R S I (t) (8.13a) where A R S and I (t) are area of south roof of uneven GiSPVT and solar radiation incident on it. (b) Energy balance equation for room air: The sum of rate of thermal energy gain from solar cell to room air through bottom glass and the rate of thermal energy gain from water surface of fish pond to room air must be equal to the rate of thermal energy lost from room air to ambient through glass walls and north roof. This energy balance equation can be expressed as Ub,cr (Tc − Tr )A R S + h 1 (Tw − Tr )Aw =

5 ∑

Ai Ui (Tr − Ta )

(8.14)

i=1

where h 1 is sum of convective, radiative, and evaporative heat transfer coefficient from water surface to room air given by Eq. (8.7a). The suffix ‘i’ refers to glazed east, south, west, north walls, and north roof. (c) Energy balance equation for water pond: In this case, we have considered water pond for aquaculture. However, the same energy balance will be applicable for plant growth by considering heat capacity of plant. So, the sum of rate of thermal energy transferred from underground heat source to fish water pond, the rate of solar radiation transmitted to fish water pond through non-packing area of PV module, and rate of solar radiation transmitted to fish water pond through glass wall must be equal to the sum of rate of thermal energy stored

208

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

by fish water pond and the rate of thermal energy transferred to room air from fish water pond. The energy balance equation for the water pond is expressed as 5 ∑

Ak Uk (T00 − Tw ) +

τg2 (1

− β)A R S I (t) + τg

k=1

3 ∑

A j I j = Mw C w

j=1

dTw dt

+ h 1 (Tw − Tr )Aw P

(8.15)

Here,k ∑ refers to east, south, west, north water pond walls, and floor of water pond, τg 3j=1 A j I j = 0 (assumed) means solar radiation incident opaque walls of uneven GiSPVT or insulated glass walls and north roof is not allowed to enter greenhouse room. The Mw and Cw are mass of water in pond and its specific, heat respectively. The proposed thermal modeling [Eqs. (8.13–8.15)] can be used for the following applications: (i) Aquaculture: In this case, water depth in the pond can be considered between 2.5 and 3 m. (ii) For plant cultivation: In this case, small water mass equivalent to plant mass inside greenhouse can be considered, and it can be referred as mass of plant ( ) Mw = M p . From Eqs. (8.13) and (8.14), one gets an expression for solar cell temperature (Tc ) and room air temperatures (Tr ) of uneven GiSPVT as: Tc =

τg β(αc − η0 )I (t) + Ut,ca Ta + Ub,cr Tr Ub,cr + Ut,ca

(8.16)

and P F1 τg β A R S (αc − η0 )I (t) + h 1 Aw P Tw + Ura1 A R S Ta + Tr = ∑5 h 1 Aw P + Ura1 A R S + i=1 Ai Ui

∑5 i=1

Ai Ui Ta (8.17)

where b,cr b,cr ×Ut,ca and Ura1 = U . P F1 = Ub,crU+U Ub,cr +Ut,ca t,ca Numerical value of P F1 and Ura1 will be same as given in Example 8.5.

8.6.1 Analytical Expression for Water pond’s Temperature Equation (8.15) can be solved by using Eqs. (8.16) and (8.17) as follows: ∑ (U A)wa + 5k=1 Ak Uk dTw + Tw dt Mw C w

8.6 Thermal Modeling of the Uneven GiSPVT

209

} τg2 (1 − β)A R S + P F2 A R S (ατ )e f f I (t) [ ] ∑5 ∑3 + τg A j I j + (U A)wa + Ak Uk Ta

{

=

j=1

k=1

Mw C w

where (ατ )e f f = P F1 τg β(αc − η0 ) P F2 =

h 1 Aw P ∑5 h 1 Aw P +Ura1 A RS + i=1 Ai Ui

and (U A)wa =

(8.18)

( ) ∑5 Ai Ui (h 1 Aw P ) Ura1 A RS + i=1 ∑5 . h 1 Aw P +Ura1 A RS + i=1 Ai Ui

(∑ ) 5 Example 8.7 Evaluate the total glazed area A U i=1 i i and water pond surface (∑ ) 5 area k=1 Ak Uk of GiSPVT for design parameters of Table 8.3. Solution: Given glazed area: A E = A W = 37.12 m2 ,A N = A S = 44.62 m2 , A R N = 83.98 m2 , and Ui = 3.5 W/m2 °C 5 ∑

Ai Ui = [( A E + A W + A N + A S + A R N )Ui ] = (74.24 + 89.24) × 3.5

i=1

= 572.18 W/◦ C Given water pond of 1 m depth: A P W E = A P W W = 24.4 m × 1 = 24.4 m2 , A P W N = A P W S = 12.2 m × 1 = 12.2 m2 , A W P = 24.4 m × 12.2 m = 297.69 m2 , and Ui = 1 W/m2 ◦ CUi = 1 W/m2 ◦ C 5 ∑

] [ Ak Uk = (A P W E + A P W W + A P W N + A+P W S + A W P )Uk

k=1

= (48.8 + 24.4 + 297.69) × 1 = 396.29 W/◦ C Example 8.8 Evaluate penalty factor 2 (P F2 ) and an overall heat transfer coefficient, (U A)wa , from water pond to ambient air from all glazed sides walls and north roof for Eq. (8.18) in case of c-Si semitransparent PV module integrated greenhouse. Solution: From Examples 8.5 and 8.6 and Table 8.3, we the following parameters: ∑have 5 P F1 = 0.286, h 1 = 16.3 W/m2 ◦ C, i=1 Ai Ui = 572.18 W/m2 , A W P = 297.69 m2 , A R N = 83.98 m2 , A R S = 245.05 m2 , and Ura1 = 1.985 W/m2 ◦ C. Now from Eq. (8.18), we have P F2 =

h 1 Aw P h 1 Aw P + Ura1 A R S +

∑5 i=1

Ai Ui

210

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

16.3 × 297.69 16.3 × 297.69 + 1.985 × 245.05 + 572.18 4852.35 4852.35 = = 0.821 = 4852.35 + 486.424 + 572.18 5910.954

=

Here, one can observe that PF2 is significantly higher than PF1 which is required condition for cooling water pond. Again from Eq. (8.18), we have an expression for an overall heat transfer coefficient, (U A)wa , from water pond to ambient air from all glazed sides walls as ) ( ∑5 Ai Ui (h 1 Aw P ) Ura1 A R S + i=1 (U A)wa = ∑5 h 1 Aw P + Ura1 A R S + i=1 Ai Ui (16.3 × 297.69)(486.424 + 572.18) = 4852.35 + 486.424 + 572.18 4852.35 × 1058.604 = 869.113 W/◦ C = 5910.954 Example 8.9 Calculate (ατ )e f f for c-Si GiSPVT by using the data of Table 8.3 and Example 8.5a. Solution: From Example 8.5a, we have P F1 = 0.286, and from Table 8.3, we have τg = 0.95, αc = 0.90, β = 0.22, and η0 = 0.12. Further from Eq. (8.18), one has (ατ )e f f = P F1 τg β(αc − η0 ) = 0.286 × 0.95 × 0.22(0.90 − 0.12) = 0.0466 Solution of Eq. (8.18): Again Eq. (8.18) can be rewritten as: dTw + aTw = f (t) dt

(8.19)

where } τg2 (1 − β) A R S + P F2 A R S (ατ )e f f I (t) ] [ ∑5 ∑3 + τg A j I j + (U A)wa + Ak Uk Ta

{

f (t) = and

j=1

k=1

Mw C w

8.6 Thermal Modeling of the Uneven GiSPVT

211

∑ (U A)wa + 5k=1 Ak Uk a= Mw C w The solution of Eq. (8.19) for water temperature (Tw ) with initial condition, i.e., T w|t = 0 = Tw0 and t = 3600 between 0 and t can be obtained with following assumptions: (i) The constant ‘a’ is fixed value between 0 and t time interval. (ii) The numerical value of f (t) can be considered as an average value of f (t) at 0 and t time as f (t). If one multiplies Eq. (8.19) by eat throughout, one gets dTw at e + aeat Tw = f (t)eat dt or [ ( )] d Tw eat = f (t)eat dt After integration between 0 and t time interval, one has {t

[ ( )] d Tw eat =

0

{t f (t)eat dt 0

After simplification and substitution of lower and upper limits, one gets Tw =

) f (t) ( 1 − e−at + Tw0 e−at a

(8.20)

where f (t) = a

[{

] } ∑ τg2 (1 − β)A R S + P F2 A R S (ατ )e f f I (t) + τg 3j=1 A j I j + Ta ∑ (U A)wa + 5k=1 Ak Uk

After substitution of above expression in Eq. (6.20), one gets [{

] } ∑ τg2 (1 − β)A R S + P F2 A R S (ατ )e f f I (t) + τg 3j=1 A j I j + Ta Tw = ∑ (U A)wa + 5k=1 Ak Uk ( ) 1 − e−at + Tw0 e−at (8.21) Example 8.10 Determine constant ‘a’ and e−at for Eq. (8.21) for 1 m water pond depth and rewrite Eq. (8.21) in terms of numerical value as a function of climatic parameters by neglecting the solar radiation coming from glazed walls.

212

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

Solution: From Eq. (8.19), we have an expression for ‘a’ as ∑ (U A)wa + 5k=1 Ak Uk a= Mw C w ∑ Here, (U A)wa = 869.113 W/◦ C, 5k=1 Ak Uk = 396.29 W/◦ C, C w = 4190 K/kg °C, and M w = Awp ×dw × ρw = 297.69 × 1000 = 297690 kg [Examples 8.7 and 8.8]. After substituting above value in above formula, one has a=

1265.403 869.113 + 396.29 = = 1.054 × 10−6 /s 297690 × 4190 1.2 × 109

Now, e−at = a 1.054×10

−6

×3600

= e−0.00379 = 0.9962

This shows that 1−e−at = 0.0038, if these values and numerical value of numerator of ‘a’ are substituted in Eq. (8.21), then [{ Tw =

} ∑ τg2 (1 − β)A R S + P F2 A R S (ατ )e f f I (t) + τg 3j=1 A j I j 1265.403

] + Ta

× 0.0038 + Tw0 × 0.9962 } { If (ατ )m,e f f = τg2 (1 − β) A R S + P F2 A R S (ατ )e f f , then [ Tw =

(ατ )m,e f f I (t) + τg

∑3

1265.403

j=1

Aj Ij

] + Ta × 0.0038 + Tw0 × 0.9962

Further from Examples 8.8 and 8.9 and Table 8.4, we have. (ατ ) = 0.0466, P F2 = 0.821, A R S = 245.05 m2 , τg = 0.95, β = 0.22, and ∑3 e f f τg j=1 A j I j = 0 due to opaque glazed wall (glass wall is covered by insulating materials, and it is one of the assumptions). Again, [

{0.9 × 0.78 × 245.05 + 0.821 × 245.05 × 0.0466}I (t) + Ta Tw = 1265.403 × 0.0038 + Tw0 × 0.9962 ] [ {172.025 + 9.375}I (t) + Ta × 0.0038 + Tw0 × 0.996 = 1265.403 = [0.1434I (t) + Ta ] × 0.0038 + Tw0 × 0.9962

]

8.6 Thermal Modeling of the Uneven GiSPVT

213

Table 8.4 Design parameters of CE-GiSPVT system (suffix WP stands for water pond) for water depth of d w = 0.01 m with effective area of GiSPVT = 24.4 m × 12.2 m Parameters

Numerical values

Parameters

Numerical values

AE = AW (glass wall)

37.12

Ura1

3.5084 W/m2 °C

AN = AS

44.62

Ut,ca

9.1794 W/m2 °C

ARN

83.979 m2

αc

0.9

A RS

245.05

m2

β

0.22, 0.5, 0.8

AW P E = AW P W

0.1219

τg

0.95

A W P B = Aw P =

297.87 m2

η0

0.15

Cw

4192 J/kg °C

(ατ )e f f

0.2179

Vw

(100–535) m3

(ατ )me f f

85.06

PF1

0.3822

γ

0.98

PF2

0.7805

T00

25 °C

(U A)wa

1375.5

Ub,cr

5.6789 W/m2 °C

Uk

1–3 W/m2 °C

Ui

3.5

W/m2

°C

} { Here, (ατ )m,e f f = τg2 (1 − β)A R S + P F2 A R S (ατ )e f f = 0.1434 Above results show that there will not be any effect of solar radiation on water temperature[due to (i) large heat]capacity of water mass in pond and (ii) by insulating ∑ glass walls τg 3j=1 A j I j = 0 . For significant increase of water pond, one should have the following arrangements: (i) Glass wall should not be covered during sunshine hours. (ii) Integration of earth air heat exchanger (EAHE) to water pond. (iii) Integration of PVT collectors to the water pond. Rate of Stored Thermal Energy in Water Pond (W/m2 ) Further, the thermal energy stored (Q u ) in J in pond water is given by Q u = Mw Cw (Tw − Tw0 ) ⎡⎡ {

} ⎤ τg2 (1 − β)A R S + P F2 A R S (ατ )e f f I (t) ∑3 ⎥ ⎢⎢ ⎥ ⎢⎢ + τg Aj Ij ⎢ ⎥ ⎢ ( ) j=1 ⎢ ⎥ = Mw Cw 1 − e−at ⎢ ∑5 ⎥ ⎢⎢ (U A)wa + k=1 Ak Uk ⎥ ⎢⎢ ⎦ ⎣⎣ −(Tw0 − Ta )]

214

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

∑ If τg 3j=1 A j I j = 0 means there is no solar radiation transferring through glazed wall due to thermal curtain used for this purpose, then Q u = Mw Cw (Tw − Tw0 ) [[ { ] } τg2 (1 − β)A R S + P F2 A R S (ατ )e f f I (t)+ ( ) −at = Mw C w 1 − e ∑ (U A)wa + 5k=1 Ak Uk −(Tw0 − Ta )]

(8.22)

Example 8.11 Determine the water pond temperature for 1 m depth for 1000 W/m2 solar radiation incident on south semitransparent roof of GiSPVT with initial and ambient air temperature of 25 °C and 20 °C, respectively. Solution: From Example 8.10, we have Tw = [0.1434I (t) + Ta ] × 0.0038 + Tw0 × 0.9962 Here, I (t) = 1000 W/m2 , Ta = 20 ◦ C, and Tw0 = 25 ◦ C. After substitution of these values in above equation, one has Tw = [0.1434 × 1000 + 20] × 0.0038 + 25 × 0.9962 = 0.62 + 24.905 = 25.53 ◦ C

Example 8.12 Evaluate GiSPVT greenhouse room air and solar cell temperature of Example 8.11 Solution: From Eqs. (8.16) and (8.17), one has Tc =

τg β(αc − η0 )I (t) + Ut,ca Ta + Ub,cr Tr Ub,cr + Ut,ca

and P F1 τg β A R S (αc − η0 )I (t) + h 1 Aw P Tw + Ura1 A R S Ta + Tr = ∑5 h 1 Aw P + Ura1 A R S + i=1 Ai Ui

∑5 i=1

Ai Ui Ta

Known parameters: (ατ )e f f = 0.0466, P F2 = 0.821, A R S = 245.05 m2 , τg = 0.95, β = 0.22, (Example 8.9), P F1 = 0.286 (Example 8.5a), αc = 0.9, Aw P = 297.87 m2 , η0 = 0.15 (Table 8.4), h 1 = 16.3 W/m2 ◦ C (Example 8.6), ∑ 5 2 2 ◦ C (Example i=1 Ai Ui = 572.18 W/m (Example 8.7), Ura1 = 1.985 W/m 2 ◦ 2 ◦ 8.5b), Ut,ca = 6.94 W/m C, and Ub,cr = 2.78 W/m C (Example 8.4). Substituting given value in the above equation, we have first evaluated GiSPVT room air temperature as follows:

8.6 Thermal Modeling of the Uneven GiSPVT

215

10, 983.47 + 123, 955.23 + 1.985 × 245.05 × 20 + 572.18 4, 854.629 + 486.42 + 572.18 145239.37 = 24.56 ◦ C = 5913.220

Tr =

After knowing GiSPVT room air temperature from above, one can calculate solar cell temperature as Tc =

363.827 156.75 + 138.8 + 68.277 = = 37.43 ◦ C 2.78 + 6.94 9.72

8.6.2 Characteristic Equation (a) For thermal heating of GiSPVT In order to derive a characteristic equation, heat capacity of water mass should be minimum, and hence, one can develop characteristic equation for least heat capacity of plants. In this, an instantaneous[ thermal efficiency](ηi ) of uneven GiSPVT for ∑ opaque glass walls and north roof τg 3j=1 A j I j = 0 can be expressed as ηi =

Qu I (t) × A R × 3600

By using Eq. (8.22), the above equation becomes ] } ( )[{ 2 τg (1 − β)A R S + P F2 A R S (ατ )e f f Mw Cw 1 − e−at (Tw0 − Ta ) − ηi = ∑ A R × 3600 I (t) (U A)wa + 5k=1 Ak Uk or [ ] (Tw0 − Ta ) ηi = Fm (ατ )me f f − U Le f f I (t) where Fm = W/°C,

Mw Cw (1−e−at ) } , per { ∑ A RS ×3600× (U A)wa + 5k=1 Ak Uk

(8.23)

} { ∑ m2 , U Le f f = (U A)wa + 5k=1 Ak Uk ,

5 ∑ Ak Uk = 396.29 W/◦ C (Examples 8.7 and 8.8) (U A)wa = 869.113 W/◦ C, k=1 } { (ατ )me f f = τg2 (1 − β) A R S + P F2 A R S (ατ )e f f = 0.1434 m2 (Example 8.10) In Eq. (8.23), Mw = M p . Equation (8.23) will be referred as characteristic equation of GiSPVT for plant cultivation. It is similar to characteristic equation developed by Hottel–Whiller–Bliss (HWB) for conventional flat plate collector. For thermal

216

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

[ ] [ ] heating of GiSPVT, the gain (ατ )me f f and loss factors U Le f f should be maximum and minimum, respectively, as required by conventional as well as PVT collectors, Tiwari et al. (2018). [ ] Example 8.13 Evaluate thermal loss coefficient U Le f f and GiSPVT thermal efficiency factor [Fm ]. Solution: From Eq. (8.23), we have [ U Le f f = (U A)wa +

5 ∑

] A k Uk

= 869.113 + 396.29 = 1265.403 W/◦ C

k=1

Here, Mw = Awp ×dw ×ρw = 297.69×1×1000 = 297690 kg, Cw = 4190 J/kg ◦ C, e−at = 0.9962 (Example 8.10), and A R S = 245.05 m2 (Example 8.11). Then ( ) Mw Cw 1 − e−at 297690 × 4190 × 0.0038 }= { Fm = ∑5 245.05 × 3600 × 1265.403 A × 3600 × (U A) + A U wa

RS

k=1

k

k

= 0.00425 per m

2

Now numerical value of first term in Eq. (8.23) becomes as (ατ )me f f × Fm = 0.1434 × 0.00425 = 6.09 × 10−4 (gain heating thermal efficiency) which is very small due to large value of loss factor as U Le f f × Fm = 1265.403 × 0.00425 = 5.380 W/m2 ◦ C. Hence for large water pond depth, GiSPVT is not sufficient to heat water. In this case, one needs active heating of water pond which will be discussed in next coming chapter. (a) For thermal cooling of GiSPVT However, for thermal cooling of GiSPVT generally in summer condition, the upward thermal loss should be maximum. In this case, an expression for the rate of thermal loss from the plant room air can be obtained from Eq. (8.17) as h 1 Aw (Tw − Tr ) = (U A)wa (Tw − Ta ) − P F1 P F2 τg β A R S (αc − η0 )I (t) where (U A)wa =

( ) ∑5 h 1 Aw Ura1 A RS + i=1 Ai Ui ∑5 , h 1 Aw +Ura1 A RS + i=1 Ai Ui

(8.24)

an overall heat transfer coefficient from

plant to ambient air temperature and P F2 = h A +U hA1 Aw+∑5 A U , second penalty 1 w ra1 RS i=1 i i factor. Further, we can also have an analytical expression for the rate of thermal energy loss from the plant to ambient air from Eq. (8.21) as [ ] (U A)wa (Tw − Ta ) = FM (ατ ) E F F I (t) + (UA)L,EFF (Tw0 − Ta )

(8.25)

8.6 Thermal Modeling of the Uneven GiSPVT

where FM =

217

(U A)wa ∑ , (U A)wa + 5k=1 Ak Uk

}( ) { 2 = τg (1 − β) A R S + P F2 A R S (ατ )e f f 1 − e−at (ατ ) E F F ( ) (ατ )me f f 1 − e−at , Eq. (8.23) and [ ] 5 ∑ Ak Uk e−at (UA),L,EFF = (U A)wa +

=

k=1

Now, one can define the instantaneous thermal loss efficiency of GiSPVT from the water pond to ambient air temperature as follows: ηi L =

[ ] (U A)wa (Tw − Ta ) (Tw0 − Ta ) = Fm (ατ ) E F F + (UA)L,EFF I (t) × A R I(t)

(8.26)

Here, Fm =

1 (U A)wa × ∑5 A R {(U A)wa + k=1 Ak Uk }

Equation (8.26) indicates that it is similar to characteristic equation developed for solar distillation system which characteristic for maximum yield (maximum upward loss through condensing cover) is just opposite to conventional flat plate collector for maximum thermal gain (minimum upward loss through glass cover). Example 8.14 [ Calculate ] the thermal loss efficiency factor (Fm ) and thermal loss coefficient (UA),L,EFF by using the data of Example 8.12. Solution:

∑5 ◦ Known parameters:(U A)wa = 869.113 W/◦ C, k=1 Ak Uk = 396.29 W/ C 2 (Example 8.7 and 8.8), A R S = 245.05 m (Table 8.4), (ατ )me f f = 0.1434 m2 , and e−at = 0.9962 (Example 8.10). From Eq. (8.26), we have 1 869.113 1 (U A)wa × = × ∑5 A 869.113 + 396.29 245.05 R {(U A)wa + k=1 Ak Uk } 1 869.113 × = 1265.403 245.05 = 0.0028 per m2

Fm =

( ) (ατ ) E F F = (ατ )me f f 1 − e−at = 0.1434 × (1 − 0.9962) = 0.000545 m2

218

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

[ (UA),L,EFF = (U A)wa +

5 ∑

] Ak Uk e−at = 1265.403 × 0.9962 = 1260.59 W/◦ C

k=1

[ ] In this case too, numerical value of first term [ Fm × (ατ ) E F F] in Eq. (8.26) is also negligible in comparison with second term Fm × (UA),L,EFF . This finding can help for cooling due to large value of second term.

8.6.3 Exergy Analysis After knowing the water temperature of uneven GiSPVT from Eq. (8.21), one can get the numerical value of room air temperature (Tr ) of uneven GiSPVT from Eq. (8.17) and then one can get solar cell temperature (Tc ) from Eq. (8.16). For known numerical value of solar cell temperature (Tc ), an instantaneous electrical efficiency of PV module (ηmi ), Evans (1981), of uneven GiSPVT can be obtained as ηmi = τg η0 [1 − 0.0045(Tc − 25)]

(8.27)

( ) Now, the hourly electrical power E˙ el and daily electrical energy (E el ) from semitransparent PV module of uneven GiSPVT are given by E˙ el = β A R S × I (t) × ηmi × 1h = β A R S × I (t) × τg η0 [1 − 0.0045(Tc − 25)]kWh (8.28a) and E el =

N ∑

E˙ eli (Wh), kWh

(8.28b)

i=1

Here, N is number of sunshine hour per day. Example 8.15 Calculate an electrical energy produced from GiSPVT in one hour by using the data of Example 8.10. Solution: Given parameters: Tc = 37.43 ◦ C, τg = 0.95,β = 0.22, A R S = 245.05 m2 (Table 8.4), I (t) = 1000 W/m2 , and η0 = 0.12. From Eq. (8.28a), one has the following: E˙ el = β A R S × I (t) × τg η0 [1 − 0.0045(Tc − 25)]

8.6 Thermal Modeling of the Uneven GiSPVT

219

After substitution of given values in the above expression, one gets the rate of electrical energy, W from GiSPVT system as E˙ el = 0.22 × 245.05 × 1000 × 0.95 × 0.12[1 − 0.0045(37.43 − 25)] = 5802.08 W = 5.8202 kW In one hour, energy generated, kWh, will be E˙ el = 5.8202 kW × 1 hr = 5.8202 kWh ( ) An expression for hourly Q˙ u,ex and daily (Q u,ex ) exergy of thermal energy of water pond of uneven GiSPVT can be written as follows: [ ] Tw + 273 ˙ Q u,ex = Mw Cw (Tw − Tw0 ) − (Ta + 273)ln Two + 273 1 hr kWh × 1000 × 3600 s

(8.29a)

and [

] ) Tw,max + 273 Tw,max − Tw,min − (Ta + 273)ln Tw,min + 273 1 hr kWh (8.29b) × 1000 × 3600 s ( ) An overall rate of exergy E˙ ov,ex of uneven GiSPVT in one hour is also given by: Q˙ u,ex = Mw Cw

(

E˙ ov,ex = E˙ el + Q˙ u,ex (W)

(8.30)

Example 8.16 Evaluate hourly an overall exergy of GiSPVT system for Examples 8.10, 8.11, and 8.15. Solution: Given parameters: C w = 4190 K/kg °C, M w = 297690 kg [Examples 8.9], Tw == 25.53 ◦ C, Tw0 = 25 ◦ C, and Ta = 20 ◦ C. From Eq. (8.29a), we have hourly thermal exergy as ] [ 25.53 + 273 ˙ Q u,ex = 297690 × 4190 (25.53 − 25) − (20 + 273)ln 25 + 273 = 297690 × 4190[0.53 − 0.5206] = 1.247 × 109 × 0.009355 = 11.6687 × 106 J

220

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

11.6687 × 106 kJ × 1hour 11.6687 × 106 kJ = = 3.24 kWh 1000 1000 × 3600 sec ( ) From Eq. (8.30), an overall hourly of exergy E˙ ov,ex of uneven GiSPVT is also given by: =

E˙ ov,ex = E˙ el + Q˙ u,ex = 5.8202 + 3.24 = 9.0602 kWh ( ) Also an overall rate of thermal energy Q˙ ov,th of uneven GiSPVT is given by, E˙ el + Q˙ u,ex (W) Q˙ ov,th = γ

(8.31)

where γ is the conversion factor of thermal power plants used to convert electrical energy into thermal energy. Its value varies from 0.22 to 0.38 depending upon quality of coal. Example 8.17 Evaluate hourly an overall thermal exergy of GiSPVT system for Example 8.16. Solution: From Eq. (8.31), we have 9.0602 E˙ el Q˙ ov,th = + Q˙ u,ex = + 3.24 = 41.18 + 3.24 = 44.38 kWh γ 0.22 The above numerical value will be lower for higher value of γ (good quality of coal). Further, it can be noted that an overall hourly thermal exergy is significantly higher than exergy of GiSPVT as expected.

8.6.4 Methodology for Numerical Computation for Uneven GiSPVT Greenhouse There is a water pond below uneven GiSPVT, measuring 24.4 m × 12.2 m × 1.8 m (535.824 m3 ) volume. The other design and dimension of uneven GiSPVT parameters are given in Table 1 for water depth of 0.01 m. The number of semi-transparent PV modules and its range of packing factor are also given in Table 8.4. There are direct gain of solar radiation through non-packing area of semi-transparent PV module and glazed walls and north roof to the water surface of pond depending upon availability of solar radiation. Further, there is indirect gain to water from back of solar cells through greenhouse room air. The water in pond also gets geothermal energy if its temperature is lower than underground temperature (T0 ); otherwise, it losses heat

8.6 Thermal Modeling of the Uneven GiSPVT

221

Fig. 8.2 Hourly variation of solar intensity and ambient air temperature of typical day of cold climatic condition of Srinagar, India

to the ground. Thus, the water gets heated directly as well as indirectly. After the temperature of water becomes more than greenhouse room air, then there is thermal energy loss, namely convection, radiation, and evaporation from water surface to greenhouse room air and then transferred to inner surface of semi-transparent south roof. Again, there is further transfer of thermal energy from inner surface of semitransparent south roof to outer surface and then to ambient air. Thus, cooling of semi-transparent south roof depends upon the rate of thermal energy transferred from greenhouse room air to ambient air. There are many methods of heating and cooling of water in the pond. The temperature of water in pond is very sensitive of water depth. Following methodology has been used for numerical computation for given design (Table 8.3) and climatic parameters in Fig. 8.8 (Figs. 8.2, 8.3, 8.4, 8.5, 8.6 and 8.7): Step 1: First Eq. (8.21) has been computed for water temperature (Tw ) in pond of GiSPVT. Step 2: For known value of water temperature (Tw ), Step 1, the temperature of solar cell (Tc ) and greenhouse room air (Tr ) has been computed from Eqs. (8.16) and (8.17), respectively. Step 3: After knowing the temperature of solar cell (Tc ), Step 2, and water (Tw ), ˙ u ) and electrical energy (E˙ el ) have been Step, 1, the rate of thermal (Q evaluated from Eqs. (8.22) and (8.28a), respectively. ˙ u,ex , Step 4: For known water temperature (Tw ), Step 1, one can get the hourly, Q and daily, Qu,ex thermal exergy from Eqs. (8.29a) and (8.29b), respectively. Step 5: After knowing the rate of electrical energy (E˙ el ) from Step 3, one can get daily electrical energy, Eel , from Eq. (8.28b).

222

8 Thermal Modeling of Greenhouse Integrated Semi-transparent … (a)

(b)

(c)

Fig. 8.3 a Hourly variation of water temperature (Tw ) for different depth of water pond b Hourly variation of solar cell (Tc ) and greenhouse air (Tr ) temperature for different depth of water pond c Hourly variation of solar cell (Tc ) and instantaneous electrical efficiency of EC-GiSPVT system for different depth of water pond

8.6 Thermal Modeling of the Uneven GiSPVT

223

Fig. 8.4 Hourly variation of overall exergy, E˙ ov,ex , and thermal energy, Q˙ ov,th , of CE-GiSPVT system for 0.01 m depth of water pond

Fig. 8.5 Effect of packing factor on an overall daily exergy,Eov,ex , of uneven CE-GiSPVT for 0.01 m depth of water pond

Step 6: Finally by using the data of daily electrical energy (Eel ), Eq. (8.28b), Step 5, and exergy of thermal energy (Qu,ex ), Eq. (8.29b), Step 4, an overall exergy (Eov.ex ) has been obtained from Eq. (8.32).

Fig. 8.6 Effect of water depth on an overall exergy, Eov,ex , of uneven CE-GiSPVT for packing factor of 0.22

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

Overall exergy (Wh)

224

1.00E+08 9.00E+07 8.00E+07 7.00E+07 6.00E+07 5.00E+07 4.00E+07 3.00E+07 2.00E+07 1.00E+07 0.00E+00 0.010.05 0.1 0.25 0.5 0.75 1 1.25 1.5 1.83 Height of water in pond (m)

−Ta ) Fig. 8.7 Variation of ηi with (Tw0I (t) (characteristic curve) for 0.01 m depth of water pond for different packing factor of GiSPVT

8.6.5 Results and Discussion Figure 8.2 shows the hourly variation of solar intensity and ambient temperature for a typical day of Srinagar, India, as a climatic parameter used for numerical computation. Effect of water depth in pond on water temperature of GiSPVT has been shown in Fig. 8.3a. It can be seen that the water temperature decreases with increase of water depth and becomes saturated after 0.5 m depth. It indicates that there is not much change in fluctuation in water temperature due to large heat capacity of water.

8.6 Thermal Modeling of the Uneven GiSPVT

225

45.00 40.00 35.00

Tfo in oC

30.00 25.00 20.00 15.00 10.00 5.00 0.00 1

2

3

4

5

6

7

8

9 10 11 12 13 14 15 16 17 18 19 20

Length in m Tfo (Winter)

Tfo (Summer)

Fig. 8.8 Variation of T f o with length of heat exchanger L ex between zero and 20 m for T f i = 22 ◦ C(winter heating) and 45 °C (summer cooling)

The water temperature can be further enhanced by reducing packing factor of semitransparent PV roof and can be maintained at suitable temperature for growth of any plantation/aquaculture/acquaponics. Even water depth and temperature can be optimized for use of swimming pool for human being. Here, one has to note that the water content in all green vegetables is about 90–95%, and hence, heat capacity of the plant can be considered at par with water. By the use of the hourly data of water temperature from Fig. 8.3a in Eqs. (8.16) and (8.17), one can get hourly variation of solar cell and greenhouse room air temperature for different depth of water. The results have been shown in Fig. 8.3b. It is seen that effect of water depth on hourly variation of solar cell and greenhouse room air temperature is obvious. Both temperatures decrease with increase in water depth. It is very interesting to see the effect of water depth on both hourly variation of solar cell temperature and its electrical efficiency as shown in Fig. 8.3c. One can find that the electrical efficiency of solar cell decreases with increase in solar cell which is in accordance with other results reported earlier. Further, as packing factor increases, solar cell temperature decreases along with water temperature (Fig. 8.3a), and hence electrical efficiency increases with all time. So the users have to choose between thermal and electrical energy on its priority basis before installation of GiSPVT from application point of view. The comparison between hourly variation of overall exergy, E˙ ov,ex , and thermal ˙ ov,th , of CE-GiSPVT system for 0.01 m depth of water pond has been energy, Q depicted in Fig. 8.4. Here one can see that thermal exergy is higher most of time than an overall exergy due to low-grade energy irrespective of any value of packing factor. Further, it should also be noted that an overall thermal energy decreases with

226

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

increase in packing factor, but an overall exergy increases due to more electrical energy generation. Hence, one needs to optimize packing factor for a given design parameter. The negative value of an overall exergy means there is no electrical power generation due to low intensity/zero intensity. Effect of packing factor on an overall exergy has been shown in Fig. 8.5. I can be seen that an overall exergy decreases with increase of packing factor as per expectation. In this case, the direct gain decreases with an increase in packing factor. In the proposed GiSPVT, thermal energy dominates at low packing factor which is clearly shown in Fig. 8.5. Figure 8.6 shows the daily variation of overall exergy which consists of thermal exergy as well as electrical energy for different water depth. It can be seen that the daily overall exergy first increases up to water depth of 0.05 m and then starts decreasing, and hence, one can conclude that the optimum depth of water from an overall exergy point is 0.05 m. This means one can get maximum thermal and electrical energy at depth of 0.05 m for a given set of design parameters (Table 8.3). This optimum depth can vary for other design parameters. The characteristic equation of GiSPVT is represented by Eq. (8.23), and its plot has been shown in Fig. 8.7 for different packing factor with water depth of 0.01 m. In this case, there will be minimum thermal energy storage effect. One can observe that ( ) the thermal energy gain factor, i.e., Fm (ατ )me f f is maximum and thermal energy ( ) loss factor, i.e., −Fm U Le f f is minimum for packing factor of 0.22. It is due to fact that the direct gain to water mass is maximum due to large area of non-packing factor. This gain factor decreases with increase in packing factor due to decrease of direct gain and increase in indirect gain as per our expectation. These results are in accordance with results reported in Fig. 7.8. Further, the curve shown in Fig. 8.7 is known as characteristic curve, and its trends are similar to those of flat plate collector [30].

8.6.6 Recommendations The proposed thermal model under quasi-steady state with minor changes in energy balance equation can also be used in various applications of agriculture section as follows: (i) For any shape of CE-greenhouse, etc. (ii) For different solar cell materials of semi-transparent PV module (iii) Ventilated along with shaded CE-greenhouse as suggested by Moretti and Marucci [25] (iv) For pot and field cultivation of vegetables by reducing heat capacity of water mass in water pond inside CE-greenhouse (Fig. 8.3a). In addition to above recommendations, the thermal modeling of following proposed system can also be carried out:

8.7 Design of Earth Air Heat Exchanger (EAHE)

227

(v) Solar photo-voltaic thermal greenhouse (GiSPVT solar dryer) (vi) An integration of earth air heat exchanger (EAHE) into greenhouse room air integrated semi-transparent photo-voltaic thermal (GiSPVT) for heating and cooling of greenhouse air (Sect. 8.7) (vii) At larger depth of water pond (Fig. 8.3a) for aquaculture (fish cultivation) in winter for high return due to high selling rate of fish, an integration of PVT collectors with water pond can be carried out.

8.7 Design of Earth Air Heat Exchanger (EAHE) Following assumptions have been made: (i) Flow of air through is in stream line due to low velocity. (ii) There is no friction losses during flow due to smooth inner surface of EAHE pipe and sufficient large radius. (iii) The analysis is in steady-state condition. (iv) Underground temperature does not vary with time due to large het capacity of earth materials. (v) There is no pressure drop due to stream and reasonable velocity. (vi) In steady condition, the temperature of ground and EAHE pipes is same. (vii) The convective heat transfer does not vary during operating temperature, and its empirical value depending upon velocity has been considered.

8.7.1 Optimization of Length of EAHE ˙ u , is given The rate of thermal energy carried away by the flowing air inside EAHE, Q by ( ) ˙ u,ex = m ˙ f C f Tfo − Tfi Q

(8.33a)

where an expression for outlet air temperature, T f o,ex , from EAHE in terms of underground temperature, T0 , can be expressed as T f o,ex

[ [ ]] ] [ Aex h f Aex h f + T f i exp − = T0 1 − exp − m ˙ fCf m ˙ fCf

(8.33b)

where T f i is the inlet air temperature, surface area of heat exchanger of length, L ex , and radius,r ˙ f = πr 2 ρ f v , specific heat, C f = ( Aex ) = 2πr L ex , the mass flow rate, m ◦ 3 1000 J/kg C, density of air, ρ f = 1 kg/m and convective heat transfer from inner surface to flowing air, h f = 2.8 + 3v and v = 1.35 m, is velocity of flowing air through EAHE.

228

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

200.00 100.00

Qu in W

0.00 1

2

3

4

5

6

7

8

9 10 11 12 13 14 15 16 17 18 19 20

-100.00 -200.00 -300.00 -400.00

Length in m Qu (Winter)

Qu (Summer)

.

Fig. 8.9 Variation of Q with length of heat exchanger L ex between zero and 20 m for T f i = u

22 ◦ C(winter heating) and 45 °C (summer cooling)

The variation of outlet air temperature, T f o , and the rate of thermal energy ˙ u , at exit of EAHE have been shown in Figs. 8.8 and 8.9, respectively. available,Q One can observe that the outlet air temperature becomes constant after 20 m length of EAHE, and hence, one can conclude that the optimized length of EAHE is 20 m for given air velocity and other parameters under consideration. The increase/decrease in outlet air temperature will mostly depend on initial condition of inlet air temperature as expected. Further, the rate of useful thermal energy with length of EAHE as shown in Fig. 8.9 indicated that for thermal heating of air in winter is positive and negative for thermal cooling as expected. It is also maximum at 20 m length of EAHE.

8.7.2 Validation of Experimental Results In Eq. (8.33b), the first and second terms determine the outlet flowing air temperature, T f o . The first term plays an important role due to underground temperature in EAHE design due to{our requirement of achieving inlet temperature as T0 . To get this } Aex h f condition, exp − m˙ f C f should be as minimum as possible to minimize second term and maximize the first term. Hence, the role of EAHE length should be optimized for given design parameters.

8.7 Design of Earth Air Heat Exchanger (EAHE)

229

Generally, PVC pipe of radius 0.076 m is available everywhere, then for 20 m length of pipe, Aex = 2πr L ex = 2×3.14×0.076×20 = 0.5168×20 = 10.366 and m ˙ f = πr 2 ρa v = πr 2 × 1 × v = 0.01814 × v kgs = 0.01814 × 1.35 = 0.02448 kg/s. For above-said parameters, the outlet air temperature of EAHE for T f i = 37 ◦ C in month of November at KSU during peak sunshine hours will be. (a) For v = 1.35 m/s, h f = 2.8 + 3v = 6.85 W/m2 ◦ C, Eq. (8.33b) will be ]] [ ] [ [ 10.366 × 6.85 10.366 × 6.85 + 37 exp − T f o = 29 1 − exp − 0.02448 × 1000 0.02448 × 1000 or [ ] T f o = 29 1 − exp(−2.9006) + 37 exp(−2.9006) or T f o = 29[1 − 0.05498] + 37 × 0..05498 = 27.405 + 2.03 = 29.43, Fig. 8.8. This validates the experimental finding of underground temperature at 3 m depth.

8.7.3 Optimization of Number of Risers and Headers for a Given Number of Air Exchange Equation (8.33a) can also be rewritten as ]] [ [ ( ) ( ) Aex h f ˙ = FR m ˙ f C f To − T f i , W ˙ f C f To − T f i 1 − exp − Qu,ex = m m ˙ fCf (8.34a) For present case, ]] [ Aex h f = 1 − 0.05498 = 0.9459 FR = 1 − exp − m ˙ fCf [

(8.34b)

The energy available in one hour from one length of EAHE, Q u , Eq. (8.34a) is given by ˙ u,ex × 3600 J Q u,ex = Q

(8.34c)

( ) The volume of hot/cool air available VH/C per hour from one length (20 m) with radius of 0.076 m and air velocity of 1.35 m of EAHE is. VH/C = πr 2 v × 3600, m3 = 0.01814 × 1.35 × 3600 = 88.060 m3

(8.34d)

230

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

The value of proposed Quonset greenhouse (V0 ) = 20 × 8 × 4 + 20 × 8 × 1 (approximately) = 800 m3 . So, the number of heat exchanger pipe for a given length of 20 m and NEAHE for one number of air exchange change of Quonset greenhouse air will be as follows: V0 Volume of Quonset greenhouse V0 = = 2 Volume of hot/cooled air VH/C πr v 3600 800 800 = = = 9.0744 ≈ 9 0.01814 × 1.35 × 3600 88.160

NEAHE =

(8.35)

With nine risers of each length 20 m and header of 3 m width has been shown in Fig. 8.10. The radius of each riser is 0.076 m, so total width of 9 riser will be 0.076 × 2 × 9 = 1.368 m. If distance between two risers is about 0.15 m, then total width of space between risers will be 0.15 0.15 × 9 = 1.35 m, and hence, the length of each header will be 1.368 m + 1.35 = 2.718 ≈ 3 m. This configuration shown in Fig. 8.10 will replace one time 800m3 volume of Quonset greenhouse air in one hour with velocity of 1.35 m/s which can be created by 1HP air blower. If one required replacing greenhouse air (800m3 ) N0 times, then number of required riser and length of header will be as follows: for air exchange of greenhouse air, number of EAHE pipe will be. Number of risers N = 9 N0 and Length of header = 3 × N0 m

(8.36)

For example, if number of required air exchange (N 0 ) is 5, then total number of riser EAHE pipe and length of headers will be 45 and 15 m, respectively, Fig. 8.11.

Fig. 8.10 Layout plan of one EAHE with 9 risers of each 20 m and two headers of each 3 m which will replace one time Quonset greenhouse room air in one hour

8.7 Design of Earth Air Heat Exchanger (EAHE)

231

Fig. 8.11 Layout plan of EAHE sets having 9 × 5 = 45 risers which will replace five times greenhouse room air in one hour (length of header = 15 m)

If V0 is the volume of greenhouse (800 m3 ) to be heated/cooled and N0 is the number of air change per hour, then required volume of heated/cooled air can be V = N0 × V0 = 5 × 800 = 4500 m3

(8.37)

Layout configuration with 5 times replacement of greenhouse air in one hour has been shown in Fig. 8.11.

8.7.4 Final Design of EAHE Integration with Quonset Greenhouse Integration of EAHE with Quonset greenhouse has been shown in Fig. 8.12. As can be seen from Fig. 8.12, exit hot air is fed near floor of greenhouse and inlet of EAHE is connected with top of greenhouse because hot air has tendency to move upward direction. This arrangement is always recommended for thermal heating of greenhouse during lowest ambient air temperature, and it is referred as closed-loop integration of EAHE with greenhouse. For thermal cooling of greenhouse, there is open-loop interaction, and in this case, inlet of EAHE is connected to ambient air. Now arrangment of risers and headers as shown in Fig. 8.12 is not practical because the hot/cooled air is fed at one point which will not be used for uniform heating/ cooling of greenhouse, and hence, configuration of Fig. 8.13 is recommneded. In

232

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

Fig. 8.12 Symbolic representation of integration of one EAHE set with Quonset greenhouse

this case, Fig. 8.10 will be considered as one block just like representation of riser and headers in conventional flate plate collector.

8.7.5 Final Recommendations Based on above results and discussions about EAHE design, following recommendations should be considered before implementation: (a) General 1. Fig. 8.13 is final design of greenhouse integration of EAHE. 2. The radius and length of EAHE should be 0.076 m and 20 m, respectively. 3. Radius of header should be higher than radius of riser depending upon exit of air locally available blower of capacity at least 5hp. 4. The EAHE should be placed at 2.5 m depth from economical point of view. (b) Summer cooling 1. The green plant should be grown over area covered by EAHE during summer, and hence, underground temperature will be slightly lower and hence more cooling effect. 2. The EAHE should be only operated during peak sunshine hours only.

8.7 Design of Earth Air Heat Exchanger (EAHE)

233

Fig. 8.13 Final design of greenhouse integrated 5-EAHE

3. The greenhouse should have green shed cover below/above roof during peak sunshine hour to curtail solar radiation inside greenhouse for better cooling effect of EAHE. 4. There is also provision of roof vents for natural transferring of thermal energy from inside greenhouse to outside. 5. The open loop of EAHE should be used for cooling of greenhouse. (c) Winter heating 1. In winter condition, the area over EAHE if possible should be covered with plastic sheet which will help to increase underground temperature marginally for more thermal heating of greenhouse. 2. Closed-loop system between EAHE and greenhouse should be adopted for thermal heating during early morning to maintain the temperature for healthy plants. 3. Further, a shade over roof of greenhouse should be used during off-sunshine hours as per requirement.

234

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

8.8 Thermal Modeling of an Integration of EAHE with Room Air of GiSPVT Based on one of the recommendations of Sect. 8.7, in this section, we will discuss a thermal modeling of an integration of earth air heat exchanger (EAHE) (Sect. 8.7) with room air of uneven GiSPVT (Sect. 8.6) for heating/cooling of greenhouse room air for vegetable production during off-season period for high return (Sect. 8.6.6). Figure 8.13 Schematic diagram of integration of EAHE with GiSPVT room air. In the present case referring to Fig. 8.13, now Eq. (8.14) can be rewritten as Q˙ u,ex + Ub,cr (Tc − Tr )A R S + h 1 (Tw − Tr ) Aw =

5 ∑

Ai Ui (Tr − Ta )

(8.39)

i=1

where an expression of Q˙ u,ex , Eq. (8.34a), which is the rate of thermal energy available from an earth air heat exchanger will be used for thermal heating/cooling of greenhouse air as per requirement for plant growth and cultivation. The rate of useful thermal energy from serpentine tube earth air heat exchanger (EAHE) buried in the ground below GiSPVT can be written as follows: )] [ ( n2πr h f L Q˙ u,ex = εm˙ f C f 1 − exp − (T00 − Tr ) m˙ f C f

(8.40a)

Vρ πr 2 Lρ Acr Lρ M = = = = Acr uρ m˙ f = t t t t ( ) ( kg ρ = 1.225 3 , Acr = 3.14 2.52 = 0.002 m2 for r = 2.54 cm = 0.0254 m, m ) C f = 1.00 kJ/kg and u = 0.2 − 1 m/s where ε = 0.9 effectiveness of earth air heat exchanger (EAHE) and L is length of EAHE, Aex = 2πr L = 2 × 3.14 × 24 = 150 m2 n = 2 and 4, number EAHE connected in series will be referred as one array. [ ( )] n Aex h f is heat removal factor of an earth air heat FR = m˙ f C f 1 − exp − m˙ f C f exchanger T f o,ex

[ ( )] ) ( n Aex h f n Aex h f + Tr exp − = T00 1 − exp − m˙ f C f m˙ f C f

(8.40b)

If such heat exchanger is connected in m-parallel column, then [ ( )] n Aex h f ˙ Q u,ex−m = m × m˙ f C f 1 − exp − (T00 − Tr ) = m FR (T00 − Tr ) m˙ f C f (8.40c)

8.8 Thermal Modeling of an Integration of EAHE with Room Air of GiSPVT

235

m = 20, 40, 60, and 80, number of array connected in parallel. Energy balance for roof of GiSPVT will be same as Eq. (8.13) as αc τg β A R S I (t) = Ut,ca (Tc − Ta )A R S + Ub,cr (Tc − Tr )A R S + η0 τg β A R S I (t) (8.41) Energy balance for plant mass (equivalent to water mass) will also be same as Eq. (8.15) as 5 ∑

Ak Uk (T00 − Tw ) + τg2 (1 − β)A R S I (t) + τg

k=1

3 ∑

A j I j = Mw C w

j=1

+ h 1 (Tw − Tr )Aw P

dTw dt (8.42)

Further, the first term of Eq. (8.42) can be approximated as 5 ∑

Ak Uk (T00 − Tw ) = A W P UW P (T00 − Tw )

k=1

In the above case, there is transfer of earth thermal energy from ground to plant due to small water depth which is equivalent to plant mass. Then, Eq. (8.42) will be as follows: A W P UW P (T00 − Tw ) + τg2 (1 − β) A R S I (t) + τg

3 ∑

A j I j = Mw C w

j=1

+ h 1 (Tw − Tr )Aw P

dTw dt (8.43)

Following the procedure of Sect. 8.6, Eqs. (8.39), (8.41), and (8.43) can be solved for Solar cell temperature Tc =

τg β(αc − η0 )I (t) + Ut,ca Ta + Ub,cr Tr Ub,cr + Ut,ca

(8.41)

GiSPVT room air ] [ ∑5 Ai Ui Ta (ατ )e f f A R S I (t) + m FR T00 + Ura1 A R S Ta + h 1 Aw Tw + i=1 [ ] Tr = ∑5 m FR + Ura1 A R S + h 1 Aw + i=1 Ai Ui (8.42)

236

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

and plant/water temperature Tw =

) f (t) ( 1 − e−at + Tw0 e−at a

(8.43)

where [{ ] ∑3 } τg2 (1 − β) + P F2 (ατ )e f f A R S I (t) + τg Aj Ij j=1 ∑5 {Ak Uk + P F3 }T00 + (U A)wa Ta + f (t) k=1 [ ] = ∑ a P F3 + (U A)wa + 5k=1 Ak Uk [ ] ∑ P F3 + (U A)wa + 5k=1 Ak Uk a= Mw C w and m FR h 1 A w ]. P F3 = [ ∑5 m FR + Ura1 A R S + h 1 Aw + i=1 Ai Ui

Problems 8.1. Find out respiration/convective heat transfer coefficient (h c ) for a horizontal rectangular surface (30 m × 35 m) maintained at 30 ◦ C exposed to water/air at 25 ◦ C. Hint: Example 8.1 8.2. Fine out evaporative heat teamster coefficient (he ) from plant at temperature of 30 ◦ C which is exposed to 25 ◦ C with surrounding relative humidity of 60%. Hint: Example 8.3 8.3. Find out radiative heat transfer coefficient (hr ) for Problem 8.2. Hint: Example 8.2 8.4. Find out total heat transfer coefficient (h1 ) from the plant to greenhouse air for Problem 8.2 for a given convective heat transfer coefficient of 2.8 W/m2 °C. Hint: h1 = h c + hr + he . 8.5. Determine the variation of an overall heat transfer coefficient (U) from. (i) Inside greenhouse air to ambient air through glass walls (ii) Solid surface to ambient through glazed surface and greenhouse room air (iii) Greenhouse floor surface to inside ground Given: L g,wall = 0.005 − 0.01 m, L s,solar cell = 0.002 − 0.006 m, K g,wall = K g,solar cell = 0.96 W/m/◦ C and V = 1 m/s. Hint: Example 8.4

8.8 Thermal Modeling of an Integration of EAHE with Room Air of GiSPVT

237

8.6. Find out variation of an electrical efficiency of PV module for the following parameters: τg = 0.9, η0 = 0.15 → 0.20, and Tc = 30 → 50 ◦ C. Hint: Eq. (8.27) and ηmi = τg η0 [1 − 0.0045(Tc − 25)]. 8.7. Calculate ‘a’ for design parameters of Table 8.3. Hint: Eq. (8.19). 8.8. Find the variation of mass flow rate (F R ) with mass flow rate for design parameters of[ Sect. 8.6.1. }] { A h Hint: FR = 1 − exp − m˙ exf C ff . 8.9. Find the variation of mass flow rate (F R ) with surface area of EAHE for design parameters of Sect. 8.6.1. Hint: Problem 8.9 8.10. Discuss limiting cases of mass flow rate and surface area of EAHE factor (F R ). ˙ f as zero and infinity in Problem Hint: Consider numerical value of Aex and m 8.8 8.11. Determine electrical energy of GiSPVT for Fig. 8.2 and Problem 8.6 for different packing factor from 0.8 to 0.2. Hint: Eq. (8.28). 8.12. Evaluate penalty factor 2 (P F2 ) and an overall heat transfer coefficient, (U A)wa , from water pond to ambient air from all glazed sides walls and north roof for Eq. (8.18) in case of organic semitransparent PV module integrated greenhouse. Hint: See Examples 8.5 and 8.8. 8.13. Calculate (ατ )e f f for organic roof of GiSPVT by using the data of Table 8.3 and Example 8.5a. Hint: Example 8.9 8.14. Evaluate (ατ )e f f of c-Si and organic roof of GiSPVT for different packing factor. Hint: Example 8.9 8.15. Determine constant ‘a’ for Eq. (8.19) for different water pond depth from 0.01 m to 1.5 m, and draw conclusion out of this results. Hint: See Example 8.7–8.10. 8.16. Repeat Example 8.10 for different water depth ranging from 0.01 to 1 m. Hint: Follow Example 9.10. 8.17. Make a software program for Example 8.10 by incorporating solar radiation falling on east, south, and west ∑ glazed wall. Hint: Include program on τg 3j=1 A j I j by considering Liu and Jordon Formula given in Chap. 1. Objective Questions 8.1. What is the orientation of uneven greenhouse integrated semi-transparent photo-voltaic thermal (GiSPVT) system? (a) North–south (b) East–west (c) East-south (d) West-north Answer: (a)

238

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

8.2. What is the roof position of semi-transparent photo-voltaic? (a) East (b) West (c) North (d) South Answer: (d) 8.3. Which internal heat transfer coefficient in GiSPVT dominates? (a) Conduction (b) Evaporation/respiration (c) Radiation (d) Convection Answer: (b) 8.4. The cooling of GiSPVT room air can be affected by (a) Sliding window (b) Roof vent (c) Earth air heat exchanger (EAHE) (d) All of them Answer: (d) 8.5. The depth of water in GiSPVT for aquaculture should be (a) Small (0.01 m to 0.10 m) (b) Large (3 m to 4 m) (c) Water film (d) All of them Answer: (b) 8.6. The thermal gain inside GiSPVT will increase due to (a) (b) (c) (d)

Increase in non-packing area Decrease in packing factor Without changing non-packing area None of them

Answer: (a) and (b) 8.7. The area of south roof is (a) (b) (c) (d)

Bigger then north roof Less then north roof More than north wall More than west wall

Answer: (a) 8.8. Uneven GiSPVT means (a) (b) (c) (d)

Area of north and south roof is equal Area of north and south roof is not equal Area of north and south walls is equal Area of north and south roof is not equal

Answer: (b) 8.9. The external heat transfer coefficient from solid surface to air significantly depends on (a) (b) (c) (d)

Physical properties of air Physical properties of water Physical properties of soil None of them

Answer: None of them 8.10. Radiative heat transfer coefficient depends on (a) The temperature difference between two surfaces

8.8 Thermal Modeling of an Integration of EAHE with Room Air of GiSPVT

239

(b) Physical properties of air (c) Physical properties of water (d) Physical properties of soil Answer: (a) 8.11. Evaporative/respirative heat transfer coefficient depends on (a) (b) (c) (d)

Partial vapor pressure Convective heat transfer coefficient Conductive heat transfer coefficient All of them

Answer: (a) and (b) 8.12. Electrical power produced by GiSPVT system is (a) AC power (b) DC power (c) Both AC and DC power (d) All of them Answer: (b) 8.13. Electrical power produced by GiSPVT system is (a) High-grade power (b) Low-grade power (c) Zero power (d) All of them Answer: (a) 8.14. The GiSPVT produces (a) High-grade power (b) Low-grade power (c) Zero power (d) All of them Answer: (a) and (b) 8.15. By increasing packing factor of semi-transparent Pv module (a) (b) (c) (d)

Electrical power increases Thermal power increases Electrical power decreases Thermal power decreases

Answer: (a) and (c) 8.16. By increasing packing factor of semi-transparent PV module (a) (b) (c) (d)

Greenhouse room air temperature increases Greenhouse room air temperature decreases Greenhouse room air temperature unaffected None of them

Answer: (b) 8.17. By decreasing packing factor of semi-transparent PV module (a) (b) (c) (d)

Greenhouse room air temperature increases Greenhouse room air temperature decreases Greenhouse room air temperature unaffected None of them

Answer: (a)

240

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

8.18. By increasing packing factor of semi-transparent PV module (a) (b) (c) (d)

Direct gain of solar radiation inside greenhouse increases Direct gain of solar radiation inside greenhouse decreases Unaffected All true

Answer: (b) 8.19. By decreasing packing factor of semi-transparent PV module (a) (b) (c) (d)

Direct gain of solar radiation inside greenhouse increases Direct gain of solar radiation inside greenhouse decreases Unaffected All true

Answer: (a) 8.20. The GiSPVT system is most appropriate and self-sustain in (a) (b) (c) (d)

For all climatic and weather condition For cloudy condition For cold climatic and blue sky clear condition Composite climate and all weather condition

Answer: (c) 8.21. The GiSPVT system needs cooling by earth air heat exchanger (EAHE) in (a) (b) (c) (d)

For all climatic and weather condition For cloudy condition For cold climatic and blue sky clear condition Composite climate and all weather condition

Answer: (d) 8.22. The GiSPVT system needs heating by earth air heat exchanger (EAHE) in (a) (b) (c) (d)

For all climatic and weather condition For cloudy condition For cold climatic and blue sky clear condition Composite climate and all weather condition

Answer: (c)

References

241

References 1. Tiwari GN (1984) Int J Solar Energy 3(1):19–24 2. Tiwari GN, Dubey AK, Goyal RK (1997) Energy 22(4):389–392 3. Dimokasa G, Tchamitchianb M, Kittasa C (2009) Calibration and validation of a biological model to simulate the development and production of tomatoes in Mediterranean greenhouses during winter period. Bio Syst Eng 103:217–227 4. Ezzaeria K, Fatnassib H, Wifayac A, Bazgaoua A, Aharounea A, Poncetb C, Bekkaouid A, Bouirdena L (2020) Performance of photovoltaic Canarian greenhouse: a comparison study between summer and winter seasons. Sol Energy 198:275–282 5. Mesmoudi K, Soudani A, Zitouni B, Bournet PE, Serir L (2010) Experimental study of the energy balance of unheated greenhouse under hot and arid climates: study for the night period of winter season. J Assoc Arab Univ Basic Appl Sci 9(1):27–37. https://doi.org/10.1016/j.jau bas.2010.12.007 6. Chen J, Ma Y, Pang Z (2020) A mathematical model of global solar radiation to select the optimal shape and orientation of the greenhouses in southern China. Sol Energy 205:380–389. https://doi.org/10.1016/j.solener.2020.05.055 7. Jana BB, Nandy S, Lahiri S, Bag SK, Ghosh P, Bhakta JN, Ghosh D, Biswas JK, Bhattacharjee A, Jana S (2018) Does solar heated structure mimicking greenhouse effective to impede winter growth reduction of some tropical fishes? Aqua. https://doi.org/10.1016/j.aquaculture.2018. 09.017 8. Paparozzi ET, Meyer GE, Schlegel V, Blankenship EE, Adams SA, Conley ME, Read PE (2018) Strawberry cultivars vary in productivity, sugars and phytonutrient content when grown in a greenhouse during the winter. Sci Hortic 227:1–9. https://doi.org/10.1016/j.scienta.2017. 07.048 9. Cervantes VM, Sarfraz RM, Myers JH (2011) Survival of cabbage looper, Trichoplusia ni (Lepidoptera: Noctuidae), through winter cleanups of commercial vegetable greenhouses: implications for insecticide resistance management. Crop Prot 30(8):1091–1096. https://doi.org/10. 1016/j.cropro.2011.03.021 10. Chen S, Zhu Y, Chen Y, Liu W (2020) Usage strategy of phase change materials in plastic greenhouses, in hot summer and cold winter climate. Appl Energy 277:115416. https://doi. org/10.1016/j.apenergy.2020.115416 11. Sánchez-Guerrero MC, Lorenzo P, Medrano E, Castilla N, Soriano T, Baille A (2005) Effect of variable CO2 enrichment on greenhouse production in mild winter climates. Agric For Meteorol 132(3–4):244–252. https://doi.org/10.1016/j.agrformet.2005.07.014 12. Tiwari GN (2003) Greenhouse technology for controlled environment, alpha science (UK). Narosa Publishing House, New Delhi 13. Sun Y, Zhang J, Wang H, Wang L, Li H (2019) Identifying optimal water and nitrogen inputs for high efficiency and low environment impacts of a greenhouse summer cucumber with a model method. Agric Water Manag 212:23–34. https://doi.org/10.1016/j.agwat.2018.08.028 14. Murakami K, Fukuoka N, Noto S (2017) Improvement of greenhouse microenvironment and sweetness of melon (Cucumis melo L.) fruits by greenhouse shading with a new kind of nearinfrared ray-cutting net in mid-summer. Sci Hortic 218:1–7. https://doi.org/10.1016/j.scienta. 2017.02.011 15. Durner EF (2018) Plug size and density during greenhouse conditioning do not affect late summer and early fall production of June-planted “Albion” strawberry (Fragaria X ananassa Duch.) in the plasticulture system. Sci Hortic 240:268–272. https://doi.org/10.1016/j.scienta. 2018.06.040 16. Çakir R, Kanburoglu-Çebi U, Altintas S, Ozdemir A (2017) Irrigation scheduling and water use efficiency of cucumber grown as a spring-summer cycle crop in solar greenhouse. Agric Water Manag 180:78–87. https://doi.org/10.1016/j.agwat.2016.10.023 17. Friman-Peretz M, Ozer S, Geoola F, Magadley E, Yehia I, Levi A, Brikman R, Gantz S, Levy A, Kacira M, Teitel M (2020) Microclimate and crop performance in a tunnel greenhouse

242

18. 19.

20.

21. 22. 23. 24.

25. 26.

27.

28.

29.

30.

31. 32.

33.

34.

35. 36.

8 Thermal Modeling of Greenhouse Integrated Semi-transparent … shaded by organic photovoltaic modules—comparison with conventional shaded and unshaded tunnels. Biosyst Eng 197:12–31. https://doi.org/10.1016/j.biosystemseng.2020.06.007 Sharma PK, Tiwari GN, Sorayan VPS (1998) Parametric studies of a greenhouse for summer conditions. Energy 23(9):733–740. https://doi.org/10.1016/s0360-5442(98)00001-2 Perigees A, García JL, Romero A, Rodríguez A, Luna L, Raposo C, de la Plaza S (2008) Cooling strategies for greenhouses in summer: control of fogging by pulse width modulation. Biosys Eng 99(4):573–586. https://doi.org/10.1016/j.biosystemseng.2008.01.001 Bazgaou A, Fatnassi H, Bouharroud R, Elame F, Ezzaeri K, Gourdo L, Wifaya A, Demrati H, Tiskatine R, Bekkaoui A, Aharoune A, Bouirden L (2020) Performance assessment of combining rock-bed thermal energy storage and water filled passive solar sleeves for heating Canarian greenhouse. Sol Energy 198:8–24. https://doi.org/10.1016/j.solener.2020.01.041 Yano A, Onoe M, Nakata J (2014) Prototype semi-transparent photovoltaic modules for greenhouse roof applications. Biosys Eng 122:62–73 Hassanien R, Hassanien E, Ming L (2017) Influence of greenhouse-integrated semi-transparent photovoltaics on microclimate and lettuce growth. Int J Agric Biol Eng Open Access 10:11 Zisis C, Pechlivani EM, Tsimikli S, Mekeridis E, Laskarakis A, Logothetidis S (2019) Organic photovoltaics on greenhouse rooftops: effects on plant growth. Mater Today: Proc 19:65–72 Ravishankar E, Booth RE, Saravitz C, Sederoff H, Ade HW, O’Connor BT (2020) Achieving net zero energy greenhouses by integrating semitransparent organic solar cells. Joule 4:1–17. 19 Feb, 2020 ª 2019 Elsevier Inc Moretti S, Marucci A (2019) A photovoltaic greenhouse with variable shading for the optimization of agricultural and energy production. Energies 12(13):2589 Tiwari GN, Akhtar MA, Shukla A, Emran Khan M (2006) Annual thermal performance of greenhouse with an earth–air heat exchanger: an experimental validation. Renew Energy 31(15):2432–2446 Chel A, Tiwari GN (2009) Performance evaluation and life cycle cost analysis of earth to air heat exchanger integrated with adobe building for New Delhi composite climate. Energy Build 41(2009):56–66 Chel A, Tiwari GN (2010) Stand-alone photovoltaic (PV) integrated with earth to air heat exchanger (EAHE) for space heating/cooling of adobe house in New Delhi (India). Energy Convers Manage 51(3):393–409 Ozgener O, Ozgener L, Goswami DY (2011) Experimental prediction of total thermal resistance of a closed loop EAHE for greenhouse cooling system. Int Commun Heat Mass Transfer 38(6):711–716 Ozgener O, Ozgener L, Goswami DY (2017) Seven years energetic and exergetic monitoring for vertical and horizontal EAHE assisted agricultural building heating. Renew Sustain Energy Rev 80:175–179 Bisoniya TS, Kumar A, Baredar P (2013) Experimental and analytical studies of earth–air heat exchanger (EAHE) systems in India: a review. Renew Sustain Energy Rev 19:238–246 Díaz-Hernández HP, Macias-Melo EV, Aguilar-Castro KM, Hernández-Pérez I, Xamán J, Serrano-Arellano J, López-Manrique LM (2020) Experimental study of an earth to air heat exchanger (EAHE) for warm humid climatic conditions. Geothermics 84:101741 Barbares A, Maioli V, Bovo M, Tinti F, Torreggiani D, Tassinari P (2020) Application of basket geothermal heat exchangers for sustainable greenhouse cultivation. Renew Sustain Energy Rev 129:109928 Ghosal MK, Tiwari GN, Das DK, Pandey KP (2005) Modeling and comparative thermal performance of ground air collector and earth air heat exchanger for heating of greenhouse. Energy Build 37(6):613–621 Hepbasli A (2013) Low exergy modelling and performance analysis of greenhouses coupled to closed earth-to-air heat exchangers (EAHEs). Energy Build 64:224–230 Li H, Ni L, Yao Y, Sun C (2020) Annual performance experiments of an earth-air heat exchanger fresh air-handling unit in severe cold regions: operation, economic and greenhouse gas emission analyses. Renew Energy 146:25–37

References

243

37. Li H, Ni L, Yao Y, Sun C (2019) Experimental investigation on the cooling performance of an earth to air heat exchanger (EAHE) equipped with an irrigation system to adjust soil moisture. Energy Build 196(1):280–292 38. Li H, Ni L, Liu G, Yao Y (2019) Performance evaluation of earth to air heat exchange (EAHE) used for indoor ventilation during winter in severe cold regions. Appl Therm Eng 160:114111 39. Yang L-H, Huang B-H, Hsu C-Y, Chen S-L (2019) Performance analysis of an earth–air heat exchanger integrated into an agricultural irrigation system for a greenhouse environmental temperature-control system. Energy Build 2021:109381 40. Hermes VF, Ramalho JVA, Rocha LAO, dos Santos ED, Marques WC, Costi J, Rodrigues MK, Isoldi LA (2020) Further realistic annual simulations of earth-air heat exchangers installations in a coastal city. Sustain Energy Technol Assessments 37:100603 41. Peretti C, Zarrella A, De Carli M, Zecchin R (2013) The design and environmental evaluation of earth-to-air heat exchangers (EAHE). A literature review. Renew Sustain Energy Rev 28:107– 116 42. Rosa N, Soares N, Costa JJ, Santos P, Gervásio H (2020) (2020), Assessment of an earth-air heat exchanger (EAHE) system for residential buildings in warm-summer Mediterranean climate. Sustain Energy Technol Assess 38:100649 43. Amanowicz Ł, Wojtkowiak J (2018) Validation of CFD model for simulation of multi-pipe earth-to-air heat exchangers (EAHEs) flow performance. Therm Sci Eng Prog 5:44–49 44. Bharadwaj SS, Bansal NK (1981) Temperature distribution inside ground for various surface conditions. Build Environ 16(3):183–192 45. Vidhi R (2018) A review of underground soil and night sky as passive heat sink: design configurations and models. Energies 11(11):2941 https://doi.org/10.3390/en11112941 46. Bisoniya TS, Kumar A, Baredar P (2015) Energy metrics of earth–air heat exchanger system for hot and dry climatic conditions of India. Energy Build 86:214–221 47. Bisoniya TS (2015) Design of earth–air heat exchanger system. Geoth Energy 3(1). https://doi. org/10.1186/s40517-015-0036-2 48. Zhang C, Wang J, Li L, Wang F, Gang W (2020) Utilization of earth-to-air heat exchanger to pre-cool/heat ventilation air and its annual energy performance evaluation: a case study. Sustainability 12(20):8330. https://doi.org/10.3390/su12208330 49. Nayak S, Tiwari GN (2009) Theoretical performance assessment of an integrated photovoltaic and earth air heat exchanger greenhouse using energy and exergy analysis methods. Energy Build 41(8):888–896 50. Nayak S, Tiwari GN (2010) Energy metrics of photovoltaic/thermal and earth air heat exchanger integrated greenhouse for different climatic conditions of India. Appl Energy 87(10):2984– 2993 51. Ghosal MK, Tiwari GN (2006) Modeling and parametric studies for thermal performance of an earth to air heat exchanger integrated with a greenhouse. Energy Convers Manage 47(13– 14):1779–1798 52. Ghosal MK, Tiwari GN, Srivastava NSL (2004) Thermal modeling of a greenhouse with an integrated earth to air heat exchanger: an experimental validation. Energy Build 36(3):219–227 53. Tiwari GN (2016) Arvind Tiwari and Shyam. Springer, Handbook of Solar Energy 54. Malik MAS, Tiwari GN, Kumar A, Sodha MS (1982) Solar distillation. Pergamon Press Ltd., U.K.

Recommended Additional Reference for Further Studies 55. Abu-Hamdeh NH, Reeder RC (2000) Soil thermal conductivity. Soil Sci Soc Am J 64(4):1285. https://doi.org/10.2136/sssaj2000.6441285x 56. Castilla N, Hernandez J (2007) Acta Hortic 761(38):285–297

244

8 Thermal Modeling of Greenhouse Integrated Semi-transparent …

57. Le AT, Wang L, Wang Y, Li D (2020) Measurement investigation on the feasibility of shallow geothermal energy for heating and cooling applied in agricultural greenhouses of Shouguang City: ground temperature profiles and geothermal potential. Inf Proc Agric. https://doi.org/10. 1016/j.inpa.2020.06.001

Chapter 9

Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

9.1 Introduction The basic need for survival of human beings on planet earth is food after air and water. Globally, the air and water have been polluted due to heavy industrialization after Second World War (WW-II). Industrialization was totally based on fossil fuels mainly underground limited coal, petroleum and natural gases. Food and Agriculture Organization (FAO) estimated that more than 852 million people worldwide were undernourished in the year 2000–2002 across world [1]. The projected figure of world’s population is more than 7.6 billion up to the year 2020. As per the United Nations, World Food Security means that all people should have physical, social, and economic access to sufficient, safe, and nutritious food that meets their food preferences at all times. Hence, the agricultural production should be increased to meet the food demand of the fast growing population across world. Demand and supply gap due for food requirement can be achieved by the following means: (i) by increasing the crop/food productivity in the next 25 years (around 50% more food has to be produced particularly in developing countries) (ii) by controlling the population growth and (iii) by reducing the food losses or combination of all. In this chapter, we will discuss the problem of reduction of the food losses before/ after harvesting by using solar drying. Solar drying of agricultural product is one of the most important pre/post-harvest operations in order to conserve the grain from postharvest losses. Solar crop drying is the process of removal of initial moisture to optimum moisture level for an optimum drying temperature from a produce to optimum level for its long-term storage, Table 9.1. There are many types of solar dryer which has been classified in Fig. 9.1. Solar crop drying system as mentioned in Fig. 9.1 helps in (a) to facilitate early or preharvest, (b) to plan the harvest season, (c) long-term storage, (d) to fetch better © Bag Energy Research Society 2023 G. N. Tiwari, Advance Solar Photovoltaic Thermal Energy Technologies, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4993-9_9

245

246

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

Table 9.1 Initial and final moisture contents and maximum allowable temperature for drying of some crops (Brooker et al. 1992; Sharma et al. 1993) S. No.

Crop

Initial moisture content (% w.b)

Final moisture content (% w.b)

Maximum allowable temperature (°C)

1

Green peas

80

5

65

2

Cauliflower

80

6

65

3

Carrots

70

5

75

4

Green beans

70

5

75

5

Onion

80

4

55

6

Garlic

80

4

55

7

Cabbage

80

4

55

8

Sweet potato

75

7

75

9

Potatoes

75

13

75

10

Chillies

80

5

65

11

Apple

80

24

70

12

Apricot

85

18

65

13

Grapes

80

15–20

70

14

Bananas

80

15

70

15

Guavas

80

7

65

16

Okra

80

20

65

17

Pineapple

80

10

65

18

Tomatoes

96

10

60

19

Brinjal

95

6

60

Crop Drying using Solar Energy

Crop Drying in Open Sun

Crop Drying using Solar Dryers

Passive Solar Dryers

Direct Mode (Integral Type) Dryers

Cabinet Dryer

Indirect Mode (Distributed Type) Dryers

Active Solar Dryers

Mixed Mode Dryers

Direct Mode (Integral Type) Dryers

Indirect Mode (Distributed Type) Dryers

Mixed Mode Dryers

Greenhouse Dryer

GiSPVT cabinet dryer

Fig. 9.1 Classification of crop dryers using solar energy

Conventional Dryer using Grid Electricity for forced mode

Semi-transparent PV module ( SPV) Operated Dryer under forced mode operation

9.2 Classification of Solar Dryer

247

returns for farmers, (e) to maintain viability of seeds, (f) to sell a better quality product by farmers, (g) to handle transport and distribution of crops and reduction of the requirement of storage space [2]. Conventional drying of agricultural products in various industries is an energyintensive operation based on fossil fuel which ultimately affects the environment. In developed countries nearly 8–12% of primary energy demand is consumed in drying purposes. In this case, the rise in the price of conventional fuels directly affects the market price of the products [3]. Drying of food grains/vegetables in the open fields by exposure to solar energy (sun) has been very common since ancient times. The industrialization in the present century created a demand for controlled drying of many agricultural products. Since such dried products retain the flavor, quality and appearance and thus have better sale prospects. The other advantage is that such products could be dried in peak season and made available for consumption throughout the year. Coal, oil, or firewood is usually used in such conventional industrial dryers. The present energy crisis compels one to think of use of alternate sources of energy like solar energy which is the population free, abundant, and readily available. In this chapter, we are going to address recent development in solar crop drying. As mentioned in Chap. 5, the photon of solar energy is responsible of photosynthesis for growth of all plant. However, an electromagnetic wave (e/m) of solar energy is responsible to create favorable environmental temperature for controlled drying of crops/vegetables unlike photosynthesis.

9.2 Classification of Solar Dryer Solar energy in the form of electromagnetic waves in terrestrial region, short wavelength, (Chap. 1) can be converted into thermal energy after absorption by any surface. The solar radiation is absorbed by crop after reflection from its surface, Fig. 9.2. The thermal energy is responsible to raise the temperature of the surface and surface emits long wavelength radiation. In other words, the absorbing crops/ vegetable surface converts short wavelength into long wavelength radiation. In solar drying, absorber is crops/vegetables. After absorption of solar radiation by crops/ vegetables, its temperature rises and moisture in crops/vegetables get evaporated. The rate of moisture evaporation depends directly on crops/vegetables, ambient air (open sun drying), and greenhouse room air (controlled environment) and relative humidity (Eqs. 8.5 and 8.6). Thus, moisture content in crops/vegetable is reduced. The solar crop drying is categorized on the basis of methodology for solar energy collection and conversion of solar energy into useful thermal energy.

248

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

Fig. 9.2 Open sun drying

9.2.1 Open Solar (Sun) Drying The open solar (sun) drying as shown in Fig. 9.2 is used for drying of fruits, vegetables, and other products from ancient times by a large number of farmers. Worldwide a large part of dried fruits/vegetables/agricultural products are dried using open solar (sun) drying without using any advanced drying technology [4]. The open solar (sun) drying has inherent challenges: (i) it needs a large porous surface space area and more drying time; (ii) considerable loss of products due to rodents, birds, insects, microorganisms and hostile weather conditions (unexpected rain or storm); (iii) contamination of the crop due to foreign materials like dust, dirt, etc.; (iv) over drying/ insufficient drying as well as discoloring of crops/vegetables by ultraviolet (UV) radiation, and (v) degraded quality of dried products (due re-adsorption of moisture). Thus, open solar (sun) drying results unhygienic degraded product quality. If the quality of dried products is lower than a reference value, then it is not economical as well as marketable [5−11].

9.2.2 Controlled Environment Solar Drying System In order to overcome the limitations and disadvantages of open solar (sun) drying, a more advanced controlled environment method of solar energy harvesting has been more acceptable for solar crop drying. The advanced method is known as controlled solar drying system The controlled solar drying is more efficient, healthier, hygienic, faster, and economical than the open-air solar (sun drying) [12–15]. There are mainly two approaches for controlled environment solar drying system namely. Solar passive dryer: Solar thermal energy collection can be integrated to the drying chamber in a single unit like solar cabinet dryer, Fig. 9.3 and greenhouse dryer, Fig. 9.4, etc. In this case, flowing air inside drying chamber receives thermal energy

9.2 Classification of Solar Dryer

249

from the heated crop surface which is directly exposed to solar radiation and transfers it to the adjacent layer of air above it due to temperature gradient between layers. The hot moist air is transferred to outside ambient air either (a) due to buoyancy/ pressure difference or due to the combined effect (natural mode, Fig. 9.4a) or forced mode (Fig. 9.4b) through vent provided in passive dryer. In forced mode, DC power obtained from solar PV panel installed separately is used to operate fan provided at bottom of dryer. However, solar PV panel can also be integrated to roof of cabinet dryer as shown in Fig. 9.5. The glazed sides wall and solar panel heat the crop directly and indirectly respectively. In this case, two fans are provided at top exit of moist hot air from cabinet enclosure. Solar active dryer: It consists of two units, namely (a) solar thermal energy collector and (b) a drying chamber as shown in Fig. 9.6a. In other words, solar energy may be collected separately in solar thermal collector, and it is fed into the drying chamber for indirect heating of crop. In this case, dry hot air from solar thermal collectors is circulated either natural mode or forced mode using external source such as fans or

(a) Cross-sectional view

(b) 3-d view

Fig. 9.3 Solar cabinet dryer

(a) Quonset shape of greenhouse dryer

(b) Even type of greenhoue dryer under Forced mode of operation

Fig. 9.4 Photograph of greenhouse solar dryer

250

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

(a) South oriented front view

(b) Back view from North side

Fig. 9.5 Photograph of single-slope opaque PV module integrated cabinet dryer [23]

blowers to the base of multi-layered drying chamber. Further these active dryers are classified into three major categories, namely direct mode, indirect mode, and mixed mode [16–17]. It is also established that most of solar thermal collectors gives best performance due to low operating temperature in comparison with natural mode of operation. Initially, the electrical energy needed for the forced mode circulation of air between solar thermal collector and drying chamber was met by grid power if available in the daytime drying. However, there is problem of availability of grid power in developing/under developing countries. So in this case, semi-transparent PV module is partially integrated at lower portion of solar thermal collector as shown in Fig. 9.6b which provided DC power to operate DC fan at exit of solar thermal collector to operate under force mode. The most importance of such drying system is that supply and demand of electrical power is matching to make system selfsustained and economical, and one do not need storage system of electrical power through batteries. It is due to fact that for low solar radiation level, there is low electrical power to run the fan slowly for low level of hot humid air in drying chamber. The active solar dryers are more controlled and flexible as it can be regulated for desired drying rate for fast and better drying as compared to the passive solar dryers [18−20].

9.3 Working Principle of Various Design of Solar Dryers In this section, we will discuss the brief working principle of various solar dryers including photo-voltaic (PV) module-based design of solar greenhouse dryer under forced mode of operation due to its fast drying nature with good qualities of final

9.3 Working Principle of Various Design of Solar Dryers

(a) Conventional active solar dryer under natural mode of operation

(b) Partialy covered semi-transparent PV module active dryer under forced mode of operation Fig. 9.6 Solar active dryer [24]

251

252

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

product for high return to farmers in rural area. The solar dryer works on the principle of greenhouse effect as mentioned in Chap. 1.

9.3.1 Solar Cabinet Dryer As shown in Fig. 9.2, it is a single slope with south-oriented cabinet dryer. The top surface is fixed with single/double window glass cover and side walls are made up of either an insulated materials like wood/fiber re-enforced plastic (FRP), Fig. 9.2a or transparent window glass, Fig. 9.2b. There is a provision of inlet air at bottom of lower height below perforated plate. Further, there is provision of many holes for exit of moist air at top of vertical wall, Fig. 9.2b. The drying materials are kept on perforated sheet/plate. Now solar radiation after transmission from top transparent glass cover is mostly absorbed by crop after reflection from its surface. Further, the crop is heated after absorption of solar radiation. The cold air when enters from bottom holes, Fig. 9.2b comes in contact with crop and thermal energy is transferred from crop to cold air which is finally heated with moisture content. Thus, moist hot air is transferred through top holes provided at vertical north wall due to pressure difference between moist air and outside dry air. This process continued till moisture in crop is reduced to optimum level for storage of crop for letter use. Here the width of cabinet dryer is generally less than length of cabinet dryer due to natural mode of operation otherwise there should not be any limitation in forced mode of operation. Figures 9.5 show the front and back view of modified cabinet dryer with integration of opaque PV module in roof of cabinet dryer. An electrical energy provided by PV module is used to run the both DC fan, Fig. 9.5b for fast transfer of most air from inside chamber to outside. In this case, all sides are made up of window glass for transmission of solar radiation into chamber for drying of crop. Further, there is transfer of thermal energy by convection and radiation from back of opaque PV module to crop for heating. There is provision of inlet from all side at bottom below crop tray. In this case, there is limitation in length and breadth of dryer. So there is direct from side glazed walls and indirect gain of thermal energy from back of PV module.

9.3.2 Greenhouse Integrated Semitransparent PV Thermal (GiSPVT) Dryer Figure 9.4a and b shows the Quonset and even shape of greenhouse dryer working under forced mode of operation. The transparent plastic has been used as a covering material, and hence, it will come under category of low cost greenhouse dryer as explained in Chap. 5. Multi-layer tray has been used to make drying system as a thin-layer drying process. In this case, there will be fast drying due to direct gain

9.3 Working Principle of Various Design of Solar Dryers

253

of solar radiation inside the greenhouse. The crop material after absorption of solar radiation converts it into long wavelength radiation which is not allowed by transparent canopy cover as explained in Chap. 1 due to greenhouse effect and hence inside greenhouse air temperature becomes higher then outside. Further crop gets heated. The air entering from below crop gets heated by transferring heat from crop, and it becomes moist hot air as well. Further, since mass transfer from crop depends on relative humidity of greenhouse air as mentioned previously in Sect 9.2, this moist air should be removed to outside to make lower relative humidity inside greenhouse. This can be done either natural mode, or forced mode. In Fig. 9.8, drying of jiggery has been shown by natural mode and forced mode and it has been observed that drying is faster under forced mode of operation. Forced mode of operation needs power either from grid (Fig. 9.8b) or solar PV panel. In the case of Fig. 9.4b, PV module is used separately to provide DC power to DC fan attached at lower portion from clean environment point of view. The correct position of fan should be at near ceiling of greenhouse due to hot air tendency is move upward direction.

9.3.2.1

Fully Covered GiSPVT Dryer

Figure 9.7a and b shows the another type of dryer installed on top of wind tower of SODHA BERS COMPLEX at Varanasi (UP), India. The other technical design parameters are given in Table 9.2a. In this case, a 35 Wp semi-transparent PV module with an effective area of 0.61 m2 has been used at top for transmission of solar radiation through non-packing factor area as a direct gain, Chap. 4, Fig. 4.4. Further, there will be indirect gain from back of solar cell. All side walls have been made by using transparent window glass with aluminum framing. There is provision of inlet air from bottom as well top of wind tower. In this case, there is no restriction of length and breadth of dryer. This can be referred as fully covered greenhouse integrated semi-transparent photo-voltaic thermal (GiSPVT) cabinet dryer due to greenhouse effect as mentioned in Chap. 1. If packing factor is zero, then it becomes conventional cabinet dryer. There are four AC fans of rating (20 W, 1100 rpm) which is at top of north side to remove moist air from inside of dryer for fast evaporation from the crop placed in different trays. There is also provision of two glass doors at the east side through which removal of trays as per requirement at regular interval of time to determine the loss of weight of crop in different trays. The glass of 5 mm has been fitted with Al frame with the help of U rubber gasket of 5 mm. The porous cotton has been placed inside each tray to avoid the losses of medicinal plant during drying process. The space of about 30 mm has been provided at bottom of structure to allow cold air passage from bottom to top through each tray of area 0.54 m2 along with hot air available from wind tower at base of dryer. A brick wall of height 0.6 m has been provided at top roof opening of wind tower of BERS’ complex at Varanasi (U.P). The structure of GiPVT dryer is permanently fixed at vertical wall of foundation with the help of galvanized iron angle, fitting with the help of nuts and bolts. Further, semitransparent PV module is fixed at top of structure with the help of aluminum

254

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

(a) Photo-graph of GiSPVT solar dryer25

(b) Dimension and details of semi-transparent PV module

Fig. 9.7 Photograph of fully covered single semi-transparent PV module greenhouse/cabinet dryer

9.3 Working Principle of Various Design of Solar Dryers

(c) Preparation of sample before placing in drying tray

(d) Prepared five samples for drying on first day under Varanasi climatic conditions

(e) Photographs of five medicinal/vegetable products kept on tray of Single slope GiSPVT dryer at SODHA BERS’ Complex, Varanasi

Fig. 9.7 (continued)

255

256

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

(a) Experimental set up for natural mode operation (PV modules raised and DC fan not operated)

(b) Experimental set up for forced mode operation (PV modules not raised and DC fan operated) Fig. 9.8 Photograph of partially covered semi-transparent PV module greenhouse dryer

L strip, nut, and bolts to have minimum resistance. The output of PV module is connected to 18 V battery through solar charge controller. The output of battery is further connected to fan through inverter. The charge controller and inverter are packed in one box for simple operation. The trays are provided with side support in each layer. The proposed system can be utilized to dry a minimum 12 items at a time. Though the dryer is of 100 kg capacity, it can dry 12 different samples of agricultural produce in one batch. Samples of 3.6 kg fenugreek powder, 4.6 kg coriander

9.3 Working Principle of Various Design of Solar Dryers

257

Table 9.2 a Design specification of fully covered single-slope greenhouse integrated semitransparent photo-voltaic thermal (GiSPVT) drying system S. No.

Components

Dimensions

1

Vertical upper height

2.25 m

2

Vertical lower height

1.2 m

3

Inclination

28°

4

Floor area

5.2 m2

5

Roof area

5.75 m2

6

No. of trays

12

7

Area of tray

0.54 m2

8

No. of layers

3

9

Distance between two layers of trays

0.3 m

10

Cross section of Al. channel

(0.025 × 0.025) m2

11

Rubber gasket

5 mm

12

Glass

5 mm

b Hourly variation of climatic and other parameters on March 13, 2011, at Varanasi Time

I G (W/ m2 )

I d (W/ m2 )

T fi (°C)

T fo (°C)

T a (°C)

RH (%) inside

RH (%) outside

Module temp. (T c ), (°C)

9.00 AM

480

100

25

27.0

23

43.4

38.8

28

10.00 AM

840

110

25

31.2

24

43.0

39.9

33

11.00 AM

860

220

27

37.7

26

44.0

37.4

39

12.00 AM

900

140

28

36.5

26

35.5

34.9

40

1.00 PM

740

120

30

37.6

28

31.5

27.5

40

2.00 PM

620

120

30

39.2

28

30.5

28.8

42

3.00 PM

480

100

31

38.5

28

30.3

29.6

40

4.00 PM

280

80

32

38.8

28

28.0

27.5

40

5.00 PM

60

60

30

35.8

27

34.6

32.5

36

c Drying time of various items of medicinal plants and vegetables at Varanasi Initial wt. W i , (Kg)

Difference (W i − W f ), (Kg)

Final wt., W f (Kg)

Drying time Days

Hrs

Fenugreek

3.6

0.4

3.2

Approx. 3

21

Coriander

4.6

0.41

4.2

3

22

Mint

4.4

0.52

3.8

3

21

Red chilli

4.7

1.25

3.5

5

38

Green chilli

4.5

0.53

3.9

5

40

Items

258

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

powder, 4.4 kg mint powder, 4.7 kg red chilli, and 4.5 kg green chilli were purchased from the local market for the experimental purposes. The samples were washed with fresh ground water to remove the undesirable material, i.e., dust and foreign materials. Then the samples are blanched with hot water at temperature (80 ± 1)°C for 3 min. The experiments are conducted at BERS Complex (Bag Energy Research Society), Varanasi, U.P., India, from March 13 to 17, 2011, from 9.00 AM to 5.00 PM. Samples are covered with plastic sheets during off drying hours to prevent moisture exchange from surrounding. The photograph of sampling at different stages is shown in Figs. 9.7c–e The experiments are conducted under forced convection mode for different agricultural produce, namely fenugreek, coriander and mint, red chilli and green chilli from March 13 to 17, 2011, from 9.00 AM to 5.00 PM, with the operation of four fans on the north side (20 W, 1100 rpm). Each sample is cleaned in salted hot water to avoid any living bacteria with samples. Each samples of mass (kg) were placed on each tray early in the morning. To avoid crop losses, a porous cotton cloth was used on tray as discussed earlier. The moisture loss per day was evaluated by weighing crop at end of each tray at 5 PM by electronic weighing balance. Various parameters such as solar radiation, temperature inside the greenhouse, cell, ambient and at fan and humidity outside and inside the greenhouse and are measured hourly from 9 AM to 5 PM in the evening as given in Table 9.2b. Sampling of different products was carried out in buckets and measured at 3.6 kg fenugreek, 4.6 kg coriander, 4.4 kg mint, 4.7 kg red chilli, and 4.5 kg green chilli. The samples were then placed on wire mesh trays for thin layer drying. Three samples, namely fenugreek, coriander and mint took approx. 3 days (21 h, 22 h, and 21 h, respectively) for getting the safe moisture content of different products, whereas two samples, namely red chilli and green chilli took approx. 5 days (i.e., 38 h and 40 h, respectively) to achieve the safe moisture content as shown in Table 9.2c. Example 9.1 Referring Table 9.2b, calculate beam/direct radiation falling on roof of single-slope GiSPVT dryer at 10 am. Solution: By using the data of Table 9.2b, we have global and diffuse radiation as 400 W/m2 and 100 W/m2 at 10 am. Referring Eq. (1.3b), we can get beam/direct radiation as follows: Ib = IG − Id = 400 − 100 = 300 W/m2 Similarly, beam/diffuse radiation can be obtained at all time. Example 9.2 Calculate direct gain through roof of single-slope GiSPVT dryer for Fig. 9.7b and Table 9.2b for packing factor of 0.50. Solution: Referring Fig. 9.7b, following data’s can be obtained: Area of one PV module = 1.2 × 0.54 = 0.648 m2 So area of eight PV module = area of roof of GiSPVT = 0.648 × 8 = 5.184 m2 From Eq. (4.1c), the total area of non-packing factor = (1 − βc ) × Area of PV module.

9.3 Working Principle of Various Design of Solar Dryers

259

Here non-packing area of semi-transparent PV module is an area of double glazed portion of GiSPVT roof, then the total area of double-glazed roof of GiSPVT = (1 − βc ) × Total Area of PV modules in roof = (1 − 0.5) × 5.184 = 0.5 × 5.184 = 2.592 m2 . Now if transmissivity of the toughened glass (τ ) is considered as 0.9 then solar radiation transmitted inside GiSPVT = τ 2 × I × The total area of double glazed roof of GiSPVT. At 9:10 am (Table 9.2b), direct gain through roof of single-slope GiSPVT dryer = 0.92 × 400 × 2.542 = 839.808 m2 . Similarly, direct gain can be obtained for other time of Table 9.2a. Example 9.3 Find out electrical efficiency of c-Si PV module of GiSPVT dryer by using the data’s of Table 9.7b. Given: Electrical efficiency of c-Si semi-transparent PV module (ηmo ) under STC = 0.12 and thermal expansion coefficient (βref ) = 0.0045 °C−1 Solution: From Eq. (4.2c), we have ηc = ηmo [1 − βref [Tc − Tref ]] Here at 9 am Tc = 28 ◦ C and Tref = 25 ◦ C, then An electrical efficiency of PV module of GiSPVT (ηc ) = 0.12 [1 − 0.0045(28 − 25)] = 0.11988. Further at 10 am Tc = 28 ◦ C, then. An electrical efficiency of PV module of GiSPVT (ηc ) = 0.12[1 − 0.0045(33 − 25)] = 0.11568. This indicates that an electrical efficiency of semi-transparent PV module decreases with increase of its temperature as expected.

9.3.2.2

Partially Covered GiSPVT Dryer

In order to make compact and economical, an even type greenhouse, an modification with integration of two semi-transparent photo-voltaic module (75 Wp ) with an effective area of 0.61 m2 on south roof of greenhouse as shown in Fig. 9.8. Figure 9.8 is showing operation of greenhouse dryer operating under natural, Fig. 9.8a and forced mode, Fig. 9.8b respectively. The technical specification has been given in Table 9.3a. It is a three-tier drying system which can be used for drying of different crops simultaneously. Each tier consists of two wire mesh trays, having base area of 0.9 × 1.30 m, fitted in centre of greenhouse. The front and side views of the developed dryer are shown in Figs. 9.8c and d respectively. The dryer has floor area of 2.50 × 2.60 m with 1.80 m central height and 1.05 m side walls height from ground. Its north and south roofs have inclinations of 30° each from horizontal. The integrated dryer consists of two PV modules (glass to glass; dimensions: 1.20 × 0.55 × 0.01 m; 75 Wp ) integrated on its south roof; two openings (dimension: 1.10 × 0.55 m) at the

260

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

Table 9.3 a Specification of partially covered uneven greenhouse integrated semi-transparent photo-voltaic thermal (GiSPVT) drying system Type

Roof type, even span, three-tier system

Floor area

2.50 m × 2.60 m

Central height

1.80 m

Side walls height

1.05 m

Slope of roof

30° from horizontal

Tray size

0.6 m × 1.25 m

Door size

0.62 m × 0.88 m

PV module

75 Wp , dimension: 1.20 m × 0.55 m × 0.01 m

DC fan size

Inner dia. = 0.08 m; Outer dia. = 0.15 m

Bottom side

0.15 m height open and further 0.10 m height provided with wire mesh

PV module can be raised by 0.28 m height Load capacity

100 kg (Mint)

b Experimental hourly data under forced mode of operation for a typical day (May 26, 2008) Time (hr)

T a (°C)

γa (decimal)

T r (°C)

I(t) (W/ m2 )

I p (W/ m2 )

V L (V)

I L (A)

DC fan speed (m/s)

10:00

31.0

0.388

52.4

296

590

18.1

0.4

4.9

11:00

38.0

0.325

56.6

340

670

17.9

0.4

5.1

12:00

39.0

0.301

53.5

398

690

17.8

0.5

5.0

13:00

40.0

0.281

55.3

384

650

18.0

0.5

5.2

14:00

40.0

0.286

55.4

272

570

17.9

0.4

5.2

15:00

39.0

0.271

56.7

222

440

17.9

0.4

5.1

16:00

38.0

0.304

56.6

148

280

17.5

0.4

4.7

c Testing results of various nutrients of dried samples at Varanasi climatic condition Sample no.

Moisture (% wb)

Fat (% wb)

Protein (% wb)

Ash (% wb)

Crude fiber (% wb)

Carbohydrates (% wb) excluding crude fiber

1

7.68

1.66

3.64

15.67

11.10

60.25

2

8.15

1.56

3.78

15.23

11.50

59.78

3

6.69

3.81

5.11

12.93

11.02

60.14

4

7.71

1.70

3.25

6.01

18.38

62.95

5

8.35

5.19

2.49

5.53

26.50

51.94

d Pigment (Chlorophylls) and vitamin C analysis of dried samples at Varanasi climatic condition Sl. No.

Chlorophyll a (mg/ g)

Chlorophyll b (mg/ g)

Total chlorophyll (mg/g)

Vitamin C/Ascorbic acid (mg/100g)

1

24.485

11.431

9.3075

20.74

2

25.654

12.335

9.879

22.214 (continued)

9.3 Working Principle of Various Design of Solar Dryers

261

Table 9.3 (continued) d Pigment (Chlorophylls) and vitamin C analysis of dried samples at Varanasi climatic condition Sl. No.

Chlorophyll a (mg/ g)

Chlorophyll b (mg/ g)

Total chlorophyll (mg/g)

Vitamin C/Ascorbic acid (mg/100g)

3

15.276

18.624

13.891

32.515

4

96.061

1.6925

1.6105

3.303

5

61.102

–

–

–

e Mineral analysis of various dried samples of dried samples at Varanasi climatic condition Sl. No.

Fe (mg/ 100g)

Mg (mg/ 100g)

Mn (mg/ 100g)

Ca (mg/ 100g)

Zn (mg/ 100g)

Cu (mg/ 100g)

1

105.49

314.75

5.46

390.35

8.366

2.03

2

103.98

265.40

5.261

338.25

6.73

2.51

3

83.26

243.80

4.20

284.15

7.22

2.19

4

11.196

193.06

3.92

132.15

5.02

2.24

5

41.51

185.63

1.75

68.29

2.94

4.69

north roof, symmetrical to PV modules on south roof, for natural mode operation, i.e., for natural convection. An aluminum frame door (size: 0.62 × 0.88 m) has been made on its east side wall. A DC fan (inner diameter = 0.080 m, outer diameter = 0.150 m) has been fitted at the upper end of the east side wall for rapid removal of humid air and thus to expedite the drying process to the required level. The PV module produces DC electrical power to drive a DC fan for forced mode of operation and also provides thermal heat to greenhouse environment. At bottom side, 0.15 m height is open, and further 0.10 m is provided with wire mesh to provide air inlet and air movement in the greenhouse dryer. The air at bottom becomes hot and thus moves from bottom to top through a three-tier system of perforated wire mesh trays. The produce is kept on the perforated wire mesh trays for drying purpose. The structural frame of the dryer has been covered by UV-stabilized polyethylene sheet. The dryer has been constructed using aluminum sections (e.g., L angles, Teesections, flats), two PV modules (glass to glass), a DC fan and UV-stabilized polyethylene sheet covering, etc. Aluminum sections were used in construction to avoid rusting/corrosion from surroundings and thus to increase the life of the dryer. Wire mesh trays have been made which may be easily taken out and kept in the dryer at specific places. Arrangement for easy opening/closing of the PV modules (on south roof) and symmetrical air vents (on north roof) have been made using hooks, etc. The UV-stabilized polyethylene sheet has been fitted over the structural frame of the dryer with the help of steel screws with washer, rivets and nut bolt with washer, etc. A DC fan has been fitted at the upper end of the east side wall frame with the help of nut bolt with washer, etc. The incident solar radiation, on glass of PV module (glass to glass), is transmitted to greenhouse to produce heat in the greenhouse or greenhouse effect which increases

262

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

the greenhouse air temperature. The incident solar radiation on solar cells of PV module is converted into DC electricity which is used to drive a DC fan for forced mode operation of the dryer, i.e., removal of hot and humid air from greenhouse during drying. The solar cell portion of PV module transfers heat through conduction from front surface of PV module to its back surface. So, the back surface of PV module becomes hot. The hot back surface of PV module transfers heat to greenhouse air through convection. The front surface, facing ambient, loses heat to the atmosphere. Thus, PV module provides thermal heat (which is utilized to heat the air inside greenhouse) and DC electricity (to operate DC fan for forced mode operation). The temperature of the PV module will reduce as it transfers heat to greenhouse air which will help in drying of crops. It will help in increase of efficiency of PV module also. This is so because with increase in temperature of PV module, its efficiency decreases. The incident solar radiation on UV-stabilized polyethylene sheet increases the greenhouse air temperature like glass portion of the PV modules (glass to glass). The UV-stabilized polyethylene sheet helps in trapping of infrared radiation and to prevent unnecessary circulation of ambient air which facilitates in maintaining the desire temperature inside the greenhouse. In this case, direct gain of solar radiation is much more than single-slope GiSPVT, and hence, drying time in this case will be lower. The orientation of the greenhouse dryer is taken as east–west during experiments. The experiments were conducted under natural and forced modes of operation during the months of May/June, 2006 for without load condition. The hourly data for solar radiation has been measured at five points inside the greenhouse, and the average values of solar intensity have been considered for numerical computation. The hourly variation of average solar intensity, intensity on PV modules, ambient air and greenhouse room air temperatures, relative humidity, load voltage, and current and fan speed (when in forced mode of operation) have been measured for six days. Experimental hourly observations have been shown in Table 9.3b. In this case too, we conclude that drying is faster for thin layer drying under forced mode. Figure 9.9 shows drying at different time (a) inside view on first day, (b) inside view on second day, (c) outside view on third day, and (d) finally in mint powder form for coriander (Dhaniya) in even type GiSPVT solar dryer. In such way, the mint powder can be stored for use in off-season cultivation of coriander (Dhaniya) for high return for farmers in rural area without using grid power for forced mode of operation. Further, samples of fenugreek, coriander, mint, 4.7 kg red chilli and 4.5 kg green chilli are purchased from the local market for the experimental purposes. The samples were washed with fresh ground water to remove the undesirable material, i.e., dust and foreign materials. The experiments are conducted at BERS Complex (Bag Energy Research Society), Varanasi, U.P., India from March 13 to 17, 2011 from 9.00 AM to 5.00 PM. Then the dried samples are grinding into powder form as shown in Fig. 9.9e and sent to IIT Kharaghpur Lab for testing analysis. Results of the different dried medicinal plants and vegetable powder samples are analyzed. Various dried samples such as 1-coriander powder (inside greenhouse), 2-coriander powder (in open condition), 3-fenugreek powder, 4-green chilli powder, and 5-red chilli powder

9.3 Working Principle of Various Design of Solar Dryers

263

(a) Inside view on first day

(b) Inside view on second day

(c) Outside view on third day

(d) Coriander (Dhaniya) powder packed in plastic jar

(e) Photographs of dried powdered samples at BERS’ Complex, Varanasi Fig. 9.9 Solar drying of coriander (Dhaniya) in PVT greenhouse solar dryer

264

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

were taken for analysis of different nutrients. Results of the analysis of different dried medicinal plants & vegetable powder samples have been shown in Table 9.3c–e. The results clearly show that the fat, protein, ash, crude fiber and total chlorophyll content in dried samples are higher than the fresh samples (values as shown in Table 9.3c and d) respectively. This is primarily due to reduction in moisture content of the samples post drying. The results indicate that all the critical ingredients of the samples are maintained post drying, thus ensuring the retention of its calorific as well as nutritional values. Maintenance of the total chlorophyll content also helps to retain the original color of the sample. With the retention of its nutritional, calorific values as well as the original color, and with significant reduction in moisture content after drying, the product can now be used extensively for various herbal/medicinal/Ayurvedic applications with significant commercial applications. From the results, it is observed that coriander powder has higher carbohydrates, crude fiber, and ash content as compared to other dried samples. Vitamin C/ascorbic acid and protein content in fenugreek powder are higher, i.e., 32.515 mg/100 and 5.11% than the other samples as shown in Table 9.3b and c respectively. It is further found that green chilli powder has higher chlorophyll content, i.e., 96.061 mg/g as compared to other dried samples. It is also seen that coriander powder has higher minerals content than the other dried samples as shown in Table 9.3e. Figure 9.10 shows the drying of grapes of different qualities after harvest under different condition. It has been GiSPVT-dried grapes is better in color under forced mode of operation than shade and open condition Fig. 9.8 is considered as partially covered GiSPVT dryer. In both cases, fully and partially covered GiSPVT, shading is also provided over crop due to presence of solar cell in PV module. So in directly, one can say that GiSPVT is a mixed mode dryer due to direct as well as indirect gain for crop drying. Drying time depends on weather and climatic condition and packing factor of semi-transparent PV module. These dryers are self-sustained and eco-friendly dryer. The solar dryer discussed in Sects. 9.3.1 and 9.3.2 is always referred as solar passive dryer as explained earlier.

9.3.3 Active Indirect Solar Dryer As explained earlier, in an active solar dryer, air heating solar thermal collector and drying chamber are separate identity as shown in Fig. 9.6a. Here, air is heated by solar thermal air collector which is directly exposed to solar radiation, and it is fed at bottom of drying chamber, Fig. 9.6a, under natural mode of operation. The crop in drying chamber is indirectly heated, and hence, the color of crop is unaffected like directly exposed crop to solar radiation in cabinet/greenhouse dryer. In natural mode, hot air moves slowly with high operating temperature in vertical direction due to its low density, and hence, the solar thermal collector is inclined for smooth movement of hot air. Inclination of solar thermal collector depends upon latitude of place as per

9.4 Heat and Mass Transfer

265

(a) Inside view of grapes of different qualities on First day

(b) Dried gapes in different condition

Fig. 9.10 Solar drying of grapes in PVT greenhouse solar dryer

weather and climatic condition. For better drying of crop, slow heating is required and hence force mode is preferred in crop drying. For this, one needs forced mode of operation. For self-sustained forced mode of operation, a semi-transparent PV module is attached at lower portion of solar thermal air collector and fan is attached at exit of collector below drying chamber. In force mode of operation, the operating temperature is lower than natural mode of operation. Further, a window glass wall is used in exposed wall of drying chamber for direct heating of crop and hence such drying system can be referred as mixed mode of drying.

9.4 Heat and Mass Transfer For thermal modeling of any solar thermal system, one should know the physical value of various heat transfer evolved in basic equation of thermal modeling. The solar dryer system is no exception. Hence, we will try to explain basic heat and mass transfer evolved in developing thermal model of solar drying system.

9.4.1 Convective Heat Transfer Coefficient Following Malik et al. [21] one can see that there is good relation between convective heat transfer coefficient and mass transfer by using Lewis relation. The relation for respiration (evaporation) from water content green plant to surrounding (Sect. 8.4.4) can be expressed as follows: q˙ew = 0.016 × h c Pw − γ Ps

(9.1)

266

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

where Pw and Ps are partial vapor pressure at water (plant surface) to surrounding temperature and γ is relative humidity of above drying product. The surrounding temperature can be ambient air/greenhouse room air temperature. An expression for partial vapor pressure at given temperature is given by P(T ) = exp 25.713 −

5144 T + 273

Further, h c is a convective heat transfer coefficient from crop surface to surrounding. This is an important parameters, and it can vary due to reduction in moisture content from time to time unlike growth of plant inside greenhouse (Chap. 8). Before modeling of any solar dryer particularly GiSPVT solar dryer, it important to develop a method to determine convective heat transfer coefficient which can be used for any kind of crop to be dried. Following Sect. 8.4 and Tiwari et al. [22] ,the convective heat transfer coefficient (h c ) from crop surface to surrounding moist air can be obtained by using following dimensionless formula given below: Nu =

hc X = C(Gr.Pr)n Kv

or, hc =

Kv C(Gr.Pr)n X

(9.2)

where Nu, Pr, and Gr are Nusselt, Prandtl, and Grashof numbers given in Sect. 8.4.2 (Eq. 8.3). The average crop temperature T c , exit air temperature T e and exit air relative humidity (γ ) have been used for determining the physical properties of humid air which, in turn, where used for calculating the values of Reynolds number and Prandtl number. Further, temperature-dependent physical properties of most air can be obtained by using the following expressions: Density(ρ) =

353.44 Ti + 273.15

Thermal conductivity(K ) = 0.0244 + 0.6673 × 10−4 × Ti Specific heat(C) = 999.2 + 0.1434Ti + 1.104 × 10−4 Ti2 − 8.7581 × 10−8 Ti3 Viscosity(μi ) = 1.718 × 10−5 + 4.820 × 10−8 Ti where Ti =

Tc +Te , 2

Tc and Te are crop and exit hot air temperatures.

9.4 Heat and Mass Transfer

267

The numerical values of C and n depend of type of crop to be dried, and these are constants for a given crop. The K and X are thermal conductivity of humid air and characteristic dimension of drying chamber respectively. The characteristic dimension ‘X’ can be taken as average value of length and breadth of crop tray. The amount of moisture evaporated (m˙ ev ) in time ‘t’ and tray area At can be determined by using Eq. (9.1) as m˙ ev =

0.016 × h c Pw − γ Ps × t q˙ew × t = × At L L

(9.3)

The mass evaporated,m˙ ev , in Eq. (9.3) in time ‘t’ can be experimentally determine by weighing the crop at initial time and after time ‘t’. With help of Eqs. (9.2), (9.3) can be expressed as follows: m˙ ev =

0.016 K v C(Gr.Pr)n P(Tc ) − γ P(Ts ) At t L X

(9.4)

If we assume Z=

0.016 K v P(Tc ) − γ P(Te ) At t L X

Then, Eq. (9.4) can be rewritten as m˙ ev = C(Gr.Pr)n Z

(9.5)

After taking logarithm of both sides of above equation, one gets m˙ ev ln Z

 = ln C + n ln(Gr.Pr)

or, Y0 = m X 0 + C0

(9.6)

where Y0 = m˙Zev , X 0 = ln(Gr.Pr) and C0 = ln C Further, Eq. (9.6) is a linear equation and its constant can be determined by simple regression analysis by using the experimental data as n=m=

N

∑ ∑ ∑ ∑ ∑ X 0 Y0 X 0 Y0 X 0 Y0 − X 0 Y0 − and C = 0 ∑ 2 ∑ 2 ∑ 2 ∑ 2 X0 X0 N X0 − N X0 −

∑

(9.7)

Further, from Eq. (9.6), C0 = ln C, then C = eC0

(9.8)

268

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

For known values of ‘n’ and ‘C’ from Eqs. (9.7) and (9.8) and substituting the numerical values of K v , X , Gr, and Pr number, one can get the values of convective mass transfer coefficient (h c ) from Eq. (9.2) as hc =

Kv C(Gr.Pr)n X

(9.9)

Here, mass evaporated (m ev ), crop temperature (Tc ), surrounding air temperature (Ts ), and relative humidity of moist air (γ ) are experimentally recorded numerical value. Further, it is to be noted that for N set of experimental data for m ev , Tc ,Te , and γ , one has to take (N + 1) by repeating the first numerical value for each one.

9.4.2 Evaporative Heat Transfer Coefficient After knowing convective heat transfer coefficient, one can easily determine an evaporative and mass transfer from Eqs. (9.1) and (9.3) respectively as q˙ew = 0.016 × h c Pc − γ Pe

(9.10)

and, m ev =

0.016 × h c Pc − γ Pe × t q˙e × t = × At L L

(9.11)

Also Eqs. (9.1) or (9.10) can be linearized and rewritten as follows: q˙ew =

0.016 × h c Pc − γ Pe × (Tc − Te ) (Tc − Te )

or q˙ew = h ew × (Tc − Te ) where h e is an evaporative heat transfer coefficient and it can be expressed as h ew =

0.016 × h c P c − γ P e

Tc − Te

(9.12)

The partial vapor pressures and temperatures can be considered at an average value of crop and exit (outlet) hot air temperature between two consecutive time say at ‘t’ and ‘t + 1’.

9.4 Heat and Mass Transfer

269

9.4.3 Evaluation of C and N Under Forced Mode of Operation for Indoor Simulation For indoor simulation, a closed chamber having three compartments each effective area of 0.042 m2 (0.2049 ×0.2049 m) have been used. Each compartment has been divided horizontally into two chambers by wooden plate to dry six products by wooden plate. A provision has been made for keeping a thermal storage material (rock bed) between the two compartments for reducing thermal fluctuations and, thus, maintaining a constant temperature. The top of the chamber is made of glass for viewing inside the chamber. Provision has also been provided for stirring the crop in the wire mesh tray. The front of the chamber is also provided with a sliding glass to put and remove the crop for the experiments. The upper half of the last compartment has been used for keeping the crop to avoid the change in exit air properties. The heat convector was connected to the inlet of the first compartment. Thermocouples were placed at different points for measurements of crop temperature and at the exit for exit air temperature. Here also, the relative humidity of the exit air was measured with the help of a dial-type thermohygrometer. For observation of moisture removal, the crop tray was removed each time from the chamber, and after taking its weight on the electronic balance, it was placed again in its position. The experiment was repeated five times for each crop for more accuracy. The whole setup for green chillies is shown in Fig. 9.11. Before conducting the experiment, the crops were subjected to some treatment, like peeling, coring, size reduction, slicing and soaking with water, in the case of white gram. These treatments have been summarized in Table 9.4. Experimental observations for forced mode of each crop mentioned in Table 9.4 have been given in Table 9.5. The values of the constants C and n have been determined by linear

Fig. 9.11 Experimental setup for indoor simulation

270

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

regression analysis (Eq. 9.7) by using measured average data of the crop namely exit air temperatures, exit air relative humidity, and moisture evaporated during a certain time period (Tables 9.5). The results for C and n obtained for all the crops, Table 9.4, and data of Tables 9.5, have been given in Table 9.6. After knowing C and n, convective heat transfer coefficient can be determined by using Eq. (9.9) which is given in Table 9.5 for each crop. Other details of experiments and observations are available in the paper by Anwar and Tiwari [26]. Example 9.4 Evaluate Grashof (Gr) and Prandtl numbers of data of Table 9.5 for green chillies with characteristic dimension of X = 0.2049 m (Sect. 9.4.3) and first set of observation. Solution: From Sect. 8.4.1, one has the expression for Grashof and Prandtl numbers as follows: Gr =

gβ' ρ 2 X3 ΔT μ2

and Pr =

μCp K

where an expression for temperature-dependent physical properties of vapor at Ti is e , Tc and Te are crop and exit hot air temperatures, given in Sect. 9.4.1 and Ti = Tc +T 2 respectively. From Table 9.6, an average value of crop (Tc ) and exit air (Te ) temperatures are 56.30 °C and 61.95 °C respectively, then, 1 1 Ti = 56.30+61.95 = 59.125 ◦ C ∼ = 332.125 = 0.003 ◦ C−1 and = 59 ◦ C, β' = 273+T 2 i g = 9.81 m/sec2 and ΔT = 61.95 − 56.30 = 5.65 ◦ C. At Ti = 59 ◦ C, the physical properties of vapor (Sect. 9.4.1) are as follows: Density(ρ) =

353.44 = 1.06 ≈ 1 kg/m3 332.15

Table 9.4 Treatment given to crops before drying and their resulting bulk density Crop

Treatment

Bulk density (kg/m3 )

Green chillies

No treatment

280

Green peas

Grains were taken out, and only the healthy grains were selected

575

White gram

Soaked in water for 6 h to raise the moisture content to 30% (w.b.)

550

Onion

Peeled and cut with the help of slicer in the form of flakes of 2 mm thickness

450

Potato

Peeled and cut with the help of slicer in the form of slices of 2 mm thickness (average diameter 35 mm)

500

Cauliflower

The flower was cut with the knife into small pieces of 2 cm size

415

9.4 Heat and Mass Transfer

271

Table 9.5 Observations for closed heating [T c , T a and γ are average values of crop (T c ), exit air temperature (T e ), and relative humidity, γ ] T c (°C)

T e (°C)

γ (%)

Weight of crop (g)

0

55.8

61.3

25

730.3

–

15

56.8

62.6

24

726.6

3.7

56.30

61.95

24.5

30

57.8

64.4

23

720.0

6.6

57.30

63.50

23.5

45

58.1

66.0

22

710.5

9.5

57.95

65.20

22.5

60

57.7

66.7

22

700.6

9.9

57.90

66.35

22.0

75

57.4

67.1

21

691.6

9.0

57.55

66.90

21.5

90

57.2

67.4

21

684.2

7.4

57.30

67.25

21.0

105

57.1

67.7

21

675.0

9.2

57.15

67.55

21.0

120

57.1

68.0

21

667.4

7.6

57.10

67.85

21.0

135

58.4

68.3

21

656.6

10.8

57.75

68.15

21.0

150

60.9

68.6

21

641.9

14.7

59.65

68.45

21.0

0

25.5

28.8

40

698.5

–

15

30.3

36.4

45

654.1

44.4

27.90

32.60

42.5

30

34.0

41.2

60

612.0

42.1

32.15

38.80

52.5

45

36.8

42.5

55

578.4

33.6

35.40

41.85

57.5

60

40.0

47.6

44

551.2

27.2

38.40

45.05

49.5

75

38.1

49.2

28

535.6

15.6

39.05

48.40

36.0

90

37.2

50.5

26

519.8

15.8

37.65

49.85

27.0

105

39.3

49.6

25

503.0

16.8

38.25

50.05

26.0

120

40.0

49.2

16

486.6

16.4

39.65

49.40

20.5

135

40.1

47.5

15

471.7

14.9

40.05

48.35

15.5

150

40.7

50.7

14

458.5

13.2

40.40

49.10

14.5

0

28.1

55.8

45

725.6

–

15

29.0

56.6

48

708.7

16.9

28.55

56.20

46.5

30

30.8

58.3

50

688.8

19.9

29.90

57.45

49.0

45

34.4

58.8

52

664.8

24.0

32.60

58.55

51.0

60

33.7

62.3

42

636.6

28.2

34.05

60.55

47.0

75

40.4

67.7

31

610.5

26.1

37.05

65.00

36.5

90

41.4

63.3

28

586.5

24.0

40.90

65.50

29.5

105

52.6

68.7

27

565.5

21.0

47.00

66.00

27.5

120

60.0

69.1

27

545.5

20.0

56.30

68.90

27.0

135

62.2

70.2

20

528.3

17.2

61.10

69.65

23.5

Time (min)

m˙ ev (g)

T c (°C)

T e (°C)

γ (%)

Green chillies –

–

–

Green peas –

–

–

White guam –

–

–

(continued)

272

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

Table 9.5 (continued) Time (min)

T c (°C)

T e (°C)

γ (%)

Weight of crop (g)

m˙ ev (g)

T c (°C)

T e (°C)

γ (%)

150

63.5

71.9

19

506.5

21.8

62.85

71.05

20.0

0

46.8

54.7

24

625.3

–

15

47.9

55.8

25

602.4

22.9

47.35

55.25

24.5

30

49.7

56.1

36

572.2

30.3

48.80

55.95

30.5

45

50.7

56.2

31

548.9

23.2

50.20

56.15

33.5

60

50.3

56.0

28

523.5

25.4

50.50

56.10

29.5

75

48.6

56.0

28

498.3

25.2

49.45

56.00

28.0

90

49.0

56.3

25

481.5

16.8

48.80

56.15

26.5

105

49.2

55.8

24

464.6

16.9

49.10

56.05

24.5

120

49.2

55.8

23

450.7

13.9

49.20

55.80

23.5

135

51.1

58.4

22

435.3

15.4

50.15

57.10

22.5

150

53.9

59.4

22

420.4

14.9

52.50

58.90

22.0

0

44.1

56.9

32

752.4

–

15

43.4

57.7

30

732.3

20.1

43.75

57.30

31.0

30

43.3

58.5

25

718.2

14.1

43.35

58.10

27.5

45

43.2

57.9

27

696.6

21.6

43.25

58.20

26.0

60

43.8

57.1

33

673.0

23.6

43.50

57.50

30.0

75

43.6

56.1

35

650.2

22.8

43.70

56.60

34.0

90

42.2

57.1

26

631.3

18.9

42.90

56.60

30.5

105

41.8

58.1

22

607.4

23.9

42.00

57.60

24.0

120

41.6

58.7

28

581.2

26.2

41.70

58.40

25.0

135

42.0

57.7

28

562.5

18.7

41.80

58.20

28.0

150

42.8

55.4

26

543.2

19.3

42.40

56.55

27.0

0

63.2

65.8

31

733.4

–

15

59.5

67.2

28

710.7

22.7

61.35

66.50

29.5

30

58.2

68.7

26

685.8

24.9

58.85

67.95

27.0

45

52.5

65.5

24

660.5

25.3

55.35

67.10

25.0

60

55.2

63.2

19

639.4

21.2

53.85

64.35

21.5

75

53.3

59.6

18

613.4

26.0

54.24

61.40

18.5

90

49.4

64.7

17

590.3

23.1

51.35

62.15

17.5

105

46.8

66.4

18

571.3

19.0

48.10

65.55

17.5

120

44.6

68.3

17

552.2

19.1

45.70

67.35

17.5

135

43.2

69.8

17

531.3

20.9

43.90

69.05

17.0

150

43.0

69.8

16

514.0

17.3

43.10

69.80

16.5

Onion flakes –

–

–

Potato slices –

–

–

Cauliflower –

–

–

9.4 Heat and Mass Transfer Table 9.6 Values of C and n and convective heat transfer coefficient (hc ) in indoor open simulation under forced mode

273 hc (W/m2 °C)

Crop

C

n

Green chillies

1.00

0.39

1.31

Green peas

0.95

0.88

3.65

White gram

0.96

0.88

3.95

Onion flakes

0.99

0.75

4.75

Potato slices

1.00

0.72

5.40

Cauliflower

1.00

0.57

12.80

Thermal conductivity(K ) = 0.0244 + 0.0038 = 0.0283 W/m ◦ C Specific heat(C) = 999.2 + 8.439 + 0.38 − 0.018 = 1008 J/Kg ◦ C Viscosity(μi ) = 1.718 × 10−5 + 0.284 × 10−5 = 2 × 10−5

kg ms

Now, substitute the above numerical value in expression for Gr and Pr as. 2 3 −4 ×5.65 Gr = 9.81×0.003×(1) ×(0.2049) = 14.18×10 = 3.545 × 106 and Pr = 2 4×10−10 −5 (2×10 ) 2×10−5 ×1008 = 0.7123. 0.0283 Example 9.5 Calculate convective heat transfer coefficient (h c ) for Example 9.4 Solution: From Eq. (9.9) one has an expression for convective heat transfer coefficient (h c ) as hc =

Kv C(Gr.Pr)n X

where Gr = 3.545 × 106 , Pr = 0.7123, X = 0.2049 m, K = 0.0283 W/m ◦ C (Example 9.4), and C = 1.0 and n = 0.39 (Table 9.6) for green chillies Now substitute above values in the above equation, one gets

0.39

0.39 0.0283 × 1 × 3.545 × 106 × 0.7123 = 0.1381 × 2.525 × 106 0.2049 = 0.1381 × 1.425 × 218 = 42, 9 W/m2 ◦ C

hc =

But for C = 0.54 and n = 0.2522 for hot surface facing upward, the numerical value convective heat transfer coefficient (h c ) will be as follows:

0.25 0.0283 × 0.54 × 3.545 × 106 × 0.7123 0.2049 = 0.0345 × 39.86 = 2.97 W/m2 ◦ C

hc =

274

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

So one can conclude that an importance of ‘C’ and ‘n’ forms above example. Example 9.6 Calculate an evaporative heat transfer coefficient (h ew ) for Example 9.4 Solution: From Eq. (9.12) we have an expression for an evaporative heat transfer coefficient (h ew ) as h ew =

0.016 × h c P c − γ P e

Tc − Te

with P(T ) = exp 25.713 −

5144 T + 273

For Tc = 56.30 ◦ C and Te = 61.95 ◦ C, P(Tc ) = 24, 100.79 N/m2 , P(Te ) = 31, 429.43 N/m2 and γ = 24.5%, Table 9.5, an evaporative heat transfer coefficient will be calculated as follows: h ew =

0.016 × 2.97 × (24, 100.79 − 0.245 × 31, 429.43) 779.32 = 137.93 W/m2 ◦ C = |56.30 − 61.95| 5.65

So, one can be importance of an evaporative heat transfer coefficient which many folds higher than convective heat transfer coefficient.

9.5 Thermal Modeling of Single-Slope Fully Covered GiSPVT Dryer (Fig. 9.7, Section 9.3.2.1) Following Sect. 8.6 and referring Fig. 9.7a, one can write the energy balance equation for fully covered GiSPVT dryer as: (a) Semi-transparent PV module roof of GiSPVT dryer αc τg β A R S I (t) = Ut,ca (Tco − Ta ) A R S + Ub,cr (Tco − Tr )A R S + η0 τg β A R S I (t) (9.13) where, (i) Left-hand side (LHS) term = αc τg β A R S I (t) = the rate of thermal energy absorbed by solar cell of PV module and it depends on packing factor of PV module and I(t) can be evaluateed by using the program given in Appendix-D (ii) First term of right-hand side (RHS) = Ut,ca (Tco − Ta )A R S = the rate of thermal energy lost from solar cell to ambient from top glass cover (iii) Second term of right-hand side (RHS) = Ub,cr (Tco − Tr )A R S = the rate of thermal energy lost from back of solar cell to drying chamber air from bottom glass cover of PV module and (iv) Third term of right-hand side (RHS) = η0 τg β A R S I (t) the rate of DC electrical power produced by semi-transparent PV roof of GiSPVT dryer

9.5 Thermal Modeling of Single-Slope Fully Covered GiSPVT Dryer …

275

(b) Drying chamber Ub,cr (Tco − Tr )A R S + h 1 (Tc − Tr ) Ac =

4 ∑

Ai Ui (Tr − Ta ) + Q˙ e

(9.14)

i=1

where (i) The first term of right-hand side (LHS) = Ub,cr (Tco − Tr )A R S = the rate of thermal energy gain from back of solar cell to drying chamber air from bottom glass cover of PV module, (ii) The second term of right-hand side (LHS) = h 1 (Tc − Tr )Ac = the rate of total thermal energy (convection, radiation, and evaporation) gain from crop of tray to drying chamber air, 4 ∑ (iii) The first term of right-hand side (RHS) = Ai Ui (Tr − Ta ) = the rate of i=1

thermal energy lost from all glazed wall side and Q˙ e = 0.33N V (Tc − Ta ), natural mode of operation and, Q˙ e = m˙ e Ce (Tc − Ta ), forced mode, forced mode of operation where N is the number of air change and its value is always less than 10 for natural mode of operation and m˙ e mass flow rate of exit air from GiSPVT sryer. (c) Crop tray of GiSPVT system αc τg2 (1 − β)A R S I (t) + τg

4 ∑

A j I j = Mc C c

j=1

dTc + h 1 (Tc − Tr ) Aw P dt

(9.15)

where (i) The first term in LHS = τg2 (1 − β) A R S I (t) = The direct gain absorbed by crop through non-packing are of semi-transparent PV roof ∑ (ii) The second term in LHS = τg 4j=1 A j I j = Transmitted direct gain through glazed walls and (iii) The second term in RHS = h 1 (Tc − Tr )Aw P = = the rate of total thermal energy (convection, radiation, and evaporation) loss from crop of tray to drying chamber air, Eqs. (9.13) to (9.15) can be solved for solar cell, GiSPVT chamber air, and crop temperatures as done in Chap. 8 (Sect. 8.6). Example 9.7 Derive expressions for solar cell (Tco ) and GiSPVT chamber air (Tr ) temperatures by using Eqs. (9.13) and (9.14), respectively. Solution: From Eqs. (9.13) and (9.14), one has

276

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

Tco =

(ατ )e f f I (t) + Ub,cr Tr + Ut,ca Ta

Ut,ca + Ub,cr

(E-9.1)

with (ατ )e f f = (αc − η0 )τg β I and,

∑ 4 Ub,cr A R S Tco + (h 1 Ac − m˙ e Ce )Tc + ˙ e Ce Ta i=1 Ai Ui + m ∑

Tr = 4 i=1 Ai Ui + h 1 Ac + Ub,cr A R S

∑ 4 A U + m ˙ C (h 1 Ac − m˙ e Ce )Tc + e e Ta i=1 i i ∑

= P F 1 Tco + with 4 i=1 Ai Ui + h 1 Ac + Ub,cr A R S Ub,cr A R S

P F 1 = ∑ 4 i=1

Ai Ui + h 1 Ac + Ub,cr A R S

Substituting an expression of Tco in the above equation, we get (ατ )e f f I (t) + Ub,cr Tr + Ut,ca Ta

Ut,ca + Ub,cr

∑ 4 ˙ e Ce Ta (h 1 Ac − m˙ e Ce )Tc + i=1 Ai Ui + m ∑

+ 4 A U + h A + U A i i 1 c b,cr R S i=1

Tr = P F 1

or, 

 (ατ )e f f I (t) + Ut,ca Ta Ub,cr

Tr = P F 1

1 − P F1 Ut,ca + Ub,cr Ut,ca + Ub,cr

∑ 4 Ta A U + m ˙ C (h 1 Ac − m˙ e Ce )Tc + i i e e i=1

∑ + 4 i=1 Ai Ui + h 1 Ac + Ub,cr A R S If, P F 2 = ∑ 4

(h 1 Ac − m˙ e Ce ) Ai Ui + h 1 Ac + Ub,cr A R S ∑

4 A U + m ˙ C i i e e i=1

and

i=1

P F 3 = ∑ 4

i=1

then,

Ai Ui + h 1 Ac + Ub,cr A R S

9.5 Thermal Modeling of Single-Slope Fully Covered GiSPVT Dryer …

Tr =

P F1

(ατ )e f f I (t)+Ut,ca Ta (Ut,ca +Ub,cr )

 1 − P F1

+ P F 2 Tc + P F 3 Ta 

Ub,cr (Ut,ca +Ub,cr )

277

(E-9.2)

From above equation, one can determine the GiSPVT chamber air (Tr ) temperature for a given hourly climatic and design parameters for known hourly crop temperature (Tc ). Then hourly solar cell (Tco ) temperature can be determined for evaluated GiSPVT chamber air temperature (Tr ) from Eq. (E-9.1). Example 9.8 Derive an expression for crop temperature (Tc ) of GiSPVT dryer discussed in Example 9.7. Solution: From Eq. (E-9.2) of Example 9.7, one can write Tc − Tr = Tc −

P F1

(ατ )e f f I (t)+Ut,ca Ta (Ut,ca +Ub,cr )

 1 − P F1

+ P F 2 Tc + P F 3 Ta  Ub,cr

(Ut,ca +Ub,cr )

Or,

Tc − Tr =

 Tc 1 − P F 2 − P F 1

Ub,cr (Ut,ca +Ub,cr )



  (ατ ) I (t)+U T − P F 1 Ue f f +U t,ca a + P F 3 Ta ( t,ca b,cr ) 

 1 − P F1

Ub,cr

(Ut,ca +Ub,cr )

Substitute Above Expression in Eq. (9.15), We Got 4 ∑

dTc dt j=1     (ατ ) I (t)+U T b,cr − P F 1 Ue f f +U t,ca a + P F 3 Ta Tc 1 − P F 2 − P F 1 U U+U ( t,ca b,cr ) ( t,ca b,cr )   + h 1 Aw P Ub,cr 1 − P F 1 U +U ( t,ca b,cr )

αc τg2 (1 − β) A R S I (t) + τg

A j I j = Mc C c

The above equation can be rewritten as follows: dTc + aTc = f (t) dt where   Ub,cr 1 − P F − P F 2 1 h 1 Aw P (Ut,ca +Ub,cr )   a= Ub,cr Mc C c 1 − P F1 U +U ( t,ca b,cr ) and

(E-9.1)

278

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

  ∑ αc τg2 (1 − β) A R S I (t) + τg 4j=1 A j I j + f (t) =

h 1 Aw P P F 1

(ατ )e f f I (t)+Ut,ca Ta

(

Ut,ca +Ub,cr

1− P F 1

)

Ub,cr

 + P F 3 Ta 

(Ut,ca +Ub,cr )

Mc C c

Equation (E-9.1) is one-order differential equation which solution for crop temperature (T c ) can be written as Tc =

f (t) 1 − e−at + T ci e−at a

with the following assumption: (i) The ‘a’ is constant parameter during 0-t time interval, (ii) I(t) and T a have been considered as average value during 0-t time interval, and (iii) T c = T ci at t = 0. Now an analytical expression for Tc can be written as 

αc τg2 (1 − β)A R S I (t) + τg

Tc =

∑4 j=1



Aj Ij +

 h 1 Aw P 1 − P F2 − P F1



1 − e−at + T ci e−at

h 1 Aw P P F 1

(ατ )e f f I (t)+Ut,ca Ta

(Ut,ca +Ub,cr )

1− P F 1 Ub,cr (Ut,ca +Ub,cr )



Ub,cr

 + P F 3 Ta 

(Ut,ca +Ub,cr )

(E-9.2)

Problems 9.1. Evaluate hourly beam/direct radiation falling on roof of single-slope GiSPVT dryer by using the data of Table 9.2b. Hint: Example 9.1 9.2. Evaluate total solar radiation on inclined roof of GiSPVT (Fig. 9.7a) at angle of 25° for data of Table 9.2b with ground reflectivity (ρ) of 0.2 Hint: By using Eq. (1.13) (Chap. 1). 9.3. Evaluate hourly direct gain through roof of single-slope GiSPVT dryer for Fig. 9.7b and Table 9.2b for different packing factor of 0.20, 0.50, and 1.0. Hint: Example 9.2 9.4. Compute an electrical efficiency of all PV module of Table 4.3a of GiSPVT dryer by using the data of Table 9.7b. Hint: Example 9.3 and Table 4.3 9.5. Compute physical properties of moist air at 30 °C, 50 °C, 70 °C, and 100 °C and find out which physical property is sensitive. Hint: Use expressions given in Eq. (9.2) 9.6. Compute Grashof (Gr) and Prandtl numbers at 30 °C, 50 °C, 70 °C, and 100 °C of with characteristic dimension of X = 0.2049 m (Sect. 9.4.3). Hint: Example 9.4.

9.5 Thermal Modeling of Single-Slope Fully Covered GiSPVT Dryer …

279

9.7. Compute Grashof (Gr) and Prandtl numbers at 50 °C with characteristic dimension of X = 0.20, 0.40, 0.6, and 1.00 (Sect. 9.4.3) and compare the results Hint: Example 9.4 9.8. Compute convective heat transfer coefficient (h c ) for Problem 9.7 for C = 0.54 and N = 1/3 and see the effect of n on convective heat transfer coefficient (h c ). Hint: Example 9.5 9.9. Compute an evaporative heat transfer Coefficient (h ew ) for Problem 9.8 Hint: See Example 9.6 9.10. Repeat Examples 9.7 and 9.8 respectively for Q˙ e = 0.33N V (Tc − Ta ), natural mode of operation for solar cell (T co ), GiSPVT drying chamber air (Tr ), and Crop Temperatures (T c ). Hint: Follow Examples 9.7 and 9.8 Objective Questions 9.1. Solar radiation is dominating in case of (a) For blue sky condition; (b) Cloudy condition; (c) Hazy condition and (d) In all condition Answer: (a) 9.2. The GiSPVT dryer will better performance in the case of packing factor is (a) Maximum; (b) Zero; (c) One and (d) 0.5 Answer: (a) and (b) 9.3. What is the optimum inclination of single roof of GiSPVT for summer condition? (a) Latitude angle; (b) Latitude angle +15°; (c) Latitude angle −15° and ±15° Answer: (c) 9.4. What is the optimum inclination of single roof of GiSPVT for winter condition? (a) Latitude angle; (b) Latitude angle +15°; (c) Latitude angle −15° and ±15° Answer: (b) 9.5. What is the optimum annual inclination of single roof of GiSPVT? (a) Latitude angle; (b) Latitude angle +15°; (c) Latitude angle −15° and ±15° Answer: (a) 9.6. Which PV module is best for GiSPVT dryer? (a) Opaque; (b) Semi-transparent; (c) Flexible and (d) Semi-transparent thin film Answer: (b) and (d) 9.7. Out of convective and evaporative heat transfer coefficient, which one is significant?

280

9.8.

9.9.

9.10.

9.11.

9 Thermal Modeling of GiSPVT Solar Dryer: Quasi-Steady State Analysis

(a) Convective heat transfer coefficient (b) Evaporative heat transfer coefficient (c) Both convective and evaporative heat transfer coefficient (d) All of them Answer: (c) For single-slope GiSPVT dryer, the orientation of roof should be (a) South oriented; (b) East oriented; (c) West oriented and North oriented Answer: (a) Drying time and quality of dried product is better for (a) Open sun drying; (b) Cabinet dryer; (c) Mixed mode dryer and (d) Indirect dryer Answer: (c) and (d) The color of crop is retained in (a) Open sun drying; (b) Cabinet dryer; (c) Mixed mode dryer and (d) Indirect dryer Answer: (c) and (d) The dried crop is hygienic in (a) Open sun drying; (b) Cabinet dryer; (c) Mixed mode dryer and (d) Indirect dryer Answer: (b), (c) and (d)

References 1. Anon (2004) The state of food insecurity in the world 2004. Food and agriculture organization of the United Nations. Viale delle Terme di Caracalla, 00100 Rome, Italy 2. Tiwari GN (2004) Solar energy: fundamental, design, modelling and applications. Narosa Publishing House, New Delhi and CRC Press, New York 3. lmre L, Palaniappan C (1996) Drying Technol: Int J 14(6):1381 4. Szulmayer W (1971) Food Technol Aust 23:440 5. Sodha MS, Dang A, Bansal PK, Sharma SB (1985) Energy Convers Manage 25(3):263 6. Sodha MS, Chandra R (1994) Energy Convers Manage 35(3):219 7. Esper A, Mühlbauer W (1998) Renew Energy 15:95 8. Lutz K, Muhlbauer W, Muller J, Reinsinger G (1987) Sol Wind Technol 4(4):417 9. Mulet A, Berna A, Rossello C, Canellas J (1993) Drying Technol: Int J 11(6):1385 10. Oztekin S, Bascetincelik A, Sosyal Y (1999) Renew Energy 16:789 11. Koyuncu T (2006) Renew Energy 31(7):1055 12. Zaman MA, Bala BK (1989) Sol Energy 42(2):167 13. Arata A, Sharma VK, Spagna G (1993) Energy Convers Manage 34(5):417 14. Budin R, Mihelic-Bogdanic A (1994) Energy Convers Manage 35(2):97 15. Chua KJ, Chou SK (2003) Trends Food Sci Technol 14(12):519 16. Ekechukwu OV, Norton B (1999) Energy Convers Manage 40:593 17. Tiwari GN, Ghosal MK (2005) Renewable energy resources: basic principles and applications. Narosa Publishing House, New Delhi, India 18. Tiwari GN, Kumar S, Prakash O (2004) J Food Eng 63:219 19. Manohar KR, Chandra P (2000) Int Agric Eng J 9(3):139

References

281

20. Jain D, Tiwari GN (2004) Energy Convers Manage 45:765 21. M.A.S. Malik, G. N. Tiwari, A. Kumar, and M.S. Sodha, Solar Distillation, Pergamon Press Ltd., U.K., 1982 22. Tiwari GN (2016) Arvind Tiwari and Shyam. Springer, Handbook of Solar Energy 23. Tiwari S (2013) Thermal modeling of PVT dryer: a heat and mass transfer approach, Ph.D. Thesis, IIT Delhi 24. Singh AK (2012) Performance evaluation of mixed mode and greenhouse PVT dryer, Ph.D. Thesis, IIT Delhi 25. Kumar A (2012) Drying of medicinal/vegetables products by PVT greenhouse dryer, Ph.D. Thesis, IIT Delhi 26. Anwar SI, Tiwari GN (2001) Convective heat transfer coefficient of crops in forced convection drying—an experimental study. Energy Convers Manage 42:1687–1698

Chapter 10

Thermal Modeling of Greenhouse Integrated Semi-transparent Photo-Voltaic Thermal (GiSPVT) System: A Periodic Analysis

10.1 Background Solar thermal, photo-voltaic, and photo-voltaic thermal (PVT) system can be analyzed by following method.

10.1.1 Steady-State Thermal Analysis In this case, it is evaluating the thermal equilibrium performance of solar energybased any thermal system in which the operating temperature (T ) remains constant =0 . over time period dT dt For example, consider Eq. 8.9a, the correct energy balance in W/m2 of c-Si semitransparent PV east roof at a time is as follows: i=3

αc τg β

i=3

A i Ii = Mc C c i=1

i=3

dTci + Ut,ca (Tci − Ta ) Ai + Ub,cr (Tci − Tr ) Ai dt i=1 i=1 i=3

+ η0 τg β

A i Ii

(10.1)

i=1

The first term in left hand side can be evalauted by using Appendix-D and the term Mc Cc dTdtci in Eq. 10.1 is defined as rate of thermal energy stored in c-Si solar cell material with Cc as specific heat of solar cell material and dTdtci as temperature gradient in solar cell material. The term Mc Cc dTdtci will be zero if (i) Either specific heat, Cc , of c-Si solar cell material is considered as negligible due to high thermal conductivity of solar cell material, i.e., one of the assumptions. © Bag Energy Research Society 2023 G. N. Tiwari, Advance Solar Photovoltaic Thermal Energy Technologies, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4993-9_10

283

284

10 Thermal Modeling of Greenhouse Integrated Semi-transparent …

(ii) The temperature gradient dTdtci is zero due to negligible temperature rise in solar cell material. In all conducting materials, the temperature gradient is considered as zero. The above condition satisfies the steady-state condition, and hence, Eq. 8.9 has been considered as energy balance in a steady-state condition.

10.1.2 Transient Analysis It is the analysis of solar energy-based any thermal system during the time it changes /= 0 . It can from one steady-state condition to another steady-state condition dT dt be applied for linear as well as nonlinear behavior of thermal system such as cloudy condition. In this case, initial condition of the system should be known. Consider Eq. 8.12 as ⎡ U00 T00 − Tp Af + Fs τg2 (1 − β)⎣

A j I j ⎦ + τg

A i Ii + i=1

= Mp C p

⎤

j=3

i=3

j=1

dTp + h 1 Tp − Tr Ap dt

In Eq. 10.2, one cannot neglect the term Mp Cp

k=4

A k Ik k=1

(10.2) dTp dt

due to two reasons, namely

(i) Heat capacity of plant Mp Cp which is equivalent to heat capacity of water due to maximum water content in plant

dT (ii) The temperature gradient dtp of plant can also be not neglected due to temperature rise per unit time of plant. Further, above equation can be rewritten from Eq. 8.19 as dTw + aTw = f (t) dt

(10.3)

where f (t)  

τg2 (1 − β)ARS + P F2 ARS (ατ )eff I (t) + τg 3j=1 A j I j + (U A)wa + 5k=1 Ak Uk Ta = Mw C w

(10.3a)

and

(U A)wa + 5k=1 Ak Uk a= Mw C w

10.1 Background

285

Equation 10.3 is a nonlinear one-order deferential equation in transient condition because f (t) is a function of time which depends on solar intensity and ambient air temperature and dTdtw /= 0. Equation 10.3 can be solved by many ways, namely Laplace transform, numerical methods, etc., with known initial condition but not analytical one. Since Laplace transforms/numerical methods are a complex method, hence one considers quasi-steady-state analysis to get analytical solution.

10.1.3 Quasi-steady-State Condition It combines characteristic advantages of steady-state and transient techniques but avoids major drawbacks of both these classes of methods. As mentioned above, quasi-steady-state analysis is carried out with mainly two assumptions in solar energy system which is as follows: (i) Climatic parameters which are unstable are considered as average value between time interval of 0–t. For this, the function f (t) should be considered as constant by considering its average value between 0–t time interval, so Eq. 10.3 becomes one-order simple differential equation. (ii) All heat transfer coefficient involved in ‘a’ and f (t) is also considered as constant due to negligible variation in their physical properties during 0–t time interval. In this case, Eq. 10.3 can be solved analytically as done in Sect. 8.6.1

10.1.4 Periodic Condition It is a function [solar radiation, I(t); ambient air condition, Ta ; wind velocity; and other climatic parameters] that repeats itself at regular intervals, may be in days, month, and year. In this case, there is no need of initial condition just like in transient and quasi-steady-state condition. Since climatic input parameters, namely solar radiation, I(t); ambient air condition, Ta , repeat approximately same in a number of days and month, and hence it can be expressed in periodic form as follows: 6

In ei (nωt−σn )

(10.4a)

Tan ei (nωt−ψn )

(10.4b)

I (t) = I0 + Re n=1

and 6

Ta = Ta0 + Re n=1

286

10 Thermal Modeling of Greenhouse Integrated Semi-transparent …

where I 0 and T a0 are time-independent part and I n and T an are time-dependent part of Fourier coefficients of solar intensity and ambient air temperature. The derivation of Fourier coefficient of a periodic function, f (t), and programming for evaluating these constants are given in Appendix E. Since input parameters such as solar intensity, I(t), and ambient air temperature, T a , are in periodic form, hence all output parameters such as solar cell (T c ), room air (T a ), and plant (T p ) temperature in greenhouse integrated semi-transparent photovoltaic thermal (GiSPVT) will be in periodic form. In this case, no initial conditions of any parameters are required. This is advantage of periodic model over other techniques to solve many order nonlinear coupled one-order differential equation. In periodic modeling of GiSPVT system, one can even consider the heat capacity term of solar cell and glass material and greenhouse room air, etc. Periodic modeling is most preferred modeling for heavy-structured solar thermal system such as building and underground greenhouse structure, etc. Example 10.1 Solve Eq. 10.3 for water temperature (T w ) for periodic climatic condition by using Eq. 10.4. Solution Since climatic conditions, namely I(t) and T a , are periodic in nature, hence f (t) can be expressed mathematically as 6

f n e(inωt−φn )

f (t) = f 0 +

(E.1)

n=1

where f 0 , f n , and φn are Fourier constants, and these can be obtained by the having hourly values of f (t) from Eq. E.1 from hourly data of I(t) and T a . Further, the water temperature T w can also be expressed in periodic form due to periodic nature of climatic data, Eqs. 10.4a and b, as 6

Tw = Two +

Twn einωt

(E.2)

n=1

With the help of Eqs. E.1 and E.2, time independent and time dependent of Eq. 10.3 can be written as follows: aTw0 = f 0 ≈ Tw0 =

f0 a

and inωe−iφn Twn + aTwn = f n e−i φn ≈ Twn =

f n e−iφn a + inωe−iφn

10.2 Introduction

287

Substituting the above expression in Eq. 10.4b, one gets 6

f n e−i φn f0 + Real Tw = einωt −i φn a a + inωe n=1

(E.3)

Above equation can be computed by knowing the value of Fourier coefficients, namely f 0 , f n , and φn . In this case, there is no need of any initial condition unlike transient and quasi-steady-state condition.

10.2 Introduction Greenhouse offers a possibility of crop production in adverse hot climatic conditions as it provides a favorable micro-controlled environment for plant growth. The environment inside the greenhouse is maintained by suitable heating or cooling of greenhouse room air as per requirement. In the hot climatic condition, the ambient air temperature and greenhouse air temperature rise to an undesirable level during summer days that adversely affect plant growth. In desert areas, the ambient air temperature reaches 50–65 °C during summer, which makes the greenhouse unfit for plants [1]. Many researchers investigated alternative means for cooling the greenhouse air temperature to a desirable level for plant growth. The amount of solar radiation permitted inside a greenhouse has been controlled by shading provided through nets of different colors, external shade cloths, and reflective shade screens. Ilic et al. [2] studied the effect of external shading nets having different colors on crop yield and quality. It was concluded that the crop yield increased by 18.5% by using red and pearl nets with 40% relative shading. In a similar study [3], the greenhouse air temperature was reduced by 5 °C by applying NIR-cut nets during a sunny day in summer. Ahmed et al. [4] investigated the cooling effects of shading on a greenhouse’s microclimate to find the best shading method for hot and arid regions. The study revealed that the application of shading methods such as whitewash and shade netting, along with other cooling methods such as evaporation cooling and natural ventilation, can decrease the indoor air temperature up to 10 °C, increase the humidity by up to 20%, and reduce solar irradiation up to 50%. As another alternative, the considerable thermal energy storage of earth can also be utilized as a heat source for heating or heat sink for cooling with the help of air flowing through a buried pipe system, and this system is known as earth air heat exchanger (EAHE) [5–9]. EAHE uses the constant annual earth temperature available inside the earth at a particular depth. This particular depth inside the ground depends on the water level, physical properties of soil, and the cost of digging. The value of particular depth corresponding to constant annual ground temperature for different locations as reported in the literature is presented in Table 10.1. The ground temperature

288

10 Thermal Modeling of Greenhouse Integrated Semi-transparent …

mentioned in Table 10.1 can be reasonably utilized for heating and cooling of greenhouse enclosed space during winter and summer, respectively. EAHE utilizes PVC pipes to carry air at particular depths inside the ground, and the air gets heated or cooled according to the ambient condition. EAHE can be classified as closed-loop EAHE or open-loop EAHE. In closed-loop EAHE, both inlet and outlet of EAHE are directly connected with the greenhouse enclosed space [10–14]. However, in openloop EAHE, the inlet is connected with the ambient, while the outlet is connected with the greenhouse [15–21]. Chiesa et al. [22] discussed 3 key performance indicators (KPI) to analyze the early phase potential of the EAHE technology to cover the expected building energy demand. These three KPIs include activation hours based on a psychrometric chart, calculation of expected sensible heat exchange of the system, and estimation of COP of the system. Ghosal et al. [23] experimentally investigated the heating and cooling potential of an EAHE coupled with the greenhouse located at IIT Delhi, India. The greenhouse temperature coupled with EAHE was found to be 7–8 °C higher during winters and 5–6 °C lower during the summer when compared with the temperature of a conventional greenhouse. Further, the operating hours of an EAHE were optimized on the basis of its heating/cooling potential [24]. Ghosal et al. [25] carried a parametric study to find the influence of EAHE parameters on greenhouse air temperature. It was concluded that the increase/decrease of greenhouse air temperature during winters/summer is directly proportional with pipe length and inversely proportional to the pipe diameter. The influence of mass flow rate of air flowing through the pipes and soil depth on cooling potential of an EAHE under real climatic condition in Greece was studied by Mihalakakou et al. [26]. The cooling potential of the EAHE increases with increase in mass flow rate and soil depth. Wu et al. [27] proposed a transient and implicit model based on numerical heat transfer and computational fluid dynamics to predict the thermal performance of an EAHE. It was reported that the outlet temperature of EAHE follows the variation of ambient temperature, and the cooling capacity of EAHE increases with increase in pipe length. Moreover, for a holistic assessment of greenhouse coupled with EAHE, both energy and exergy should be evaluated to check the self-sustainability of the system [28]. Table 10.1 Ground temperature at different depth Location

Depth (m)

Constant ground temperature (°C)

Tabasco, Mexico (Diaz Hernandez et al. [37])

2.5

27

Rio Grande, Brazil (Hermes et al. [18])

2.0

18.7

Bhopal, India (Bisoniya et al. [38])

2.0

25.0

New Delhi, India (Bhardwaj et al. [39])

4.0

29.0 (dry exposed surface) 19.0 (wet exposed surface) 17.0 (wet shaded surface)

Shouguang, China (Wang et al. [40])

3.6

17.6

10.3 Design of Uneven GiSPVT with Partition with Porous Green Jute Net

289

Energy and exergy of a greenhouse integrated with a PVT system were carried out by Nayak and Tiwari [29], and the exergy efficiency of the system was reported to be 4%. Further, they have also evaluated the exergy of greenhouse integrated with both PVT and EAHE under the quasi-steady-state assumption for different weather types of Delhi, India. The authors reported the yearly thermal energy, net electrical energy, and thermal exergy as 24,728.8, 805.9, and 1006.2 kWh. Ajmi et al. [30] developed a theoretical model for predicting the cooling potential of an earth air heat exchanger integrated with domestic buildings in the desert climate of Kuwait. It was reported that the indoor temperature of the building was reduced by 2.8 °C for an air mass flow rate of 100 kg/h which resulted in a reduction of 420 kWh in the cooling demand for July. Multi-objective optimization of a hybrid building integrated photovoltaic/thermal (BIPVT) system combined with an earth air heat exchanger (EAHE) on the basis of annual total energy and exergy output was carried out by Li et al. [31]. The annual energy and exergy of the system were found to be 96,448.6 kWh and 10,015.5 kWh, respectively. Ozgener et al. [11] computed the exergy of an underground air tunnel system for cooling greenhouse under steady-state conditions to identify process efficiencies and losses. In the open literature, analytical models for greenhouses have been developed in a quasi-steady-state condition which requires knowledge of the initial condition (Sect. 10.1.3). However, the periodic analysis (Sect. 10.1.4) should be used to analyze any thermal system as the system exhibits periodic behavior in the long run. The periodic analysis does not require any known initial condition, and it holds good for a typical day and can also be extended to evaluate the system’s monthly performance. In the present chapter, periodic modeling of a semi-transparent photovoltaic thermal (SPVT) greenhouse system combined with an earth air heat exchanger (EAHE) has been developed on basic energy balance equations. A green net is provided beneath the semi-transparent photovoltaic roof of the SPVT greenhouse system to cut the solar radiation incident on the plants. The matrix inversion method is used to solve the time-dependent and time-independent coefficients of the energy balance equations in order to calculate hourly PV cell temperature, zone-1/zone-2 greenhouse air temperature, and plant temperature. The hourly exergy of the SPVT greenhouse system combined with EAHE is also carried out along with thermal load leveling (TLL) and decrement factor (DF) for a comprehensive performance assessment on a typical harsh summer day.

10.3 Design of Uneven GiSPVT with Partition with Porous Green Jute Net An uneven span-type greenhouse integrated with a semi-transparent photovoltaic thermal (SPVT) system is proposed to cultivate plants in the hot climatic condition of Saudi Arabia (φ = 24.72°). The south roof of greenhouse is integrated with semi-transparent PV modules which cause direct (through the non-packing area) and

290

10 Thermal Modeling of Greenhouse Integrated Semi-transparent …

indirect gain (from the back of the PV module) of solar energy to plants as shown in Fig. 10.1a. The proposed greenhouse system will be referred as greenhouse integrated photo-voltaic thermal (GiSPVT) system, Chap. 8. North roof and side walls of the greenhouse are made up of transparent glass, contributing to the direct gain of solar radiation that is sufficient for plants’ photosynthesis. Solar radiation incident on sloped roof and side walls is computed by following Liu and Jordan model [32]. A porous green jute net is provided beneath PV roof for cutting the excessive solar radiation reaching inside GiSPVT. The green net bifurcates the enclosed space of GiSPVT greenhouse system into zone-1, which is below the roof, and zone-2, which is above the plants. The air temperature of zone-2 is conditioned by heating/ cooling provided by earth air heat exchanger (EAHE), which utilizes the geothermal energy at a shallow depth. If the plant temperature becomes more than the zone-2 air temperature, heat losses occur from the plant surface by convection, radiation, and evaporation to zone-2 and vice-versa. Further, there are heat losses from semitransparent PV south roof, north roof, and side walls to the ambient. All of the heat transfers indicated in Fig. 10.1 are quantified by suitable heat transfer coefficients, and these are discussed in detail in the mathematical modeling section. The zone-2 air temperature and plant temperature of the GiSPVT system constructed in hot climatic conditions become very high during the summer months because of high ambient air temperature. Hence, it is required to bring down the plant temperature and zone-2 temperature within the optimum temperature range for plant growth, i.e., 30–37 °C. To reduce the temperature of plants/zone-2 of GiSPVT system, forced ventilation of air, i.e., air changes in zone-1, is provided by an exhaust fan. The temperatures are further reduced by integrating an earth air heat exchanger (EAHE) into the GiSPVT system (Chap. 7). It is economical to use EAHE below the greenhouse floor area before constructing the SPVT greenhouse system to avoid additional land requirements. It is better to use a heat exchanger in series and parallel combinations, as shown in Fig. 10.1b and Fig. 8.12 because the energy requirement for heating/cooling of greenhouse air is considerable. The series connection of PVC pipes depends upon the mass flow rate. The mass flow rate can be optimized by either increasing the pipes’ diameter or increasing the flowing air velocity. The design parameters of the GiSPVT system integrated with the EAHE system, as shown in Fig. 10.1c, are given in Table 10.2.

10.4 Periodic Thermal Mathematical Modeling of GiSPVT Following assumptions have been made for hot climatic condition to analyze the proposed system. (i) The flow in earth air heat exchanger (EAHE) is laminar (not turbulent). (ii) There is no stratification of greenhouse air due to the forced mode of operation. (iii) The physical properties of materials, including ground soil, PV module, air, etc., do not change the system’s operating temperature range of GiSPVT.

10.4 Periodic Thermal Mathematical Modeling of GiSPVT

291

Fig. 10.1 a Cross-sectional view of GiSPVT with two zones. c View of integrating earth air heat exchanger with zone-1 of GiSPVT

292

10 Thermal Modeling of Greenhouse Integrated Semi-transparent …

Table 10.2 Design parameters of GiSPVT and EAHE Af

288.0 m2

Kc

1.1 W/m °C

Ui

3.5 W/m2 °C

AE = AW

37.12 m2

L

11.0 m

Uf

1.0 W/m2 °C

AN = AS

44.67

m2

Lc

0.003 m

Ut,ca

9.17 W/m2 °C

Arn

83.97

m2

M2

655 kg

V1

177.0 m3

Ars

245.05 m2

ns

13

V2

535.0 m3

np

20

αc

0.9

N1

30

αP

0.25

m2

AP

288.0

Ca

1012 J/kg °C

CP

4912 J/kg °C

N2

0

βref

0.0045

hi

5.7 W/m2 °C

r

0.0762 m

ρa

1.2 kg/m3

h0

9.5

W/m2

°C

T00

25.0 °C

τg

0.9

ha

2.8

W/m2

°C

Tref

25.0 °C

τn

0.5

hP

13.69 W/m2 °C

Ub,cr

3.67 W/m2 °C

η0

0.15

(iv) As the sky condition is clear, diffuse radiation has been assumed to be 10% of total radiation, and this has been validated by Tiwari et al. [33, 34]. (v) The whole system is in periodic condition. (vi) Heat capacity of each components of GiSPVT system has been considered negligible. Following Sect. 8.6, energy balance equations of each component of GiSPVT system (Fig. 10.1) combined with EAHE are as follows: (a)

For semi-transparent PV south roof: αc τg βc Ars I (t) = Ut,ca (Tc − Ta )Ars + Ub,cr1 (Tc − Tr ) Ars + η0 τg βc Ars I (t) (10.5) where Ut,ca and Ub,cr1 are overall top heat loss coefficient from PV cell to ambient and overall bottom heat loss coefficient from PV cell to zone-1, respectively, Example 8.4. Other constants are defined in Sect. 8.4 (Eqs. 8.9a, 8.13a). Mathematically, these are defined here as given below.  Ut,ca =

(b)

Lc 1 + h0 Kc

−1

 ; Ub,cr1 =

1 Lc + hi Kc

−1 (10.5a)

For zone-1 of greenhouse: Ub,cr1 (Tc − Tr1 )Ars + τg2 (1 − βc )(1 − τn )Ars I (t) = 0.33N1 V1 (Tr1 − Ta ) + A5 U5 (Tr1 − Ta )

(10.6)

where A5 and U5 are area of the north roof and overall heat transfer coefficient from zone-1 room air to ambient through north roof, respectively. τn is the

10.4 Periodic Thermal Mathematical Modeling of GiSPVT

293

transmittivity of green net that divides zone-1 which is below roof and zone-2 which is above plants. (c) For zone-2 greenhouse: Q˙ u,ex + Ur1,r2 (Tr1 − Tr2 ) An + h P (TP − Tr2 ) AP 4

=

Ai Ui (Tr2 − Ta ) + 0.33N2 V2 (Tr2 − Ta )

(10.7)

i=1

where Ur1,r2 is the overall heat transfer coefficient between zone-1 and zone-2 and n p is number of pipes connected in series in EAHE. Ur1,r2 is defined as given below  Ur1,r2 =

Ln 1 1 + + 2.8 Kn 2.8

−1 (10.7a)

‘ Q˙ u,ex ’ is the rate of useful thermal energy from serpentine tube EAHE buried in the ground below SPVT greenhouse system, and following Eq. 8.34a, it can be written as follows: Q˙ u,ex = FR (T00 − Tr 2 )

(10.7b)

‘FR ’ is heat removal factor of an earth air heat exchanger (EAHE), and it is expressed as below 



−n s (2πr L)h a FR = εm˙ a Ca 1 − exp m˙ a Ca

 (10.7c)

where ‘ε’ is the effectiveness of EAHE; ‘h a ’ is the heat transfer coefficient from ground to air flowing through pipe; ‘n s ’ is the number of pipes connected in series; and ‘L’& ‘r ’ are the length of pipe connected in series and radius of pipe, respectively. If such heat exchangers are connected in ‘n p ’ parallel columns, then resultant rate of useful thermal energy is given as below Q˙ u,ex = n p FR (T00 − Tr2 )

(10.7d)

(d) For plants: Af Uf (T00 − TP ) + αP τn τg2 (1 − βc )Ars I (t) 3

+ αP τg

Ai Ii − h P (TP − Tr2 )AP = MP CP i=1

dTP dt

(10.8)

Since, solar radiation and ambient air temperature are periodic in nature. Hence, these can be expressed in terms of Fourier coefficients [34] and

294

10 Thermal Modeling of Greenhouse Integrated Semi-transparent …

Sect. 10.1.4 as written below 6

In ei(nωt−σn )

(10.9a)

Tan ei(nωt−ψn )

(10.9b)

I (t) = I0 + Re n=1 6

Ta = Ta0 + Re n=1

6

( AI )Tn ei (nωt−φn )

( AI )T = (AI )T0 + Re

(10.9c)

n=1

where I0 , Ta0 , and ( AI )T0 are time-independent constants and In , σn ; Tan , ψn ; and (AI )Tn , φn are time-dependent Fourier constant of solar intensity I (t), ambient Ta , Appendix-F and effective total solar intensity incident on air temperature 3 Ai Ii , respectively. walls (AI )T = i=1 Further, 3

(AI )T =

6

(AI )Tn ei(nωt−φn )

A j I j = (AI )T0 + Re

(10.9c)

n=1

j=1

These coefficients on a typical day of harsh summer month (June 29, 2020, Saudi Arabia) are presented in Table 10.3 (Appendix E). Since the input climatic parameters of GiSPVT system (Eq. 10.9) are periodic in nature, so output results of solar cell (Tc ), greenhouse air (Tr1 and Tr2 ), and plant (Tp ) temperatures will also be periodic in nature, and these can be expressed as follows: Table 10.3 a Fourier constant of solar radiation, b Fourier constant of ambient air, c Fourier constant of effective solar radiation (a) n

0

1

2

3

4

5

6

In

285.49

435.97

176.85

15.17

29.96

20.32

13.79

3.32

0.30

3.60

2.99

6.28

5.96

σn (b) n

0

1

2

3

4

5

6

Ta n

40.91

7.70

0.96

0.72

0.28

0.47

0.15

3.72

0.19

0.40

0.11

3.78

5.81

ψn (c) n

0

1

2

3

4

5

6

(AI )T n

17,457.0

20,990.29

8008.15

9146.27

1536.60

4327.48

2503.76

3.82

2.85

0.92

0.38

5.15

3.89

φn

10.4 Periodic Thermal Mathematical Modeling of GiSPVT

295

6

Tc = Tc0 + Re

Tcn einωt

(10.10a)

Tr1n einωt

(10.10b)

Tr2n einωt

(10.10c)

TPn einωt

(10.10d)

n=1 6

Tr1 = Tr10 + Re n=1 6

Tr2 = Tr20 + Re n=1 6

TP = TP0 + Re n=1

The periodic expressions of I (t), Ta , (AI )T , Tc , Tr1 , Tr2 , and TP from Eqs. 10.9 and 10.10 are substituted in energy equilibrium expressions (10.5–10.8), and separate time-independent and time-dependent parts. These time-independent and time-dependent equations are written in terms of matrices as. Example 10.2 Write down time-independent part of Eqs. 10.5 to 10.8. Solution Substituting Eqs. 10.9 and 10.10 in Eqs. 10.5 to 10.8, we have time-independent part as follows: αc τg βc I0 = Ut,ca (Tc 0 − Ta 0 ) + Ub,cr 1 (Tc0 − Tr1 0 ) + η0 τg βc I0 Ub,cr 1 (Tc 0 − Tr1 0 )Ars + τg2 (1 − βc )(1 − τn )I0 Ars = [0.33N1 V1 + A5 U5 ](Tr 1 0 − Ta 0 ) n p FR (T00 − Tr2 0 ) + Ur1,r2 (Tr1 0 − Tr2 0 ) Ar + h p Tp 0 − Tr 2 0 Ap  4  =

Ai Ui + 0.33N2 V2 (Tr 2 0 − Ta 0 ) i=1

Af Uf T00 − Tp 0 + αp τg2 τn (1 − βc )I0 Ars + αp τg (AI)T 0 − h p Tp 0 − Tr2 0 Ap = 0 Transferring all unknown parameters, namely Tc 0 ,Tr1 0 , Tr2 0 , and Tp 0 , in sequence of in left-hand side (LHS) and known parameters in right-hand side (RHS) in the above four equations, one gets Ut,ca + Ub,cr1 Tc 0 − Ub,cr1 Tr1 0 + 0 × Tr2 0 + 0 × Tp 0 = (αc − η0 )τg βc I0 + Ut,ca Ta 0

(E.4)

296

10 Thermal Modeling of Greenhouse Integrated Semi-transparent …

  Ub,cr1 Tc 0 − Ub,cr1 Ars + 0.33N1 V1 + A5 U5 Tr1 0 + 0 × Tr2 0 + 0 × Tp 0   (E.5) = − τg2 (1 − βc )(1 − τn )I0 Ars + (0.33N1 V1 + A5 U5 )Ta 0  0 × Tc 0 + Ur1,r2 Ar Tr1 0 − n p FR + Ur1,r2 Ar + h p Ap + 



4



Ai Ui + 0.33N2 V2 Tr2 0 i=1



4

+ h p Ap Tp 0 = − n p FR T00 +



Ai Ui + 0.33N2 V2 Ta 0

(E.6)

i=1

0 × Tc 0 + 0 × Tr1 0 − h p Ap Tr2 0 + h p Ap + Af Uf Tp 0   = αp τg2 τn (1 − βc )I0 Ars + αp τg ( AI )T 0

(E.7)

10.4.1 Time-Independent Matrix Equations E-(4.7) (Example 10.2) can be written in the following matrix form: ⎡ ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎣

(Ut,ca + Ub,cr1 ) −Ub,cr1 Ub,cr1 Ars −(Ub,cr1 Ars + 0.33N1 V1 + A5 U5 ) 0 0 ⎡ T ⎢ c0 ⎢ Tr1 0 ⎢ ×⎢ ⎣ Tr2 0 TP 0

0

0

0

0

⎤

⎥ ⎥ ⎥ ⎥ −(n p F R + Ur1,r2 An + h P AP ⎥ Ur1,r2 An h P AP 4 ⎥ + Ai Ui + 0.33N2 V2 ) ⎦ i=1 0 −h P AP (h P AP + Af Uf ) ⎤ ⎤ ⎡ (αc − η0 )τg βc I0 + Ut,ca Ta 0  ⎥ ⎥ ⎢ − τg2 (1 − τn )(1 − βc ) Ars I0 + (0.33N1 V1 + A5 U5 )Ta 0 ⎥ ⎥ ⎢ ⎥ ⎥=⎢  ⎥

4 ⎥ ⎢ ⎥ − n p F R T00 + ( i=1 Ai Ui + 0.33N2 V2 )Ta 0 ⎦ ⎢ ⎣ ⎦ 2 αP τn τg (1 − βc ) Ars I0 + αP τg ( AI )T 0 + Af Uf T00

(10.11)

Example 10.3 Write down time-dependent part of Eqs. 10.5 to 10.8. Solution Substituting Eqs. 10.9 and 10.10 in Eqs. 10.5 to 10.8, we have time-dependent part as follows: αc τg βc Ia n = Ut,ca (Tc n − Ta n ) + Ub,cr1 (Tc n − Tr 1 n ) + η0 τg βc In Ub,cr1 (Tc n − Tr1 n )Ars + τg2 (1 − βc )(1 − τn )In Ars = [0.33N1 V1 + A5 U5 ](Tr1 n − Ta n ) n p FR (T00 − Tr2 n ) + Ur1,r2 (Tr1 n − Tr2 n ) Ar + h p Tp n − Tr2 n Ap

10.4 Periodic Thermal Mathematical Modeling of GiSPVT





4

=

297

Ai Ui + 0.33N2 V2 (Tr2 n − Ta n ) i=1

Af Uf T00 − Tp n + αp τg2 τn (1 − βc )In Ars + αp τg (AI )T n − h p T p n − Tr 2 n Ap = inωMp Cp Transferring all unknown parameters, namely Tc n , Tr1 n , Tr2 n , and Tp n , in sequence of in left-hand side (LHS) and known parameters in right-hand side (RHS) in the above four equations, one gets Ut,ca + Ub,cr1 Tc n − Ub,cr1 Tr1 n + 0 × Tr2 n + 0 × Tp n = (αc − η0 )τg βc In + Ut,ca Ta n

(E.8)

  Ub,cr1 Tc n − Ub,cr1 Ar s + 0.33N1 V1 + A5 U5 Tr1 n + 0 × Tr2 n + 0 × Tp n   (E.9) = − τg2 (1 − βc )(1 − τn )In Ars + (0.33N1 V1 + A5 U5 )Ta n  0 × Tc n + Ur1,r2 Ar Tr1 n − n p FR + Ur1,r2 Ar + h p Ap  4 +

Ai Ui + 0.33N2 V2 Tr2 n + h p Ap Tp n i=1







4

= − n p FR T00 +



Ai Ui + 0.33N2 V2 Ta n

(E.10)

i=1

0 × Tc n + 0 × Tr1 n − h p Ap Tr2 n + h p Ap + Af Uf inωMp Cp + Tp n   (E.11) = αp τg2 τn (1 − βc )I0 Ars + αp τg (AI )T n

10.4.2 Time-Dependent Matrix Equations E-(8-11) (Example 10.3) can be written in the following matrix form: ⎡ ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎣

(Ut,ca + Ub,cr1 )

0 0 ⎡ Tc n ⎢ ⎢ Tr1 n ×⎢ ⎢T ⎣ r2 n TP n

−Ub,cr1 −(Ub,cr1 Ars + 0.33N1 V1 + A5 U5 )

0

0

0

0

⎤

⎥ ⎥ ⎥ ⎥ −(n p F R + Ur1,r2 An + h P AP ⎥ Ur1,r2 An h A 4 ⎥ P P + Ai Ui + 0.33N2 V2 ) ⎦ i=1 0 −h P AP (inωM P C P + h P A P + A f U f ) ⎤ ⎤ ⎡ (αc − η0 )τg βc In e−iσn + Ut,ca Ta n e−iψn  ⎥ ⎥ ⎢ 2 −i σ −i ψ n + (0.33N V + A U )Ta n e n ⎥ − τg (1 − τn )(1 − βc ) Ars In e ⎥ ⎢ 1 1 5 5 ⎥ ⎥=⎢  ⎥ ⎥ ⎢ 4 A U + 0.33N V )T e−i ψn ⎥ − ( i=1 ⎦ ⎢ 2 2 an i i ⎣ ⎦ αP τn τg2 (1 − βc ) Ars In e−iσn + αP τg ( AI )T n e−iφn

Ub,cr1 Ars

(10.12)

298

10 Thermal Modeling of Greenhouse Integrated Semi-transparent …

After evaluating Tc0 , Tr1 0 , Tr2 0 , TP0 , and Tc n , Tr1 n , Tr2 n , TP n from Eqs. 10.11 and 10.12 by matrix inversion, Appendix-H, periodic behavior of solar cell, zone-1/ zone-2 air, and plant temperature can be determined from Eq. 10.10. Here, it is important to note that (i) Each component of time-independent part of matrix is real value. The matrix program of real components of Eq. 10.11 is given in Appendix F. (ii) Equation 10.12 is a complex matrix, and program of complex matrix (Eq. 10.12) is given in Appendix G. Example 10.4 Write down energy balance of solar cell, zone-1 and zone-2 by considering heat capacity of solar cell and air in both zone. Solution The energy balance solar cell, zone-1 and zone-2, with their heat capacity is as follows: Solar cell: dTc + Ut,ca (Tc − Ta )Ars + Ub,cr1 (Tc − Tr1 )Ars dt + η0 τg βc Ars I (t) (E.12)

αc τg βc Ars I (t) = Mc Cc

where Mc (density = 2330 kg/m3 , thickness = 0.003 m) and Cc = 0.7 kJ/kgK are mass and specific heat of solar cell materials, respectively. Zone-1: Eq. 10.6 can be written after considering heat capacity of zone-1 as Ub,cr1 (Tc − Tr1 )Ars + τg2 (1 − βc )(1 − τn )I (t)Ars dTr1 + 0.33N1 V1 (Tr1 − Ta ) + A5 U5 (Tr1 − Ta ) = Mr1 Cr1 dt

(E.13)

Zone-2: Eq. 10.7 can be written after considering heat capacity of zone-2 as n p FR (T00 − Tr2 ) + Ur1,r2 (Tr1 − Tr2 )Ar + h p Tp − Tr2 Ap = Mr2 Cr2

dTr2 + dt

4

Ai Ui (Tr2 − Ta ) + 0.33N2 V2 (Tr2 − Ta )

(E.14)

i=1

Note: By considering heat capacity of solar material, zone-1 and zone-2 air ( E.12–E.14), and plant (Eq. 10.8), only periodic analysis is convenient and simple in comparison with others model (Sect. 10.1). For the known numerical value of solar cell temperature (Tc ), an instantaneous electrical efficiency of PV module (ηmi ) of GiSPVT system can be obtained [35] as ηmi = η0 [1 − βref (Tc − Tref )]

(10.13)

10.4 Periodic Thermal Mathematical Modeling of GiSPVT

299

10.4.3 An Overall Exergy of GiSPVT Hourly electrical exergy ( E˙ e ) from semi-transparent PV module of GiSPVT is given by E˙ e = ηmi αc τg βc Ars I (t)

(10.14)

Hourly thermal exergy ( E˙ ex ) of zone-2 air temperature can be evaluated as   T|t=t + 273 ˙ E ex = M2 Ca (T|t=t − T|t=t −1 ) − (Tam + 273) ln T|t=t −1 + 273

(10.15)

Similarly, overall hourly exergy (E ex,overall ) of GiSPVT system is the sum of electrical and thermal exergy of the system which is referred to as overall exergy of GiSPVT system (Sect. 8.6.3), and it can be calculated as E ex,overall = E˙ e + E˙ ex

(10.16)

10.4.4 Thermal Load Leveling Thermal load leveling (TLL): TLL quantifies the fluctuation in any temperature which causes thermal stress. It can be expressed for zone-2 air temperature and plant temperatures as follows: TLLr2 =

Tp,max − Tp,min Tr2,max − Tr2,min ; TLLp = Tr2,max + Tr2,min Tp,max + Tp,min

(10.17)

10.4.5 Decrement Factor (DF) It indicates the reduction in amplitude of temperature fluctuation from outside to inside through roof. Decrement factor for SPVT greenhouse system with respect to zone-2 air temperature and plant temperature is given as below DFr2 =

Tp,max − Tp,min Tr2,max − Tr2,min ; DFp = Tc,max − Tc,min Tc,max − Tc,min

(10.18)

300

10 Thermal Modeling of Greenhouse Integrated Semi-transparent …

10.4.6 Computational Methodology The following methodology has been used for numerical computation for a given design and climatic parameters. Step 1: Evaluation of unknown time-independent (Tc 0 , Tr1 0 , Tr2 0 , Tp 0 ) and timedependent (Tc n , Tr1 n , Tr2 n , Tp n ) constants for known design and climatic parameters from Eqs. 10.11 and 10.12, respectively. Step 2: For the known value of time-independent and time-dependent constants from Step 1, the hourly variation of the solar cell (Tc ), greenhouse zone-1 air (Tr1 ), greenhouse zone-2 air (Tr2 ), and plant (Tp ) temperatures have been computed from Eq. 10.10. Step 3: Maximum and minimum temperatures of greenhouse zone-2 air, plant temperature, and cell temperature have been calculated to evaluate thermal load leveling and decrement factor using Eqs. 10.17 and 10.18, respectively.

10.5 Numerical Results and Discussions For analyzing the periodic energy equilibrium equations of the greenhouse integrated semi-transparent photovoltaic thermal (GiSPVT) system, it is required to express insolation and ambient air temperature values in terms of Fourier approximation (Sect. 10.1.4). Figure 10.2a presents the convergence of insolation computed by Fourier approximation with the experimentally observed insolation for Saudi Arabia (φ = 24.72°). The variation of insolation with time is plotted for the different number of Fourier series harmonics (n). It is observed that the insolation values converge after the first six harmonics of the Fourier series (Appendix E). Further, the PV solar cell temperature of a rooftop semi-transparent BIPVT system determined by employing the periodic theory is validated with the experimentally measured solar cell temperature available in the literature [36], as shown in Fig. 10.2b. The correlation coefficient value is found to be 0.98, which represents a fair agreement with the experimental results. Hourly variations of solar intensity (insolation), I(t), ambient air temperature (T a ), PV solar cell temperature (T c ), plant temperature (T p ), and greenhouse zone1(T r1 )/zone-2 (T r2 ) air temperature of GiSPVT system for a typical summer day are presented in Fig. 10.3. All the temperatures mentioned above exhibit similar variation as that of insolation due to negligible heat capacity of each components (AssumptionVI). The maximum temperature of PV cell, zone-1, zone-2, and the plant is 54 °C, 52 °C, 24 °C, and 22 °C higher than that of maximum ambient air temperature, respectively, as per expectation. The zone-2 air temperature (T r2 ) is more than plant temperature during morning hours due to direct gain of insolation in zone-2 from side walls, and plant temperature becomes more than zone-2 temperature during evening hours due to heat capacity and to minimum direct gain in zone-2. Because

10.5 Numerical Results and Discussions

301

Fig. 10.2 a Hourly variation of insolation for different harmonics and b experimental validation of hourly variation of PV cell temperature with periodic model

heat stored by the plant in morning hours is released to zone-2 during evening hours. Moreover, it is noticed from Fig. 10.3 that during sunshine hours, the value of the plant as well as greenhouse zone-2 air temperature is very high due to low heat loss from zone-2 to ambient air, which is not ideal for plant growth. Hence, different techniques such as ventilation by air changes in zone-1 and integration of EAHE can be used to bring down the plant/zone-2 temperature of GiSPVT system within the optimum temperature range for plant growth, i.e., 30–37 °C. The influence of air changes of zone-1 and EAHE on the PV cell temperature, zone-1/zone-2 greenhouse air temperature, and plant temperature are investigated in detail. Figures 10.4a and b show the influence of air changes of zone-1 on hourly PV cell temperature and zone-1 air temperature of SPVT greenhouse system. During sunshine hours, the value of both PV cell temperature (T c ) and zone-1 air (T r1 ) temperature decreases with the increase in the air changes of zone-1 from N 1 = 0 to N 1 = 10 as the amount of heat transferred to the ambient increases through ventilation. One can see that there is marginal effect on PV solar cell temperature (Fig. 10.4a) in comparison with zone-1 air temperature (Fig. 10.4b). Similarly, the hourly variation of plant temperature (T p ) and zone-2 air (T r2 ) temperature of GiSPVT greenhouse system for different air changes of zone-1 has similar effect with number of air change, but there is no significant effect on its variation. For 30 air changes in zone1, the value of plant temperature and zone-2 air temperature is reduced by 9 °C and 10 °C, respectively. Further, the maximum and minimum fluctuations in zone-2 air temperature and plant temperature are determined by thermal load leveling (TLL), Eq. 10.17, and amplitude reduction of temperature fluctuation from outside to inside through PV roof is determined by decrement factor (DF), Eq. 10.18, as presented in Fig. 10.4c. TLL should be as minimum as possible to avoid stress for the human being in the residential sector and plants in the greenhouse room. TLL and DF’s value for both plant and zone-2 air temperature decreases with an increase in the air changes of zone-1 up to a particular value, then TLL and DF become constant for further increase in air changes. It is noticed that for the given design and climatic parameters

302

10 Thermal Modeling of Greenhouse Integrated Semi-transparent …

Fig. 10.3 Hourly variation of solar intensity (insolation) I(t), ambient air temperature (T a ), PV solar cell temperature (T c ), plant temperature (T p ), and greenhouse zone-1(T r1 )/zone-2 (T r2 ) air temperature of GiSPVT system for a typical day

of SPVT greenhouse system, the optimum value of zone-1 air changes per hour is 30. For this optimum value, the overall hourly exergy of SPVT greenhouse system is also presented in Fig. 10.4d. The system daily generates 128 kWh of exergy to become self-sustainable. The effect of the mass flow rate of air flowing through EAHE on hourly PV cell temperature and zone-1 air temperature of SPVT greenhouse system is presented by Fig. 10.5a(i) and a(ii), respectively. It is noticed that both of the temperatures remain unaffected for different values of the mass flow rate of air flowing through EAHE. The effect of the mass flow rate of air flowing through EAHE on the hourly variation of plant temperature (T p ) and zone-2 air (T r2 ) temperature for different values of the mass flow rate of air flowing through EAHE is shown in Fig. 10.5a and b, respectively. The value of plant and zone-2 air temperature decreases with an increase in the mass flow rate of air flowing through EAHE. There is a significant reduction of both plant and zone-2 temperature due to airflow, but the reduction is marginal after mass flow rate of air of 0.5 kg/s. For a mass flow rate of 0.5 kg/s, the maximum reduction in plant temperature and zone-2 air temperature is 24 °C and 26 °C, respectively. It is also noticed that the reduction in plant/zone-2 air temperatures is significant during sunshine hours as compared to off-sunshine hours. Hence, it is recommended to operate EAHE only during sunshine hours. Further, the maximum and minimum fluctuation in temperature is determined by thermal load leveling (TLL), and amplitude reduction of temperature fluctuation from outside to inside through PV roof is

10.5 Numerical Results and Discussions

(a)

(c)

303

(b)

(d)

Fig. 10.4 Hourly variation of a PV solar cell temperature (T c ) and b zone-1 room air temperature (T r1 ) with different number of air change in zone-1. c Effect of air change (N) on TLL and DF and d hourly variation of exergy of GiSPVT

determined by decrement factor (DF). TLL and DF values for both plant and zone2 air temperatures decrease with an increase in the mass flow rate of air up to a particular value, then TLL and DF become constant for further increase in mass flow rate as presented in Fig. 10.5c. It is observed that for the given design and climatic parameters of SPVT greenhouse system integrated with EAHE, the optimum value of mass flow rate is 0.5 kg/s. For the optimum value of mass flow rate, the hourly variation of overall exergy of SPVT greenhouse system is presented by Fig. 10.5d. The hourly variation of PV cell temperature (T c ) and zone-1 air temperature (T r1 ) of GiSPVT system for different packing factor (βc ) values of PV roof is shown in Fig. 10.6a and b, respectively. The value of PV cell temperature increases with an increase in the PV panel’s packing factor as PV cell area increases. However, zone-1 air temperature decreases with increased packing factor as incoming transmitted direct insolation in the greenhouse reduces. It is also noticed from Fig. 10.6a and b that the influence of packing factor on PV cell temperature and zone-1 air temperature is non-significant during off-sunshine hours. Similarly, Fig. 10.6c and

304

10 Thermal Modeling of Greenhouse Integrated Semi-transparent …

Fig. 10.5 Effect of mass flow rate through EAHE on a plant temperature (T p ) and b zone-2 room air temperatures (T r2 ). c Effect of mass flow rate through EAHE on TLL and DF and d hourly variation of exergy of GiSPVT system

d show the hourly variation of plant temperature (T p ) and zone-2 air (T r2 ) temperature for different packing factor values, respectively. During sunshine hours, the value of plant and zone-2 air temperatures decreases with an increase in packing factor. Because, the non-packing area of PV panels decreases with an increase in packing factor, which results in the reduction of direct insolation (solar intensity) received by the greenhouse. The variation of TLL and DF for plant and zone-2 air temperatures is shown in Fig. 10.6e. The value of DF and TLL of both plant and zone-2 air temperatures decreases with an increase in the packing factor. It is noticed that for the given design and climatic parameters of GiSPVT system integrated with EAHE, the optimum value of the packing factor of PV roof is 0.9. For the packing factor’s optimum value, the hourly variation of the overall exergy of GiSPVT system is shown in Fig. 10.6f.

10.5 Numerical Results and Discussions

(a)

(c)

(e)

305

(b)

(d)

(f)

Fig. 10.6 Hourly variation of a PV cell temperature (T c ) and b zone-1 air temperature (T r1 ) of GiSPVT system for different packing factor (βc ). Effect of packing factor on the hourly variation of c plant temperature (T p ) and d zone-2 air (T r2 ) temperature. e Effect of packing factor on TLL and DF and f hourly variation of exergy of GiSPVT

306

10 Thermal Modeling of Greenhouse Integrated Semi-transparent …

10.6 Conclusions and Recommendations A periodic thermal model of a greenhouse integrated semi-transparent photovoltaic thermal (GiSPVT) system combined with an earth air heat exchanger (EAHE) is developed in this chapter. The GiSPVT system is analyzed on a harsh summer day for the hot climatic condition of Saudi Arabia. Following are the key conclusions of the proposed study: • It is noticed that during sunshine hours, the value of the plant as well as greenhouse zone-2 temperature becomes very high. The maximum value of the plant and the zone-2 temperatures reaches 73 °C and 72 °C, respectively. These levels of temperature are not ideal for plant growth. • Both plant and zone-2 air temperatures decrease with an increase in the mass flow rate of air flowing through EAHE. However, the reduction in both of the temperatures is significant during sunshine hours as compared to off-sunshine hours. Hence, it is recommended to operate EAHE only during sunshine hours. For a mass flow rate of 0.5 kg/s, the maximum reduction in plant temperature and zone-2 air temperature is found to be 24 °C and 25 °C, respectively. • TLL and DF’s value for both plant and zone-2 air temperature decreases with an increase in the mass flow rate of air up to a particular value, then TLL and DF become constant for further increase in mass flow rate. For the given design and climatic parameters of the SPVT greenhouse system integrated with EAHE, the optimum mass flow rate value is found to be 0.5 kg/s. • It is also concluded that the optimum temperature range (30–37 °C) for plant growth within the GiSPVT system on a hot day can be achieved through a combination of ventilation in zone-1 and integration of EAHE. • It is further recommended that the EAHE should be also used for heating of a GiSPVT system during night by using the underground heat source. Problems 10.1 Write matrixes of time independent of Eqs. 8.13 to 8.15 (Sect. 8.6). Hint: Use Eq. 10.5 for climatic parameters and other temperatures, namely T c , T r , and T w in the form of Fourier series. 10.2 Write matrixes of time dependent of Eqs. 8.13 to 8.15 (Sect. 8.6). Hint: Use Eq. 10.5 for climatic parameters and other temperatures namely T c , T r , and T w in the form of Fourier series. 10.3 Rewrite matrix given in Eqs. 10.11 and 10.12 without an earth air heat exchanger (EAHE). Hint: Substitute FR = 0 in Eqs. 10.11 and 10.12. 10.4 Compute matrix of Problem 10.3 for climatic parameters of Fig. 10.2a and Tables 10.2 and 10.3. Hint: Use Appendices F–G.

10.6 Conclusions and Recommendations

307

10.5 Derive a one-order differential equation by using Eqs. 10.5–10.7 by elimination of T c , T cr1 , and T cr2 from Eq. 10.8. Hint: Follow Sect. 8.6. 10.6 Find out analytical expression for water temperature (T w ) by using Fourier analysis of Problem 10.7. Hint: See Example 10.1 10.7 Write down time-independent and time-dependent matrixes of Eqs. 10.4– 10.8 by considering the heat capacity of air in zone-1 and zone-2, respectively. Hint: See Examples 10.2–10.4 10.8 Write down the time-independent and time-dependent parts of Eqs. 9.13–9.15 Hint: Express solar cell ( Tco ), drying chamber room air (Tr ), and crop ( Tc ) temperatures in Fourier series form (Sect. 10.1.4 and Eq. 10.10). 10.9 Derive an analytical solution of E.1 of Example 9.8 (Chap. 9) by using Fourier method. Hint: Follow Example 10.1 10.10 Write down energy balance of solar cell (Tco ), Eq. 9.13, and drying chamber air (Tr ), Eq. 9.14, of GiSPVT dryer by considering hate capacity. Hint: See Example 10.4 Objective Questions 10.1 What can be the number of peak for eight harmonics in FOURIER analysis? (a) Four

(b) Eight

(c) Twelve

(d) None

Answer: (b) 10.2 Which number of harmonics is dominant in Fourier analysis? (a) Fourth (b) Eighth (c) First Answer: (c). 10.3 Initial condition is required for

(d) All

(a) Periodic analysis (b) Transient analysis analysis (d) All analyses.

(c) Quasi-steady-state

Answer: (b) and (c). 10.4 There is no need of initial condition in (a) Periodic analysis (b) Transient analysis analysis (d) All analyses

(c) Quasi-steady-state

Answer: (a). 10.5 For any number of harmonics in periodic analysis, which type of matrixes are required in the present case of Eqs. 10.5–10.8:

308

10 Thermal Modeling of Greenhouse Integrated Semi-transparent …

(a) 6 × 6

(b) 12 × 12

(c) 8 × 8 (d) 4 × 4

Answer: (d) 10.6 The ω for 24-h cycle in exponential part of Eq. 10.4 is defined as (a)

2π period

(b)

2π 12

(c)

2π 24

(d)

π 12

Answer: (c) and (d) 10.7 The porous green jute net in GiSPVT (Fig. 10.1) helps in (a) (b) (c) (d)

Reducing temperature in zone-2 Reducing temperature in zone-1 Reducing temperature in zone-1 and zone-2 None of them

Answer: (a) 10.8 An integration of earth air heat exchanger (EAHE) has (a) (b) (c) (d)

Effect on solar cell temperature Effect on zone-1 room temperature No effect on solar cell temperature No effect on zone-1 room temperature

Answer: (c) and (d) 10.9 An integration of earth air heat exchanger (EAHE) has (a) (b) (c) (d)

No effect on solar cell temperature No effect on zone-1 room temperature Effect on zone-1 room temperature Effect on zone-2 room temperature

Answer: (c) and (d) 10.10 An integration of earth air heat exchanger (EAHE) has (a) (b) (c) (d)

Effect on solar cell temperature Effect on zone-1 room temperature No effect on solar cell temperature No effect on zone-1 room temperature

Answer: (a) and (b) 10.11 Thermal load leveling (TLL) and decrement factor (DG) should be minimum: (a) (b) (c) (d)

For best performance of GiSPVT For maximum overall exergy of GiSPVT No effect on performance of GiSPVT None of them

Answer: (a) and (b) 10.12 Time-independent matrixes are (a) Real matrix (b) Complex matrix (c) Both real and complex matrixes (d) All of them Answer: (a)

References

309

10.12 Time-dependent matrixes are (a) Real matrix (b) Complex matrix (c) Both real and complex matrixes (d) All of them Answer: (b) 10.12 Time-independent and time-dependent parts of Eqs. 8.13 to 8.15 (Sect. 8.6) will form (a) 6 × 6 matrix (b) 12 × 12 matrix

(c) 3 × 3 matrix (d) 4 × 4 matrix

Answer: (c) 10.13 Periodic analysis is required (a) (b) (c) (d)

For multiple coupled nonlinear one-order differential equations For one-order differential equation For nonlinear one-order differential equation None of them

Answer: (a) and (c)

References 1. Aljubury IMA, Ridha HD (2017) Enhancement of evaporative cooling system in a greenhouse using geothermal energy. Renew Energy 111:321–331 2. Ili´c ZS, Milenkovi´c L, Stanojevi´c L, Cvetkovi´c D, Fallik E (2012) Effects of the modification of light intensity by color shade nets on yield and quality of tomato fruits. Sci Hortic (Amsterdam) 139:90–95 3. Murakami K, Fukuoka N, Noto S (2017) Improvement of greenhouse microenvironment and sweetness of melon (Cucumis melo L.) fruits by greenhouse shading with a new kind of nearinfrared ray-cutting net in mid-summer. Sci Hortic (Amsterdam) 218:1–7 4. Ahemd HA, Al-Faraj AA, Abdel-Ghany AM (2016) Shading greenhouses to improve the microclimate, energy and water saving in hot regions: a review. Sci Hortic (Amsterdam) 201:36– 45 5. Santamouris M, Argiriou A, Vallindras M (1994) Design a N D operation of a low energy consumption passive solar. Sol Energy 52(5):371–378 6. Vishwavidayalya DA (1991) thermal performance of underground A I R pipe: different earth surface treatments. Energy Convers Manag 31(1):95–104 7. Sodha MS, Buddhi D, Sawhney RL (1991) Thermal performance of underground air pipe: different earth surface treatments. Energy Convers Manag 31(1):95–104 8. Misra R, Bansal V, Das Agarwal G, Mathur J, Aseri T (2013) Evaluating Thermal performance and energy conservation potential of hybrid earth air tunnel heat exchanger in hot and dry climate—in situ measurement. J Therm Sci Eng Appl 5(3) 9. Mahach H, Benhamou B (2020) Extensive parametric study of cooling performance of an earth-to-air heat exchanger in hot semi-arid climate. J Therm Sci Eng Appl 13(3) 10. Stanciu D, Stanciu C, Paraschiv I (2016) Mathematical links between optimum solar collector tilts in isotropic sky for intercepting maximum solar irradiance. J Atmos Solar-Terrestrial Phys 137:58–65 11. Ozgener O, Ozgener L, Goswami DY (2011) Experimental prediction of total thermal resistance of a closed loop EAHE for greenhouse cooling system. Int Commun Heat Mass Transf 38(6):711–716

310

10 Thermal Modeling of Greenhouse Integrated Semi-transparent …

12. Ozgener O, Ozgener L, Goswami DY (2017) Seven years energetic and exergetic monitoring for vertical and horizontal EAHE assisted agricultural building heating. Renew Sustain Energy Rev 80:175–179 13. Hepbasli A (2013) Low exergy modelling and performance analysis of greenhouses coupled to closed earth-to-air heat exchangers (EAHEs). Energy Build 64:224–230 14. Bisoniya TS, Kumar A, Baredar P (2013) Experimental and analytical studies of earth-air heat exchanger (EAHE) systems in India: a review. Renew Sustain Energy Rev 19:238–246 15. Li H, Ni L, Yao Y, Sun C (2019) Experimental investigation on the cooling performance of an earth to air heat exchanger (EAHE) equipped with an irrigation system to adjust soil moisture. Energy Build 196:280–292 16. Li H, Ni L, Liu G, Yao Y (2019) Performance evaluation of earth to air heat exchange (EAHE) used for indoor ventilation during Winter in severe cold regions. Appl Therm Eng 160(160):114111 17. Amanowicz Ł, Wojtkowiak J (2018) Validation of CFD model for simulation of multi-pipe earth-to-air heat exchangers (EAHEs) flow performance. Therm Sci Eng Prog 5(5):44–49 18. Hermes VF, Ramalho JVA, Rocha LAO, dos Santos ED, Marques WC, Costi J, Rodrigues MK, Isoldi LA (2020) Further realistic annual simulations of earth-air heat exchangers installations in a coastal city. Sustain Energy Technol Assessments 37 19. Peretti C, Zarrella A, De Carli M, Zecchin R (2013) The design and environmental evaluation of earth-to-air heat exchangers (EAHE). A literature review. Renew Sustain Energy Rev 28:107– 116 20. Li H, Ni L, Yao Y, Sun C (2020) Annual performance experiments of an earth-air heat exchanger fresh air-handling unit in severe cold regions: operation, economic and greenhouse gas emission analyses. Renew Energy 146:25–37 21. Rosa N, Soares N, Costa JJ, Santos P, Gervásio H (2020) Assessment of an earth-air heat exchanger (EAHE) system for residential buildings in warm-summer mediterranean climate. Sustain Energy Technol Assessments 38 22. Chiesa G (2018) EAHX—earth-to-air heat exchanger: simplified method and KPI for early building design phases. Build Environ 144(August):142–158 23. Ghosal MK, Tiwari GN, Srivastava NSL (2004) Thermal modeling of a greenhouse with an integrated earth to air heat exchanger: an experimental validation. Energy Build 36(3):219–227 24. Tiwari GN, Akhtar MA, Shukla A, Emran Khan M (2006) Annual thermal performance of greenhouse with an earth-air heat exchanger: an experimental validation. Renew Energy 31(15):2432–2446 25. Ghosal MK, Tiwari GN (2006) Modeling and parametric studies for thermal performance of an earth to air heat exchanger integrated with a greenhouse. Energy Convers Manag 47(13– 14):1779–1798 26. Mihalakakou G, Santamouris M, Asimakopoulos D (1994) On the cooling potential of earth to air heat exchangers. Energy Convers Manag 35(5):395–402 27. Wu H, Wang S, Zhu D (2007) Modelling and evaluation of cooling capacity of earth-air-pipe systems. Energy Convers Manag 48(5):1462–1471 28. Yadav S, Panda SK, Hachem-Vermette C, Tiwari GN (2020) Exergetic performance assessment of optimally inclined BIPV thermal system by considering cyclic nature of insolation. J Sol Energy Eng, 1–30 29. Nayak S, Tiwari GN (2009) Theoretical performance assessment of an integrated photovoltaic and earth air heat exchanger greenhouse using energy and exergy analysis methods. Energy Build 41(8):888–896 30. Al-Ajmi F, Loveday DL, Hanby VI (2006) The cooling potential of earth-air heat exchangers for domestic buildings in a desert climate. Build Environ 41(3):235–244 31. Li ZX, Shahsavar A, Al-Rashed AAAA, Kalbasi R, Afrand M, Talebizadehsardari P (2019) Multi-objective energy and exergy optimization of different configurations of hybrid earth-air heat exchanger and building integrated photovoltaic/thermal system. Energy Convers Manag 195(June):1098–1110

References

311

32. Gupta R, Tiwari GN (2005) Modeling of energy distribution inside greenhouse using concept of solar fraction with and without reflecting surface on north wall. Build Environ 40(1):63–71 33. Tiwari GN, Tiwari A (2016) Handbook of solar energy. Springer 34. Tiwari GN (2003) Greenhouse technology for controlled environment. Alpha Science Int’l Ltd 35. Evans DL (1981) Simplified method for predicting photovoltaic array output. Sol Energy 27(6):555–560 36. Deo A, Mishra GK, Tiwari GN (2017) A thermal periodic theory and experimental validation of building integrated semi-transparent photovoltaic thermal (BiSPVT) system. Sol Energy 155:1021–1032 37. Díaz-Hernández HP, Macias-Melo EV, Aguilar-Castro KM, Hernández-Pérez I, Xamán J, Serrano-Arellano J, López-Manrique LM (2020) Experimental study of an earth to air heat exchanger (EAHE) for warm humid climatic conditions. Geothermics 84 38. Bisoniya TS (2015) Design of earth–air heat exchanger system. Geotherm Energy 3(1) 39. Bharadwaj SS, Bansal NK (1981) Temperature distribution inside ground for various surface conditions. Build Environ 16(3):183–192 40. Le AT, Wang L, Wang Y, Li D (2020) Measurement investigation on the feasibility of shallow geothermal energy for heating and cooling applied in agricultural greenhouses of Shouguang City: ground temperature profiles and geothermal potential. Inf Process Agric, 1–19

Chapter 11

Application of Photovoltaic Thermal (PVT) Technology

Nomenclature Aam Arm Aac Arc b bo Cf F' hi hi ' ho hpf Ib I(t) Kg Ki Kp Lg L rm L am Li Lp m˙ f N PF1 PF2

Aperture area of SPV-CPC mod (m2 ) Receiver/absorber area of PV module (m2 ) Aperture area of collector (m2 ) Receiver area of collector (m2 ) Breadth of receiver (m) Breadth of aperture area (m) Specific heat of fluid (J/kg K) Collector efficiency factor Heat transfer coefficient for space between the glazing and absorber plate (W/m2 K) Heat transfer coefficient from bottom of PVT to ambient air (W/m2 K) Cheat transfer coefficient from top of glass cover (W/m2 K) Heat transfer co efficient from absorber plate to working fluid (W/ m2 K) Solar beam radiation (W/m2 ) Total solar radiation (W/m2 ) Thermal conductivity of glass (W/m K) Thermal conductivity of insulation (W/m K) Thermal conductivity of absorber plate (W/m K) Thickness of glass cover (m) Length of receiver of PV module (m) Length of aperture of PV module (m) Thickness of insulation (m) Thickness of absorber plate (m) Mass flow rate of working fluid (kg/s) Number of SPVT collectors Penalty factor due to glass covers of SPV module Penalty factor due to absorber plate below PV module

© Bag Energy Research Society 2023 G. N. Tiwari, Advance Solar Photovoltaic Thermal Energy Technologies, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4993-9_11

313

314

Q˙ uth,N th Ta Tc Tf T fi T fo T foN Tp T0 U L,m U L,c U tc,a U tc,p, U tc,f U tp,a V

11 Application of Photovoltaic Thermal (PVT) Technology

The rate of useful thermal energy (W) Ambient air temperature (°C) Solar cell temperature (°C) Working fluid temperature (°C) Working fluid inlet temperature (°C) Working fluid outlet temperature (°C) Fluid outlet temperature at the end of Nth PVT-CPC collector (°C) Absorber plate temperature (°C) Reference cell temperature for optimum cell efficiency, i.e., 25 °C Overall heat loss coefficient from PV module to ambient air (W/m2 K) Overall heat loss coefficient from glazing to ambient air (W/m2 K) Overall heat loss coefficient from cell to ambient air (W/m2 K) Overall heat loss coefficient from cell to plate/absorber (W/m2 K) Overall heat loss coefficient from absorber plate to ambient air (W/m2 K) Air velocity (m/s)

Greek Letter α β β0 ρ τ η ηi (ατ )eff

Absorptivity Packing factor Temperature coefficient of electrical efficiency Reflectivity Transmittivity of glass cover Electrical efficiency Instantaneous thermal efficiency Product of effective absorptivity and transmittivity

Subscript a c eff f fi fo g m p

Ambient air Solar cell/collector Effective Working fluid Inlet working fluid Outlet working fluid fluid Glass cover PV module Absorber plate

11.1 Background

315

11.1 Background Today, everyone on the planet Earth is feeling insecure due to sudden ruining/ deterioration of environment (quality of air) and ecosystem (quality of water, Chaps. 2 and organic food, Chaps. 5–8) due to increased industrialization based on fossil fuel which has limited source of energy, to fulfill the greed of people in terms of energy per (kWh) capita irrespective of any citizen of country. In view of this, most of the countries, through Tokyo protocol and Paris agreement, decided to go for renewable energy sources which has infinite source of energy. The basic source of renewable energy source is solar energy coming from the Sun with generation of about 99% energy at core of the Sun (Sect. 1.3) due to nuclear fusion. The solar energy is clean, green, and friendly with environment and climate to sustain biosphere/nature [1]. The solar energy in the past had been used by human only for heating of building and water and as a Vitamin ‘D’ (as electromagnetic, e/m, wave) with efficiency of about 60–70%. However, solar energy has also been used as an electrical power after invention of solar cell, Chap. 3 [2] (as photon, E = hv = hc , c, the velocity of light = 3 × 108 m/s, λ, the varying wavelength, λ one photon at 1 Hz carry energy of 6.62607015 × 10−34 J = 4.135667697 × 10−15 eV) with electrical efficiency (ηc ) of 15–20%, Eq. 3.15, depending upon the material of solar cell and operating temperature of solar cell (Tc ). In recent past, an attempt was made to utilize the remaining thermal energy associated with PV module, Chap. 4 by cooling either lowering its temperature by redesign PV module, such as semitransparent PV module or flowing water/air over/below photovoltaic module (PV) which consists of solar cell [3]. The application of semitransparent PV module has many applications such as building [4, 5], greenhouse [6], Chaps. 5–8, solar dryer, Chap. 9, and water/air flat plate collectors [7]. If semitransparent PV module, Chap. 4, is used in building and greenhouse, it is referred as building integrated semi-transparent photovoltaic thermal (BiSPVT) [4, 5] and greenhouse integrated semitransparent photovoltaic thermal (GiSPVT) systems, Chaps. 5–8. In both cases, electrical as well as thermal energy has been used to make both systems as a self-sustain which minimizes the use of fossil fuel responsible for deteriorating biosphere. If semitransparent PV module is integrated with conventional flat plate water/air collector, then it is referred as PVT water/sir collectors also known as hybrid solar collectors. The PVT collectors are also referred as solar cogeneration systems due to generation of electrical as well as thermal power/energy. In PVT collectors, unused waste heat/ thermal energy is used for photosynthesis as well as to heat water and air by transmission of solar radiation and heat transfer fluid. In such case, a higher overall thermal and exergy efficiencies can be achieved in comparison with alone solar photovoltaic (PV) or solar thermal (T) alone [8, 9]. A lot of significant research work on PVT technology based on opaque, semitransparent, and flexible PV module has been done in increasing its overall efficiency in diverse range applications since the 1970s which are as follows: (a) Greenhouse integrated semi-transparent photovoltaic thermal (GiSPVT) system (Fig. 6.8a, Fig. 9.7a): In addition to vegetable growing, Chap. 7 and vegetable/

316

11 Application of Photovoltaic Thermal (PVT) Technology

medicinal plant drying, the GiSPVT can be more useful to aquaculture/ hydroponics which will be discussed in coming section. (b) The different PVT water/air collectors technologies have also many applications, namely water/swimming/biogas slurry, indirect crop/vegetables drying, space heating, etc. The water quality differs substantially in their PVT collector application, e.g., aquaculture, water heating design, Chapter +II, and heat transfer fluid, and addresses different applications ranging from low-temperature heat below ambient up to hightemperature heat above 100 °C.

11.2 Aquaculture and Hydroponics/Aquaponics Aquaculture is referred as many words, namely aquiculture/aqua farming. It is a controlled farming/cultivation of aquatic organisms, namely fish, crustaceans, mollusks, algae, etc. It involves cultivating of aquatic organism in freshwater, brackish water, and saltwater/marine under controlled or seminatural controlled environment conditions. The marine farming/marine culture refers specifically to aquaculture practiced in seawater habitats and lagoons; it is opposed to in freshwater aquaculture. Pisciculture is a type of aquaculture for culturing of fish to obtain fish and fish products as food. It can also be defined as the breeding, growing, harvesting of fish, etc. It is also known as farming in water unlike vegetation on land. Aquaculture can also be carried out by creating artificial facilities constructed on land (onshore aquaculture) such as (a) fish water tank, Fig. 11.1a, (b) water ponds, Fig. 11.1b, Fig. 5.6, and (c) aquaponics/hydroponics, Fig. 5.7 or raceways. The living conditions of aqua farming are controlled by human. These are as follows: (i) Water quality: The required water quality, namely alkalinity ammonia, dissolved oxygen (DO)/carbon dioxide (CO2 ), hardness/salinity, nitrites, temperature, and pH value, has been discussed in detail in Chap. 2 (Sect. 2.4). (ii) The oxygen (O2 ) level: The optimum dissolved oxygen (DO) level for fish culture varies between 5 and 20 ppm. Oxygen (O2 ) production in water pond decreases by aquatic plants in cloudy condition due to the absence of photosynthesis activities, Eq. 1.1a, when there is not enough solar radiation. The GiSPVT can maintain the level of oxygen (O2 ) through non-packing factor area. The level of oxygen level in water decreases with increase of its temperature. (iii) Water/feed temperature: The optimum water pond temperature for fish growth in the pond is 25–35 °C (Fig. 2.3). This is the optimum temperature for all living organism existing on the planet Earth too. In the presence of solar radiation through non-packing factor of semitransparent PV module, the plants present in the water produce food and oxygen by photosynthesis, Eq. 1.1a. It is very mandatory to make their habitat compatible/safe for them. (iv) Solar intensity, I(t): In addition to increase the water pond temperature by solar energy, one also needs electrical power for purification of water pond systems

11.2 Aquaculture and Hydroponics/Aquaponics

317

Greenhouse transparent wall

Tank for fish growth in greenhouse Underground fish water Underground fish water tank tank (a) Underground fish tank in even type greenhouse (b)

The Pond culture of fish inside Greenhouse

Water fish pond in quotient shape greenhouse

Fig. 11.1 a Underground metallic and b RCC tank in greenhouse

and the pond aerator and recirculation of water to increase oxygen level in water pond, respectively, which can be met by electrical power produced by GiSPVT system. The power demand in these cases is in ration of 2.5:1.8:1 [10]. (v) Relative humidity (γ ): It should be as maximum as possible for growth of algae which is food of fish. This high relative humidity also reduced the losses from water pond surface to retain its temperature for any climatic condition.

318

11 Application of Photovoltaic Thermal (PVT) Technology

11.2.1 The Freshwater Aquaculture Systems The freshwater aquaculture system refers to raising and breeding of aquatic animals, namely fish, shrimp, crab, shellfish, etc., and plants by the use of ponds, reservoirs, lakes, rivers, etc., for commercial applications/purposes. There are three carps, namely (a) Nani/Mrigal, Fig. 11.2a and common/ European carp, Fig. 11.2b: It is grown at the bottom of water pond (Bottom feeder). The water depth for Magur carp is to be maintained at 0.50–1.0 m. (b) Rohu, Fig. 11.2c and grass crap, Fig. 11.2d: The Rohu occurs in rivers throughout. It is available in northern, central, and eastern India, Pakistan, Vietnam, Bangladesh, Nepal, and Myanmar. The Rohu is an important aquaculture freshwater species in South Asia too. It grows in middle order water depth (2–3 m). (c) Katla/Catla, bighead: Catla/katla fish, Fig. 11.2e, is also referred as the major South Asian carp. It is an economically important South Asian freshwater fish. Catla/katla and bighead are native to rivers and lakes. It is available in northern India, Bangladesh, Myanmar, Nepal, and Pakistan. It has also been introduced in South Asia. It is commonly farmed. Bighead carps are native to larger and both are associated with floodplain lakes of eastern Asia. The bighead carp has a very fast growth rate. It is a lucrative and important aquaculture fish. Required water depth is 1.2 m–2.8 m.

11.2.2 The Brackish Water Aquaculture System Brackish water is also known as brack water. It is water occurring in a natural environment. It has salinity between freshwater (1500 ppm) and less than seawater (45000 ppm). It can also be prepared by either mixing seawater (salt water) and freshwater or mixing underground salty and freshwater together. Brackish (brack) water aquaculture is an important source of seaweed, shellfish, and finfish for human food. It is likely to expand well in the next century. It has both direct and indirect impacts on biodiversity through the consumption of natural resources and the production of sea wastes.

11.2.3 The Marine Aquaculture System Marine aquaculture/mariculture deals with marine organisms for food and other animal products. It refers to the breeding, rearing, and harvesting of aquatic plants and animals (finfish and shellfish). It can take place in either the open ocean or land in tanks and ponds filled with seawater/offshore.

11.2 Aquaculture and Hydroponics/Aquaponics

(a) Nani/Mrigal

319

(b) Common crap

(c ) Rohu

(d) Grass carp

(c ) Catla/Katla fish Fig. 11.2 Different types of fish

11.2.4 Advantages and Disadvantages of Aquaculture Followings are some advantages: (a) Nutritious and healthy protein: It has the important source of excellent nutritious and healthy protein sources and healthy oils. The fish farms can be built anywhere if the body of water is available

320

11 Application of Photovoltaic Thermal (PVT) Technology

(b) Affordable price: Due to low production of fish during winter/low-temperature region, it can be supplied at an affordable price even to poorer peoples living in the coastal region (c) Recirculating aquaculture: Cultured fishes are safe from captured fish due to recirculating aquaculture systems. It is also a big help in reducing, reusing, and recycling waste materials. It is healthy not only for the cultured species of fish due to increasing DO in pond and also to the environment. (d) Food security: It provides good quality food security for the growing population. The consumers will be assured of continuous food supply chain all over the years. (e) Employment: It offers more employment opportunities to the global economy. It is also a source of income. Followings are some disadvantages: (a) Flora and fauna: The infrastructure development for aquaculture will affect the local flora (plant life) and fauna (animals), namely wetlands and mangroves. Mangroves means small grown trees in saline water due to photosynthesis and offers ecosystems for wild animals, birds, reptiles, and aquatic fauna. (b) The untreated effluent: If it is discharged with heavy organic load, it will adversely affect the local ecosystem/environment. (c) Farming of exotic species: It is non-indigenous species. It has their origin in another country and has been introduced into the Indian waters. They generally have established culture technologies. It has the economics of production and marketability with new employment generation. It will also bring with new pathogen (an organism causing disease to its host) to the new environment. (d) Fish disease and parasite: Its transfer from captive stock to wild poses a significant threat to fish populations.

11.2.5 Experimental GiSPVT Water Pond Here, the GiSPVT means greenhouse integrated semitransparent photovoltaic thermal as used in Chap. 8. Further, all notations and constant used in this section are exactly same as defined in Chap. 8 as well. It has been selected for fish growing in winter condition during December to March. Referring inside view of zones-5 and 6 of Fig. 6.8d, we have chosen zone-6 as shown in Fig. 11.3 having minimum packing factor (PF) to allow maximum solar radiation to create suitable environment for fish growth. In this case, most of the basic parameters, namely algae formation (photosynthesis, Eq. 1.1a) to maintain DO level, temperature in comparison with open pond condition and relative humidity, will be maintained so that fish can survive in harsh cold climatic condition. A water depth of about 0.8 m has been maintained. Also regular feeding [biogas waste, waste of oil seeds (Khali), rice waste, etc.] is available to fish. It has been observed that

11.2 Aquaculture and Hydroponics/Aquaponics

321

(a) RCC pillar

Glazed wall of GiSPVT Aquaculture water pond inside GiSPVT

(b) GiSPVT

RCC open aquaculture pond

Glazed sliding walls of GiSPVT

Fig. 11.3 a Photograph of aquaculture pond inside GiSPVT (zone-6) and b open RCC water pond

(i) There is an increase in growth about 10–15% by weight in harsh period of December/January, 2023. (ii) The relative humidity of about 90% is maintained throughout day/night. (iii) There is about 3–4 °C higher temperature in comparison with outside top surface temperature of 17 °C due to trapped solar radiation and less heat loss from water surface due to higher relative humidity. (iv) The salinity of inside and outside ponds is equal due to feeding of water regularly.

322

11 Application of Photovoltaic Thermal (PVT) Technology

Figure 11.3b shows open aquaculture pond for comparison purposes.

11.3 Thermal Modeling of Aquaculture Water Pond In this section, analytical expression for thermal as well as electrical energy in terms of design and climatic parameters will be derived for GiSPVT water pond for aquaculture.

11.3.1 Analytical Expressions for Water Pond Temperature Following Sects. 8.6.1 and 8.21, an expression for water pond temperature inside greenhouse integrated semi-transparent (GiSPVT) can be expressed as follows:  ⎧ ⎫ ∑ ⎨ {τg2 (1 − β) + PF2 (ατ )eff }ARS I (t) + τg 3j=1 A j I j ⎬   Tw = T 1 − e−at + a ∑ ⎩ ⎭ (U A)wa + 5k=1 Ak Uk + Tw0 e−at ,

(11.1)   ∑ (U A)wa + 5k=1 Ak Uk

where Tw0 is initial value of water temperature in pond at t = 0, a = Mw C w w ∑5 and PF2 = h A +U hA1 A+ . 1 w ra1 RS i=1 Ai Ui Now, an average water temperature between 0 and t time interval can be determined as: {t 1 Tw = Tw dt t 0  ⎧ ⎫ ∑ ⎨ {τg2 (1 − β) + PF2 (ατ )eff }ARS I (t) + τg 3j=1 A j I j ⎬   T = + a ∑ ⎩ ⎭ (U A)wa + 5k=1 Ak Uk   1 − e−at 1 − e−at 1− + Tw0 (11.2) at at The above expression has been used to compute a monthly average pond water temperature for aquaculture. After evaluating monthly variation of average water temperature (T w ) of aquaculture from Eq. 11.2 for a given design (Table 8.4) and climatic parameters, Fig. 11.4, the monthly average variation room and solar cell temperatures of GiSPVT can be written with the help of Eqs. 8.16 and 8.17 as:

11.3 Thermal Modeling of Aquaculture Water Pond

323

  ∑5 Ai Ui T a (ατ )eff ARS I (t) + Ura1 ARS T a + h1AP T w + i=1   Tr = ∑5 Ura1 ARS + h1AP + i=1 Ai Ui   ∑5 Ai Ui Ura1 A R S + i=1 (ατ )eff ARS I (t) + Ta = ∑5 ∑5 Ura1 ARS + h1AP + i=1 Ura1 ARS + h1AP + i=1 Ai Ui Ai Ui h1A P Tw + ∑5 Ura1 ARS + h1AP + i=1 Ai Ui

(11.3)

and Tc = =

τg β(αc − η0 )I (t) + Ut,ca T a + Ub,cr T r Ub,cr + Ut,ca τg β(αc − η0 )I (t) + Ut,ca T a Ub,cr + Tr Ub,cr + Ut,ca Ub,cr + Ut,ca

(11.4)

Substitute an expression of T r from Eq. 11.3 into Eq. 11.4, one has

Fig. 11.4 Monthly average variation of solar radiation (W/m2 ) and ambient temperature for a composite Indian climatic condition

324

11 Application of Photovoltaic Thermal (PVT) Technology

τg β(αc − η0 )I (t) + Ut,ca Ta Ub,cr + Ut,ca ⎡ Ub,cr (ατ )eff ARS I (t) ⎣  + ∑5 Ub,cr + Ut,ca Ura1 ARS + h1AP + i=1 Ai Ui   ∑5 Ura1 ARS + i=1 Ai Ui  Ta + ∑5 Ura1 ARS + h1AP + i=1 Ai Ui ⎤ h1AP  T¯ w ⎦ + ∑5 Ura1 ARS + h1AP + i=1 Ai Ui

Tc =

or, τg β(αc − η0 )I (t) + Ut,ca T a Ub,cr + Ub,cr + Ut,ca Ub,cr + Ut,ca Ub,cr (ατ )eff ARS I (t) + × ∑5 U b,cr + Ut,ca Ura1 ARS + h1AP + i=1 Ai Ui   ∑5 Ura1 ARS + i=1 Ai Ui Ub,cr Ta + × ∑5 U b,cr + Ut,ca U A + h1A + AU

Tc =

ra1 RS

P

i=1

i i

h1A P  T w. × ∑5 Ura1 ARS + h1AP + i=1 Ai Ui

(11.5)

Now substitute an expression for T w from Eq. 11.2 into Eq. 11.5, one gets Tc =

τg β(αc − η0 )I (t) + Ut,ca T a Ub,cr + Ub,cr + Ut,ca Ub,cr + Ut,ca

Ub,cr (ατ )eff ARS I (t) + × ∑5 U b,cr + Ut,ca Ura1 ARS + h1AP + i=1 Ai Ui   ∑5 Ura1 ARS + i=1 Ai Ui Ub,cr Ta + × ∑5 U b,cr + Ut,ca Ura1 ARS + h1AP + i=1 Ai Ui h1A P  × ∑5 Ura1 ARS + h1AP + i=1 Ai Ui  ⎫ ⎡⎧  ∑ ⎨ {τg2 (1 − β) + PF2 (ατ )eff }ARS I (t) + τg 3j=1 A j I j ⎬ ⎣   + Ta ∑ ⎩ ⎭ (U A)wa + 5k=1 Ak Uk    1 − e−at 1 − e−at + Tw0 1− at at

(11.6)

11.3 Thermal Modeling of Aquaculture Water Pond

325

11.3.2 Electrical Power of GiSPVT  For known analytical expression for monthly average solar cell temperature T c , for monthly average instantaneous electrical Eq. 11.6 an analytical expression  efficiency of PV module ηmi of uneven GiSPVT [11] can be obtained as 



ηmi = τg η0 1 − β0

τg β(αc − η0 )I (t) + Ut,ca T a Ub,cr + Ub,cr + Ut,ca Ub,cr + Ut,ca

Ub,cr (ατ )eff ARS I (t) + × ∑5 Ub,cr + Ut,ca Ura1 ARS + h1AP + i=1 Ai Ui   ∑5 Ura1 ARS + i=1 Ai Ui Ub,cr Ta + × ∑5 U b,cr + Ut,ca Ura1 ARS + h1AP + i=1 Ai Ui h1AP  × ∑5 Ura1 ARS + h1AP + i=1 Ai Ui  ⎫ ⎡⎧  ∑ ⎨ {τg2 (1 − β) + PF2 (ατ )eff }ARS I (t) + τg 3j=1 A j I j ⎬ ⎣   T + a ∑ ⎩ ⎭ (U A)wa + 5k=1 Ak Uk     1 − e−at 1 − e−at 1− + Tw0 − 25 (11.7) at at Equation 11.7 can be directly used to find out average monthly PV module efficiency for numerical value of η0 and β0 for different solar cell materials which is given in Table 11.1 [12–14]. Table 11.1 Specifications for various silicon and non-silicon-based PV modules (Durisch et al. [12], Virtuani et al. [13] and Tiwari and Mishra [14]) Different solar cell materials

PV module efficiency ηmo (%)

Expected life nPV (Yrs)

Specific energy density E in (kWh m−2 )

(E in ) of PV module, Am = 0.71 m2 (kWh)

Average temp. coefficient β (o C−1 )

c-Si (Single-crystalline)

16

30

1190

8449

0.00535

mc-Si (Multi-crystalline silicon)

14

30

910

646.1

0.00425

nc-Si (Nanocrystalline silicon)

12

25

610

433.1

0.0036

a-Si (Amorphous silicon)

6

20

378

268.38

0.00115

CdTe (Cadmium telluride)

8

15

266

188.86

0.00205

10

5

24.5

17.395

0.00335

CIGS (Copper–indium–gallium–selenide)

326

11 Application of Photovoltaic Thermal (PVT) Technology

11.3.3 Monthly Average Electrical Output  By using the monthly average value of PV module electrical efficiency ηmi obtained from Eq. 11.7 for monthly electrical energy, E monthly in kWh is given as E monthly (kWh) ηmi × I (t) × Am × Number of PV module × N × number of days in month , = 1000 (11.8) where N is number of sunshine hours in a day. It varies from January to December for a given location.

11.3.4 The Yearly Electrical Output Yearly electrical output of monthly electrical energy from January to December can be obtained by E yearly (kWh) =

12 ∑

E monthly,k .

(11.9)

k=1

11.3.5 Thermal Energy of GiSPVT The average monthly thermal energy can be obtained as follows: Q u,monthly,th

 Mw Cw T w − Ta × 24 × number of days in month, (kWh) = 1000 × 3600 (11.10)

where T w is average monthly variation of water temperature obtained from Eq. 11.2. The average monthly thermal exergy, Q u,monthly,th-ex can be determined by using the data of Eq. 11.13 as follows: Mw C w 1000 × 3600    T w + 273  × T w − Ta − T a + 273 ln 24 T a + 273

Q u,monthly,th-ex (kWh) =

× number of days in month

(11.11)

11.3 Thermal Modeling of Aquaculture Water Pond

327

The average yearly thermal exergy, Q u,yearly,th is given by Q u,yearly,th (KWh) =

  T w,max + 273  Mw Cw × 24 × 365  , T w,max − Tw,min − T a + 273 ln 1000 × 3600 T w,min + 273

(11.12) where T w,max and Tw,min can be obtained from monthly variation from analytical expression for water temperature (T w ) from Eq. 11.2 for given monthly climatic and design parameters. Total yearly exergy of GiSPVT can be written by using Eqs. 11.9 and 11.12, respectively, as ExT, yearly = E yearly (kWh) + Q u,yearly, th (kWh).

(11.13)

11.3.6 Energy Matrices Energy payback time (EPBT), energy production factor (EPF), and lifecycle conversion efficiency (LCCE) are three main energy matrices. In the following subsection, without thermal exergy and with thermal exergy, these matrices have been assessed for various solar cells.

11.3.6.1

Energy Payback Time (EPBT)

Now total embodied energy (E in,T ) in kWh of semitransparent roof of GiSPVT can be evaluated as E in,T = Number of semitransparent PV module in south roof  × area of one PV module m2 × Embodied energy E in (kWh). (11.14) Here, embodied energy for a given design of GiSPVT system will be constant for different solar cell materials. The embodied energy E in (kWh), for PV module of 0.71 m2 for different solar cell material is given in Table 11.1. Then energy payback time (EPBT) of GiSPVT system is defined as ratio of embodied energy (E in ) to annual energy. It may be thermal, electrical, and overall thermal and overall exergy calculated as follows: EPBT =

E in,T . E yearly

(11.15)

328

11 Application of Photovoltaic Thermal (PVT) Technology

The numerical value of E yearly and E in,T can be considered for different solar cell materials from Eqs. 11.13 and 11.14, respectively. In this case, we will analyze the GiSPVT system without thermal exergy. If EPBT is much less than expected life of semi-transparent PV roof system, then PV system will be considered as economical; otherwise, the concept of GiSPVT water pond for aquaculture should be rejected.

11.3.6.2

Energy Production Factor (EPF)

Energy production factor (EPF) is the ration of energy generated to the embodied energy. It depends on life of GiSPVT water pond system and annual thermal, electrical energy, thermal and electrical exergy and embodied energy (E in,T ). The expression for EPF is given by EPF =

E yearly × Life of PV system > 1. E in,T

(11.16)

Further, the numerical value of EPF should be as maximum as possible along with minimum energy payback time (EPBT).

11.3.6.3

Life Cycle Conversion Efficiency (LCCE)

The life cycle conversion efficiency (LCCE) will also depend on annual thermal, electrical energy, thermal and electrical exergy and embodied energy (E in,T ), and life of GiSPVT system and embodied energy (E in,T ) along with annual solar radiation, and it is defined as LCCE =

Eyearly × Life of PV system − Ein,T < 1. Yearly solar radiation × Life of PV system

(11.17)

Here, Yearly solar radiation on roof (kWh) =

number of PV module × area of PV module × 1000

∑12 j=1

I j × 11 h

.

(11.18)

It is to be seen that among all cases considered for different solar cell materials, if • EPBT should be as minimum as possible. • EPF should be as maximum as possible. • LCCE should also be as maximum as possible. Then the GiSPVT system will be economical from energy point of view.

11.3 Thermal Modeling of Aquaculture Water Pond

329

11.3.7 Methodology for Computation Following flow chart given in Fig. 11.5, numerical computations have been carried out as follows: Step 1: Eqs. 11.2, 11.3, and 11.6 have been directly used to compute monthly average (i) water, T w , (ii) room air, T r , and (iii) solar cell, T c , temperatures for 0 to t time interval by using initial condition of water temperature at t = 0 (known) for a known average monthly solar radiation and ambient air temperature (Fig. 11.4). Step 2: Computed water pond temperature at time t becomes initial condition for next set calculation and so on. Step 3: After knowing monthly (i) water, T w , (ii) room air, T r , and (iii) solar cell, T c , temperatures, an instantaneous PV module electrical efficiency, ηmi , can be evaluated from 11.7. Step 4: Thus, the remaining monthly/yearly variable can be obtained by using appropriate mathematical derived expressions [11.9–11.13] in various subsections. Step 5: Eqs. 11.14 and 11.18 can be used to evaluate embodied energy of south roof of GiSPVT for different solar cell materials by using the data of Table 11.2 and annual solar radiation, respectively. Fig. 11.5 Flowchart to compute various variable parameters of the GiSPVT water pond system

Start

Design Parameter α c, τ g, β, ηo, Ut,ca, Ub,cr etc

Input Parameters I(t), Ta (Fig.2)

Calculate Tw, (Eqn.5)

Calculate Tr , (Eqn.6)

Calculate Tc, (Eqn.7)

Calculate ηmi, Qu,yearly,th 14, 13a)

Calculate , Eyearly (Eqn.12)

Calculate ExT,yearly (Eqn. 15)

End

330

11 Application of Photovoltaic Thermal (PVT) Technology

Table 11.2 Effect of solar cell materials on energy matrices of GiSPVT system Energy matrices

Without thermal exergy

With thermal exergy

Life of PV module, nPV (Yrs)

Exergy efficiency of PV module, nPV (Yrs) Without thermal exergy

With thermal exergy

30

22.04

25.54

30

23.33

26.33

25

24.78

22.34

20

13.47

17.79

15

11.59

13.6

5

2.48

c-Si EPBT

7.96

4.46

EPF

3.77

6.72

LCCE

6.39

13.21

EPBT

6.67

3.67

EPF

4.50

8.20

10.85

22.30

EPBT

5.22

2.66

EPF

4.79

9.40

LCCE

9.46

20.93

EPBT

6.53

2.21

EPF

3.06

9.04

LCCE

3.99

15.53

mc-Si

LCCE nc-Si

a-Si

CdTe EPBT

3.41

1.40

EPF

4.40

10.76

LCCE

6.16

17.68

EPBT

2.52

1.17

EPF

1.99

4.28

LCCE

4.94

16.44

CIGS 3.83

Step 6: After knowing embodied energy from step r each solar cell material, following Sect. 7.3.6, energy matrices for each solar cell materials will be computed.

11.3.8 Results and Discussion The results for average monthly variation of water pond, T w , GiSPVT solar cell, T c , room air, T r , and electrical efficiency, ηmi , are shown in Figs. 11.6, 11.7, 11.8, 11.9

11.3 Thermal Modeling of Aquaculture Water Pond

331

and 11.10a. One can easily conclude that there is not much effect of solar cell material on average monthly variation of water pond, T w , GiSPVT solar cell, T c , room air, T r , respectively. Figure 11.6 shows that the maximum temperature occurs in the month of May due to maximum solar radiation incident on roof of GiSPVT with packing factor of 0.89. In this case, the hot room air should be thrown out of GiSPVT to save inside cultivated plant/aquatic animals (fish). Some cooling arrangement should be made between February and November, namely by roof vent, forced mode of operation by fans and evaporative cooling, etc. The energy consumed by fan will be recovered from energy produced by GiSPVT. As mentioned earlier, there is marginal effect of solar cell materials on solar cell temperature which is also at peak about 90 °C which is also not good for its electrical efficiency (Fig. 11.7). This high temperature of solar cell can also be controlled by making an arrangement of water flow over roof. It can solve two problems, namely roof cleaning and reducing solar cell temperature for higher efficiency during summer condition. Room air temperature, Fig. 11.8, can also be controlled along with temperature of solar cell and water mass. Figure 11.9 shows the significant effect on electrical efficiency of various solar cells due to different value of temperature coefficient (Table 11.2). The c-Si solar cell has maximum electrical efficiency. However, Fig. 11.10a shows a tremendous effect on exergy with and without thermal exergy. It can be concluded that c-Si solar cell material gives the best performance on the basis of exergy with and without thermal exergy. Further, energy matrices, namely energy payback times (EPBT), energy production factor (EPF), and life cycle conversion efficiency (LCCE), are given in Table 11.2 for different solar cell materials. Following observations can be made out of Table 11.2: (a) Al silicon (Si) base solar cell has maximum life cycle conversion efficiency (LCCE) as well exergy efficiency with maximum life time. (b) Among silicon (Si) base solar cell, nc-Si solar cell has minimum energy payback time (EPBT) but has lower life time. (c) Rest of the solar cells have the stability problem. (d) Due to this fact, c-Si.mc-Si has maximum production (about 85% market) globally. Example 11.1 Derive an expression of room air temperature (Tr ) in the term of water temperature (Tw ) of GiSPVT system. Solution From Eqs. 8.13 and 8.14, one has αc τg β ARS I (t) = Ut,ca (Tc − Ta )ARS + Ub,cr (Tc − Tr ) ARS + η0 τg β ARS I (t) and

(11.1.1)

332

11 Application of Photovoltaic Thermal (PVT) Technology

Fig. 11.6 Monthly variation of water pond temperature of GiSPVT system

Ub,cr (Tc − Tr )ARS + h 1 (Tw − Tr )Aw =

5 ∑

Ai Ui (Tr − Ta )

(11.1.2)

i=1

In order to eliminate solar cell temperature (Tc ), we have from Eq. 11.1.1 as Tc =

τg β(αc − η0 )I (t) + Ut,ca Ta + Ub,cr Tr Ub,cr + Ut,ca

Or, τg β(αc − η0 )I (t) + Ut,ca Ta + Ub,cr Tr − Tr Ub,cr + Ut,ca τg β(αc − η0 )I (t) − Ut,ca (Tr − Ta ) = Ub,cr + Ut,ca

Tc − Tr =

or,

11.3 Thermal Modeling of Aquaculture Water Pond

333

Fig. 11.7 Monthly variation of various solar cell temperatures of GiSPVT system

Ub,cr (Tc − Tr ) =

Ub,cr Ut,ca Ub,cr τg β(αc − η0 )I (t) − (Tr − Ta ) Ub,cr + Ut,ca Ub,cr + Ut,ca

or, Ub,cr (Tc − Tr )ARS = PF1 ARS τg β(αc − η0 )I (t) − Ura1 ARS (Tr − Ta ).

(11.1.3)

Substitute the above expression in Eq. 11.1.2, one gets PF1 ARS τg β(αc − η0 )I (t) − Ura1 ARS (Tr − Ta ) + h 1 (Tw − Tr )Aw =

5 ∑

Ai Ui (Tr − Ta ).

i=1

The expression of room air temperature (Tr ) in terms of water temperature (Tw ) can be obtained from the above equation as

334

11 Application of Photovoltaic Thermal (PVT) Technology

Fig. 11.8 Monthly room air temperature of GiSPVT water pond system

Fig. 11.9 Average monthly variation of electrical efficiency of solar cell for different solar cell materials

11.3 Thermal Modeling of Aquaculture Water Pond

335

(a) 35000 Yearly genration of exergy (W)

With Thermal Exergy 30000

Without Thermal Exergy

25000 20000 15000 10000 5000 0 cSi

mcSi

ncSi

aSi

CdTe

CIGS

Different solar cell materials

(b)

Top and Inside view of 7.5 kWp BiSPVT system Ladder for cleaning Semitransparent PV roof

Top view

Inside view

Fig. 11.10 a Yearly exergy of GiSPVT system with and without thermal exergy. b Top and inside view of building integrated semitransparent photo-voltaic thermal (BiSPVT) system

PF1 ARS τg β(αc − η0 )I (t) + Ura1 ARS Ta + h 1 Aw Tw +   Tr = ∑5 Ura1 ARS + h 1 Aw + i=1 Ai Ui

∑5 i=1

Ai Ui Ta

.

(11.1.4) The above equation is exactly same as Eq. 11.3.

336

11 Application of Photovoltaic Thermal (PVT) Technology

Example 11.2 Derive (Tw − Tr ) to solve Eq. 8.15 to find out analytical expression for water pond temperature. Solution From Example 11.1, we have an expression of room air temperature (Tr ) in terms of water temperature (Tw ), Eq. 11.1.3 as PF1 ARS τg β(αc − η0 )I (t) + Ura1 ARS Ta + h 1 Aw Tw +   Tr = ∑5 Ura1 ARS + h 1 Aw + i=1 Ai Ui

∑5 i=1

Ai Ui Ta

.

Now, we can get (Tw − Tr ) as PF1 ARS τg β(αc − η0 )I (t) + Ura1 ARS Ta + h 1 Aw Tw +   Tw − Tr = Tw − ∑5 Ura1 ARS + h 1 Aw + i=1 Ai Ui

∑5

i=1 Ai Ui Ta

or Tw − Tr     ∑5 ∑5 Ai Ui − PF1 ARS τg β(αc − η0 )I (t) + Ura1 ARS Ta + h 1 Aw Tw + i=1 Ai Ui Ta Ura1 ARS + h 1 Aw + i=1   = ∑5 Ai Ui Ura1 ARS + h 1 Aw + i=1

    ∑5 Ura1 ARS + i=1 Ai Ui (Tw − Ta ) − PF1 ARS τg β(αc − η0 )I (t)   Tw − Tr = ∑5 Ura1 ARS + h 1 Aw + i=1 Ai Ui   ∑5 h 1 Aw Ura1 ARS + i=1 Ai Ui  (Tw − Ta ) h 1 Aw (Tw − Tr ) =  ∑5 Ura1 ARS + h 1 Aw + i=1 Ai Ui

  h 1 Aw  P F1 ARS τg β(αc − η0 ) I (t) − ∑5 Ura1 ARS + h 1 Aw + i=1 Ai Ui   h 1 Aw (Tw − Tr ) = (U A)wa (Tw − Ta ) − PF2 PF1 ARS τg β(αc − η0 ) I (t)   = (U A)wa (Tw − Ta ) − PF2 ARS I (t)

(U A)wa

and

  ∑5 h 1 Aw Ura1 ARS + i=1 Ai Ui  ; (ατ )eff = PF1 ARS τg β(αc − η0 ) = ∑5 Ura1 ARS + h 1 Aw + i=1 Ai Ui

11.5 PVT Water Collectors Connected in Series

337

h 1 Aw  PF2 =  ∑5 Ura1 ARS + h 1 Aw + i=1 Ai Ui These constants are exactly same as derived in Eq. 8.18 (here Awp = Aw = Surface area of water pond).

11.4 The BiSPVT Passive Heating If greenhouse integrated semitransparent photo-voltaic thermal (GiSPVT) system/ semitransparent photo-voltaic thermal (SPVT) is integrated with roof of building, it is referred as building integrated semi-transparent photo-voltaic thermal (BiSPVT) system as shown in Fig. 11.10b. In this case too, there is direct and indirect gain into room. The direct gain provides thermal as well as daylighting, and indirect gain is utilized to heat room only. The direct gain in BiSPVT is mostly used for daylighting, and in the case of GiSPVT, it is used for photosynthesis. It is always economical to use semi-transparent PV module in the roof. It can be integrated to façade as well for daylighting only. The ladder is used to clean the top roof of PV module for better performance. The thermal modeling of BiSPVT system is similar to those of GiSPVT system (Chap. 8). The details about BiSPVT system, known as SODHA BERS COMPLEX (SBC) at Varanasi (UP), India, have been described in a book entitled “Photovoltaic Thermal Passive House System” by Tiwari and Gupta [5]. The SBC includes all passive concepts including Trombe wall, cross-ventilation, daylighting, underground shelter, wind tower, height of room, etc. The roof system provides about 20% of electricity to the building and comfort temperature during winter and summer condition in Varanasi. Further, if opaque PV module (OPV) is integrated with roof of a building, then it will referred as building integrated opaque photovoltaic thermal (BiOPVT) system [15].

11.5 PVT Water Collectors Connected in Series 11.5.1 Introduction The photovoltaic thermal (PVT) collector was first studied by Kern and Russell [16] to provide both electrical and thermal energy as mentioned earlier. After that, later on, many other researchers [17–23] have developed the photovoltaic thermal (PVT) system for increasing its electrical and thermal efficiency. The classification of flat plate collector is given in Table 11.3.

338

11 Application of Photovoltaic Thermal (PVT) Technology

Table 11.3 Classification of flat plate collectors

Flat Plate Collector (FPC)

Conventional Flat Plate Collector

Photovoltaic Thermal Flat Plate Collector (PVT FPC)

Semi Transparent PVT-FPC

Opaque PVT-FPC

Tedlar Base PVTFPC

Al/Cu Base PVTFPC

The flat plate collector (FPC) and photovoltaic thermal (PVT) collector are designed, analyzed, and classified by various scientists/researchers, Table 11.3, which are as follows: (a) (b) (c) (d)

Flat plat collector (FPC), Fig. 11.11 [24–27] Opaque/semitransparent PVT air collectors, Fig. 11.12 [19, 28] Opaque and semitransparent PVT water collectors, Fig. 11.13 [30–32] Opaque aluminum (Al) PVT collector, Fig. 11.14 [33–35].

Fig. 11.11 Cross-sectional view of flat plate collector (FPC)

11.5 PVT Water Collectors Connected in Series

339

Fig. 11.12 Semitransparent photovoltaic thermal (SPVT) air collector

Figure 11.13b shows the three-dimensional view of opaque PVT water collector. At top of PVT water collector, there is anti-reflecting toughen glass to minimize the reflection losses before transmission. Further, there is ethyl vinyl acetate (EVA) above and below solar cells connected in series for higher durability and to avoid corrosion if any taking place die to the presence of moist air. The bottom EVA is fixed on back sheet which can be Tedlar (opaque), glass (semitransparent), and aluminum (flexible). After that there is tube below conducting plate (heat exchanger) to carry fluid which is insulated to reduce bottom heat loss. In this case, Fig. 11.13b, there is an overall heat transfer from the heat exchanger to working fluid unlike Fig. 11.13a. In Fig. 11.13a, there is gap between back of PV module and heat exchanger. In the case of Fig. 11.13a, there can be direct as well as indirect gain to heat exchanger if opaque PV module is replaced by semitransparent PV module. If back sheet is glass, then it is referred as semitransparent PV (SPV) module; otherwise, it is opaque PV module. In the absence of tube, it can be used as air collector. It has been observed that semitransparent PV (SPV) module has higher electrical efficiency in comparison with opaque PV (OPV) module [25]. In semitransparent PV (SPV) module, the thermal energy available through non-packing area can be used directly for the purpose of thermal heating of any system. Hottel-Whillier-Bliss (HWB) equation is an instantaneous thermal efficiency of flat plate collector (FPC) in the term of design parameters and climatic parameters. They have the experimental validation of Hottel-Whillier-Bliss (HWB) equation flat plate collector was carried out under standard test condition (STC) (Duffie and Beckman) [24]. This equation is also known as characteristic equation [25]. It is useful for testing the flat plate collectors of different design on the basis of energy gain and loss factors. The Hottel-Whillier-Bliss (HWB) equation for N-photovoltaic thermal (PVT)compound parabolic concentrators (CPC) [N-PVT-CPC] has been developed by Tiwari et al. [35] which is applicable to all type of flat plate collectors mentioned above. The same has also been validated like flat plate collector which can be valid for most of configuration of PVT collectors as well as conventional flat plate collector (FPC).

340

11 Application of Photovoltaic Thermal (PVT) Technology

(a)

(b)

1.Anti reflecting coating glass 2. Encapsulate (EVA)

3. Solar cells connected in series

4. Encapsulate (EVA)

5. Back sheet (Tedlar/glass/aluminium) 6. Heat exchanger (copper/aluminium) Copper tubes for fluid flow 7. Insulating material

Fig. 11.13 a Cross-sectional view of opaque SPVT water collector. b Three-dimensional view of PVT water collector

11.5.2 System Description of N-PVT-CPC The cross-sectional side view, cut-sectional front view, and three-dimensional view of single semitransparent photovoltaic thermal-compound parabolic concentrator (SPVT-CPC) collector configuration is shown in Fig. 11.15a–c. The incident solar radiation on the reflector of concentrator, Fig. 11.15b, c, gets reflected on SPVT collector (Fig. 11.15a). The area of PVT-CPC on which received solar radiation is known as the aperture area (Aa ) and the area of semitransparent SPV module which receives the reflected useful solar radiation is termed as the receiver area (Ar ). The

11.5 PVT Water Collectors Connected in Series

341

Fig. 11.14 Aluminum (Al) base PVT collector

solar radiation falling on the SPV module will be transmitted through non-packing area and then absorbed by the absorber. The rest of solar radiation incident on the solar cells of SPV is partially converted into electrical energy and the remaining transfer into thermal energy to raise the solar cell’s temperature. The thermal energy associated with the solar cells of the SPV module is transferred to the absorber/ receiver by convection for further heating of the receiver/absorber plate. Finally, the heat gets transferred from absorber plate to water flowing through the pipe below the absorber plate. Thus, this results in an increase in the temperature of flowing water. So, SPVT-CPC collector produces thermal as well as electrical energy by harnessing solar radiation. In order to produce the large amount of thermal and electrical energy, a number of SPVT-CPC collectors are connected in series as shown in Fig. 11.15d. Table 11.4 gives the design parameters of the system under consideration.

11.5.3 Analytical Expression In the present section, an analytical expression for (i) temperature solar cell, (ii) the outlet water temperature of working fluid, (iii) the rate of thermal energy, and (iv) an instantaneous thermal and electrical efficiency of SPVT-CPC collector and an

342

11 Application of Photovoltaic Thermal (PVT) Technology

(a)

Absorber Plate

x

Solar Cell

Semi-transparent PV module

Air Gap Water Inlet

Water Outlet

Thermal insulation

Cut section of metallic tube

x’

(b)

b0

Reflector

Fully covered PV module

Water flowing tubes

Fig. 11.15 a Cross-sectional sides view of fully covered PVT-CPC water collector. b Cut-sectional xx' front view of fully covered PVT-CPC water collector system as given in a. c Three-dimensional view of PVT-CPC collector. d Series connected arrangement of fully covered N-PVT-CPC water collector

11.5 PVT Water Collectors Connected in Series

343

(c)

1st Collector

(d)

2nd Collector

Tfo1

3rd Collector

Nth Collector

Tfo3

TfoN-1

Water Inlet, Tfi

Water Outlet, TfoN

Tfo2

Fig. 11.15 (continued) Table 11.4 Design parameters used in numerical computation

Aam = 4.2 m2 Arm = 2.1 m2 Arc = 2.1 m2 F ' = 0.968 K g = 0.816 W/m K L g = 0.003 m K i = 0.166 W/m K L i = 0.100 m K p = 6 W/m K L p = 0.002 m L i = 0.100 m UL1 = 3.47 W/m2 K ULm = 7.87 W/m2 K Utc,a = 9.17 W/m2 K ULc = 4.7 W/m2 K Utc,p = 5.58 W/m2 K

Utp,a = 4.8 W/m2 K PF1 = 0.3782 PF2 = 0.9512 PFc = 0.9842 h pf = 100 W/m2 h i = 5.7 W/m2 h 'i = 5.8 W/m2 h o = 9.5 W/m2 αc = 0.9 αp = 0.8 βc = 0.89 τg = 0.95 ρ = 0.84 Cf = 4179 J/kg K m˙ f = 0.0025 kg/s

344

11 Application of Photovoltaic Thermal (PVT) Technology

electrical energy of N-semitransparent photovoltaic thermal-compound parabolic concentrator (SPVT-CPC) collectors connected in series, Fig. 11.15c, has been derived. The proposed N-SPVT-CPC collectors, Fig. 11.15c, has following advantages: (a) It is easy and feasible to fabricate SPVT-CPC as compared to partially covered SPVT-CPC collector [21]. (b) Maintenance cost is lower due to the absence of joint between PV and glass covered of SPVT collectors. (c) Packing factor (β) can be optimized as per requirement of electrical as well thermal energy by users. 11.5.3.1

The Rate of Thermal Energy

In order to simplify the mathematical model, the limitations and physical assumptions assumed by Parapas et al. [37] have been considered. Some additional assumptions are as follows: (a) The N-SPVT-CPC collectors have been analyzed in quasi-steady-state condition. (b) One-dimensional heat conduction has been considered due to larger absorber area in comparison with side walls. (c) The heat capacity of solar cell, absorber plate, glass cover, reflector, and insulation materials has been neglected due to its low heat capacity as well as insulating properties. (d) The ohmic losses between two solar cells have been neglected due to cooper wiring. (a) The basic energy balance equations Referring to thermal circuit of single SPVT-CPC collector, Fig. 11.16a, followings are energy balance of each component: [The rate of absorbed solar radiation received by solar cells after transmission from top glass through packing area of PV module] = [The rate of heat transferred from solar cells to ambient through top glass cover] + [The rate of heat transferred from solar cells to absorber pate through the bottom glass of SPV module] + [The rate of electrical energy generated by SPV module]  ραc τg βc Iu Aam = Ut,ca (Tc − Ta )Arm + Ut,cp Tc − Tp Arm + ρηc τg βc Iu Aam (11.19a) Figure 11.16b shows the hourly variation of solar radiation (Iu ) available on aperture area as well as ambient air temperature (T a ) for a typical day of summer month for New Delhi climatic conditions obtained from Indian Metrological Department (IMD), Pune, India.

11.5 PVT Water Collectors Connected in Series

345

(a)

(b)

Fig. 11.16 a Thermal circuit diagram of single SPVT-CPC collector. b Hourly variation of solar intensity and ambient air temperature for a typical day of May, New Delhi, India

346

11 Application of Photovoltaic Thermal (PVT) Technology

where Utc,a =



Lg Kg

+

1 h0

−1

; Utc,p =



Lg Kg

+

−1

1 hi Id , C

; h 0 = 5.7 + 3.8V W/m2 K; V =

1 m/s; and h i = 5.7 W/m2 K and I u = I b + C = AAam (Prapas et al. [37]). rm Above equation gives an expression for solar cell’s temperature (Tc ) Tc =

(ατ )1,eff Iu + Ut,ca Ta + Ut,cp Tp , Ut,ca + Ut,cp

(11.19b)

where ; for SPVT-CPC collector, Fig. 11.5a, b. (ατ )1,eff = (αc − ηc )ρτg βc AAam rm = (αc − ηc )τg βc ; = 1, Aam = Arm ; for SPVT collector, Fig. 11.13. = αc ; βc = 1, ρ = 1 and Aam = Arm ; for FPC, Fig. 11.11. Here C =

is a concentration ration > 1.

Aam Arm

(b) Energy balance for absorber plate [The rate of absorbed solar energy on absorber plate through non-packing area of SPV module] + [The rate of heat transferred from solar cells to absorber pate through the bottom glass of SPV module] = [The rate of heat transferred to working fluid flowing in tubes/duct below the absorber plate] + [The rate of heat transferred from absorber plate to ambient through bottom insulation]  ραp τg2 (1 − βc )Iu Aam + Ut,cp Tc − Tp Arm   = F ' h pf Tp − Tf Arm + Ut,pa Tp − Ta Arm

(11.20)

The numerical value of F ' < 1 for water collector; Fig. 11.5a, b; Fig. 11.13; Fig. 11.11, and F ' = 1 for PVT air collector (Fig. 11.12). From Eq. 11.19b, we can obtain  Ut,cp Tc − Tp =

Ut,cp Ut,cp Ut,ca  Tp − Ta (ατ )1,eff Iu − Ut,ca + Ut,cp Ut,ca + Ut,cp

or   Ut,cp Tc − Tp = PF1 (ατ )1,eff Iu − UL1 Tp − Ta , U

U

U

t,cp where PF1 = Ut,ca +U and UL1 = Ut,cat,cp+Ut,cat,cp . t,cp Substitute Eq. 11.21 in to Eq. 11.20, one gets

   ραp τg2 (1 − βc )Iu Aam + PF1 (ατ )1,eff Iu − UL1 Tp − Ta Arm   = F ' h pf Tp − Tf Arm + Ut,pa Tp − Ta Arm or,

(11.21)

11.5 PVT Water Collectors Connected in Series



347

  Aam ραp τg2 (1 − βc ) + PF1 (ατ )1,eff Iu + UL1 + Ut,pa Ta + F ' h pf Tf Aam   = UL1 + Ut,pa + F ' h pf Tf

or, Tp =

[(ατ )2,eff + PF1 (ατ )1,eff ]Iu + UL2 Ta + F ' h pf Tf , UL2 + F ' h pf

(11.22)

where [(ατ )2,eff = ραp τg2 (1 − βc ) AAam ; for SPVT-CPC collector, Fig. 11.5a, b. am = ραp τg2 (1 − βc ) for ρ = 1, Aam = Arm ; for SPVT collector, Fig. 11.13. = 0; for βc = 0 ρ = 1, Aam = Arm for ρ = 1, Aam = Arm ; for FPC, Fig. 11.11,  and U L2 = UL1 + Ut, pa . From Eq. 11.22, we can derive    h pf Tp − Tf = PF2 (ατ )m,eff Iu − ULm (Tf − Ta ) , where PF2 =

h pf , F ' h pf +UL2

ULm =

h pf UL2 F ' h pf +UL2

(11.23)

and (ατ )eff = [(ατ )2,eff + PF1 (ατ )1,eff .

(c) Energy balance for flowing water in tube as fluid below the absorber plate [The rate of thermal energy carried away by flowing water] = [The rate of thermal energy transferred from absorber plate to flowing water] m˙ f Cf

 dTf dx = F ' h pf Tp − Tf b dx dx

(11.24)

Here F ' = 1 for PVT air collector, Fig. 11.12. From Eqs. (11.23) and (11.24), one gets m˙ f Cf

dTf dx = F ' [PF2 (ατ )m,eff Iu − ULm (Tf − Ta )]b dx. dx

(11.25)

Equation 11.25 is one order differential equation which can be solved by using initial condition, Tf |x=0 = Tfi , the solution can be obtained as:  Tf =

PF2 (ατ )m,eff Iu + Ta ULm

     −F ' ULm bx −F ' ULm bx 1 − exp + Tfi exp m˙ f Cf m˙ f Cf (11.26)

Referring to Fig. 11.15c, the outlet fluid temperature at end of the first PVT-CPC combination can be obtained as:

348

11 Application of Photovoltaic Thermal (PVT) Technology

Tfo1 = Tf |x=L rm or,    PF2 (ατ )m,eff Iu −F1' ULm1 bL rm + Ta 1 − exp ULm1 m˙ f Cf   ' −F1 ULm1 bL rm + Tfi1 exp m˙ f Cf 

Tfo1 =

or,    P F2 (ατ )m,eff Iu −F1' ULm1 Arm1 + Ta 1 − exp ULm1 m˙ f Cf   −F1' ULm 1Arm1 . + Tfi1 exp m˙ f Cf 

Tfo1 =

(11.27)

(d) Analytical expression for outlet temperature at N th SPVT-CPC collector Similarly, the outlet fluid temperature at the end of second SPVT-CPC combination can be written as     PF2 (ατ )m,eff Iu −F2' ULm2 Arm2 Tfo2 = + Ta 1 − exp ULm2 m˙ f Cf   −F2' ULm2 Arm2 , (11.28) + Tfi2 exp m˙ f Cf where Tfi2 is inlet temperature of water for second SPVT-CPC collector which is equal to outlet water temperature for first SPVT-CPC, i.e., Tfi2 = Tfo1 . After substitution Tfo1 as given in Eq. 11.27, into Eq. 11.28, one can obtain the expression for Tfo2 as follows:    PF2 (ατ )m,eff Iu −F2' ULm2 Arm2 = + Ta 1 − exp ULm2 m˙ f Cf   PF2 (ατ )m,eff Iu + + Ta ULm1      −F2' ULm2 Arm2 −F1' ULm1 Arm1 exp 1 − exp m˙ f Cf m˙ f Cf   ' −(F'1 ULm1 Arm1 + F2 ULm2 Arm2 ) + Tfi1 exp m˙ f Cf 

Tfo2

Similarly, the outlet fluid temperature for N th SPVT-CPC collector can be obtained as follows:

11.5 PVT Water Collectors Connected in Series

349

   PF2 (ατ )m,ef f Iu −FN' ULm N Arm N + Ta 1 − exp ULm N m˙ f Cf     ' −FN −1 ULm N −1 Arm N −1 PF2 (ατ )m,eff Iu + + Ta 1 − exp ULm N −1 m˙ f Cf      ' PF2 (ατ )m,eff Iu −FN U Lm N Arm N + exp + Ta m˙ f Cf ULm N −2    ' −FN −2 ULm N −2 Arm N −2 1 − exp m˙ f Cf    −(F' N ULm N Arm N + FN' −1 ULm N −1 Arm N −1 ) exp m˙ f Cf     PF2 (ατ )m,ef f Iu −F1' ULm1 Arm1 + ··· + + Ta 1 − exp ULm1 m˙ f Cf    ' −(F' N ULm N Arm N + · · · + F1 ULm1 Arm1 ) exp m˙ f Cf    −(F' N ULm N Arm N + · · · + FN' −1 ULm N −1 Arm N −1 ) . + Tfi1 exp m˙ f Cf (11.29) 

TfoN =

In this case, all SPVT-CPC are identical, then there should be following condition: ULm1 = ULm2 = · · · = ULm N = ULm Arm1 = Arm2 = · · · = Arm N = Arm Tfi = Tfi1 and F1' = F2' = · · · = FN' = F ' . Now, on applying above condition into Eq. 11.29, one can get expression for TfoN as follows:     PF2 (ατ )m,eff Iu −N F'ULm Arm TfoN = + Ta 1 − exp ULm m˙ f Cf   −N F'ULm Arm (11.30) + Tfi exp m˙ f Cf Equation 11.30 has been discussed for the following cases:

350

11 Application of Photovoltaic Thermal (PVT) Technology

Case (i): For βc = 0 means no electrical power, then Eq. 11.30 reduces to    PFc (ατ )c,eff Iu −N F'ULc Arc = + Ta 1 − exp ULc m˙ f Cf   −N F'ULc Arc , + Tfi exp m˙ f Cf 

TfoN

(11.31)

which is same as the outlet fluid temperature at Nth flat plate collector-compound parabolic concentrator (FPC-CPC) configuration. Case (ii): For Arm = Aam = Am , ρ = 1 and I u = I(t), then Eq. 11.30 is reduced to    PF2 (ατ )m,eff I (t) −N F'ULm Am = + Ta 1 − exp ULm m˙ f Cf   −N F'ULm Am . + Tfi exp m˙ f Cf 

TfoN

(11.32)

The above equation can also be obtained from the expression derived by Shyam et al. [32] [Eq. 11.18 with Ac = 0] for fully covered Nth-PVT-FPC collector. Case (iii): For Arm = Aam = Ac , ρ = 1, I u = I(t) and βc = 0, Eq. 11.30 is reduced to    PFc (ατ )c,eff I (t) −N F'ULc Ac = + Ta 1 − exp ULc m˙ f Cf   −N F'ULc Ac . + Tfi exp m˙ f Cf 

TfoN

(11.33)

Equation 11.33 is similar to those derived for N-FPC connected in series [Eq. 3.88a Tiwari [27]]. Case (iv): For N = 1, Eq. 11.30 is reduced to 

Tfo1

PF2 (ατ )m,eff Iu = + Ta ULm

     −F ' ULm Arm −F ' ULm Arm 1 − exp + Tfi exp m˙ f Cf m˙ f Cf (11.34)

The above equation can also be obtained from the expression derived by Atheaya et al. [21] [Eq. 11.19, with Ac = 0] for single fully covered SPVT-CPC collector. Case (v): For Arm = Aam = Ac , ρ = 1, I u = I(t), N = 1 and βc = 0, Eq. 11.30 is reduced to       PFc (ατ )c,eff I (t) −F ' ULc Ac −F ' ULc Ac + Tfi exp Tfo1 = + Ta 1 − exp ULc m˙ f Cf m˙ f Cf (11.35)

11.5 PVT Water Collectors Connected in Series

351

(e) Modified Hottel-Whillier-Bliss (HWB) equation for N-SPVT-CPC collectors The rate of useful thermal energy available at the outlet of N-SPVT-CPC collector can be evaluated by following equation: Q˙ uth,N = m˙ f Cf (TfoN − Tfi )

(11.36)

After substituting an expression of TfoN from Eq. 11.30 into Eq. 11.36, the rate of useful thermal energy ( Q˙ uth,N ) can be written as follows:   Q˙ uth,N = N Arm FRm N PF2 (ατ )m,eff Iu − ULm (Tfi − Ta ) ,

(11.37)

where FRm N is mass flow rate factor of N-SPVT-CPC collector and it is given by FRm N =

   −N F'ULm Arm m˙ f Cf 1 − exp N Arm ULm m˙ f Cf

(11.38)

Further, an instantaneous thermal efficiency of N-SPVT CPC water collectors can be defined as ηi,th =

Q˙ uth,N N Aam Iu

After substitution of the expression of Q˙ uth,N from Eq. 11.37 into above equation, one gets the  ηi,th = FRm N

 PF2 (ατ )m,eff ULm (Tfi − Ta ) , − C C Iu

(11.39)

where C = AAam > 1 is concentration ratio of compound parabolic concentrators. rm Equation 11.39 is the thermal characteristic equation for N-SPVT-CPC configuration. This is similar to Hottel-Whillier-Bliss (HWB) equation for flat plate collector (FPC) (Duffie and Beckman [24] and Tiwari [27]). Equation 11.39 is referred as the modified Hottel-Whillier-Bliss (HWB) equation.

11.5.3.2

The Rate of Electrical Energy

Tiwari et al. [36] have considered Eqs. 11.19b and 11.22 to evaluate average solar cell and absorber temperature at Nth SPVT-CPC collector by average fluid temperature at Nth SPVT-CPC collector

352

11 Application of Photovoltaic Thermal (PVT) Technology

T fN =

TfoN + TfoN −1 2

(11.40)

After evaluating T fN from above equation, an average solar cell (T cN ), Eqs. 11.19b and absorber (T pN ), Eq. 11.22 temperature at Nth SPVT-CPC collector was evaluated from T cN = T pN =

(ατ )1,eff Iu + Ut,ca Ta + Ut,cp T pN Ut,ca + Ut,cp

[(ατ )2,eff + PF1 (ατ )1,eff ]Iu + UL2 Ta + F ' h pf T fN UL2 + F ' h pf

(11.41)

(11.42)

Following steps were considered to evaluate an electrical efficiency of N-SPVTCPC: Step 1: The hourly variation of TfoN by using Eq. 11.30 for design parameters of Table 11.4 and climatic data’s of Fig. 11.6b was computed. Step 2: By using the hourly data of TfoN , the hourly T fN from Eq. 11.40 was computed. Step 3: The hourly variation of T fN was used to compute hourly T pN , Eq. 11.42. Step 4: After knowing hourly T pN (step 3), the hourly average solar cell (T cN ) temperature. Step 5: After step 4, hourly solar cell electrical efficiency (ηcN ) was evaluated by expression proposed by Evans [11] as follows:    ηcN = η0 1 − β0 T cN − T0 ,

(11.43)

where η0 = 0.12 is efficiency at standard test condition (i.e., at T0 = 25 °C and I(t) = 1000 W/m2 ) and β0 is temperature coefficient of solar cell efficiency (0.0045 °C for known T cN . (step 4). Further, the electrical efficiency and electrical energy of SPVT module of N-PVTCPC collectors have been evaluated as follows: ηmN = τg βc ηcN

(11.44)

E el = N Aam Iu ηmN ,

(11.45)

and,

where ηcN is given by Eq. 11.45.

11.6 SPVT Air Collectors Connected in Series

11.5.3.3

353

Results and Discussion

The computation was carried out for following cases: (a) (b) (c) (d)

Flat plate collector [FPC] At plate collector-compound parabolic concentrator [FPC-CPC] Semitransparent photovoltaic thermal (SPVT) collector Semitransparent photovoltaic thermal-compound parabolic concentrator [SPVT-PV] collector.

Some of the results are shown in Fig. 11.17. On the basis of results shown in Fig. 11.17, following observations have been made: (a) Maximum temperature of 265 °C has been observed in the case of flat plate collector-compound parabolic concentrator [FPC-CPC] at noon time as per expectation at fifth collector. The FPC-CPC system may be used for power generation because its temperature can be increased further by increasing the number of FPC-CPC (Fig. 11.17a). (b) Minimum temperature of 70 °C has been observed in the case of SPVT/PVT collector along with maximum electrical efficiency at end of fifth collector. This can be referred as self-sustain unlike FPC-CPC and FPC (Fig. 11.17a). (c) However, the rate of thermal energy and electrical energy is maximum in the case of FPC-CPC and SPVT/PVT-CPC due to input solar radiation is maximum at aperture of CPC (Fig. 11.17b). (d) Figure 11.17c suggests that thermal and electrical efficiency is maximum and minimum at minimum packing factor. This is can be justified that at low packing factor, direct thermal energy is more and the number of solar cell is least for a given PVT-CPC collector. (e) It is also to be observed that with decrease of thermal efficiency, an electrical efficiency has trend of increasing approach. (f) In the two cases, namely case (c) and (d), the electrical energy is obtained due to integration of PV module to make system self-sustained. (g) Experimental validation of the thermal model for the rate thermal as well as rate of electrical energy was also carried out as shown in experimental setup (Fig. 11.18). For details, kindly refer the paper published by Tiwari et al. [36].

11.6 SPVT Air Collectors Connected in Series 11.6.1 Introduction As we know that the convective heat transfer in the water from absorber plate is more in comparison with convective heat transfer from absorber plate to air due to its physical properties and storage capacity. So, the design of flat plate air collector is slightly

354

11 Application of Photovoltaic Thermal (PVT) Technology

(a)

(b)

(c)

Fig. 11.17 a Hourly variation of outlet fluid temperature and electrical efficiency for N = 5. b Hourly variation of rate of useful thermal and electrical energy for N = 5. c Effect of packing factor on the characteristic curve for thermal energy and electrical energy of PVT-CPC

11.6 SPVT Air Collectors Connected in Series

355

Fig. 11.18 Photograph of the complete experimental setup

different from water collector as shown in Fig. 11.14. In order to improve the overall efficiency of PVT air collector by increasing the convective heat transfer, an effect of, fin [38]; phase change materials (PCM) [39]; heat pump/pipe [40, 41]; baffle plate [42] on its performance have been studied. Chaibi et al. [43] have analyzed the performance of PVT air collector by using artificial neural network (ANN). Senthilraja et al. [44] have used PVT air collector to produce hydrogen for commercial purposes. Fudholi et al. [45] have reviewed the work on PVT air collector. If semitransparent PV module is used, then it is referred as SPVT air collector.

11.6.2 Working Principle of SPVT Air Collector Figure 11.14 shows the cross-sectional view of semi-transparent photo-voltaic thermal (SPVT) air collector. The solar radiation, I(t), after transmission from τ β A I is absorbed by top glass cover of semitransparent PV module, (t) g c cm  solar cell, αc τg βc Acm I (t) , a part of it is converted into electrical, and the rest is transferred into thermal energy. Further, the solar radiation, I(t), is transmitted from top as well as bottom of semitransparent PV module through nonpacking area [τg2 (1 − βc )Acm I (t)], and is directly absorbed by blackened aboberber [αp τg2 (1 − βc ) Acm I (t)] below semitransparent PV module. The fluid (air) flowing below absorber plate gets (i) indirect thermal energy from back of solar cell by a

356

11 Application of Photovoltaic Thermal (PVT) Technology

tc,f penalty factor of h p1 = Utc,aU+U which has value less than 1 due to indirect gain tc,f from bottom of semi-transparent PV module and (ii) top of absorber plate, another penalty factor due to absorber plate, h p2 to the flowing fluid which gets heated. Thus, the outlet fluid temperature, Tfo1 , becomes higher than inlet fluid temperature, Tfi . The outlet of first SPVT, Tfo1 , is connected to inlet, Tfi2 = Tfo1 of second one as has been done in case of SPVT water collector (Sect. 11.3) and the outlet of second one, Tfo2 to inlet of third one, Tfi3 , and it goes up to Nth SPVT air collector (n = N) as shown in Fig. 11.19a. The design parameters of SPVT are given in Table 11.5.

(a)

(b)

Fig. 11.19 a N-SPVT air collectors connected in series. b Hourly variation of solar intensity, I(t) and ambient air temperature, T a , for a typical day of Srinagar, India [46]

11.6 SPVT Air Collectors Connected in Series Table 11.5 Design parameters of SPVT air collector

357

Acm

1.07 m2

b

0.5 m

Cf

1005 J/kg °C

n

1–10

h pf

14.82 W/m2 °C

m˙ f

0.02–0.08 kg/s

Ubp,a

0.68 W/m2 °C

U Lm

3.58 W/m2 °C

Utc,a

5.7 W/m2 °C

Utc,f

9.5 W/m2 °C

αc

0.9

βc

022–0.84

ηo

0.15

αp

0.8

τg

0.95

11.6.3 Thermal Modeling of SPVT Air Collector, Tiwari et al. [47] In this case, assumptions for writing of energy balance of each components of SPVT air collector are exactly same as assumed in Tiwari et. al. [47].

11.6.3.1

Basic Energy Balance Equations of SPVT Air Collector

(a) For semitransparent PV module Following Sect. 11.3, the energy balance equation in terms of W for solar cells of semitransparent PV module can be written as follows:   αc τg βc I (t)bdx = Utc,a (Tc − Ta ) + Utc,f (Tc − Tf ) bdx + τg ηc αc βc I (t)bdx (11.46a) From above equation, one has Tc =

τg αc βc (1 − ηc )I (t) + Utc,a Ta + Utc,f Tf Utc,a + Utc,f

(11.46b)

358

11 Application of Photovoltaic Thermal (PVT) Technology

(b) For blackened absorber plate Energy balance for absorber plate can also be expressed in terms of W as     αp (1 − βc )τg2 I (t) bdx = [h p,f Tp − Tf + Ubp,a Tp − Ta bdx

(11.47a)

Further, the above equation can be rewritten as Tp =

αp (1 − βc )τg2 I (t) + h p,f Tf + Ubp,a Ta

(11.47b)

Ubp,a + h p,f

(c) For flowing fluid through the air duct In this case, the rate of thermal energy carried away by fluid in W is given by m˙ f Cf

   dTf dx = h p,f Tp − Tf + Utc,f (Tc − Tf ) bdx. dx

(11.48)

Following the procedures given in Sect. 11.3, the solution of Eq. 11.17 can be obtained. The solution of Eq. 11.3 with initial condition of Tf = Tfi at x = 0 will be obtained as        (ατ )m,eff I (t) bUL,m x bUL,m x + Tfi exp − , Tf = + Ta 1 − exp − UL,m m˙ f Cf m˙ f Cf (11.49) where (ατ )m,eff = [h p1 αc τg βc (1 − ηc ) + h p2 αp (1 − βc )τg2 ] and UL,m = Ut,fa + Ub,fa h p1 =

Utc,f Utc,a +Utc,f

and Ut,fa =

Utc,a Utc,f ; Utc,a +Utc,f

h p2 =

h pf Ub,p,a +h pf

and Ub,fa =

Ub,p,a h pf . Ub,p,a +h pf

(d) Analytical expression for fluid temperature at outlet of N-SPVT air collector Further, following the method given in Sect. 11.3, an expression for an outlet fluid temperature air temperature at end of N-SPVT air collector can be written as follows:    (ατ )m,eff I (t) NUL,m Acm + Ta 1 − exp − UL,m m˙ f Cf    NUL,m Acm + Tfi exp − m˙ f Cf 

TfoN =

(11.50)

The above equation is similar to Eq. 11.30 with minor changes due to change in design.

11.6 SPVT Air Collectors Connected in Series

359

11.6.4 New Mass Flow Rate Factor at nth SPVT Air Collector By using Eq. 11.50, an average fluid (air) temperature of n th . SPVT air collector can be obtained as T f,n th The outlet fluid temperature at nth + The outlet fluid temperature at (n − 1)th SPVT air collector 2 Tfo,n + Tfo,n−1 (11.51) = 2

=

By using the numerical values of T f,n th in Eqs. 11.46b and 11.47b, an average solar cell, T c,n th and absorber plate, T p,n th temperatures of n th SPVT air collector can be determined from the following equations: T cn th =

τg αc βc (1 − ηc )I (t) + Utc,a Ta + Utc,f T f,n th Utc,a + Utc,f

(11.52a)

and T pn th =

αp (1 − βc )τg2 I (t) + h p,f + T f,n th + Ubp,a Ta Ubp,a + h p,f

(11.52b)

The rate of thermal energy available at n th semi-transparent PVT (SPVT) air collector is given by  Q˙ u,the-n th = m˙ f Cf Tfo,n − Tfo,n−1

(11.53a)

The total rate of thermal energy from N-SPVT air collector can also be obtained as   Q˙ u,th,N = m˙ f Cf Tfo,1 − Tfi + m˙ f Cf Tfo2 − Tfo,1   + m˙ f Cf Tfo,3 − Tfo,2 + · · · + m˙ f Cf Tfo,N − Tfo,N −1 = m˙ f Cf (TfoN − Tfi ). (11.53b) Now, an instantaneous thermal efficiency of n th semi-transparent PVT (SPVT) air collector can be defined as  m˙ f Cf Tfo,n − Tfo,n−1 Q˙ u,the-n th = (11.54a) ηi,n th = AC × I (t) AC × I (t) After solving above equation with help of Eq. 11.50, one gets

360

11 Application of Photovoltaic Thermal (PVT) Technology

  (Tfi − Ta ) ηi,n th = FR,n th (ατ )m,eff − UL,m I (t)

(11.54b)

In Eq. 11.54b, an improved mass flow rate factor for n th semi-transparent PVT (SPVT) air collector is given by FR,n th =

   nUL,m Acm m˙ f Cf 1 − exp − CF, n Acm UL,m m˙ f Cf

(11.54c)

   Ac ULm ≤ 1. It is referred as a correction factor (CF) and where CF = exp − (n−1) m˙ f Cf varies between 1 and 0 for n = 1 to infinity. Further, Eq. 11.54b is another characteristic equation for nth-PVT air collectors connected in series with improved mass flow rate factor of FR,nth . It should be noted that Case 1: For n = 1, CF = 1, Eq. 11.54b reduces to a characteristic equation for single SPVT air collector as ηi =

    UL,m Acm m˙ f Cf (Tfi − Ta ) 1 − exp − (11.55a) (ατ )m,eff − UL,m Acm UL,m m˙ f Cf I (t)

Equation 11.55a can also be used to test the individual SPVT air collector’s performance. Case 2: For n = 1, CF = 1 and βc = 0, (ατ )m,eff = h p2 αp τg2 , then Eq. 11.54b reduces to     UL,m Acm m˙ f Cf (Tfi − Ta ) 2 1 − exp − h p2 αp τg − UL,m (11.55b) ηi = Acm UL,m m˙ f Cf I (t) Equation 11.55b is Hottel-Whiller-Bliss (HWB) equation for a conventional air collector [1, 2]. Case 3: For very large value of ‘n’, FRn = FR,nth = 0. This means there is no gain of thermal energy. This indicates that the thermal gain and loss become equal. This will help to optimize for a given mass flow rate.

11.6.5 Expression for the Rate of Thermal Energy of N-SPVT Air Collector Connected in Series An analytical expression for the rate of useful thermal energy at outlet of N-semitransparent PVT air collectors, Eq. 11.53b, can be written as Q˙ uth,N = m˙ f Cf (TfoN − Tfi )

(11.56a)

11.6 SPVT Air Collectors Connected in Series

361

Substitute an expression for TfoN from Eq. 11.6 in to Eq. 11.11, one gets     (ατ )m,eff NUL,m Acm ˙ I (t) − (Tfi − Ta ) (11.56b) Q uth,N = m˙ f Cf 1 − exp − m˙ f Cf UL,m An instantaneous thermal efficiency of N-semi-transparent PVT (SPVT) air collector can be defined as Q˙ u,th,N n × AC × I (t)     N Acm UL,m m˙ f Cf Tfi − Ta 1 − exp − = (ατ )m,eff − N Acm UL,m m˙ f Cf I (t)

ηin =

or,   Tfi − Ta = FR N (ατ )m,eff − I (t)

(11.57)

   NUL,m Acm m˙ f Cf 1 − exp − = N Acm UL,m m˙ f Cf

(11.58)

ηin where FR N

Equation 11.57 is a characteristic equation for N-SPVT air collectors connected in series with mass flow rate factor of FR N which is similar to those derived by Hottel-Whiller-Bliss [1] for single flat plate collector (N = n = 1), [1, 2]. For N = n = 1, Eq. 11.44 reduces for single SPVT air collector.

11.6.6 Electrical Efficiency of nth SPVT Air Collector Following [27], the temperature-dependent average electrical efficiency, ηel,n th , of solar cell of n th SPVT air collector can be obtained from    ηel,n th = η O 1 − 0.0045 T c,n th − 25

(11.59)

The average value of solar cell temperature, T c n th , can be obtained from Eq. 11.7 as a function of design and climatic parameters. (a) Electrical energy at n th SPVT air collector The rate of an electrical energy, E˙ el,n th , produced by n th SPVT air collector be obtained by

362

11 Application of Photovoltaic Thermal (PVT) Technology

E˙ el,n th = ηel,n th × I (t) × Acm (W ) =

ηel,n th × I (t) × Acm (kW) 1000

(11.60a)

The rate of total electrical energy, E˙ T,el-n th , produced from N-SPVT air collector is given by E˙ T,el-N =

N ∑

E el,n th

(11.60b)

n=1

No one has computed the rate of total electrical energy, E˙ T,el-n th , produced from N-SPVT air collector given by Eq. 11.60b. (b) Overall thermal energy gain from N-SPVT collectors connected in series The rate of an overall useful thermal energy, Q˙ u N ,overall-thermal-energy , from N-semitransparent PVT air collectors by using Eq. 11.56b and Eq. 11.60b can be written as E˙ T,el-N , Q˙ u N ,overall-thermal-energy = Q˙ u N th + γ

(11.61)

where γ is conversion power factor from thermal power plant. It depends on quality of coal. For best coal in the present study, it is considered as γ = 0.37. (c) Overall exergy analysis of n and nth SPVT air collectors connected in series Following Tiwari et al. [2], the rate of thermal exergy, Q˙ u N -th-exergy , is obtained by using Eq. 11.8 as Q˙ u N -th-exergy = m˙ f Cf

 

TfoN + 273 Tfo,N − Tfi − (Ta + 273) ln Tfi + 273

 (11.62a)

The rate of thermal exergy at n th , Q˙ u,ex-th-n th , PVT air collectors connected in series    Tfo,n + 273 ˙ (11.62b) Q u,ex-th-n th = m˙ f Cf Tfo,n − Tfo,n−1 − (Ta + 273) ln Tfo,n−1 + 273 ˙ u N ,total-exergy , from n-semi-transparent PVT The rate of an overall useful exergy, Ex air collectors is sum of rate of total electrical energy, Eq. 11.11, and thermal exergy, Eq. 11.13, and can be written as ˙ u N ,total-exergy = E˙ T,el-N + Q˙ u N ,th-exergy . Ex

(11.63a)

˙ u,n th ,total , connected in The rate of an overall exergy at n th PVT air collectors, Ex series is the sum of Eqs. 11.15 and 11.17 and can be written as

11.6 SPVT Air Collectors Connected in Series

363

˙ u,n th ,total-exergy = E˙ el,n th + Q˙ u,ex,th-n th Ex

(11.63b)

An overall exergy efficiency of N-SPVT air collector, ηex-total and n th SPVT air collector, ηex-n th connected in series can be defined and written as ηex-total =

˙ u N ,total-exergy Ex ˙ in Acm × N × Ex

(11.64a)

ηex-n th =

˙ u,n th ,total-exergy Ex ˙ in Acm × N × Ex

(11.64b)

and

˙ in , is given by [27, 28] where an exergy of solar radiation, Ex 

˙ in = I (t) 1 − 4 × Ex 3



Ta Ts



1 + × 3



Ta Ts

4  ,

(11.65)

where Ta and Ts (sun temperature) are in Kelvin.

11.6.7 Methodology for Numerical Computation For a given design parameter of PVT air collector, Table 1.5 and climatic data of Fig. 11.2, [46], following methodology has been adopted: Step 1: Eqs. 11.50 and 11.51 have been used to compute the hourly variation of the outlet fluid temperature (TfoN ) and average fluid, T f,n , for different nth of N-SPVT air collectors connected in series for different n varies from 1 to N. Step 2: After knowing hourly variation of an average fluid, T f,n temperatures for different nth of N-SPVT air collectors, step 1, hourly average solar cell, T cnth, and plate, T pnth , temperatures can be evaluated from Eqs. 11.52a and 11.52b, respectively. Step 3: By using the hourly data of TfoN for different N, step 1, an instantaneous thermal efficiency of nth-semi-transparent PVT a collector with correction factor (CF), Eq. 11.54a, has been obtained. Step 4: For known outlet fluid at end of N-SPVT air collector, TfoN , step 1, the hourly variation of the rate useful thermal energy, Q˙ u N th , and an instantaneous thermal efficiency, ηin , from Eqs. 11.56a and 11.57 can be achieved. Step 5: An average hourly electrical efficiency, ηel,nth , the rate of an electrical energy, E˙ el,nth , at nth PVT air collector, and the total electrical energy, E˙ T,el-N , of N-SPVT air collector can be obtained from Eqs. 11.59, 11.60a, and 11.60b for known hourly average solar cell, T cn temperature, as in step 2.

364

11 Application of Photovoltaic Thermal (PVT) Technology

Step 6: The rate of thermal exergy of N-SPVT, Q˙ u N th-exergy , and at nth, SPVT air collector, Q˙ u,ex,th-nth SPVT air collector can be determined from Eqs. 11.7a and 11.17b, respectively, for data of step 1. ˙ u N ,total-exergy Step 7: The rate of an overall useful exergy of N-SPVT air collector, Ex ˙ u,n th,total−exergy can be determined from Eq. 11.62a and at n th SPVT air collector, Ex and 11.62b, respectively. Step 8: An overall exergy efficiency of N-SPVT air collector, ηex-total and at n th SPVT air collectors, ηex-n th connected in series can be evaluated from Eq. 11.64a and 11.64b, respectively.

11.6.8 Results and Discussion As per methodology mentioned above, a program in MATLAB has been prepared to compute various variable parameters by using the design parameters of Table 11.1 and climatic data of Fig. 11.19b [46]. The results for hourly variation of average solar cell temperature, T c,n th (Eq. 11.52a) and its electrical efficiency, ηel,n th (Eq. 11.52b) for various nth SPVT air collectors (from first to 12th) are shown in Fig. 11.20. It can be seen that first SPVT air collector has minimum average solar cell temperature with its highest average electrical efficiency due to low operating temperature range. However, the temperature of solar cell increases with increase of nth SPVT air collector because the outlet of previous SPVT air collector is connected with inlet of next SPVT air collector as shown in Fig. 11.19a. This indicates that as nth number increases, an average electrical efficiency decreases and hence electrical power decreases. Then average electrical power for each PVT air collector will be different, and hence, sum of all electrical power will be total power from N-SPVT air collector, Eq. 11.60b, which has not been studied earlier. It is also important to note that the operating temperature of solar cell becomes beyond 100 °C after third SPVT air collector. It is not good for solar cell reliability point of view, and hence, it is concluded that the optimum number of SPVT air collector is three for a given design parameter and mass flow rate of 0.02 kg/s. The optimum value of number of SPVT will be higher for higher mass flow rate. Equation 11.54b has been further computed to have characteristic curve (relation a) ) with and without correction factor (CF), and the results are between ηi,n th and (TfiI −T (t) shown in Fig. 11.21. It is clearly shown that there is significant effect of correction factor on characteristic curve. It is further observed that an effect of correction factor (CF) (dotted line) decreases as nth number of SPVT air collector increases. In other words, the thermal performance is reduced with correction factor (CFF) for any nth SPVT air collector. This effect has also not been considered earlier. Further, a) has also been shown in same figure the variation of ηel,n th (Eq. 11.59) with (TfiI −T (t) for comparison. This indicates that the trend of thermal characteristic curve is just opposite to electrical characteristic curve as expected.

11.6 SPVT Air Collectors Connected in Series

365

Fig. 11.20 Hourly variation of solar cell temperature and its average electrical energy for different nth SPVT air collector

Fig. 11.21 Variation of thermal and electrical efficiency of SPVT air collector with without correction factor for different nth SPVT air collector

Tfi −Ta I (t)

with and

366

11 Application of Photovoltaic Thermal (PVT) Technology

Fig. 11.22 Daily electrical energy for different nth of SPVT air collector

The daily electrical energy for each SPVT air collector is also shown in Fig. 11.22 with decreasing its value with increase of n as expected due to high operating temperature range with higher losses. One can observe from Fig. 11.23 that the daily thermal energy decreases with increase of nth SPVT air collector as explained earlier; however, the daily thermal exergy first increases up to third SPVT air collector and then starts decreasing for mass flow rate of 0.02 kg/s, and hence, one can also conclude here that the optimum number of SPVT air collector is three (3) like on the basis of electrical efficiency. The optimum value of number of SPVT will be higher for higher mass flow rate as mentioned earlier. The total thermal energy and exergy increases with increase of N as per our expectation. Effect of correction factor (CF) on variation of mass flow rate, FR,nth , at nth SPVT m˙ f Cf is shown in Fig. 11.24. It can be seen that for n = 1, there air collector with Acm UL,m is no effect of correction factor due to its numerical value of one as explained in case (i) of Eq. 11.55a. However, for n > 1, there is significant effect of correction factor as shown in Fig. 11.24. Further it is to be noted that this effect increases with increase of nth number. This effect is maximum at 12th SPVT air collector. The numerical value of CF varies from 1 to 0.123 for n from 1 to 12. Since all basic parameters including solar cell, plate, and fluid temperature at nth SPVT collector are depending upon each other, the role of correction factor (CF) becomes an important parameter which has not been considered earlier as mentioned earlier. There is drop of about 26.8% in electrical yield from first SPVT air collector to 12th SPVT air collector due to increase in operating temperature. The daily thermal exergy and an overall thermal exergy for different N are shown in Fig. 11.6, and it has been seen that both exergy decreases with increase of n. It

11.6 SPVT Air Collectors Connected in Series

367

Fig. 11.23 Daily thermal energy and its exergy at different nth of PVT air collector

Fig. 11.24 Variation of mass flow rate factor, FR,nth . at nth SPVT air collector with and without correction factor (CF), Eq. 11.10

m˙ f Cf Acm UL,m

with

368

11 Application of Photovoltaic Thermal (PVT) Technology

Fig. 11.25 Overall variation of thermal energy, Eq. 11.16, and exergy efficiency (ηex-total ), a Eq. 11.19a, of N SPVT air collector connected in series with TfiI −T (t)

may be due to higher operating temperature range for higher value of N SPVT air collector. The variation of an overall thermal energy, Eq. 11.61, and an overall exergy efficiency, Eq. 11.64a, of N-SPVT air collector connected in series are shown in Fig. 11.25. In all cases, effect of correction factor (CF) has been taken into account through an average value of solar cell and absorber plate temperature. It has been clear from these figures that (a) an overall thermal energy decreases with increase of Tfi −Ta . for a given number of SPVT air collector due to increase in thermal losses; I (t) a (b) an overall thermal energy increases with increase of N for a given TfiI −T and (c) (t) Tfi −Ta an exergy efficiency (ηex-total ) increases slightly with I (t) for all N but reaches at saturation for higher N. This means saturation of exergy efficiency is reached.

11.7 The PVT Air Collector for Room Air/Space Heating of Building Cremers et al. [48] have considered two PVT air collectors, namely (a) The home + 2.0: In this case, PVT air collector consists of a laminated glass-PV-absorber module and aluminum fins with serpentine copper tubes attached together with a heat conductive silicon glue. It is referred as zero-energy building.

11.7 The PVT Air Collector for Room Air/Space Heating of Building Fig. 11.26 PVT air collector integrated with roof for space heating

369

PVT air collector

Insulated Walls

(b) The “ecolar”: In this case, the PVT air collector consists of a holohedral polypropylene absorber pressed against a laminated glass-PV-glass module with aluminum U-profile in diagonal which provides more contact zones between the absorber and the PV module as shown in Fig. 11.26. Further, they have classified both into two categories, namely (a) Shielded: In this case, the PVT air collectors are mounted close to the next construction roof layer with an air gap as air duct for thermal heating of room air. (b) Unshielded: In this case, the PVT air collector is almost surrounded by ambient air all over, e.g., as a shading device or a shading/protecting roof for cooling purposes. The results for various parameters, namely collector efficiency factor (η0 ), heat loss coefficient, W/m2 K, wind speed dependence of heat loss coefficient, J/m3 K, and wind dependence of collector efficiency factor, s/m are given in Table 11.6. On the basis of Table 11.6, following conclusions have been drawn: (i) An electrical efficiency of the home + 2 is better due to higher wind dependence of collector efficiency than ecolar due to minimum heat loss from top cover of PV module. (ii) An electrical efficiency is better in shielded case due to uniform cooling of PV module (heat loss coefficient and low wind speed dependence of heat loss coefficient), in comparison with unshielded due to irregular wind velocity of air around PV module.

370

11 Application of Photovoltaic Thermal (PVT) Technology

Table 11.6 Efficiency of tested PVT air collectors S. No. Parameters

Home+ 2.0 Shielded

Ecolar Unshielded

Shielded

Unshielded

1

Collector efficiency factor (η0 )

0.64

0.48

0.47

0.38

2

Heat loss coefficient, W/m2 K

14.97

8.45

10.12

7.66

3

Wind speed dependence of heat loss coefficient, J/m3 K

0.21

4.86

1.9

2.86

4

Wind dependence of collector efficiency factor, s/m

0.058

0.027

0.036

0.008

Referring to Fig. 11.26 and by assuming that there is no heat losses from all walls due to insulating behavior, an energy balance equation for Fig. 11.26 can be written with the help of Eq. 11.46a as follows:     (ατ )m,eff NUL,m Acm I (t) − (Tfi − Ta ) Q˙ uth,N = m˙ f Cf 1 − exp − m˙ f Cf UL,m dTr = Ma C a . (11.66) dt Here, Tfi = Tr = room air temperature, Ma and Ca are mass and specific heat of enclosed room air. Example 11.3 Find out analytical expression for room air of a PVT air collector integrated building for time interval of Δt = 0–t time interval. Solution Given Tfi = Tr , then Equation 11.56 can be rearranged follows: Ma C a

    (ατ )m,eff NUL,m Acm dT˙r = m f Cf 1 − exp − I (t) − (Tr − Ta ) dt m˙ f Cf UL,m

or, Ma C a

  (ατ )m,eff dTr = FR I (t) − (Tr − Ta ) , dt UL,m

(11.3.1)

   Acm with FR = m˙ f Cf 1 − exp − NUm˙L,m . f Cf The above equation, Eq. 11.3.1, can be rewritten as dTr + aTr = f (t), dt

(11.3.2)

11.7 The PVT Air Collector for Room Air/Space Heating of Building

371

  (ατ )m,eff where a = MFaRCa and f (t) = Ma1Ca UL,m I (t) + Ta . Following Eq. 8.19 along with assumption, the solution of above equation, Eq. 11.3.2, is given by  f (t)  1 − e−at + Tr0 e−at = Tr = a

(ατ )m,eff UL,m

 I (t) + Ta  1 − e−at + Tr0 e−at , FR (11.3.3)

where Tr0 is initial room air temperature at t = 0 for Δt = t–0 time interval. Example 11.4 Evaluate an expression for time interval, Δt, as function of climatic and design parameters to heat room air from Tr0 to Tr . Solution From Example 11.3, we have  Tr =

 I (t) + Ta 

(ατ )m,eff UL,m

FR

1 − e−at + Tr0 e−at .

Here t = Δt, then above equation becomes as  Tr =

(ατ )m,eff UL,m

 I (t) + Ta  1 − e−aΔt + Tr0 e−aΔt FR

or, Tr − Tr0 =

 ⎧  (ατ ) ⎨ U m,eff I (t) + Ta L,m

⎩

FR

⎫ ⎬ − Tr0 1 − e−aΔt ⎭

or,  1 − e−aΔt =

 (ατ )

Tr − Tr0

m,eff UL,m

I (t)+Ta

FR

!



− Tr0

or,  (ατ )

m,eff UL,m

e

−aΔt

=1−

 (ατ )

I (t)+Ta

FR

!=



− Tr0

 (ατ )

m,eff UL,m

I (t)+Ta

FR

!



FR

Tr − Tr0

m,eff UL,m

I (t)+Ta

− Tr !



− Tr0

372

11 Application of Photovoltaic Thermal (PVT) Technology

or,  (ατ )

I (t)+Ta

m,eff UL,m

1 Δt = − ln a

FR  (ατ )

m,eff UL,m

I (t)+Ta

FR

!



− Tr !



(11.4.1)

− Tr0

11.8 PVT Water Heating System It is well established that solar water heater works in two modes of operation, namely. (I) Natural mode of operation: In this case, the insulated water storage tank should be placed above the flat plate collector height by 0.3 m above. The flow of hot water by solar energy works under gravitation force (Hρg) between FPC and insulated water storage tank, and there is no need of water pump to circulate the hot water between FPC and insulated water storage tank. It is self-sustain water heating system and most suitable for domestic hot water system for a capacity of maximum 1000 L. There is also a temperature stratification along the depth of water column; hence, tanks is always placed horizontally as shown in Fig. 11.27. For more details, see the book written by Tiwari [25, 27]. (II) Forced mode of operation: For larger capacity of solar water heater, there is some problem of circulation of hot water between FPC and insulated water storage tank due to blockage of created air babbles at joints of pipes, and

Photograph of a hybrid photovoltaic thermal(PVT) solar heating system Storage Tank

Insulated Pipe

Flat Plat Collector

Fig. 11.27 Photograph of SPVT water heating system

PV Module

11.8 PVT Water Heating System

373

hence, forced mode of operation was considered by using water pump between FPCs and storage tank. For forced mode of operation, one needs grid power during the sunshine hour to operate the water pump. To avoid such problem, a semitransparent PV module of 75 Wp has been integrated at lower portion of first collector to provide power to DC pump for hot water circulation as shown in Fig. 11.27. It is referred as partially covered PVT collector. If FPC collector is completely covered by semitransparent PV module, then it is referred as fully covered PVT collector. Figure 11.27 shows a photograph of PVT water heating system can be classified as follows: (a) Partially covered PVT water heating system: Fig. 11.27 shows a photograph of partially covered PVT water heating system developed at IIT Delhi. This has its own advantages and disadvantages. For example, the maintenance of toughen glass is expensive if broken with any reason. Further, toughen glass is not available everywhere in small pieces to be fitted along with semitransparent PV module as shown in Fig. 11.27. Further, it is economical to have minimum use of semitransparent PV module in comparison with glass cover area. For details of thermal modeling, see Chap. 7 in the book written by Tiwari and Dubey [3]. (b) Fully covered PVT water heating system: In this case, the one toughen glass of flat plate collector (FPC) is replaced by semitransparent photovoltaic (SPV) module as shown in Fig. 11.13b. At large-scale fabrication, it would be economical and easy to maintain along with sufficient electrical as well as thermal energy. The semitransparent PV module can be easily available if it is accepted by users at large scale. It will be most suitable for cold climatic condition. Thermal modeling which is special case of partially covered PVT water heating system is very easy. Energy balance of fully covered PVT water heating system for any given capacity of water heat capacity (Mw Cw ) with the help of Eq. 11.37 without any loss from insulated storage tank can be written as Mw C w

  dTw = N Arm FRm N PF2 (ατ )m,eff Iu − ULm (Tfi − Ta ) dt

(11.67)

Here Tw = Tfi because there is no stratification in water storage tank due to forced mode of operation. In this case, an electrical as well as thermal energy can be achieved as per requirement of users by either decreasing or increasing packing factor of semitransparent PV module or its number, N. Some results of aluminum base PVT water heating system [49] are shown in Fig. 11.28. It can be seen that packing factor (PF) plays an important role in relation to produce thermal and electrical energy. If thermal energy is in priority, then packing factor should be minimum (Fig. 11.28a). For more electrical energy, packing factor should be maximum say 1 (Fig. 11.28b).

374

11 Application of Photovoltaic Thermal (PVT) Technology

Fig. 11.28 a Effect of packing factor (β) on maximum fluid outlet temperature [49]. b Effect of packing factor (β) on electrical efficiency of solar cell [49]

11.10 PVT Integrated Swimming Pool

375

11.9 The PVT Integrated Biogas Plant [50, 51] The biogas consists of methane (CH4 , 60%) and carbon dioxide (CO2 , 40%) at operation of slurry at 37 °C in digester anaerobic digestion in the absence of oxygen. The biogas plant is mainly classified as fixed dome type (whole system consists of digester, and dome is underground) and floating dome type (consists of floating dome and only digester is in underground). There is review on biogas plants including classification, working principle, thermal modeling, etc. [49, 50]. Review also discussed passive and active heating of slurry to maintain the optimum temperature. The active heating is fast heating process, Fig. 11.29a, and generally most suitable for cold climatic condition. The energy balance for active heating of biogas plant can be written with help of Eq. 11.37 as follows: (U A)s (Ts − T0 ) + Ms Cs

  dTs = εN Arm FRm N PF2 (ατ )m,eff Iu − ULm (Tfi − Ta ) dt (11.68)

Here Ts = Tfi , ε < 1 is an effectiveness of coil type heat exchanger for indirect heating of slurry inside digester. (U A)s is total overall heat transfer coefficient from slurry to underground temperature, i.e., T0 = 25 °C. The daily variation of slurry temperature with number of days and exergy variation with mass flow rate is shown in Fig. 11.29b and c, respectively, for all four cases discussed earlier. In this case, exergy consists of both thermal and electrical. An electrical energy can only available from self-sustained PVT water collector. One can observed that (a) Without heating, the slurry temperature drops very fast due to loss of heat from slurry to ground. (b) The maximum slurry temperature is achieved by FPC-CPC, but it is not selfsustain. It has to depend on grid power to operate motor. (c) PVT-CPC and PVT water collector are very close to each other which is selfsustain which is not depending on grid power. It uses electrical power generated from the PVT water collector itself (Fig. 11.29b). (d) Based on exergy, PVT-CPC gives better performance (Fig. 11.29c).

11.10 PVT Integrated Swimming Pool There are two ways of operation of PVT water collector working in forced mode of operation. First, it can be operated in constant flow mode (m˙ f = constant.) which we have discussed in previous sections from Sects. 11.5 to 11.7. Another way of operation is in constant collection mode (Tw = constant = T00 which will be discussed in heating of swimming pool as shown in Fig. 11.30a. In this case, a number of N PVTCPC collectors, Fig. 11.15c, have been connected in series as shown in Fig. 11.15d which we can refer to one string of PVT-CPC collector, and further such sting is

376

11 Application of Photovoltaic Thermal (PVT) Technology

Fig. 11.29 a Schematic diagram of the PVT-CPC integrated fixed dome biogas plant [50, 51]. b Variation of daily average temperature of the slurry with days. c Effect of mass flow rate on daily exergy in all four cases

11.10 PVT Integrated Swimming Pool

377

connected in parallel in ‘m’ column. The whole system is referred as one array similar to Fig. 4.2, and it is shown in Fig. 11.30a. Following Singh and Tiwari [52], the energy balance equation for one array of PVT-CPC integrated swimming pool can be written with the help of Eq. 11.37 as follows:   εm N Arm FRm N PF2 (ατ )m,eff Iu − ULm (Tfi − Ta ) + αw I (t) Ap  ∑  dTpw + h 1pw Ap Tpw − Ta + Ui Ai Tpw − T0 , = Mpw Cpw dt

(11.69a)

where αw = the absorptivity of swimming pool water with surface area of Ap ; ε is effectiveness of heat exchanger placed at bottom of inside swimming pool; Tpw and T0 . are swimming pool and underground temperature; is heat capacity of swimming pool; h 1pw = h pwr + h pwc + h pwe is total heat loss coefficient from swimming pool water surface to ambient air, Eq. 8.7a, Appendix-H and mass flow rate (FRm N ) FRm N

   −N F'ULm Arm m˙ f Cf 1 − exp = N Ar m ULm m˙ f Cf

(11.69b)

In Eq. 11.69, the mass flow rate in PVT-CPC collector loop has been considered as constant [m˙ f = constant]; however, in constant collection temperature mode, the swimming pool water temperature (Tpw ) should be constant, i.e., Tpw = T00 = 28 °C. It can be considered lower and higher depending upon requirement of swimming pool temperature. In such condition, dTpw = 0. dt Then Eq. 11.69 reduces to   εm N Arm FRm N PF2 (ατ )m,eff Iu − ULm (Tfi − Ta ) + αw I (t)Ap ∑  = h 1pw Ap (T00 − Ta ) + Ui Ai Tpw − T0 or, FRm N

 ∑ h 1pw Ap (T00 − Ta ) + Ui Ai Tpw − T0 − αw I (t) Ap   = εm N Arm PF2 (ατ )m,eff Iu − ULm (Tfi − Ta )

Or, f (m˙ f ) = FRm N

 ∑ h 1pw Ap (T00 − Ta ) + Ui Ai Tpw − T0 − αw I (t) Ap   − . (11.70) εm N Arm PF2 (ατ )m,eff Iu − ULm (Tfi − Ta )

378

11 Application of Photovoltaic Thermal (PVT) Technology

(a)

(b)

(c)

Fig. 11.30 a PVT active heating of swimming pool. b Mass flow rate in collector at different collection temperature. c Electrical energy generated by PVT-CPC collectors

11.10 PVT Integrated Swimming Pool

379

Here, it is important to mention that in order to keep constant swimming pool temperature, one has to vary mass flow rate. It is only possible if temperature sensor in swimming pool water pond should be connected to pump. If swimming pool water temperature goes beyond the required temperature, the motor should stop working. To get variable mass flow rate with time, Eq. 11.70 should be solved by iteration method which will be discussed in the next section.

˙f 11.10.1 Methodology to Evaluate the Variation of m with Time and Electrical Power Following methods have been adopted for numerical computation: Step 1: Chose desired swimming pool temperature T00 . Step 2: Calculate f (m˙ f ) for different mass flow rate m˙ f for a given Iu , I (t), and Ta . Step 3: Plot a curve between f (m˙ f ) with mass flow rate m˙ f . Step 4: Select the value of mass flow rate m˙ f at which f (m˙ f ) becomes zero. Step 5: Repeat the calculation for each Iu , I (t) and Ta at each time during sunshine hour. Step 6: Plot the curve between mass flow rate, m˙ f and time. Step 7: For known Tf = T00 , Eqs. 11.19b and 11.22 will be used to evaluate solar cell and plate temperatures, Tcn and Tpn respectively. The efficiency of PV module of N PVT-CPC collectors has been calculated as follows: ηm = τg ηc .

(11.71)

For known constant swimming pool temperature, T00 , an electrical efficiency ηc can be evaluated by using Eq. 8.27 as ηc = η0 [1 − 0.0045(Tcn − 25)]. Thus, electrical energy generated (Wh) by one modules of PVT-CPC collectors is E˙ ele = ηm βc Arm Iu .

(11.72)

The total electrical power generated (Wh) from the series–parallel connected PVT-CPC collectors: E˙ t,ele = mnηm βc Arm Iu .

(11.73)

380

11 Application of Photovoltaic Thermal (PVT) Technology

The electrical power requirement of water pump to circulate the pool water from the filter to swimming pool through heat exchanger tank has been calculated using following equation: Pp =

H.Q p .ρw .g ηp

(11.74)

The variation of mass flow rate for different constant collection temperatures from 30 to 60 °C and hourly electrical energy are shown in Fig. 11.30b, c. It has been seen that the variation in mass flow rate decreases with increase of constant collection temperature from 30 to 60 °C by 75% as expected. It is because mass flow rate has to be reduced for maximum heat transfer in SPVT_CPC water collect at higher constant collection temperature. Further, electrical energy variation is the same of solar intensity for constant electrical efficiency. Problems 11.1 Derive an expression for slurry temperature as a function of design and climatic parameter under constant flow rate mode by using Eq. 11.58. Hint: Use derivation given in Chap. 8 (Sect. 8.6). 11.2 Find out an expression for time interval Δt for slurry to be heated from T so to T s as a function of climatic and design parameters. Hint: See Example 11.4 11.3 Solve Eq. 11.58 for constant collection temperature of biogas plant. Hint: See Sect. 11.8. 11.4 Derive an expression for swimming pool temperature as a function of design and climatic parameter for constant mass flow rate. Hint: See Sect. 8.6. 11.5 Derive an expression for mass flow (m˙ f ) rate for N-PVT-CPC collector for constant collection temperature. Hint: Use Eq. 11.40 and consider T foN = T00 . 11.6 Obtain an analytical expression for variable mass flow rate of space heating under constant room air temperature for Example 11.3 Hint: See Sect. 11.8. Objective Questions 11.1 The maximum outlet fluid temperature is achieved in (a) Flat plate collectors (FPCs) (b) Flat plate collector-compound parabolic concentrators (FPC-CPC)

11.10 PVT Integrated Swimming Pool

381

(c) Photovoltaic thermal-compound parabolic concentrators (PVT-CPC) (d) Photovoltaic thermal (PVT) collectors Answer: (b) 11.2 The minimum outlet fluid temperature is achieved in (a) (b) (c) (d)

Flat plate collectors (FPCs) Flat plate collector-compound parabolic concentrators (FPC-CPC) Photovoltaic thermal-compound parabolic concentrators (PVT-CPC) Photovoltaic thermal (PVT) collectors

Answer: (d) 11.3 The maximum outlet electrical energy is achieved for a given packing factor in (a) (b) (c) (d)

Flat plate collectors (FPCs) Flat plate collector-compound parabolic concentrators (FPC-CPC) Photovoltaic thermal-compound parabolic concentrators (PVT-CPC) Photovoltaic thermal (PVT) collectors

Answer: (d) 11.4 The minimum outlet electrical energy is achieved for a given Packing factor in (a) (b) (c) (d)

Flat plate collectors (FPCs) Flat plate collector-compound parabolic concentrators (FPC-CPC) Photovoltaic thermal-compound parabolic concentrators (PVT-CPC) Photovoltaic thermal (PVT) collectors

Answer: (c) 11.5 With increase of packing factor, the rate of thermal energy with time is maximum in (a) (b) (c) (d)

Flat plate collectors (FPCs) Flat plate collector-compound parabolic concentrators (FPC-CPC) Photovoltaic thermal-compound parabolic concentrators (PVT-CPC) Photovoltaic thermal (PVT) collectors

Answer: (b). 11.6 The packing factor has no effect on the rate of thermal energy with time in (a) (b) (c) (d)

Flat plate collectors (FPCs) Flat plate collector-compound parabolic concentrators (FPC-CPC) Photovoltaic thermal-compound parabolic concentrators (PVT-CPC) Photovoltaic thermal (PVT) collectors

Answer: (a) and (b) 11.7 The packing factor has effect on the rate of thermal energy with time in (a) Flat plate collectors (FPCs) (b) Flat plate collector-compound parabolic concentrators (FPC-CPC)

382

11 Application of Photovoltaic Thermal (PVT) Technology

(c) Photovoltaic thermal-compound parabolic concentrators (PVT-CPC) (d) Photovoltaic thermal (PVT) collectors Answer: (c) and (d). 11.8 Electrical efficiency of collector increase with increase number of collector in (a) (b) (c) (d)

Flat plate collector-compound parabolic concentrators (FPC-CPC) Photovoltaic thermal-compound parabolic concentrators (PVT-CPC) Photovoltaic thermal (PVT) collectors None of them

Answer: (d) 11.9 Electrical efficiency of collector decreases with increase number of collector in (a) (b) (c) (d)

Flat plate collector-compound parabolic concentrators (FPC-CPC) Photovoltaic thermal-compound parabolic concentrators (PVT-CPC) Photovoltaic thermal (PVT) collectors None of them

Answer: (b) and (c) 11.10 For plant cultivation, the increase of GiSPVT/building room air temperature is more practical in (a) Flat plate collector-compound parabolic concentrators (FPC-CPC) air collector (b) Photovoltaic thermal-compound parabolic concentrators (PVT-CPC) air collector (c) Photovoltaic thermal (PVT) collectors air collector (d) None of them Answer: (c) 11.11 The space requirement for maximum thermal heating is minimum in (a) (b) (c) (d)

Flat plate collectors (FPCs) Flat plate collector-compound parabolic concentrators (FPC-CPC) Photovoltaic thermal-compound parabolic concentrators (PVT-CPC) Photovoltaic thermal (PVT) collectors

Answer: (b) 11.11 The space requirement for maximum electrical energy is minimum in (a) (b) (c) (d)

Flat plate collectors (FPCs) Flat plate collector-compound parabolic concentrators (FPC-CPC) Photovoltaic thermal-compound parabolic concentrators (PVT-CPC) Photovoltaic thermal (PVT) collectors

Answer: (d)

References

383

11.12 With increase of mass flow rate, the outlet fluid temperature of any collector (a) Decreases

(b) Increases

(c) Unaffected

(d) None of them

Answer: (a) 11.13 With increase of mass flow rate, the thermal efficiency of any collector (a) Decreases

(b) Increases

(c) Unaffected

(d) None of them

Answer: (b) 11.14 With increase of length of collector for a given mass flow rate, the outlet fluid temperature of any collector (a) Decreases

(b) Increases

(c) Unaffected

(d) None of them

Answer: (b) 11.15 In the case of unglazed collector, the upward heat loss coefficient depends on (a) Solar radiation (b) Absorptivity of surface absorber (d) Wind velocity

(c) Thickness of

Answer: (d)

References 1. Tiwari GN (2014) Energy, ecology and environment: sustainable nature. Springer 2. Agrawal B, Tiwari GN (2008) Developments in environmental durability for photovoltaics. Pira International Ltd., UK 3. Tiwari GN, Dubey S (2010) Fundamentals of photovoltaic modules and their applications. Royal Society of Chemistry (RSC), UK 4. Agrawal B, Tiwari GN (2010) Building integrated photovoltaic thermal systems. Royal Society of Chemistry (RSC), UK 5. Tiwari GN, Gupta N (2023) Photovoltaic thermal passive house system. Taylor & Francis group and CRC Press 6. Tiwari GN (2003) Greenhouse technology for controlled environment. Alpha Science (UK) also published by Narosa Publishing House, New Delhi 7. Tiwari GN, Tiwari A, Shyam (2016) Handbbok of solar energy. Springer 8. Chow TT (2010) A review on photovoltaic/thermal hybrid solar technology. Appl Energy 87(2):365–379. https://doi.org/10.1016/j.apenergy.2009.06.037 9. Zondag HA, Bakker M, van Helden WGJ (2006) PVT Roadmap—a European guide for the development and market introduction of PV-thermal technology 10. Ko H, Huh J-H, Park N (2021) Overview of solar energy for aquaculture: the potential and future trends. Energies 14(21):6923. https://doi.org/10.3390/en14216923. https://www.mdpi. com 11. Evans DL (1981) Simplified method for predicting photo-voltaic output. Solar Energy 27:555– 560. https://doi.org/10.1016/0038-092X(81)90051-7 12. Durisch W, Bitnar B, Mayor JC, Kiess H, Lam K, Close J (2007) Efficiency model for PV modules and demonstration of its application to energy yield estimation. Sol Energy Mater Sol Cells 91:79–84. https://doi.org/10.1016/j.solmat.2006.05.011

384

11 Application of Photovoltaic Thermal (PVT) Technology

13. Virtuani A, Pavanello D, Friesen G (2010) Overview of temperature coefficients of different thin film photovoltaic technologies. In: 25th European photovoltaic solar energy conference and exhibition/5th world conference on photovoltaic energy conversion, 6–10 Sept 2010, Valencia, Spain. https://doi.org/10.4229/25thEUPVSEC2010-4AV.3.83 14. Tiwari GN, Mishra RK (2011) Advanced renewable energy sources.Royal Society of Chemistry (RSC), UK 15. Gaur A, Tiwari GN (2015) Analytical expressions for temperature dependent electrical efficiencies of thin film BIOPVT systems. Appl Energy 146:442–452 16. Kern EC, Russell MC (1978) Combined photovoltaic and thermal hybrid collector systems. In: Proceedings of the 13th IEEE photovoltaic specialists, Washington, DC, USA, pp 1153–1157 17. Florchuetz LW (1979) Extension of the Hottel-Whillier model to the analysis of combined photovoltaic/thermal flat plate collectors. Sol Energy 22(4):361–366 18. Zondag HA, De Vries DW, Van Helden WGJ, Van Zolingen RJC (2003) The yield of different combined PV-thermal collector designs. Sol Energy 74:253–269 19. Hegazy AA (2000) Comparative study of the performances of four photovoltaic/thermal solar air collectors. Energy Convers Manage 41(8):861–881 20. Hendrie SD (1980) Evaluation of combined photovoltaic/thermal collectors. In: ISES international congress and silver jubilee, Atlanta, GA, 28 May–1 June 1980 21. Atheaya D, Tiwari A, Tiwari GN, Al-Helal IM (2015) Analytical characteristic equation for partially covered photovoltaic thermal (PVT) compound parabolic concentrator (CPC). Sol Energy 111:176–185 22. Kim JH, Park SH, Kang JG, Kim JT (2014) Experimental performance of heating system with building integrated PVT (BIPVT) collector. Energy Proc 48:1374–1381 23. Dubey S, Tiwari GN (2008) Thermal modeling of a combined system of photovoltaic thermal (PV/T) solar water heater. Sol Energy 82:602–612 24. Duffie JA, Beckman WA (1991) Solar engineering of thermal processes. Wiley, New York 25. Tiwari GN, Tiwari A, Shyam (2016) Handbook of solar energy: theory, analysis and application. Springer 26. Struckmann F (2008) Analysis of a flat-plate solar collector. Project Report, 2008 MVK 160 Heat and Mass Transport. Lund, Sweden, 8 May 2008 27. Tiwari GN (2002) Solar energy: fundamentals, design, modelling and application. Narosa Publishing House, New Delhi 28. Shyam, Tiwari GN (2016) Analysis of series connected photovoltaic thermal air collector partially covered by semitransparent photovoltaic module. Sol Energy 137:452–462 29. Chow TT, He W, Ji J (2007) An experimental study of facade-integrated photovoltaic/waterheating system. Appl Therm Eng 27:37–45 30. Chow TT, He W, Ji J (2006) Hybrid photovoltaic-thermosyphon water heating system for residential application. Sol Energy 80:298–306 31. Mishra RK, Tiwari GN (2013) Energy and exergy analysis of hybrid photovoltaic thermal water collector for constant collection temperature mode. Sol Energy 90:58–67 32. Shyam, Tiwari GN, Al-Helal IM (2015) Analytical expression of temperature dependent electrical efficiency of N-PVT water collectors connected in series. Sol Energy 114:61–76 33. Michael JJ, Selvarasan I, Goic R (2016) Fabrication, experimental study and testing of a novel photovoltaic module for photovoltaic thermal applications. Renew Energy 90:95–104 34. Fatima H, Tiwari GN (2019) Theoretical validation of photovoltaic thermal (PVT) module with a copper base for thermal and electrical performance. J Renew Sustain Energy 11:043704 35. Tiwari GN, Singh RK, Sinha ASK (2022) An electrical power output for nth of N-Al/Cu integrated photovoltaic thermal-module (PVT-M) collectors cum water storage system: an experimental validation. Int J Green Energy. https://doi.org/10.1080/15435075.2022.2154608 36. Tiwari GN, Meraj M, Khan ME, Mishra RK, Garg V (2018) Improved Hottel-WhillierBliss equation for N-photovoltaic thermal-compound parabolic concentrator (N-PVT-CPC) collector. Sol Energy 166:203–212 37. Prapas DE, Norton B, Probert SD (1987) Thermal design of compound parabolic concentrating solar-energy collectors. ASME J Sol Energy Eng 109:161–168

References

385

38. Fan W, Kokogiannakis G, Ma Z (2018) A multi-objective design optimisation strategy for hybrid photovoltaic thermal collector (PVT)-solar air heater (SAH) systems with fins. Sol Energy 163:315–328. https://doi.org/10.1016/j.solener.2018.02.014 39. Tariq R, Xamán J, Bassam A, Ricalde LJ, Soberanis MAE (2020) Multidimensional assessment of a photovoltaic air collector integrated phase changing material considering Mexican Climatic conditions. Energy, 118304. https://doi.org/10.1016/j.energy.2020.118304 40. Hengel F, Heschl C, Inschlag F, Klanatsky P (2020) System efficiency of PVT collector-driven heat pumps. Int J Thermofluids 100034:5–6. https://doi.org/10.1016/j.ijft.2020.100034 41. Kilkis B (2019) Development of a composite PVT panel with PCM embodiment, TEG modules, flat-plate solar collector, and thermally pulsing heat pipes. Sol Energy. https://doi.org/10.1016/ j.solener.2019.10.075 42. Ahn J-G, Yu J-S, Boafo FE, Kim J-H, Kim J-T (2021) Simulation and performance analysis of air-type PVT collector with interspaced Baffle-PV cell design. Energies 14(17):5372.https:// doi.org/10.3390/en14175372 43. Chaibi Y, Malvoni M, El Rhafiki T, Kousksou T, Zeraouli Y (2021) Artificial neural-network based model to forecast the electrical and thermal efficiencies of PVT air collector systems. Clean Eng Technol 4:100132. https://doi.org/10.1016/j.clet.2021.100132 44. Senthilraja S, Gangadevi R, Marimuthu R, Baskaran M (2019) Performance evaluation of water and air based PVT solar collector for hydrogen production application. Int J Hydrogen Energy. https://doi.org/10.1016/j.ijhydene.2019.02.223 45. Fudholi A, Musthafa MF, Ridwan A, Yendra R, Hartono, Desvina AP, Bin Majahar Ali MK, Sopian K (2019) Review of solar photovoltaic/thermal (PV/T) air collector. Int J Elec Comp Eng 9(1):126–133.https://doi.org/10.11591/ijece.v9i1 46. Bhardwaj P, Nayak S, Tiwari A, Tiwari GN (2021) Design and simulation of semitransparent photovoltaic thermal (PVT) indirect solar dryer integrated with kitchen chimney using ANN technique. Indian J Eng Mater Sources 28:633–639 47. Tiwari GN, Bhardwaj P, Nayak S (2023) New mass flow rate factor for nth-semi-transparent photovoltaic thermal (nth-SPVT) air collectors connected in series. ASME J Thermal Sci Eng Appl, Revised 48. Cremers J, Mitina I, Palla N, Klotz F, Jobard X, Eicke U (2015) Experimental analyses of different PVT collector designs for heating and cooling applications in buildings. In: 6th international building physics conference, IBPC 2015, energy procedia 49. Tiwari GN, Singh T, Sinha ASK (2022) An electrical power output for nth of N-Al/Cu integrated photovoltaic thermal-module (PVT-M) collectors cum water storage system: an experimental validation. Int J Green Energy. https://doi.org/10.1080/15435075.2022.2154608 50. Tiwari GN, Mishra RK, Singh AK (2022) Thermal modeling of solar heating of bio-gas plant: a review. Int J Ambient Energy. TAEN-2020-0330 (revised) 51. Singh AK, Singh RG, Tiwari GN (2020) Thermal and electrical performance evaluation of photo-voltaic thermal compound parabolic concentrator integrated fixed dome biogas plant. Renew Energy 154(2020):614–624 52. Singh AK, Tiwari GN (2021) Performance of active solar heating of outdoor swimming pool: a constant collection temperature mode. Asian J Phys 30(1):185–194

Some Additional References 53. Benemann J, Chehab O, Schaar-gabriel E (2001) Building-integrated PV modules. Solar Energy Mater Sol Cells 67:345–354 54. Saini V, Tiwari S, Tiwari GN (2017) Environ economic analysis of various types of photovoltaic technologies integrated with greenhouse solar drying system. J Clean Prod 156:30–40 55. Tiwari S, Tiwari GN (2016) Thermal analysis of photovoltaic-thermal (PVT) single slope roof integrated greenhouse solar dryer. Sol Energy 138:128–136

386

11 Application of Photovoltaic Thermal (PVT) Technology

56. Tripathi R, Tiwari GN, Al-Helal IM (2016) Thermal modelling of N partially covered photovoltaic thermal (PVT)—compound parabolic concentrator (CPC) collectors connected in series. Sol Energy 123:174–184 57. Vats K, Tiwari GN (2012) Performance evaluation of a building integrated semi-transparent photovoltaic thermal system for roof and façade. Energy Build 45:211–218 58. Tiwari GN, Sahota L (2017) Advanced solar distillation systems: basic principles, thermal modeling and its application. Springer 59. Photovoltaic thermal hybrid solar collector—Wikipedia. https://en.wikipedia.org·

Appendix A

Conversion of Units

(i) Length, m 1 yd (yard) = 3 ft = 36 in (inches) = 0.9144 m 1 m = 39.3701 in = 3.280839 ft = 1.093613 yd = 1,650,763.73 wavelength 1 ft = 12 in = 0.3048 m 1 in = 2.54 cm = 25.4 mm 1 mil = 2.54 × 10–3 cm 1 μm = 10–6 m 1 nm = 10–9 m = 10–3 μm (ii) Area, m2 1 ft2 = 0.0929 m2 1 in2 = 6.452 cm2 = 0.00064516 m2 1 cm2 = 10–4 m2 = 10.764 × 10–4 ft2 = 0.1550 in2 1 ha = 10,000 m2 (iii) Volume, m3 1 ft3 = 0.02832 m3 = 28.3168 l (liter) 1 in3 = 16.39 cm3 = 1.639 × 102 l 1 yd3 = 0.764555 m3 = 7.646 × 102 l 1 UK gallon = 4.54609 l 1 US gallon = 3.785 l = 0.1337 ft3 1 m3 = 1.000 × 106 cm3 = 2.642 × 1012 US gallons = 109 l 1 l = 10–3 m3 1 fluid ounce = 28.41 cm3 (iv) Mass, kg 1 kg = 2.20462 lb = 0.068522 slug 1 ton (short) = 2000 lb (pounds) = 907.184 kg 1 ton (long) = 1016.05 kg (continued) © Bag Energy Research Society 2023 G. N. Tiwari, Advance Solar Photovoltaic Thermal Energy Technologies, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4993-9

387

388

Appendix A: Conversion of Units

(continued) 1 lb = 16 oz (ounces) = 0.4536 kg 1 oz = 28.3495 g 1 quintal = 100 kg 1 kg = 1000 g = 10,000 mg 1 μg = 10–6 g 1 ng = 10–9 g (v) Density and specific volumes, kg/m3 , m3 /kg 1 lb/ft3 = 16.0185 kg/m3 = 5.787 × 10–4 lb/in3 1 g/cm3 = 103 kg/m3 = 62.43 lb/ft3 1 lb/ft3 = 0.016 g/cm3 = 16 kg/m3 1 ft3 (air) = 0.08009 lb = 36.5 g at N.T.P 1 gallon/lb = 0.010 cm3 /kg 1 μg/m3 = 10–6 g/m3 (vi) Pressure, Pa (Pascal) 1 lb/ft2 = 4.88 kg/m2 = 47.88 Pa 1 lb/in2 = 702.7 kg/m2 = 51.71 mm Hg = 6.894757 × 103 Pa = 6.894757 × 103 N/m2 1 atm = 1.013 × 105 N/m2 = 760 mm Hg = 101.325 kPa 1 in H2 O = 2.491 × 102 N/m2 = 248.8 Pa = 0.036 lb/in2 1 bar = 0.987 atm = 1.000 × 106 dynes/cm2 = 1.020 kgf/cm2 = 14.50 lbf/in2 = 105 N/m2 = 100 kPa 1 torr (mm Hg 0 °C) = 133 Pa 1 Pa (Pa) = 1 N/m2 = 1.89476 kg 1 inch of Hg = 3.377 kPa = 0.489 lb/in2 (vii) Velocity, m/s 1 ft/s = 0.3041 m/s 1 mile/h = 0.447 m/s = 1.4667 ft/s = 0.8690 knots 1 km/h = 0.2778 m/s 1 ft/min = 0.00508 m/s (viii) Force, N 1 N (Newton) = 105 dynes = 0.22481 lb wt = 0.224 lb f 1 pdl (poundal) = 0.138255 N (Newton) = 13.83 dynes = 14.10 gf 1 lbf (i.e., wt of 1 lb mass) = 4.448222 N = 444.8222 dynes 1 ton = 9.964 × 103 N 1 bar = 105 Pa (Pascal) 1 ft of H2 O = 2.950 × 10–2 atm = 9.807 × 103 N/m2 1 in H2 O = 249.089 Pa 1 mm H2 O = 9.80665 Pa 1 dyne = 1.020 × 10–6 kg f = 2.2481 × 10–6 lb f = 7.2330 × 10–5 pdl = 10–5 N (continued)

Appendix A: Conversion of Units

389

(continued) 1 mm of Hg = 133.3 Pa 1 atm = 1 kg f/cm2 = 98.0665 k Pa 1 Pa (Pascal) = 1 N/m2 (ix) Mass flow rate and discharge, kg/s, m3 /s 1 lb/s = 0.4536 kg/s 1 ft3 /min = 0.4720 1/s = 4.179 × 10–4 m3 /s 1 m3 /s = 3.6 × 106 l/h 1 g/cm3 = 103 kg/m3 1 lb/h ft2 = 0.001356 kg/s m2 1 lb/ft3 = 16.2 kg/m2 1 L/s (l/s) = 10–3 m3 /s (x) Energy, J 1 cal = 4.187 J (Joules) 1 kcal = 3.97 Btu = 12 × 10–4 kWh = 4.187 × l03 J 1 W = 1.0 J/s 1 Btu = 0.252 kcal = 2.93 × 10–4 kWh = 1.022 × 103 J 1 hp = 632.34 kcal = 0.736 kWh 1 kWh = 3.6 × 106 J = 1 unit 1 J = 2.390 × 10–4 kcal = 2.778 × 10–4 Wh 1 kWh = 860 kcal = 3413 Btu 1 erg = 1.0 × 10–7 J = 1.0 × 10–7 Nm = 1.0 dyne cm 1 J = 1 Ws = 1 Nm 1 eV = 1.602 × 10–19 J 1 GJ = 109 J 1 MJ = 106 J 1 TJ (Terajoules) = 1012 J 1EJ (Exajoules) = 1018 J (xi) Power, Watt (J/s) 1 Btu/h = 0.293071 W = 0.252 kcal/h 1 Btu/h = 1.163 W = 3.97 Btu/h 1 W = 1.0 J/s = 1.341 × 10–3 hp = 0.0569 Btu/min = 0.01433 kcal/min 1 hp (F.P.S.) = 550 ft lb f/s = 746 W = 596 kcal/h = 1.015 hp (M.K.S.) 1 hp (M.K.S.) = 75 mm kg f/s = 0.17569 kcal/s = 735.3 W 1 W/ft2 = 10.76 W/m2 1 ton (Refrigeration) = 3.5 kW 1kW = 1000 W 1 GW = 109 W 1 W/m2 = 100 lx (continued)

390

Appendix A: Conversion of Units

(continued) (xii) Specific heat, J/kg °C 1 Btu/lb °F = 1.0 kcal/kg °C = 4.187 × 103 J/kg °C 1 Btu/lb = 2.326 kJ/kg (xiii) Temperature, °C and K used in SI T

(Celcius, °C)

= (5/9) [T (Fahrenheit, °F) + 40] – 40

T (°F) = (9/5) [T (°C) + 40] – 40 T (Rankine, °R) = 460 + T (°F) T (Kelvin, K) = (5/9) T (°R) T (Kelvin, K) = 273.15 + T (°C) T (°C) = T (°F) /1.8 = (5/9) T (°F) (xiv) Rate of heat flow per unit area or heat flux, W/m2 1 Btu/ft2 h = 2.713 kcal/m2 h = 3.1552 W/m2 1 kcal/m2 h = 0.3690 Btu/ft2 h = 1.163 W/m2 = 27.78 × 10–6 cal/s cm2 1 cal/cm2 min = 221.4 Btu/ft2 h 1 W/ft2 = 10.76 W/m2 1 W/m2 = 0.86 kcal/hm2 = 0.23901 × 10–4 cal/s cm2 = 0.137 Btu/h ft2 1 Btu/h ft = 0.96128 W/m (xv) Heat transfer coefficient, W/m2 °C 1 Btu/ft2 h °F = 4.882 kcal/m2 h °C = 1.3571 × 10–4 cal/cm2 s °C 1 Btu/ft2 h °F = 5.678 W/m2 °C 1 kcal/m2 h °C = 0.2048 Btu/ft2 h °F = 1.163 W/m2 °C 1 W/m2 K = 2.3901 × 10–5 cal/cm2 s K = 1.7611 × 10–1 Btu/ft2 °F = 0.86 kcal/m2 h °C (xvi) Thermal conductivity, W/m °C 1 Btu/ft h °F = 1.488 kcal/m h° C = 1.73073 W/m °C 1 kcal/m h °C = 0.6720 Btu/ft h °F = 1.1631 W/m °C 1 Btu in/ft2 h °F = 0.124 kcal/m h °C = 0.144228 W/m °C 1 Btu/in h °F = 17.88 kcal/m h °C 1 cal/cm s °F = 4.187 × 102 W/m °C = 242 Btu/h ft °F 1 W/cm°C = 57.79 Btu/h ft °F (xvii) Angle, rad 2π rad (radian) = 360° (degree) 1° (degree) = 0.0174533 rad = 60' (minutes) 1' = 0.290888 × 10–3 rad = 60'' (seconds) 1'' = 4.84814 × 10–6 rad 1 hour = 15° (xviii) Illumination 1 lx (lux) = 1.0 lm (lumen)/m2 1 lm/ft2 = 1.0 foot candle (continued)

Appendix A: Conversion of Units (continued) 1 foot candle = 10.7639 lx 100 lx = 1 W/m2 (xix) Time, h 1 week = 7 days = 168 h = 10,080 min = 6,04,800 s 1 mean solar day = 1440 min = 86,400 s 1 calender year = 365 days = 8760 h = 5.256 × 105 min 1 tropical mean solar year = 365.2422 days 1 sidereal year = 365.2564 days (mean solar) 1 s (second) = 9.192631770 × 109 Hz (Hz) 1 day = 24 h = 360° (hour angle) (xx) Concentration, kg/m3 and g/m3 1 g/l = 1 kg/m3 1 lb/ft3 = 6.236 kg/m3 (xxi) Diffusivity, m2 /s 1 ft2 /h = 25.81 × 10–6 m2 /s

391

Appendix B

Specification of Solar Cell Materials

Specifications of solar cell material (at solar intensity 1000 W/m2 and cell temperature 25 °C) and cost [from Tiwari and Mishra, 2012] Cell technology

Efficiency (%)

Fill Factor (FF)

Aperture area (10–4 × m2 )

Life timea (years)

Manufacturing cost ($/kWp in 2007)

Selling price ($/ kWp in 2007)

Monocrystalline silicon

24.7 ± 0.5

0.828

4.0

30

2.5

3.7

Multi-crystalline silicon

19.8 ± 0.5

0.795

1.09

30

2.4

3.5

Copper indium diselenide (CIS/ CIGS)

18.4 ± 0.5

0.77

1.04

5

1.5

2.5

Thin silicon cell

16.6 ± 0.4

0.782

4.02

25

2.0

3.3

Cadmium telluride (CdTe)

16.5 ± 0.5

0.755

1.03

15

1.5

2.5

Amorphous silicon (a-si)

10.1 ± 0.2

0.766

1.2

20

1.5

2.5

a

Based on experience Source B. Agarwal, G. N. Tiwari, Development in environmental durability for photovoltaics, Pira International Ltd., UK, 2008

© Bag Energy Research Society 2023 G. N. Tiwari, Advance Solar Photovoltaic Thermal Energy Technologies, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4993-9

393

394

Appendix B: Specification of Solar Cell Materials

Courtesy NREL, USA Specifications for various silicon and non-silicon-based PV modules (Durisch et al. (2007) and Virtuani et al. (2016), Tiwari and Mishra (2012)) Different solar cell types (n)

Module Expected efficiency life nPV ηmo (%) (Yrs)

Specific energy density E in (kWh m−2 )

(E in ) of PV Temp. module, coefficient β Am = 0.71 (°C−1 ) m2 (kWh)

Average temp. coefficient β (°C−1 )

c-Si 16 Single crystalline

30

1190

8449

0.0062, 0.0045

0.00535

mc-Si 14 Multi-crystalline silicon

30

910

646.1

0.0049, 0.0036

0.00425

nc-Si Nanocrystalline silicon

12

25

610

433.1

0.0036

0.0036

a-Si Amorphous silicon

6

20

378

268.38

0.001–0.0013 0.00115

CdTe Cadmium telluride

8

15

266

188.86

0.002–0.0021 0.00205

10

5

24.5

17.395

0.0031, 0.0036

CIGS Copper indium gallium selenide

0.00335

Specifications for various silicon and non-silicon-based PV modules (Durisch et al. (2007) and Virtuani et al. (2016), Tiwari and Mishra (2012))

Appendix B: Specification of Solar Cell Materials Different solar cell types (n)

Expected life nPV (Yrs)

Specific energy density E in (kWh m−2 )

(Ein ) of PV module, Am = 0.71 m2 (kWh)

Temp. coefficient β (o C−1 )

Average temp. coefficient β (o C−1 )

c-Si 16 Single crystalline

30

1190

8449

0.0062, 0.0045

0.00535

mc-Si multi-crystalline silicon

14

30

910

646.1

0.0049, 0.0036

0.00425

nc-Si Nanocrystalline silicon

12

25

610

433.1

0.0036

0.0036

a-Si Amorphous silicon

6

20

378

268.38

0.001- 0.0013

0.00115

CdTe Cadmium telluride

8

15

266

188.86

0.002–0.0021

0.00205

10

5

24.5

17.395

0.0031, 0.0036

0.00335

CIGS Copper indium gallium selenide

Module efficiency ηmo (%)

395

Durisch, W., Bitnar, B., Mayor, J.C., Kiess, H., Lam, K. and Close, J., 2007. Solar Energy Materials & Solar cells, 91, 79–84. A. Virtuani, D. Pavanello, and G. Friesen, Overview of Temperature Coefficients of Different Thin Film Photovoltaic Technologies, 25th European Photovoltaic Solar Energy Conference and Exhibition/5th World Conference on Photovoltaic Energy Conversion, 6–10 September 2010, Valencia, Spain. G. N. Tiwari and R.K. Mishra, Advanced Renewable Energy Sources, Royal Society of Chemistry (RSC), (UK), 2011.

Appendix C

Physical Properties of Some Materials

See Tables C.1, C.2, C.3, C.4, C.5 and C.6. Table C.1 Properties of air at atmospheric pressure T (K)

P (kg/m3 )

C p (kJ/ kgK)

μ (kg/ms) × 10–5

v (m2 /s) × 10–6

α (m2 /s) × 10–5

Pr

100

3.6010

1.0259

0.6924

1.923

9.239

0.2501

0.770

150

2.3675

1.0092

1.0283

200

1.7684

1.0054

1.3289

4.343

13.726

0.5745

0.753

7.490

18.074

1.017

250

1.4128

1.0046

0.739

1.488

9.49

22.26

1.3161

0.722

300

1.1774

350

0.9980

1.0050

1.983

15.68

26.22

2.216

0.708

1.0083

2.075

20.76

30.00

2.983

400

0.8826

0.697

1.0134

2.286

25.90

33.62

3.760

0.689

K (W/m2 K) × 10–3

The value of μ, K, C p , and Pr are not strongly pressure-dependent and may be used over a fairly wide range of pressures

© Bag Energy Research Society 2023 G. N. Tiwari, Advance Solar Photovoltaic Thermal Energy Technologies, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4993-9

397

398

Appendix C: Physical Properties of Some Materials

Table C.2 Properties of water (saturated liquid) Temperature °F

C p (kJ/kgK)

ρ (kg/m3 )

μk (kg/m s)

K (W/mK)

Pr

°C

32

0.00

4.225

999.8

1.79 × 103

0.566

13.25

40

4.44

4.208

999.8

1.55

0.575

11.35

50

10.00

4.195

999.2

1.31

0.585

9.40

60

15.56

4.186

998.6

1.12

0.595

7.88

70

21.11

4.179

997.4

9.8 × 104

0.604

6.78

80

26.67

4.179

995.8

8.6

0.614

5.85

90

32.22

4.174

994.9

7.65

0.623

5.12

100

37.78

4.174

993.0

6.82

0.630

4.53

110

43.33

4.174

990.6

6.16

0.637

4.04

120

48.89

4.174

988.8

5.62

0.644

3.64

130

54.44

4.179

985.7

5.13

0.649

3.30

140

60.00

4.179

983.3

4.71

0.654

3.01

150

65.55

4.183

980.3

4.3

0.659

2.73

160

71.11

4.186

977.3

4.01

0.665

2.53

170

76.67

4.191

973.7

3.72

0.668

2.33

180

82.22

4.195

970.2

3.47

0.673

2.16

190

87.78

4.199

966.7

3.27

0.675

2.03

200

93.33

4.204

963.2

3.06

0.678

1.90

210

104.40

4.216

955.1

2.67

0.684

1.66

Appendix C: Physical Properties of Some Materials

399

Table C.3 Properties of metals Metal

Properties at 20 °C ρ (kg/m3 )

Aluminum

C p (kJ/kgK)

K (W/mK)

A (m2 /s × 10–5 )

Pure

2707

0.896

204

8.418

Al-Si (silumin, copper bearing) 86% Al, 1% Cu

2659

0.867

137

5.933

Lead

Pure

11,400

0.1298

34.87

7.311

Iron

Pure Steel (carbon steel)

7897

0.452

73

2.034

7753

0.486

63

0.970

Pure

8954

0.3831

386

11.234

Aluminum bronze (95% Cu, 5% Al)

8666

0.410

383

2.330

Bronze

75%Cu, 25%Sn

8666

0.343

326

0.859

Red brass

85% Cu, 9% Sn 6% Zn

8714

0.385

61

1.804

Brass

70% Cu, 30% Zn

8600

0.877

85

3.412

German silver

62% Cu, 15% Ni, 22% Zn

8618

0.394

24.9

0.733

Constantan

60% Cu, 40% Ni

8922

0.410

22.7

0.612

Magnesium

Pure

1746

1.013

171

9.708

Nickel

Pure

8906

0.4459

90

2.266

Silver

Purest

10,524

0.2340

419

17.004

Pure (99.9%)

10,524

0.2340

407

16.563

Copper

Tin

Pure

7304

0.2265

64

3.884

Tungsten

Pure

19,350

0.1344

163

6.271

Zinc

Pure

7144

0.3843

112.2

4.106

400

Appendix C: Physical Properties of Some Materials

Table C.4 Properties of non-metals Material

Temperature (°C)

K (W/mk)

ρ (kg/m3 )

C (kJ/kgK)

α (m2 /s) × 10–7

Asbestos

50

0.08

470

–

–

Building brick

20

0.69

1600

0.84

5.2

Common face

–

1.32

2000

–

–

Concrete, cinder

23

0.76

–

–

–

Stone 1-2-4 mix

20

1.37

1900–2300

0.88

8.2–6.8

Glass, window

20

0.78 (avg)

2700

0.84

3.4

Borosilicate

30–75

1.09

2200

–

–

Plaster, gypsum

20

0.48

1440

0.84

4.0

Granite

–

1.73–3.98

2640

0.82

8–18

Limestone

100–300

1.26–1.33

2500

0.90

5.6–5.9

Marble

–

2.07–2.94

2500–2700

0.80

10–13.6

Sandstone

40

1.83

2160–2300

0.71

11.2–11.9

Fir

23

0.11

420

2.72

0.96

Maple or oak 30

0.166

540

2.4

1.28

Yellow pine

23

0.147

640

2.8

0.82

Cord board

30

0.043

160

1.88

2–5.3

Cork, regranulated

32

0.045

45–120

1.88

2–5.3

Ground

32

0.043

150

–

–

Sawdust

23

0.059

–

–

–

Wood shaving

23

0.059

–

–

–

Appendix C: Physical Properties of Some Materials

401

Table C.5 Physical properties of some other materials S. No.

Material

Density (kg/ m3 )

Thermal conductivity (W/ mK)

Specific heat (J/kgK)

1

Air

1.117

40.026

1006

2

Alumina

3800

29.0

800

3

Aluminum

41–45

211

0.946

4

Asphalt

1700

0.50

1000

5

Brick

1700

0.84

800

6

Carbon dioxide

1.979

0.145

871

7

Cement

1700

0.80

670

8

Clay

1458

11.28

879

9

Concrete

2400

1.279

1130

10

Copper

8795

385

–

11

Cork

240

0.04

2050

12

Cotton wool

1522

–

1335

13

Fiber board

300

0.057

1000

14

Glass crown

2600

1.0

670

15

Glass window

2350

0.816

712

16

Glass wool

50

0.042

670

17

Ice

920

2.21

1930

18

Iron

7870

80

106

19

Lime stone

2180

1.5

–

20

Mudphuska

–

–

–

21

Oxygen

1.301

0.027

920

22

Plaster board

950

0.16

840

23

Polyesterene—expanded

25

0.033

1380

24

PVC—rigid foam

25–80

0.035–0.041

–

25

PVC—rigid sheet

1350

0.16

–

26

Saw dust

188

0.57

–

27

Thermocole

22

0.03

–

28

Timber

600

0.14

1210

29

Turpentine

870

0.136

1760

30

Water (H2 O)

998

0.591

4190

31

Seawater

1025

–

3900

32

Water vapor

0.586

0.025

2060

33

Wood wool

500

0.10

1000

402

Appendix C: Physical Properties of Some Materials

Table C.6 Absorptivity of various surfaces for sun’s ray Surface

Absorptivity

Surface

White paint

0.12–0.26

Walls

Whitewash/glossy white

0.21

White/yellow brick tiles

0.30

Bright aluminum

0.30

White stone

0.40

Flat white

0.25

Cream brick tile

0.50

Yellow

0.48

Burl brick tile

0.60

Bronze

0.50

Concrete/red brick tile

0.70

Silver

0.52

Red sand line brick

0.72

Dark aluminum

0.63

White sand stone

0.76

Bright red

0.65

Stone rubble

0.80

Brown

0.70

Blue brick tile

0.88

Light green

0.73

Surroundings

Medium red

0.74

Sea/lake water

0.29

Medium green

0.85

Snow

0.30

Dark green

0.95

Grass

0.80

Blue/black

0.97

Light-colored grass

0.55

Sand gray

0.82

Roof

Absorptivity

Asphalt

0.89

Rock

0.84

White asbestos cement

0.59

Green leaf

0.85

Cooper sheeting

0.64

Earth (black plowed field)

0.92

Uncolored roofing tile

0.67

White leaves

0.20

Red roofing tiles

0.72

Yellow leaves

0.58

Galvanized iron, clean

0.77

Aluminum foil

0.39

Brown roofing tile

0.87

Unpainted wood

0.60

Galvanized iron, dirty

0.89

Black roofing tile

0.92

Metals Polished aluminum/copper

0.26

New galvanized iron

0.66

Old galvanized iron

0.89

Polished iron

0.45

Oxidized rusty iron

0.38

Appendix D

Program of Calculation of Solar Radiation and Solair Temperatures on Building Surfaces

%Jaipur phi=26.916*(pi/180); Isc= 1367; omega=[-75 -60 -45 -30 -15 0 15 30 45 60 75 105 105 105 105 105 105 105 105 105 105 105 105 105]*pi/180;; % 7:00 AM to 6:00 AM t=7:1:17; n=173; %nth day of the year (June 22, 2010, n=173, December 21, 2010, n=355) rho=0.2; % Reflectivity of surface TR=3.1; % Turbidity of surface TR=3.1 in June, TR=2.7 in December delta=(23.45*sin((360/365)*(n+284)*pi/180))*pi/180; Iext=Isc*(1+0.33*cos(2*pi*n/365)); for j=1:1:24 CThz(1,j)=cos(phi)*cos(delta).*cos(omega(1,j))+sin(delta) *sin(phi); if CThz(1,j)90; CThz(1,j)=0; end end CThz1=repmat(CThz,24,1); for j=1:1:24 In(1,j)=Iext.*exp(-TR/((0.9+9.4.*CThz(1,j)))); Ib(1,j)=In(1,j).*CThz1(j,j); Id(1,j)=(1/3)*(Iext-In(1,j)).*CThz1(j,j); end Ib1=repmat(Ib,24,1); Id1=repmat(Id,24,1); Ta=[28.5 28.7 29.3 30.4 31.9 33.6 35.6 37.4 38.8 39.8 40.1 39.8 38.7 37.7 36.2 34.6 33.4 32.2 31.3 30.6 30 29.4 29 28.6];% Jaipur in June %Ta=[9.5 9.8 10.6 11.9 13.9 16.1 18.7 21.1 22.9 24.1 24.6 24.1 23.1 21.4 19.5 17.5 15.8 14.3 13.1 12.2 11.5 10.7 10.1 9.7];% Jaipur in December © Bag Energy Research Society 2023 G. N. Tiwari, Advance Solar Photovoltaic Thermal Energy Technologies, Green Energy and Technology, https://doi.org/10.1007/978-981-99-4993-9

403

404

Appendix D: Program of Calculation of Solar Radiation and Solair …

gamma=[0 0 -90 90 0 -180]*pi/180; %[InclinedRoof Horizontal_Roof East West South North]; beta=[26.916 0 90 90 90 90]*pi/180; %[InclinedRoof Horizontal_Roof East West South North]; for k=1:1:6 for j=1:1:24 Thz(j,k)=cos(phi)*cos(delta).*cos(omega(j))+sin(delta) *sin(phi); Thi(j,k)=(cos(phi)*cos(beta(k))+sin(phi)*sin(beta(k)) *cos(gamma(k)))*cos(delta).*cos(omega(j))+cos(delta) .*sin(omega(j))*sin(beta(k))*sin(gamma(k))+sin(delta) *(sin(phi)*cos(beta(k))-cos(phi)*sin(beta(k)) *cos(gamma(k))); Rb(j,k)=Thi(j,k)./Thz(j,k); num=size(Rb(j,k)); for i=1:1:num; if Rb(j,k)0 &An(i)0 &An(i)>0 phin(i)=phid(i); end if Bn(i)0 phin(i) = phid(i); end % If phid is in the third quadrant% if Bn(i)