Design and Performance Optimization of Renewable Energy Systems 0128216026, 9780128216026

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Design and Performance Optimization of Renewable Energy Systems

Design and Performance Optimization of Renewable Energy Systems

Edited by Mamdouh El Haj Assad Sustainable and Renewable Energy Engineering Department, University of Sharjah, Sharjah, United Arab Emirates

Marc A. Rosen Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, Oshawa, ON, Canada

Academic Press is an imprint of Elsevier 125 London Wall, London EC2Y 5AS, United Kingdom 525 B Street, Suite 1650, San Diego, CA 92101, United States 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom Copyright © 2021 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www. elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress ISBN: 978-0-12-821602-6 For Information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

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Contents List of contributors Preface

xiii xv

1. Applications of renewable energy sources Mamdouh El Haj Assad, Mohammad Alhuyi Nazari and Marc A. Rosen 1.1 Introduction 1.2 Solar energy 1.2.1 Solar electricity generation 1.2.2 Heating and cooling 1.2.3 Desalination 1.3 Wind energy 1.4 Geothermal energy 1.4.1 Geothermal electricity 1.4.2 Geothermal heating 1.4.3 Geothermal cooling 1.5 Hydro energy 1.6 Bioenergy Conclusions Acknowledgments References

1 2 2 4 7 7 9 9 11 11 12 13 13 13 13

Marc A. Rosen Introduction Sustainability Energy Societal energy use and energy sustainability 2.5 Energy sustainability: interpretations, definitions, and needs 2.5.1 Interpretations and definitions of energy sustainability 2.5.2 Needs for energy sustainability 2.5.3 Reflection 2.6 Selected measures relating to renewable energy for enhancing energy sustainability

27 28 29

3. Heat exchangers and nanofluids Mamdouh El Haj Assad and Mohammad Alhuyi Nazari 3.1 3.2 3.3 3.4 3.5

Introduction Heat exchanger classification Effectiveness concept Nanofluids Applications of nanofluids in heat exchangers used in renewable energy technologies 3.6 Exergy analysis of nanofluidic heat exchangers Conclusions Acknowledgement References

33 33 36 37 38 40 41 41 41

4. Exergy analysis Marc A. Rosen

2. Renewable energy and energy sustainability 2.1 2.2 2.3 2.4

2.7 Illustrative example: net-zero energy buildings 2.8 Closure References

17 18 18 20

4.1 4.2 4.3 4.4 4.5 4.6 4.7

21 21 21 25 25

4.8

Introduction 43 Exergy 44 Procedure for energy and exergy analyses 44 Conventional balances: mass, energy, and entropy 44 Exergy balance 46 Exergy consumption 46 Exergy of heat, work, and electricity interactions 46 4.7.1 Exergy of heat 46 4.7.2 Exergy of work and electricity 47 Exergy of matter 47 4.8.1 Exergy of matter in a closed system 47 4.8.2 Exergy of a matter flow 47 4.8.3 Properties of materials for energy and exergy analyses 48

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Contents

4.9 Reference environment 4.10 Efficiencies and other measures of merit 4.10.1 Efficiency conceptually 4.10.2 Energy efficiencies and their deficiencies 4.10.3 Exergy and exergy-based efficiencies 4.11 Applications and implications 4.11.1 Thermodynamic applications of exergy analysis 4.11.2 Other applications of exergy analysis 4.11.3 Implications of results of exergy analyses 4.11.4 Exergy, renewable energy, and sustainability 4.12 Illustrative examples 4.12.1 Illustrative example 1: thermal energy storage 4.12.2 Illustrative example 2: heat pump versus electrical resistance heating 4.13 Closing remarks Nomenclature Greek letters Subscripts References

49 50 50 50 50 51 51 51 51 52 53 53 55 57 57 58 58 58

5. Solar power tower system Ali Khosravi, Mohammad Malekan, Juan Jose Garcia Pabon and Mamdouh El Haj Assad 5.1 Introduction 5.2 Case study 5.3 Solar power tower direct steam system 5.3.1 Technology overview 5.3.2 Heliostat field 5.3.3 Central receiver 5.3.4 Rankine cycle component 5.3.5 The heliostat field 5.3.6 Receiver 5.4 Intelligent methods 5.4.1 The proposed methodology 5.4.2 Adaptive neurofuzzy inference system 5.4.3 Biogeography-based optimization algorithm 5.4.4 ANFIS-BBO 5.5 Result and discussion 5.5.1 Receiver power loss 5.5.2 Power absorbed by the receiver 5.5.3 Receiver thermal efficiency 5.5.4 Field simulation 5.5.5 Cycle electrical power output Conclusions

61 62 62 62 65 65 66 66 67 68 68 69 69 71 72 72 76 78 79 81 82

Acknowledgment References

82 82

6. Parabolic trough solar collectors Mohammad Malekan, Ali Khosravi and Mamdouh El Haj Assad 6.1 Introduction 85 6.2 Parabolic trough solar collectors: a summary 86 6.3 Theoretical formulations 89 6.3.1 Governing equation of the CFD model 89 6.3.2 Properties of the Ferrofluid 90 6.3.3 Thermal performance 90 6.4 Parabolic trough solar collector analysis: a case study 92 Conclusions 97 References 99

7. Benefit-cost analysis and parametric optimization using Taguchi method for a solar water heater Auroshis Rout, Sudhansu S. Sahoo, Suneet Singh, Sidhartha Pattnaik, Ashok K. Barik and Mohamed M. Awad 7.1 Introduction 7.2 Economic analysis of solar water heating system 7.2.1 Concept of time value of money 7.2.2 Opportunity cost of capital or discount rate 7.2.3 Risks associated with the cash flows of an SWH 7.2.4 SWH investment evaluation criteria 7.2.5 Simple payback period 7.2.6 Discounted payback period 7.2.7 Benefit-cost ratio 7.2.8 DCF break-even analysis 7.3 Results and discussion of economic analysis 7.3.1 Simple and discounted payback period 7.3.2 Effects of various parameters on benefit cost ratio 7.3.3 DCF break-even profile 7.4 Optimization of input parameters using Taguchi method 7.5 Signal-to-noise ratio 7.6 Data analysis and parameter optimization 7.6.1 Analysis and optimization for scenario 1

101 103 103 103 104 104 104 104 104 105 105 105 106 108 109 110 111 111

Contents

7.6.2 Analysis and optimization for scenario 2 Conclusions Nomenclatures Appendix References

111 113 113 114 116

8. Fundamentals and performance of solar photovoltaic systems Di Zhang and Anis Allagui 8.1 Introduction 8.2 The pn junction model for solar cells 8.2.1 Electrostatic analysis in the depletion region 8.2.2 Solution for the quasineutral regions 8.2.3 Current voltage characteristics 8.3 Photovoltaic modules 8.3.1 Module components and characterizations 8.3.2 Environmental effects on module performance 8.4 Photovoltaic systems 8.4.1 System components 8.4.2 Design for stand-alone systems 8.4.3 Design for grid-connected systems Conclusion References

117 118 119 121 122 123 123 124 126 127 127 128 128 129

10. Geothermal power plants Mamdouh El Haj Assad, Ali Khosravi, Mohammad Alhuyi Nazari and Marc A. Rosen 10.1 Introduction 10.2 Dry steam power plant 10.2.1 Thermodynamic analysis 10.2.2 Exergy analysis 10.3 Single-flash steam power plant 10.3.1 Mass balance 10.3.2 Energy balance 10.3.3 Exergy analysis 10.4 Double-flash steam power plant 10.4.1 Mass balance 10.4.2 Energy balance 10.4.3 Exergy analysis 10.5 Binary power plant (ORC) 10.5.1 Energy balance 10.5.2 Exergy analysis 10.6 Illustrative examples 10.6.1 Example 1 10.6.2 Solution 10.6.3 Example 2 10.6.4 Solution 10.7 Exercises References

147 148 148 149 150 150 151 152 152 152 153 155 156 157 158 158 158 158 160 161 161 162

11. Heat pumps and absorption chillers Mamdouh El Haj Assad, Mohammad Alhuyi Nazari, Mehdi A. Ehyaei and Marc A. Rosen

9. Cooling systems for linear concentrating photovoltaic (LCPV) system Juan Jose Garcia Pabon, Ali Khosravi and Mamdouh El Haj Assad 9.1 Introduction 9.2 Linear concentrating photovoltaic system 9.2.1 Solar concentrator 9.2.2 Photovoltaic cell 9.3 Cooling system 9.3.1 Photovoltaic cell cooler 9.3.2 Water mechanical pumped loop system 9.3.3 Two-phase mechanical pumped loop (TMPL) system 9.3.4 Vapor compression refrigeration (VCR) system Conclusion Acknowledgments Nomenclatures Abbreviations Subscripts References

ix

131 132 132 132 134 134 136 137 141 144 144 144 144 145 145

11.1 Introduction 11.2 Types of heat pumps and their advantages 11.3 Geothermal heat pumps 11.3.1 Site evaluation for geothermal heat pumps 11.3.2 Benefits of geothermal heat pump systems 11.3.3 Basic operating principles of geothermal heat pumps 11.4 Conventional heat pump for cooling 11.5 Illustrative examples 11.5.1 Example 1 11.5.2 Solution 11.5.3 Example 2 11.5.4 Solution 11.5.5 Example 3 11.5.6 Solution 11.6 Absorption chillers 11.6.1 Thermodynamic analysis 11.6.2 Illustrative example 11.7 Closing remarks References

163 164 166 166 167 168 170 171 171 172 173 173 173 174 174 175 177 180 180

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12. Hydropower Tiia Sahrakorpi, Ali Khosravi and Mamdouh El Haj Assad 12.1 Introduction 12.2 Hydropower technology 12.2.1 Classification 12.2.2 Turbine types and their classifications 12.2.3 Large hydropower components 12.2.4 Small hydropower components 12.2.5 Micro hydropower components 12.3 Revaluation concepts for hydroelectric energy storage 12.4 Pumped storage 12.5 Modeling of micro hydroelectric power plants 12.5.1 Flow duration curve 12.5.2 Flow rate measurement 12.5.3 Weir and open channel 12.5.4 Penstock design 12.5.5 Head measurement 12.5.6 Turbine power 12.5.7 Turbine speed 12.5.8 Turbine selection 12.6 Hydroelectric optimization problem Conclusion Acknowledgment References

181 183 183 183 184 185 185 186 187 188 188 188 189 189 189 189 189 190 191 193 194 194

13. Energy and exergy analyses of wind turbines Mehdi A. Ehyaei and Mamdouh El Haj Assad 13.1 Introduction 13.2 Energy analysis of wind turbines 13.3 Exergy analysis of wind turbines 13.4 Numerical example Conclusions References

195 197 199 200 202 202

14. Energy storage Mamdouh El Haj Assad, Ali Khosravi, Mohammad Malekan, Marc A. Rosen and Mohammad Alhuyi Nazari 14.1 Introduction 14.2 Electrochemical energy storage 14.2.1 Nickel cadmium (Ni Cd) batteries 14.2.2 Nickel zinc batteries 14.2.3 Lead acid batteries 14.2.4 Lithium-ion batteries

205 206 207 207 207 207

14.3 Hydrogen energy storage 14.4 Mechanical energy storage 14.4.1 Flywheel electric energy storage 14.4.2 Compressed air energy storage 14.5 Electromagnetic energy storage 14.5.1 Super capacitor energy storage 14.5.2 Superconducting magnetic energy storage 14.6 Fuel cells 14.6.1 Thermodynamic analysis 14.6.2 Illustrative example 14.6.3 Solution 14.7 Thermal energy storage Conclusions Acknowledgment References

207 208 208 209 211 211 211 212 212 214 215 215 218 219 219

15. Use of nanofluids in solar energy systems Mohsen Izadi and Mamdouh El Haj Assad 15.1 Nanofluid: a new generation of heat transfer fluids 221 15.1.1 Nanofluid preparation 222 15.1.2 Type of nanofluids 223 15.1.3 Thermophysical properties 224 15.1.4 Other properties 225 15.1.5 Mathematical modeling convection heat transfer through nanofluids 226 15.1.6 Natural convection 230 15.1.7 Forced and mixed convection 230 15.2 Renewable energy versus nonrenewable energy 231 15.3 Solar energy 231 15.3.1 Solar collectors 232 15.4 Simulation of nanofluid flow through solar absorbers 240 15.4.1 Role of nanofluid in absorbing solar energy 243 15.5 Solar stills 243 15.6 Concluding remarks 245 References 245

16. Artificial Intelligence applications in renewable energy systems Mohammad AlShabi and Mamdouh El Haj Assad 16.1 What is Artificial Intelligence? 16.2 Artificial Intelligence and renewable energy

251 252

Contents

16.3 Artificial Intelligence examples for a photovoltaic solar cell: case study 16.3.1 Artificial Neural Network 16.3.2 Fuzzy Logic

252 252 259

16.3.3 Metaheuristic techniques 16.3.4 Case study: numerical example References Index

xi

262 269 291 297

List of contributors Mohammad Alhuyi Nazari Renewable Energy and Environmental Engineering Department, University of Tehran, Tehran, Iran

Mohammad Malekan Department of Mechanical and Production Engineering, Aarhus University, Aarhus, Denmark

Anis Allagui Sustainable and Renewable Energy Engineering Department, University of Sharjah, Sharjah, United Arab Emirates; Center for Advanced Materials Research, Research Institute of Sciences and Engineering, University of Sharjah, Sharjah, United Arab Emirates; Department of Mechanical and Materials Engineering, Florida International University, Miami, FL, United States

Juan Jose Garcia Pabon Institute in Mechanical Engineering, Federal University of Itajuba´ (UNIFEI), Itajuba´, Brazil

Mohammad AlShabi Mechanical and Engineering Department, University of Sharjah, United Arab Emirates

Nuclear Sharjah,

Mamdouh El Haj Assad Sustainable and Renewable Energy Engineering Department, University of Sharjah, Sharjah, United Arab Emirates Mohamed M. Awad Mechanical Power Engineering Department, Faculty of Engineering, Mansoura University, Mansoura, Egypt Ashok K. Barik Department of Mechanical Engineering, College of Engineering and Technology, Bhubaneswar, India Mehdi A. Ehyaei Department of Mechanical Engineering, Pardis Branch, Islamic Azad University, Pardis New City, Iran Mohsen Izadi Department of Mechanical Engineering, Faculty of Engineering, Lorestan University, Khorramabad, Iran Ali Khosravi Department of Mechanical Engineering, School of Engineering, Aalto University, Espoo, Finland

Sidhartha Pattnaik Department of Mechanical Engineering, College of Engineering and Technology, Bhubaneswar, India Marc A. Rosen Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, Oshawa, ON, Canada Auroshis Rout Department of Energy Science and Engineering, Indian Institute of Technology, Bombay, India Sudhansu S. Sahoo Department of Mechanical Engineering, College of Engineering and Technology, Bhubaneswar, India Tiia Sahrakorpi Department of Mechanical Engineering, School of Engineering, Aalto University, Espoo, Finland Suneet Singh Department of Energy Science and Engineering, Indian Institute of Technology, Bombay, India Di

Zhang Sustainable and Renewable Energy Engineering Department, University of Sharjah, Sharjah, United Arab Emirates; Center for Advanced Materials Research, Research Institute of Sciences and Engineering, University of Sharjah, Sharjah, United Arab Emirates

xiii

Preface The renewable energy sector is growing year by year, with increasingly broad applications in industry and other sectors of the economy. Still there is a lack of knowledge about this sector, in part due to the relatively small number of institutions that offer degrees in renewable energy. Furthermore, much renewable energy technology is relatively new and there often is a lack of expertise in the field. Design and Performance Optimization of Renewable Energy Systems seeks to address this need, by providing an enhanced understanding of the potential and main challenges of this emerging field. Students, researchers, and engineers who are interested in renewable energy and associated technology often face challenges in finding suitable references that encapsulate or summarize the main renewable energy technology options as well as most relevant renewable energy materials and tools for their characterization. This book presents information on various renewable energy systems in addition to their applications—in such domains as space heating and cooling, power generation, and more—and means to determine their performances using advanced thermodynamics and neural network techniques. To ensure leading edge methods are covered, a detailed chapter is included on exergy analysis for renewable energy systems, complementing the coverage of fundamentals of thermodynamics, heat transfer, and neural network analysis. The book synthesizes and describes in detail the knowledge that currently is distributed across the literature for different types of power plants driven by renewable energy sources. This material in the book is organized so as to provide an accessible and comprehensive source of information for students, engineers, and researchers interested in all aspects of renewable energy systems. The book thereby provides readers with an exhaustive guide to key concepts and the state-of-the-art of the numerous facets of renewable energy systems, as well as what is needed for advancing the field of renewable energy and the performance of renewable energy systems. The coverage of artificial neural network analysis is important for the optimization of these systems. The main objective of the book is to provide a unique work that presents design concepts for solar, geothermal, hydro, and wind energy systems based on the concepts of thermodynamics, heat transfer, and artificial neural networks. To facilitate this objective, the book includes material on energy storage and heat pumps driven by renewable energy sources, as they help in realizing the full potential of renewable energy. An understanding of the operating principles of renewable energy systems is conveyed to the reader. The book includes assessments of geothermal power plants, hydroelectric power facilities, solar power towers, linear concentrating PV units, parabolic trough solar collectors, and wind turbines. The use of nanofluids in renewable energy systems is reviewed and discussed, especially from the perspective of heat transfer enhancement. Design and Performance Optimization of Renewable Energy Systems contains 16 chapters, and serves as a reference for students, engineers, and researchers involved in the field renewable energy.

Mamdouh El Haj Assad and Marc A. Rosen

xv

Chapter 1

Applications of renewable energy sources Mamdouh El Haj Assad1, Mohammad Alhuyi Nazari2 and Marc A. Rosen3 1

Sustainable and Renewable Energy Engineering Department, University of Sharjah, Sharjah, United Arab Emirates, 2Renewable Energy and

Environmental Engineering Department, University of Tehran, Tehran, Iran, 3Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, Oshawa, ON, Canada

Chapter Outline 1.1 Introduction 1.2 Solar energy 1.2.1 Solar electricity generation 1.2.2 Heating and cooling 1.2.3 Desalination 1.3 Wind energy 1.4 Geothermal energy

1.1

1 2 2 4 7 7 9

1.4.1 Geothermal electricity 1.4.2 Geothermal heating 1.4.3 Geothermal cooling 1.5 Hydro energy 1.6 Bioenergy Conclusions References

9 11 11 12 13 13 13

Introduction

World total primary energy consumption has exhibited an increasing trend over the last decade, as shown in Fig. 1.1. Fossil fuels such as oil, coal, and natural gas presently have the highest share in the electricity generation mix, as shown in Fig. 1.2. However, due to concerns over the environmental issues associated with fossil fuels and their finite nature and potential depletion in the future, renewable energy sources are gradually being substituted in place of them. There are various types of renewable energy sources such as wind, solar, geothermal, and biomass. These are used for variety of applications including heating, cooling, electricity generation, and desalination [1,2]. Renewable energy sources have a notable role in meeting worldwide heating and cooling demands, achieving approximately a 10% share in 2016 [3]. Generally, solar collectors or geothermal heat exchangers can be employed for heating purposes. In addition to heating, the thermal energy of renewable sources can be utilized for desalination units. In renewable desalination systems, the absorbed thermal energy is used for saline water evaporation and producing fresh water. Despite the applicability of renewable sources for different purposes, developments in renewable energy sources have in recent years been mainly concentrated in the power generation area. According to the REN21 report [3], 181 GW of renewable power was added to the global capacity of renewable energy power plants in 2018. In this period, among the various types of global installed renewable energy systems, solar photovoltaic (PV) panels have the highest share of electrical generation capacity, with approximately 100 GW, and wind turbines rank second at about 50 GW. Renewable energy systems can be used for electricity generation both directly and indirectly. For instance, PV panels are employed for direct conversion of solar energy to electricity while in some cases the thermal energy of the renewable sources are extracted to drive power plants based on such thermal processes as Brayton and Rankine cycles. The efficiency of renewable energy systems for electricity production depends on several factors, including the employed technology and geographical and ambient conditions. Details of the most commonly employed renewable energy technologies are given in the remainder of this chapter.

Design and Performance Optimization of Renewable Energy Systems. DOI: https://doi.org/10.1016/B978-0-12-821602-6.00001-8 © 2021 Elsevier Inc. All rights reserved.

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Design and Performance Optimization of Renewable Energy Systems

FIGURE 1.1 World total primary energy consumption for 2008 18, based on BP report in 2018 [4].

14500 Total primary energy consumpon (Mtoe)

14000 13500 13000 12500 12000 11500 11000 10500 10000 2008

2010

2012

2014

2016

2018

Year

FIGURE 1.2 Breakdown of global share of energy sources in electricity generation in 2018 [4].

Oil Hydropower

1.2

Natural gas Renewables

Coal Others

Nuclear

Solar energy

The most abundant energy resource on the Earth is solar energy. The received energy of the Earth from the sun in 1 hour is approximately equal to the required energy for 1 year of human activities [5]. As indicated earlier, solar energy is broadly applied for electricity generation. According to the International Energy Agency (IEA), solar technologies have the potential to contribute a 14% decrease in carbon dioxide emissions in the power sector by 2050, on the basis of the BLUE Map scenario [6]. In addition to electricity generation, solar energy can be used for other purposes such as heating and desalination. The main advantages of solar energy are its wide availability and accessibility, although its intermittency makes predictability somewhat challenging. Various technologies can be applied for harvesting solar energy and convert it to required types of energy.

1.2.1 Solar electricity generation PV panels are applied for direct conversion of solar irradiance into electricity. In PV cells, special types of semiconductors are used. The solar irradiance on the semiconductor provides the energy for electron transfer, which gives rise to an electrical current [7]. The most conventional types of PV technologies are crystalline and thin film, although some innovative technologies such as organic cells are being investigated [5]. According to the IEA [5], crystalline silicone and thin film technologies account for approximately 85% 90% and 10% 15% of worldwide PV cell market, respectively. Efficiencies of PV cells based on their technology are presented in Table 1.1.

Applications of renewable energy sources Chapter | 1

3

TABLE 1.1 Confirmed single-junction terrestrial photovoltaic (PV) cell and submodule efficiencies [8]. Cell type

Efficiency range (%)

Si (crystalline cell)

26.7 6 0.5

Si (multicrystalline cell)

22.3 6 0.4

Si (thin transfer submodule)

21.2 6 0.4

Si (thin film minimodule)

10.5 6 0.3

GaAs (thin film cell)

29.1 6 0.6

GaAs (multicrystalline)

18.4 6 0.5

InP (crystalline cell)

24.2 6 0.5

CIGS (cell)

22.9 6 0.5

CdTe (cell)

21.0 6 0.4

CZTSSe (cell)

11.3 6 0.3

CZTS (cell)

10.0 6 0.2

Si (amorphous cell)

10.2 6 0.3

Si (microcrystalline cell)

11.9 6 0.3

Dye (cell)

11.9 6 0.4

Dye (minimodule)

10.7 6 0.4

Dye (submodule)

8.8 6 0.3

Organic (cell)

11.2 6 0.3

Organic (minimodule)

9.7 6 0.3

FIGURE 1.3 Schematic of concentrated photovoltaic (PV) system with thermal system [9].

As seen in Table 1.1, the efficiencies of PV cells are not very high; therefore, the generated electricity for each for a specific surface area is often low or inadequate. In order to overcome this problem, concentrators can be coupled with PV cells. In this configuration, the solar radiation is concentrated using optical tools, which boosts the supplied energy for a specific area. Due to the performance degradation of PV cells at high temperatures, it is necessary to reduce their temperatures when concentrators are used. With such approaches, thermal systems are integrated with the PV cells for cooling, by extracting the absorbed thermal energy, as represented in Fig. 1.3. Sometimes the extracted thermal energy is supplied as a coproduct.

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Design and Performance Optimization of Renewable Energy Systems

The performance of PV cells in generating electricity depends on several parameters including temperature, solar irradiance, dust accumulation, shading and soiling of PV panels. The produced electricity by a PV cell depends greatly on the solar irradiance (solar power per unit of area). An increase in the solar irradiance makes more energy available for conversion to electricity. In addition to the solar irradiance, the temperature of the PV cell affects the output power due to its impact on the efficiency of the cell. Lowering the temperature of the cell normally results in higher efficiency. Due to the importance of the PV cell in generating electricity, several approaches exist for thermal management of PV cells, such as employing water flow, phase change materials (PCMs), and heat pipes. The presence of dirt or dust on the surface of PV cells can block sunlight from the cell, which lowers the energy received; as a consequence, the output power is correspondingly decreased. The dust reduction factor is typically equal to 0.93, meaning a 7% reduction in the input solar irradiance for a cell [10]. Spraying water on the surface of PV cells is suggested to overcome problems related to dirt and dust accumulation, and it can sometimes assist in temperature control [11]. Shadowing is another unfavorable phenomenon which degrades the performance of PV cells. According to some studies [12,13], in cases where 5% 10% of the array of solar panels is shaded, the generated electricity can be reduced over 80%. In addition to direct methods, some technologies can be applied to indirectly convert solar energy to electricity. In these types of technologies, solar energy is used to drive thermal power plants. In order to produce a high quantity of thermal energy in a limited space, concentrators must be used. Generally, there are three types of concentrated solar power technologies, including linear parabolic collector systems, solar towers, and parabolic dish collectors. Linear parabolic collectors consist of a linear concentrator which has parabolic cross-sectional shape. The surface of the concentrator follows the path of the sun on a single axis. This concentrator is installed on a support structure, which keeps it fixed and permits appropriate performance in unfavorable conditions such as windy weather. In these concentrators, the received sunlight is focused on a tube along the focal point. Inside the tube there is an operating fluid which receives heat from the concentrated solar irradiation. In parabolic dishes, the reflecting panels follow the sun’s path by rotating around two axes, which are orthogonal. The panels focus the sunlight on a receiver which is located at the focal point. By employing these concentrators, high-temperature thermal energy is transferred to the operating fluid. In solar tower systems, reflecting panels with flat surfaces, known as heliostats, are used for concentrating the sunlight. These panels rotate on two axes and focus the solar radiation on the receiver located at the top of the tower which is in the center of the system. The fluid inside the solar receiver absorbs the concentrated solar energy, raising its temperature and pressure. Various types of solar thermal systems are illustrated in Fig. 1.4. Solar thermal energy systems can be integrated with existing thermal power plants to improve the efficiency. In some cases, solar energy is applied for preheating the compressed air that enters the combustion chamber in a gas turbine cycle, as shown in Fig. 1.5. The existence of a thermal energy storage unit in these configurations can further improve the efficiency of the system and make it operable at nighttime. In addition to hybrid systems that use both fossil fuels and solar thermal energy for power generation, solar energy can be used alone for electricity production. In these types of systems, solar energy is applied to increase the temperature and pressure of air (or another working fluid) to levels appropriate for input to a power generation turbine. Solar concentrators are employed to extract more energy per unit of area. The performance of these cycles can be improved by heat recovery. In Fig. 1.6, a schematic diagram of a Brayton cycle with heat recovery and intercooling units is presented. In addition to employing heat recovery units for improving the efficiency of these cycles, some other ideas have been applied for this purpose, such as using supercritical fluids and combining Brayton cycles with other cycles such as Rankine cycles. In these configurations, the outlet hot gases of the gas turbine provide the main thermal input to drive the Rankine cycle. The efficiencies are usually higher for these configurations than for simple Brayton cycles [17].

1.2.2 Heating and cooling The share of building sector energy consumption in worldwide final energy utilization, which refers to final energy consumption by end users, was 35.3% around 2010 [19]. Renewable energy systems, especially solar technologies, can be used in several sectors to provide the energy required for heating and cooling. Renewable-based heating technologies are applied in order to collect, store, and deliver thermal energy to buildings, while cooling systems are used to supply cooling capacity [19]. Various systems can be used for heating a building using solar energy, such as a Trombe wall, an unglazed transpired solar fac¸ade, and a solar chimney. Trombe walls consist of a large wall, an air channel and an outer glazing. A schematic of a Trombe wall is illustrated in Fig. 1.7. In these types of systems, the large wall is used for absorbing and storing the energy of the sun that passes through the glazing. A portion of the absorbed heat is transferred via conductive and convective heat transfer mechanisms to the interior space. In addition, cold air enters the channels through a lower vent, is heated and moves upwards due to the buoyancy effect and exits the channel via an upper vent. An

Applications of renewable energy sources Chapter | 1

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FIGURE 1.4 Schematics of three types of concentrating solar collectors: (A) linear, (B) solar tower, and (C) parabolic dish [14,15].

FIGURE 1.5 Schematic of solar-assisted gas turbine [16].

unglazed transpired solar fac¸ade consists of metal sheet walls with some holes that are employed for capturing solar thermal energy and heating air. As shown in Fig. 1.8, a fan is used for circulating the air flow. A solar chimney operates based on the principle of converting thermal energy into kinetic energy for air circulation. In addition to these methods, there are other technologies for air heating in buildings, such as solar roofs.

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Design and Performance Optimization of Renewable Energy Systems

FIGURE 1.6 Schematic of solar-driven Brayton cycle [18].

FIGURE 1.7 Schematic of Trombe wall (central vertical thick dark bar), from a top view perspective [19].

Solar thermal energy utilization in buildings is not limited to air heating as it can also be used for water heating. In most cases, water flows through sun-facing collectors. Many configurations are proposed for solar water heating systems, and these are mainly categorized as direct and indirect water heating approaches. In direct water heating systems, water flows through a collector and absorbs thermal energy, while in indirect methods heat exchangers are employed for transferring the thermal energy of the applied collectors. As noted earlier, solar energy can be applied for cooling purposes. Solar cooling systems utilize the absorbed heat from sunlight in the thermally driven cooling processes. Generally, two main processes occur in these systems. In closed cycles, sorption chillers that are thermally driven are used for producing chilled water for utilization in space conditioning facilities. In open cycle solar cooling systems, water is typically employed as the refrigerant and a desiccant as a sorbent for air treatment of the ventilation technology [20]. One of the main advantages of solar cooling systems compared with alternatives is related to its nature. Since the highest solar irradiation coincides with the maximum required cooling demand, employing these types of systems can lead to a reduction in peak electrical demands on the electrical network in comparison with conventional systems used for cooling. In addition, solar cooling technologies can be applied for heating purposes, including water heating, in cold seasons [20].

Applications of renewable energy sources Chapter | 1

7

FIGURE 1.8 Schematic of unglazed transpired solar fac¸ade [19].

1.2.3 Desalination The increasing trend in world population and consequent increase in the need for consumable freshwater necessitate the development and utilization of desalination systems. A desalination process removes salt from saline feed-water, providing useful water suitable for such purposes as drinking and agriculture [21]. Desalination systems are mainly categorized as thermal or membrane technology types. As of the end of 2016, approximately 73% of the world’s desalination units were based on membrane technology and the remaining ones were of the thermal types [21]. Renewable energy systems can be applied for desalination both directly and indirectly. Generally, in direct techniques, the thermal energy of renewable energy sources is used for water evaporation and salt removal, while in indirect methods the required electricity for membrane technologies is generated by renewable sources. Solar energy is among the most attractive renewable energy sources for desalination units. In thermal desalination systems, the heat required for saline water evaporation is supplied by the sun. Using thermal energy storage units such as PCMs makes solar thermal desalination units capable for nighttime operation [22]. Despite the improvements made to the performance of solar thermal desalination units by employing thermal storage, which have raised their costs, they can be economically feasible for large-scale systems [21]. In addition to thermal desalination systems, solar energy can be employed for indirect water desalination. In these types of desalination technologies, the electricity generated by PV panels or solar thermal power plants is used in membrane-based desalination units.

1.3

Wind energy

The utilization of wind as an energy source dates back to antiquity. The wind was used for grinding grain by employing vertical axis windmills and applied for transportation through sailboats [23]. In recent decades, wind turbines are used increasingly for electricity generation. In order to generate electricity from wind energy, wind turbines are applied. Wind turbines coupled with generators convert the kinematic energy of the wind to the electricity. According to the IEA [6], wind energy is expected to be responsible for a 12% reduction in carbon dioxide emissions by 2050, based on the BLUE map scenario. In addition to the benefits of wind turbines in decreasing emissions of carbon dioxide, their utilization can reduce the production of other pollutants such as oxides of nitrogen and sulfur [6]. Wind energy has accounted for approximately half of the world renewable energy generation in 2017 and 2018 [4]. In 2018 worldwide wind generation increased by 32 Mtoe compared with 2017, which gave it the first ranking among renewable energy sources, and its growth rate that year (2018) was about 12.6% [4].

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Design and Performance Optimization of Renewable Energy Systems

FIGURE 1.9 Vertical and horizontal axis wind turbines [24].

TABLE 1.2 Wind turbine classes according to International Electrotechnical Commission (IEC) standard [26]. Class

Annual mean speed of the wind

Level of turbulence

Extreme 50-year gust

IA

High wind speed—10 m/s

High turbulence—18%

High gust—70 m/s

IB

High wind speed—10 m/s

Low turbulence—18%

High gust—70 m/s

IIA

Medium wind speed—8.5 m/s

High turbulence—18%

Medium gust—59.5 m/s

IIB

Medium wind speed—8.5 m/s

Low turbulence—18%

Medium gust—59.5 m/s

IIIA

Low wind speed—7.5 m/s

High turbulence—18%

Low gust—52.5 m/s

IIIB

Low wind speed—7.5 m/s

High turbulence—18%

Low gust—52.5 m/s

IV

6.5 m/s

—

42 m/s

There are two major classes of wind turbines based on the orientation of their axes, as shown in Fig. 1.9. The main components of horizontal axis turbines are the electrical generator and the rotor shaft and blades. In these types of wind turbines, wind vanes are employed for small-scale turbines while sensors are usually needed for large-scale turbines. In vertical axis wind turbines, the shaft of the rotor is installed vertically. There is no requirement for the blades to be pointed into the direction of wind for effective performance, which is one of the most important advantages of these types of wind turbines [24]. Generally, the power coefficient, which is defined as the ratio of actual generated power to the total power of the wind flowing into the turbine blade for a specific speed, is lower for vertical rather than horizontal axis wind turbines. This constitutes one of the main reasons for the greater commercial availability and success of horizontal axis wind turbines [23]. In addition, horizontal axis wind turbines have higher aerodynamic yields, lower costs, lower mechanical stresses, autonomous startup, and fewer requirements for components at ground level [25]. The typical number of blades for horizontal axis turbines varies between 1 and 3. In addition to the type of wind turbine axis, various other criteria are used for their classification. Based on standard 624001 of the International Electrotechnical Commission (IEC) [26], wind turbines can be divided into several classes on the basis of their allowable ranges for parameters such as extreme wind gust in last 50 years, turbulence, and mean annual velocity, as shown in Table 1.2. In offshore regions, wind has higher speeds and its power is more constant compared with onshore locations. Moreover, air turbulence is lower in offshore regions [27]. These features make offshore locations more suitable for installing wind turbines and generating electricity. In addition to these favorable features of offshore regions for wind turbines, there are some other benefits such as the possibility of employing wind turbines with larger dimensions, which provide greater electricity generation, fewer physical restrictions such as buildings which block the flow of wind, and prevention of unfavorable visual impacts compared with onshore regions. However, offshore wind turbines also have disadvantages, the main being their higher cost due to the required structures. In addition, based on an environmental assessment [28], using onshore wind turbines leads to lower life cycle emissions of greenhouse gases compared with offshore facilities due to the requirement for floating platforms fixed in the water, when employing offshore wind turbines.

Applications of renewable energy sources Chapter | 1

1.4

9

Geothermal energy

Another renewable energy source which can be used for electricity generation and heating is geothermal energy. This type of energy is able to provide electricity and heat with low carbon emissions, from hydrothermal resources at high temperature, deep aquifer systems at low and moderate temperatures, and hot rock resources [29]. Relative to solar and wind energy, the stability in electrical power output of geothermal systems is higher. Moreover, geothermal power plants are not affected by variations in climate, which causes them to have higher capacity factors and makes them more appropriate for baseload electricity generation [30]. According to the IEA, worldwide electricity generation from geothermal systems in 2017 was approximately 84 TWh. The cumulative capacity of such geothermal systems was about 14 GW, and is expected to reach 17 GW by 2023 [30]. The IEA suggests that geothermal energy has the potential to account for a 3% reduction in emissions of carbon dioxide associated with electricity generation by 2050, based on the BLUE map scenario [6]. Geothermal energy sources can be used for heating and cooling [31], freshwater production [32], as well as electricity generation [33]. In most cases, heat exchangers are used to transfer heat from the hightemperature water extracted from geothermal resources to the working fluids used in heat pumps for heating/cooling purposes. Geothermal heat pumps are renewable energy-based units.

1.4.1 Geothermal electricity Geothermal energy can be used as a reliable source for producing electricity. Generally, conventional Rankine or Kalina cycles are used for geothermal power generation. In order to generate electricity from geothermal resources, it is necessary to extract their thermal energy. In geothermal power plants, steam from the hot sublayers of the Earth are typically used for electricity production, in systems employing turbines and generators, as shown in Fig. 1.10. Generally, there are three kinds of geothermal power plants: dry steam, flash steam (single and double flash), and binary cycle. In dry steam power plants, the steam extracted from sublayers is directly piped to the power plant to drive a steam turbine, as shown in Fig. 1.10. In single flash steam geothermal power plants, high-temperature saturated liquid water (. 182 C) is extracted. Reducing the pressure of this water in this process leads to partial boiling of the water. The produced mixture in this stage is divided by a separator into liquid and vapor flows. The steam flow passes through the steam turbine while the liquid water exits the separator and is reinjected back into the ground. The double flash steam geothermal power plant is similar to single flash system, except in the former there are two separators linked to high- and low-pressure steam turbines. Schematic diagrams of single and double flash power plants are shown in Figs. 1.11 and 1.12, respectively. In a binary cycle plant, which is typically an organic Rankine cycle (ORC), geothermal resources with lower temperatures compared with flash steam plants are applicable for electricity generation. In these types of the plants, water at a temperature range of 107 C 182 C is used for boiling a working fluid, which is mainly comprised of an organic compound with a low boiling temperature and high vaporization rate. Heat transfer between the high-temperature water and the working fluid, in a heat exchanger, results in vaporization of the working fluid. The vaporized working fluid drives the turbine, producing electricity. The geothermal water utilized for heating the working fluid is returned to the ground for reheating [35]. A schematic diagram of an ORC power plant is shown in Fig. 1.13. FIGURE 1.10 Schematic of geothermal power plant [34].

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Design and Performance Optimization of Renewable Energy Systems

FIGURE 1.11 Schematic diagram of single flash geothermal power plant.

FIGURE 1.12 Schematic diagram of double flash geothermal power plant.

Applications of renewable energy sources Chapter | 1

11

FIGURE 1.13 Geothermal organic Rankine cycle (ORC) power plant.

1.4.2 Geothermal heating In addition to electricity generation, geothermal resources can be applied for heating purposes. Extracted heat from geothermal resources can be utilized for meeting several kinds of demands at various temperature levels. Low-temperature geothermal resources are applicable for space heating while their higher temperature counterparts can be used for a range of applications. Geothermal heat is mainly used in heat pumps (49% of total uses), while it is also useful for heating swimming pools and district heating [29]. The operation of geothermal heat pumps is based on the nature of the ground temperature, which, below the top 3 5 m, is approximately constant throughout the year [36]. The temperature of the earth is lower than that of the surrounding air in hot seasons, and vice versa. This feature is exploited by geothermal heat pumps. These devices transfer heat from the ground to buildings or other facilities in cold seasons, and transfer heat from them to the ground in hot seasons. Geothermal heat pumps can be directly fed by groundwater obtained from the wells or employ ground heat exchangers [37]. These heat pumps can be used for building space heating and providing domestic hot water. As indicated previously, geothermal sources are also applicable for district heating. District heating networks are designed in order to supply space heating for several consumers from single or multiple geothermal wells. In addition to space heating, district heating systems can be utilized for such other purposes as providing warm water for pools and hot water for domestic demand. In Fig. 1.14, a simplified configuration of geothermal district heating system is presented. Typically, there are three circuits in these systems known: an energy production circuit which uses the geothermal well as heat source, a distribution circuit, and an energy consumption circuit [38]. The net result of these circuits is that thermal energy extracted from geothermal wells is used for heating purposes.

1.4.3 Geothermal cooling An important application of geothermal energy is its use to drive absorption chillers, such as water-lithium bromide absorption units, which do not require high operating temperatures. Absorption chillers consist of a generator (desorber), a condenser, throttling valves, an evaporator, a pump, a heat exchanger, and a separator. In a water-lithium bromide absorption chiller, the working fluid (absorbent) in the generator and the absorber is a lithium bromide solution, while water (refrigerant) is the working fluid in the condenser and the evaporator. This type of refrigeration system is used only for cold temperatures above 0 C to avoid water freezing. In order to produce a cooling load from the chiller using geothermal energy, the geothermal fluid is circulated, before being sent to the reinjection well, to the generator of the absorption chiller to heat the lithium bromide solution, in order to generate a vapor that is passed to the condenser of the refrigeration cycle. For a geothermal temperature in the range of 80 C to 120 C, single effect water lithium bromide absorption chiller can be used while for

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Design and Performance Optimization of Renewable Energy Systems

FIGURE 1.14 Schematic of geothermal district heating system [38]. FIGURE 1.15 Layout of hydroelectric power plant.

higher temperature than 120  C, a double effect water lithium bromide absorption chiller is typically used. The geothermal fluid exiting the power plant of Fig. 1.13 can be used to drive a single effect chiller while the geothermal fluid of Figs. 1.10 1.12 can be used to drive a double effect chiller due to its high operating temperature.

1.5

Hydro energy

Another clean, renewable energy source is hydro energy. Hydro energy is capable of satisfying a large percentage of the electricity needs in countries like Norway and the United States. According to the IEA, hydropower has the potential to account for a 2% reduction in carbon dioxide emissions in the power sector by 2050, based on the BLUE Map scenario [6]. In producing electricity from hydro energy, water falling from a high elevation having a high potential energy to a lower level is used to drive a hydraulic turbine to produce shaft work. The turbine is connected to a generator for electricity production. The main components of hydro power plants are a dam, a penstock, a turbine, and a generator, as shown in Fig. 1.15. An important advantage of hydro energy is the possibility of direct exploitation and simultaneous utilization. Hydro energy is capable of producing electrical power for all applications, for example, domestic and industrial. Types of hydro power can be classified according to the power production level, as shown in Fig. 1.16. For small communities, micro and pico hydro plants are typically used.

Applications of renewable energy sources Chapter | 1

13

Classificaon of hydropower

Large hydro >100 MW

Medium hydro up to 100 MW

Small hydro up to 5 MW

Micro hydro 100 kW

Pico hydro