Energy Storage Systems: Fundamentals, Classification and a Technical Comparative (Green Energy and Technology) 3031384199, 9783031384196

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Green Energy and Technology

José Manuel Andújar Márquez Francisca Segura Manzano Jesús Rey Luengo

Energy Storage Systems: Fundamentals, Classification and a Technical Comparative

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**.

José Manuel Andújar Márquez · Francisca Segura Manzano · Jesús Rey Luengo

Energy Storage Systems: Fundamentals, Classification and a Technical Comparative

José Manuel Andújar Márquez Department of Electronics, Computer Systems and Automation Engineering Centro de Investigación en Tecnología, Energía y Sostenibilidad (CITES) University of Huelva Huelva, Spain

Francisca Segura Manzano Department of Electronics, Computer Systems and Automation Engineering Centro de Investigación en Tecnología, Energía y Sostenibilidad (CITES) University of Huelva Huelva, Spain

Jesús Rey Luengo Department of Electronics, Computer Systems and Automation Engineering Centro de Investigación en Tecnología, Energía y Sostenibilidad (CITES) University of Huelva Huelva, Spain

ISSN 1865-3529 ISSN 1865-3537 (electronic) Green Energy and Technology ISBN 978-3-031-38419-6 ISBN 978-3-031-38420-2 (eBook) https://doi.org/10.1007/978-3-031-38420-2 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 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 Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

The current climate crisis, aggravated by the human contribution to greenhouse gas emissions, highlights the urgent need to adopt climate policies that seek both to produce energy that does not involve carbon dioxide emissions (the main man-made greenhouse gas) and to reduce, as far as possible, the use of fossil fuels (which have a high carbon footprint associated). In this sense, much financial support (both from the public and the private sectors) is being given to the renewable energy sector, which has no carbon emissions associated with it. However, some renewable energy sources (such as wind or solar energy) are weather-dependent, so they are not controllable and intermittent. Because of this, energy excess (which will occur when production surpasses energy demand) produced by renewable energies needs to be stored; to this end, it is necessary to implement the so-called energy storage systems. This book aims to introduce the reader to the different energy storage systems available today, taking a chronological expedition from the first energy storage devices to the current state of the art, so that the reader knows which is the best energy storage technology depending on the application required. Furthermore, the future challenges that each energy storage technology faces are introduced, so that the reader can know what to expect from them in the immediate future.

Summary of Table of Contents The book is organized into seven chapters. Chapter 1 introduces the concept of energy storage system, when and why humans need to store energy, and presents a general classification of energy storage systems (ESS) according to their nature: mechanical, thermal, electrical, electrochemical and chemical. The next five chapters are centred in one of each ESS. Then, Chap. 2 offers a detailed update of Mechanical ESS (pumped hydro, gravity ESS, flywheels and compressed air ESS). Thermal ESS is addressed in Chap. 3, where the three main forms, sensible, latent and thermochemical heat storage, show us that the use of thermal energy is not now in civilization history. v

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More recent energy storage methods, like electrical ESS, are the goal of Chap. 4. In this chapter, superconducting magnetic and supercapacitor ESS are presented as the best method to directly store electricity. Chapter 5 allows us to understand the power of electrochemical as ESS, by means a comprehensive review of batteries technologies, from conventional to molten salt, passing through redox flow and ending with metal-air batteries. The last group, chemical ESS, is studied in Chap. 6, where syngas and hydrogen storage are shown as a proper technology for long-term storage, taking advantage of the energy in the chemical bonds between the atoms and molecules of the materials. Finally, according to the comprehensive analysis developed along the book, there are different alternatives to energy storage depending on the application required. Then, Chap. 7 offers a technical comparison from different points of view regarding rated power, energy stored and discharge time. Book ends with five appendixes, where different examples of each type of energy storage system, currently under operation can be found, including technical data like size, rated power and energy capacity and economic information. Huelva, Spain

José Manuel Andújar Márquez Francisca Segura Manzano Jesús Rey Luengo

Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 7

2 Mechanical Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Pumped Hydro Energy Storage (PHES): The Power of Water to Store Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Gravity Energy Storage (GES): How Gravity Can Store Energy . . . 2.2.1 Tower GES (T-GES) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 Shaft GES (S-GES) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.3 Piston GES (P-GES) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.4 Compressed Air Piston GES (CAP-GES) . . . . . . . . . . . . . . . . 2.2.5 Rope-Hoisting Piston GES (RP-GES) . . . . . . . . . . . . . . . . . . . 2.2.6 Mountain Mine-Car GES (MM-GES) . . . . . . . . . . . . . . . . . . . 2.2.7 Mountain Cable-Car GES (MC-GES) . . . . . . . . . . . . . . . . . . . 2.2.8 Linear Electric Machine-Based GES (LEM-GES) . . . . . . . . 2.3 Flywheel Energy Storage (FES): The Power of Speed to Store Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Compressed Air Energy Storage (CAES): How to Store Energy in the Air? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9 9 12 12 14 16 18 20 22 23 24 26 29 32

3 Thermal Energy Storage (TES): The Power of Heat . . . . . . . . . . . . . . . 3.1 Sensible Heat Storage (SHS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Latent Heat Storage (LHS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Thermochemical Heat Storage (TCHS) . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

35 36 41 43 46

4 Electrical Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Superconducting Magnetic Energy Storage (SMES): A Magnetic Field to Store Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Supercapacitor Energy Storage (SCES): Just Stored Electricity . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

49 49 52 56

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Contents

5 Electrochemical Energy Storage (EcES). Energy Storage in Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Conventional Technology Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1 Fundamental Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.2 Mathematical Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.3 Technical Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Molten Salt Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.1 Fundamental Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.2 Technical Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Redox Flow Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.1 Fundamental Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2 Technical Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Metal–Air Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.1 Fundamental Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.2 Technical Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

59 60 60 62 64 65 65 66 67 67 70 70 70 72 72

6 Chemical Energy Storage (CES): How to Store Energy Inside a Fluid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Syngas Storage (SS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Hydrogen Storage. Energy Stored in an Invisible Fuel . . . . . . . . . . . 6.2.1 Compressed Hydrogen Storage . . . . . . . . . . . . . . . . . . . . . . . . 6.2.2 Liquid Hydrogen Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.3 Metal Hydride Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.4 Physisorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.5 Complex Hydrides Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.6 Alkalimetal + H2 O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

77 77 79 80 83 84 88 89 90 92

7 Discussion of Storage Technologies. Keys to Select the Suitable Energy Storage System for Each Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 Appendix A: Mechanical Energy Storage Technology . . . . . . . . . . . . . . . . . 103 Appendix B: Thermal Energy Storage Technology . . . . . . . . . . . . . . . . . . . . 105 Appendix C: Electrical Energy Storage Technology . . . . . . . . . . . . . . . . . . . 107 Appendix D: Electrochemical Energy Storage Technology . . . . . . . . . . . . . 109 Appendix E: Chemical Energy Storage: Hydrogen Storage . . . . . . . . . . . . 115 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

Author Contributions and Funding

Author Contributions: conceptualization, J. R. and F. S.; methodology, F. S. and J. R.; software, F. J. V.; validation, F. J. V.; formal analysis, J. R. and F. S.; investigation, J. R. and F. J. V.; resources, J. M. A.; data curation, F. J. V.; writing—original draft preparation, J. M. A., F. S. and J. R.; writing—review and editing, J. R. and F. S.; visualization, F. J. V.; supervision, F. S. and J. M. A.; project administration, J. M. A.; funding acquisition, J. M. A. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by (1) Spanish Government, grant Ref: PID2020-116616RB-C31, (2) Andalusian Regional Program of R+D+i, grant Ref: P20-00730, and (3) FEDER-University of Huelva 2018, grant Ref: UHU-1259316. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest.

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Nomenclature

A-CAES ARES ASSET ATES BBC BTES CAES CAISO CAP-GES CES CFRP CSP CTES D-CAES DOD DOE EDLC EESS ESS EVRC FACTS FES GES GTASPP GWTES HTS HWTES I-CAES IEM IM LCOE

Adiabatic Compressed Air Energy Storage Advanced Rail Energy Storage Air Storage System Energy Transfer Aquifer Thermal Energy Storage Brown, Boveri and Company Borehole Thermal Energy Storage Compressed Air Energy Storage California Independent System Operator Compressed Air Piston Gravity Energy Storage Chemical Energy Storage Carbon Fibre Reinforced Polymer Concentrated Solar Power Cavern Thermal Energy Storage Diabatic Compressed Air Energy Storage Depth Of Discharge Department Of Energy Electrochemical Double Layer Capacitors Electrical Energy Storage System Energy Storage Systems Energy Vault Resiliency Center Flexible AC Transmission Systems Flywheel Energy Storage Gravity Energy Storage Gas Turbine Air Storage Peaking Plant Gravel Water Thermal Energy Storage High-Temperature Superconductor Hot Water Thermal Energy Storage Isothermal Compressed Air Energy Storage Ion Exchange Membrane Induction Machine Levelized Cost of Energy xi

xii

LEM-GES LHS LHV LTS MC-GES MESS MHx MM-GES MSTES NKW O&M PCM PEM-FC P-GES PHES PMSM PRI RES RFB RP-GES SCES S-GES SGES SHM SHS SMES SOC SOHIO SRM SS TCHS TES T-GES UPS WESS ZEBRA

Nomenclature

Linear Electric Machine-based Gravity Energy Storage Latent Heat Storage Lower Heating Value Low-Temperature Superconductors Mountain Cable-Car Gravity Energy Storage Mechanical Energy Storage Systems Metal Hydride Mountain Mine Car Gravity Energy Storage Molten Salt Thermal Energy Storage Nordwest-deutsche Kraftwerke Operation and Maintenance Phase Change Material Polymeric Electrolyte Membrane-Fuel Cell Piston Gravity Energy Storage Pumped Hydro Energy Storage Permanent Magnet Synchronous Machine Pinnacle Research Institute Renewable Energy Sources Redox Flow Battery Rope-hoisting Piston Gravity Energy Storage Supercapacitor Energy Storage Shaft Gravity Energy Storage Solid Gravity Energy Storage Synchronous Homopolar Machine Sensible Heat Storage Superconducting Magnetic Energy Storage State Of Charge Standard Oil Company, Cleveland, Ohio Switched Reluctance Machine Syngas Storage Thermochemical Heat Storage Thermal Energy Storage Tower Gravity Energy Storage Uninterruptible Power Supply Wayside Energy Storage System Zero Emission Battery Research Activity

Symbols

Δh L E M−G E S Δh MC−G E S Δh M M−G E S Δh r Δm ΔT Δti A AM H ar B B N −A C M H max CM H cp C SC EA E C A P−G E S E E DLC SC E S EFES E L E M−G E S E MC−G E S E M M−G E S E P−G E S EPHES E pseudo SC E S ER E R P−G E S ESM E S

Height difference between the platforms of the LEM-GES system (m) Height difference between the two platforms (m) Altitude difference between the two stacking platforms of the MM-GES system (m) Heat of reaction per unit mass (J/kg) Hydrogen mass in the MH tank during charge (g) Temperature variation (ºC) Time intervals (1 s) Exponential zone amplitude (V) Fraction (molar mass H 2 /molar mass unhydrated metallic alloy) Fraction of reagents which reacted Inverse of the charge at the end of the exponential zone (Ah)−1 Noble-Abel constant (0.007691 L/g for hydrogen gas) Maximum atomic ratio of hydrogen to metal (H/M) Atomic ratio of hydrogen to metal (H/M) Specific heat at constant pressure (J/(kg ºC)) Capacitance of the supercapacitor (F) Energy stored in the compressed air (kWh) Energy storage capacity of a CAP-GES plant (kWh) Energy stored in an EDLC supercapacitor (kWh) Energy storage capacity of a FES system (kWh) Energy storage capacity of a LEM-GES plant (kWh) Energy storage capacity of a MC-GES plant (kWh) Energy storage capacity of a MM-GES plant (kWh) Energy storage capacity of a P-GES plant (kWh) Energy storage capacity of a PHES plant (kWh) Energy stored in a pseudocapacitor (kWh) Energy storage capacity of the rope and its drive motor (kWh) Energy storage capacity of a RP-GES plant (kWh) Energy stored in a SMES system (kWh) xiii

xiv

E S−G E S E T −G E S Fr g h HC h L−U h i−T −G E S hM hP HS i∫ idt I FC−i IS M J K L L H VH2 Mg M H2 m H2 (g) m H2 max m i−T −G E S mMH F m M Ht m L E M−i m MC−i m M M−i mP mt m t unhyd. ηA η FC η L E M−G E S η MC−G E S η M M−G E S η P−G E S ηP H E S ηR η S−G E S ηt. ηT −G E S n

Symbols

Energy storage capacity of a S-GES plant (kWh) Energy storage capacity of a T-GES plant (kWh) Rope pulling force (N) Gravity acceleration (9.8 m/s2 at the Earth’s surface) Metal hydride tank height (m) Height of the container (m) Height difference between the lower and upper reservoir (m) Height at which weight i is located in the T-GES plant (m) Height of the block, with respect to the shaft surface (m) Height of the gravity piston (m) Depth of the shaft (m) Battery current (A) Actual battery charge (Ah) PEM-FC operating current for a period of time (A) Current flowing through the superconducting material (A) Moment of inertia of rotor (kg m2 ) Polarization voltage (V) Inductance of the superconducting material (H) Hydrogen lower heating value (33.36 Wh/g) Molar mass of gas (g/mol) Molar mass of hydrogen (2 g/mol) Hydrogen mass charged (or discharged) into the MH tank Nominal MH tank hydrogen mass (g) Mass of the weight i in the T-GES plant (kg) Final hydrogen mass in the MH tank (g) Metal hydride tank mass (g) Mass of the LEM piston (kg) Mass of the cable-car with its load (kg) Total mass of the single mine cars with their loads (kg) Mass of the piston (kg) Hydrogen mass in the tank (g) Metal hydride tank mass when not hydrogenated (g) Circulation efficiency of isothermal compressed air (%) Yield of the PEM-FC (46.5%) Output efficiency of a LEM-GES plant (%) Output efficiency of a MC-GES plant (%) Output efficiency of a MM-GES plant (%) Output efficiency of the P-GES plant (%) Output efficiency of the PHES plant (%) Output efficiency of the rope and its motor-drive mechanism (%) Output efficiency of the S-GES plant (%) Efficiency of the turbine (%) Output efficiency of the T-GES plant (%) Dimensionless constant to be adjusted by user (in case of experimental test carried 5 by authors, n = 5)

Symbols

nLE M n MC nMM ρ ρ H2 l ρM H ρ M H initial ρP ρ packing ρ p PA P pmax pN Pr.P H E S Q Q ex p QLHS QNOM QSH S QT C H S R Relec RM H t rp S S OC t T T1 T2 TA TB TM H T TN t0 V VC VL R V0 Vb Vex p VFC V f ull ( ) V˙i NhL

xv

Number of LEM pistons Number of cable-cars in the MC-GES plant Number of mountain mine cars Gas density (g/L) Liquid hydrogen density (71 g/L) Hydrogenated metal hydride density (g/L) Initial metal hydride density (g/L) Density of the gravity piston (kg/m3 ) Metal hydride tank packing density (g/L) Water density (kg/m3 ) Gas pressure (atm) Air pressure in the container over the gravity piston (Pa) Maximum hydrogen tank pressure (atm) Pressure at normal conditions (1 atm) Rated power of a PHES system (kW) Battery capacity (Ah) Battery capacity at the end of exponential zone (Ah) Energy stored in a latent heat storage system (kWh) Battery capacity at the end of nominal zone (Ah) Energy stored by sensible heat in a material (kWh) Heat stored in the TCHS system (kWh) Universal gas constant (0.082 (atm L)/(K mol)) Internal resistance (Ω) Metal hydride tank radius (m) Radius of the gravity piston (m) Swelling of the alloy volume during absorption/desorption (%) State of charge (%) Time (s) Gas temperature (K) Initial temperature of the storage material (ºC) Final temperature of the storage material (ºC) Melting temperature of the phase change material (ºC) Boiling temperature of the phase change material (ºC) Total time to charge a MH tank (s) Temperature at normal conditions (273 K) Initial time (s) No load voltage (V) Volume of the air container (m3 ) Volume of the lower reservoir (m3 ) Battery constant voltage (V) Battery voltage (V) Voltage at end of exponential zone (V) PEM-FC operating voltage (62.13 V) Fully charged battery voltage (V) Hydrogen volumetric flow rate

xvi

Vmin SC VN O M V˙rated Vrated SC VSC Vt ωF E S

Symbols

Minimum voltage of the supercapacitor (V) Voltage at the end of nominal zone (V) Rated flow rate of the plant (m3 /s) Rated voltage of the supercapacitor (V) Voltage of the supercapacitor (V) Total volume of the hydrogen tank (L) Angular velocity of the rotor of the FES system (rad s–1 )

Chapter 1

Introduction

Throughout the history of mankind, the use of energy has been intrinsically linked to human beings. Although human beings depended on their own musculature (thanks to the energy provided by food) for the different tasks they had to perform, fire was used to obtain light and heat [1]. However, humans would soon discover how to harness other sources of energy for their own benefit. Around 300 BC, water began to be used as a source of energy. Thus, the ancient Greeks used water mills to power grinding stones and, at the end of the late eleventh century AD, water power began to be used throughout Western Europe to grind grain or process cloth, among other things, which reduced the cost of producing flour and bread, increasing the quality of life [1]. On the other hand, devices based on wind energy date back thousands of years: for example, vertical axis windmills found in the Persian-Afghan frontiers dating back to 200 BC or horizontal axis windmills used in the Netherlands and in the Mediterranean area between 1300–1875 AD [2]. However, not all energy sources (for example, wind energy) are always available, i.e., they are intermittent and are dependent on different factor such as the weather. In that sense, how to cope with energy needs when the energy sources are not available or when the energy needs are greater than the energy production? To answer that question, it can be intuited that energy needs to be stored in a device, which would act as an energy storage system (ESS), to be harnessed when needed [3]. Thus, traditional biomass (i.e., firewood), which was the main source of energy until well into the 19th century, can be considered as the first energy storage system, in the sense that the energy from firewood (in the form of heat) was released according to human needs [4]. On the other hand, regarding the use of energy storage systems based on hydropower, around 3000 BC, in Egypt, King Menes ordered the construction of a dam on the Nile River to supply water to the city of Memphis [5]. Despite the different uses that have historically been given to stored energy: as providing heat in the case of firewood or as accumulating water in the case of dams; what it is currently conceived of as energy storage, in the sense that a device stores energy that is not needed so that, when it is required, it can guarantee the electricity © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 J. M. Andújar Márquez et al., Energy Storage Systems: Fundamentals, Classification and a Technical Comparative, Green Energy and Technology, https://doi.org/10.1007/978-3-031-38420-2_1

1

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1 Introduction

supply (something that becomes especially important in the case of renewable energies such as solar or wind energy, which are not always available), is a far cry from these older devices [3]. Thus, the first devices that could be considered as an electrical energy storage system are Leyden’s jar (1745) [6, 7] and Volta’s battery (1799) [6]. However, in 1938 the director of antiquities of the Iraqi museum in Baghdad Wilhelm Konig discovered a set of four unglazed ceramic vessels found in a tomb dated to the time of the occupation of the area by the Parthians (248 BC–AD 226), of which three had copper cylinders with one end soldered with lead to the bottom of the cylinders, but only one of the three had an iron spike inside the copper cylinder. Although Konig thought that this device, popularly known as the Baghdad battery, looked like galvanic cells and could act as a battery, this has never been demonstrated [8]. Therefore, the Leyden jar and the Volta battery can be considered as the first electrical energy storage devices. The Leyden bottle, which is considered to be the first capacitor in history [6, 9], consists of a bottle with a metal foil covering its exterior and a conductor inside. This bottle, if filled, was capable of storing electricity after being charged [7]. On the other hand, Volta, based on the studies of Galvani (who, upon discovering that the legs of frogs, amputated from their bodies, contracted when in contact with two different metals in the same way as they did when in contact with a static electricity machine, affirmed that electricity was intrinsic to the organism), affirmed that electricity was produced by the metals [6]. Following this line of thought and after exhaustive research, he designed a device, which consisted of a stacked column of disks of two different metals interleaved with cardboard soaked in brine to generate current [10]. Figures 1.1 and 1.2 shows the appearance of a Leyden’s jar and a Volta battery, respectively. Throughout human history, energy storage systems have changed dramatically: see the difference between traditional biomass, i.e. firewood, which was burned for energy, and hydrogen storage systems, which store hydrogen in order to produce electricity from it later on [11]. Moreover, if the evolution of batteries is taken into account: from Volta to the current lithium-ion batteries, more than significant differences can be found. Nowadays, different energy storage systems can be found: thermal energy storage (TES), gravity energy storage (GES), pumped hydro energy storage (PHES), battery energy storage (BES), etc. [12]. So, what is the most useful energy storage system? The answer to this question will depend on the intended application of the storage system, as well as the consumer’s preferences. For example, a society concerned with using energy that is as environmentally friendly as possible will prefer to use an electric stove rather than a gas stove, because the electricity, in a country where renewable energies have a significant weight in the energy mix, would come from a cleaner energy source. On the other hand, in mobility applications, for example, a hydrogen-powered car has greater advantages than an electric car, because a hydrogen car can be refuelled in minutes, while an electric car needs a long period of hours to do so. Furthermore, in the conventional path of energy production, transmission and distribution, energy storage systems (ESS) can be considered to be crucial (Fig. 1.3). However, the aspired energy model, the smart-grid model, in which current energy consumers would become energy consumers and producers (which would facilitate

1 Introduction Fig. 1.1 Leyden’s jar

Fig. 1.2 Volta battery

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1 Introduction

Fig. 1.3 Conventional path of utility energy storage

Fig. 1.4 Energy storage technologies: classification according to nature of technology. CAES Compressed Air Energy Storage, SMES Superconducting Magnetic Energy Storage

the integration of energy storage systems) is making the current centralized, oneway power flow energy model obsolete. So-called distributed generation systems, in which the flow of energy is bidirectional, that is, prosumers (consumers and producers of energy) inject and receive energy from the main power grid, offer greater security of supply to the user by preventing blackouts, can help the environment by facilitating the integration of renewable energy sources, and increase efficiency in electricity production and distribution [13, 14]. As energy production in distributed generation systems takes place at points close to the point of consumption, this energy model facilitates the integration of the different ESS. Currently, as discussed above, a wide variety of energy storage systems are available. Each of them stores energy in different forms (mechanical energy, thermal energy or chemical energy, among others) and has different degrees of development and implementation [12]. Figures 1.4 and 1.5 present a classification of different ESS based on nature and mature of technology, respectively.

1 Introduction

5

Fig. 1.5 Energy storage technologies: classification according to mature technology

To know when to use one or the other ESS, it is necessary to know the properties of each of the energy storage technologies, as these properties make them ideal for certain applications [15]. In that sense, Table 1.1 shows the advantages and drawbacks of the different ESS presented in Figs. 1.4 and 1.5. In order for the reader to know which are the best ways to store energy depending on the required application, as well as the historical evolution of the different ESS, in the following sections of this book, a detailed description of them will be made (exposing the technical parameters, the benefits and the drawbacks that correspond to each technology).

6

1 Introduction

Table 1.1 Advantages and drawbacks of different ESS Nature

Technology

Advantages

Drawbacks

Mechanical

Hydro pumped [16]

– Low operating costs per energy unit – Available for long-term storage – Fast response – High energy storage capacity

– Very high investment costs – Environmental issues – Geographical and topographical limitations

GES [17]

– – – –

Flywheels [16]

– – – – – –

CAES [16]

– Large energy storage capacity – High lifetime – Lower cost per kW than hydro pumped

– Originally, non-environmentally friendly – Geographical restrictions to select underground reservoirs where the air is pressurised

Thermal

TES [18]

– Independent of hydrogeological conditions – High storage efficiencies and temperatures – Storage capacity adaptable to demand

– High costs – Limitation of tank volume to site characteristics – Heat losses in storage if stratification is not preserved

Electrical

Ultracapacitors [16, 19]

– – – – – –

High efficiency (80–90%) – Non-developed technology (only High lifetime (35–50 years) engineering prototype in Low storage costs concept stage) Better geographical adaptability than pumped hydro and CAES – Safe, reliable, non-polluting and high-capacity energy storage system Environmentally friendly High specific power Low maintenance cost High life span High efficiency (85–90%) No temperature control needed

– High costs – Short discharge time – Mechanical stress and fatigue

High efficiency – High costs Low environmental impact – Low specific energy High lifetime Medium capacity of storage High specific power Used in grid systems to stabilise them during peak demands (continued)

References

7

Table 1.1 (continued) Nature

Technology

Advantages

Drawbacks

SMES [16]

– – – –

– Need of continuous cooling – High investment and operation costs – Temperature sensitive

Electrochemical Batteries [16]

Chemical

High efficiency (~ 95%) High power capacity Environmentally friendly Fast response time

– Widely used – Slow charging process – Can be used in devices of – Low specific energy different sizes (from mobile phones to electric vehicles)

SynGas storage – Key role in reducing – Low volumetric density (CO + H2 + greenhouse gas emissions if – High costs CO2 + minority carbon capture is included – Restricted to stationary gases) [20] applications in reforming process – High specific energy Hydrogen storage [21]

– Hydrogen produced via – Low volumetric density renewable powered – Variable gravimetric electrolysis plays a key role density, depending on for greenhouse gas the storage option reduction – High specific energy – Quick charging process

References 1. Pain S (2017) Power through the ages. Nature 551:S134–S137. https://doi.org/10.1038/d41 586-017-07506-z 2. Kaldellis JK, Zafirakis D (2011) The wind energy (r)evolution: a short review of a long history. Renew Energy 36:1887–1901. https://doi.org/10.1016/j.renene.2011.01.002 3. Russo MA, Carvalho D, Martins N, Monteiro A (2022) Forecasting the inevitable: a review on the impacts of climate change on renewable energy resources. Sustain Energy Technol Assess 52:102283. https://doi.org/10.1016/J.SETA.2022.102283 4. Vaclav S (2017) Energy transitions: global and national perspectives. Praeger 2 5. Price T, Probert D (1997) Harnessing hydropower: a practical guide. Appl Energy 57:175–251. https://doi.org/10.1016/S0306-2619(97)00033-0 6. Piccolino M (2000) The bicentennial of the voltaic battery (1800–2000): the artificial electric organ. Trends Neurosci 23:147–151. https://doi.org/10.1016/S0166-2236(99)01544-1 7. Grimnes S, Martinsen ØG (2000) History of bioimpedance and bioelectricity. Bioimpedance Bioelectr Basics 313–9. https://doi.org/10.1016/B978-012303260-7/50009-5 8. Von Handorf DE (2002) The Baghdad battery-myth or reality? Plat Surf Finish 84–7 9. He X, Zhang X (2022) A comprehensive review of supercapacitors: properties, electrodes, electrolytes and thermal management systems based on phase change materials. J Energy Storage 56:106023. https://doi.org/10.1016/J.EST.2022.106023 10. Fara P (2009) Alessandro volta and the politics of pictures. Endeavour 33:127–128. https://doi. org/10.1016/j.endeavour.2009.09.007 11. Zhang Z, Ding T, Zhou Q, Sun Y, Qu M, Zeng Z et al (2021) A review of technologies and applications on versatile energy storage systems. Renew Sustain Energy Rev 148. https://doi. org/10.1016/J.RSER.2021.111263

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12. Mitali J, Dhinakaran S, Mohamad AA (2022) Energy storage systems: a review. Energy Storage Sav. https://doi.org/10.1016/J.ENSS.2022.07.002 13. Fan D, Ren Y, Feng Q, Liu Y, Wang Z, Lin J (2021) Restoration of smart grids: current status, challenges, and opportunities. Renew Sustain Energy Rev 143:110909. https://doi.org/10.1016/ J.RSER.2021.110909 14. Babayomi O, Zhang Z, Dragicevic T, Hu J, Rodriguez J (2023) Smart grid evolution: predictive control of distributed energy resources—a review. Int J Electr Power Energy Syst 147:108812. https://doi.org/10.1016/J.IJEPES.2022.108812 15. Eustis C, Gyuk I (2014) Energy storage safety strategic plan acknowledgements. US Dep Energy 16. AL Shaqsi AZ, Sopian K, Al-Hinai A (2020) Review of energy storage services, applications, limitations, and benefits. Energy Rep 6:288–306. https://doi.org/10.1016/J.EGYR.2020.07.028 17. Tong W, Lu Z, Chen W, Han M, Zhao G, Wang X et al (2022) Solid gravity energy storage: a review. J Energy Storage 53:105226. https://doi.org/10.1016/J.EST.2022.105226 18. Mahon H, O’Connor D, Friedrich D, Hughes B (2022) A review of thermal energy storage technologies for seasonal loops. Energy 239:122207. https://doi.org/10.1016/j.energy.2021. 122207 19. Pershaanaa M, Bashir S, Ramesh S, Ramesh K (2022) Every bite of supercap: a brief review on construction and enhancement of supercapacitor. J Energy Storage 50. https://doi.org/10. 1016/J.EST.2022.104599 20. Fiore M, Magi V, Viggiano A (2020) Internal combustion engines powered by syngas: a review. Appl Energy 276. https://doi.org/10.1016/J.APENERGY.2020.115415 21. Rullo P, Braccia L, Luppi P, Zumoffen D, Feroldi D (2019) Integration of sizing and energy management based on economic predictive control for standalone hybrid renewable energy systems. Renew Energy 140:436–451. https://doi.org/10.1016/J.RENENE.2019.03.074

Chapter 2

Mechanical Storage

Mechanical energy storage systems (MESS), which store energy to be released again in the form of mechanical energy, offer several advantages compared to other ESSs: lower environmental impact, lower levelized energy costs and greater sustainability. Although different MESS can be found, the best option for storing mechanical energy will depend on different factors, such as available space, for example. In this chapter, different MESS will be presented in order to let the reader know which is the best MESS depending on the intended use.

2.1 Pumped Hydro Energy Storage (PHES): The Power of Water to Store Energy The energetic power of water has been known since ancient times. Thus, water mills were already used by the ancient Greeks to grind stones and, at the end of the 11th century A.D., water mills were used in Western Europe to grind wheat, facilitating the work of the millers [1, 2]. However, it was not until the 19th century that water began to be used to produce electricity. Thus, after the advent of modern turbines (such as the Francis, Kaplan or Pelton turbine) [3], hydroelectric plants began to be put into operation: the first of these, with a power of 12 kW, was located on the Fox River in Appleton (USA) and commissioned in 1882 [4]. Although hydroelectric power plants make it possible to obtain energy, they cannot meet energy demand when the resource (water) is not available. In that case, how could supply be guaranteed? To solve this problem [5], pumped-storage hydroelectric power plants are used to store water in a lower reservoir and, by means of a hydraulic pump, raise it to an upper reservoir (at times of low consumption and, therefore, lower electricity costs). At times of high demand, this water will be released to produce electricity from a turbine; in this way, energy can be obtained from the stored water.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 J. M. Andújar Márquez et al., Energy Storage Systems: Fundamentals, Classification and a Technical Comparative, Green Energy and Technology, https://doi.org/10.1007/978-3-031-38420-2_2

9

10

2 Mechanical Storage

Fig. 2.1 Scheme of a current PHES plant

The first PHES plant was commissioned in the 1890s [5] in the Alpine regions of Switzerland, Italy and Austria. In the first pumped hydro power plants, different elements were used as pump and turbine. Since the 1950s [5], however, a single reversible element that can act as both pump and turbine has been used. Figure 2.1 shows the scheme of a current PHES plant. In the 1960s, electric utilities in many countries found nuclear power a dominant role for energy supply. As a consequence, many PHES facilities were conceived as a complement to nuclear power to supply peak power, resulting in a further growth of PHES [5]. However, in the 1990s, low natural gas prices made gas turbines more competitive for supplying peak power demand than PHES, and environmental concerns [5] (due to the loss of biodiversity resulting from hydraulic pumping plants, as suggested by several studies [6]) led to the cancellation of several PHES projects. However, in recent years, the interest in this technology has grown again due to the environmental policies of several countries that establish as primary objectives to produce energy in a clean and sustainable way [7]; this is something to which such energy storage technology can contribute, which can integrate RES [5, 8]. In a PHES system, the energy stored can be expressed as Eq. (2.1) [9]: E PHES = (ηPHES ρw VLR gh L−U ) ·

1 kWh 3.6 · 106 J

Where: E PHES ηPHES ρ VLR

energy storage capacity of a PHES plant (kWh) round trip efficiency of a PHES plant (%) water density (kg/m3 ) volume of the lower reservoir (m3 )

(2.1)

2.1 Pumped Hydro Energy Storage (PHES): The Power of Water to Store …

g h L−U

11

gravity acceleration (m/s2 ) height difference between the lower and upper reservoir (m)

On the other hand, if the rated power for a PHES plant is desired to be known, it can be expressed as, Eq. (2.2): ) 1 kW ( Pr.PHES = ηt. ρ V˙rated gh L−U · 1000 W

(2.2)

Where: Pr.PHES rated power of a PHES system (kW) ηt efficiency of the turbine (%) rated flow rate of the plant (m3 /s) V˙rated PHES [7] are currently the only large-scale energy storage option and, moreover, this technology has 300 plants installed around the world with a total capacity of 158 GW of power; in fact, in Japan (which has an installed capacity of 27.6 GW, as of 2021, according to International Hydropower Association [10]), there are 34 plants installed with a capacity of more than 200 MW (while in the USA there are more than 39) [7]. In Europe, which together with Japan are the regions in the world where most of the world’s PHES plant projects are currently being carried out, had an installed capacity of 36 GW as of 2009 (to put this into perspective, 4.3% of its total installed capacity) [7], while the USA has an installed capacity of 22.9 GW and China has an installed capacity of 30.3 GW, as of 2021 according to International Hydropower Association [10]. This technology presents, as technical parameters, a round trip efficiency of 81.5% [11], 75–85% [8], 65–87% [12], 79.2% [13]; a lifetime of 40–60 years [8, 11], >40 years [14], 20–80 years [12], 80 years [13]; a discharge time of 1–24 h [14]; a cycle life of 10,000–30,000 cycles [11], 10,000–60,000 cycles [12]; an energy density of 0.5–1.5 Wh/L [8], 0.5–2 Wh/L [11], 0.5–1.33 Wh/L [12]; a power density of 0.5–1.5 W/L [8, 11], 0.01–0.12 W/L [12]; a specific power of 0.01–0.12 W/kg [12]; and a specific energy of 0.3–1.33 Wh/kg [12], 0.5–1.5 Wh/kg [14]. Among the advantages, from a techno-environmental point of view [6, 16], of this energy storage technology, are a great capacity to adapt to the electrical grid, as this technology can store energy on a long-term and large scale (which means that it can play a complementary role in guaranteeing energy supply in some regions); a commercial-scale storage capacity, as a result of being the most advanced energy storage technology on the market; being a technology that stores energy produced in an environmentally sustainable way and with a long useful lifetime; ability to control flow and sedimentation, which occur due to soil degradation and the construction of upstream settlements; a high efficiency; a negligible self-discharge capacity; and a high capacity to adapt production to demand at short notice. From a socio-economic point of view [6], this technology offers the possibility of creating numerous jobs, especially for the local population, for construction and operation tasks, as well as a proximity that allows a reduction in transmission losses of between 8 and 15%.

12

2 Mechanical Storage

On the other hand, among the disadvantages that can be found in this technology, from the techno-environmental point of view, it can be found an absence of infrastructure that allows, through roads and transmission lines, the access of PHES plants to cheap surplus energy; the difficulty of finding a land that suits the requirements of this technology (difference in height between high and low reservoir, or capacity to locate two reservoirs); the difficulty of acquiring land and clearing it of vegetation; problems with water, since an eventual water shortage would create a conflict between energy storage and local water supply; a geological failure that endangers the water reservoirs, as a result of an eventual seismic activity, for example; and a loss of biodiversity, since the presence of reservoirs may hinder the activity of fish [6]. From a socioeconomic point of view, PHES technology has some disadvantages, such as a high initial investment; public opposition to projects of this nature; difficulty in obtaining financing due to political, social or economic reasons; or difficulty in finding qualified workers to perform the tasks of a PHES plant [6, 16]. Furthermore, the construction of new PHES plants in areas where there are installed wind and PV farms supposes a great opportunity to reduce the need of building new project plans based on fossil fuels and to increase the electric grid reliability, because the excess energy produced by renewable energies would be used to pump water to the upper reservoir (to be used later for power production) [17]. Regarding the challenges this storage technology faces, the integration of PHES with other storage technologies can make easier to meet the energy demand more accurately and the need of a more favourable legislation in order to shorten licensing processes to build new PHES plants [17].

2.2 Gravity Energy Storage (GES): How Gravity Can Store Energy Solid gravity energy storage (SGES), which is most commonly referred as gravity energy storage (GES) uses the vertical movement of a heavy object subject to a gravitational field to store or release energy, depending on the need [18]. Although PHES can be considered to be a gravity storage technology, in this section, only solid gravity storage technology will be considered. It can be found, as will be seen below in the different subsections, that there are 8 types of SGES systems.

2.2.1 Tower GES (T-GES) A T-GES plant has different weights that, in times of excess energy, will be lifted by ropes driven by a motor-generator unit and placed on top of the weights that are higher. In times of energy deficit, the weights that are located at a certain height are picked up by the ropes and dropped to a lower level in order to produce electricity

2.2 Gravity Energy Storage (GES): How Gravity Can Store Energy

13

Fig. 2.2 Scheme of a T-GES plant

from the gravitational potential energy by means of the motor-generator unit. For the system to be able to perform all these operations, there is a weight-bearing tower, six cantilevers (in Fig. 2.2, only 2 are shown for simplicity) and a control center that will serve to balance the weight on both sides of the cantilevers, since on the different sides of the cantilever there will be a mobile trolley, each of which contains a motor-generator unit, which will be connected to the ropes that will raise or lower the different weights [18]. Figure 2.2 shows a schematic of a T-GES plant. The energy storage capacity of a T-GES system can be obtained thanks to Eq. (2.3) [18]: ( E T −GES = ηT −GES

n ∑ i=1

) m i−T −GES gh i−T −GES ·

1 kWh 3.6 · 106 J

(2.3)

Where: E T −GES ηT −GES m i−T −GES g h i−T −GES

energy storage capacity of a T-GES plant (kWh) output efficiency of the T-GES plant (%) mass of the weight i in the T-GES plant (kg) gravity acceleration (9.8 m/s2 at the Earth’s surface) height at which weight i is located in the T-GES plant (m)

This technology requires a high number of weights because the ones forming the base are not used for energy storage. However, composite weights made from recycled materials can be designed so that this technology can be more cost-effective [18]. Currently, the US company Energy Vault strongly represent the T-GES technology. In fact, this company has launched two types of tower gravity storage products:

14

2 Mechanical Storage

the EV1 tower gravity storage, which was built in July 2020 in Castion, Ticcino, Switzerland, stores between 20 and 80 MWh energy (the standard energy storage capacity is 35 MWh) thanks to concrete blocks made from local industrial waste, has a height of 120 m, can reach a 4 MW power peak during 2.9 s, has a 90 % cycle efficiency, has a estimated lifetime of 30–40 years and has a levelized cost of energy (LCOE) 80% lower than PHES (considering initial investment and operance and maintenance costs) [18]; and the EVx integrated tower gravity storage device, which was built in April 2021, has an estimated lifetime of more than 35 years, has design that requires 45% less height to achieve the same energy storage capacity and its platforms can be integrated into Energy Vault Resiliency Center (EVRC), which can scale from 10 MWh to several GWh by integrating the EV1 into indoor environments and allows to store the same energy as EV1 with 40% less height and with a higher lifetime than EV1 [18]. In addition to the facilities already built, Energy Vault has several projects underway. Thus, in October 2021, it announced an agreement with DG Fuels in the USA to achieve gravity storage capacities of 1.6 GWh for sustainable aviation fuel projects; and, in January 2022, it signed an agreement with the Chinese company Tian-Ying to build a 100 MWh demonstration project in Jiangsu Province, China [18]. This type of GES has several advantages, such as good scalability (without restrictive geographical conditions), a high cycle-efficiency, as a result of low friction losses and a more reliable technology (due to its simplicity and its maturity) and an easy expandability, as a result of the modular equipment that are found in this technology. However, it has disadvantages such as a slow response, not a high lifespan (due to friction, which, although small, is not zero) compared to other gravity storage technologies [19].

2.2.2 Shaft GES (S-GES) Contrary to a T-GES, a S-GES plant only uses one mass block, which is introduced inside a vertical mine shaft. The block will be connected to two motor-generator units, each located on either side of the well, by means of ropes, so that at times when there is surplus energy, this will be used to raise the mass block, and at times of energy deficit, the block will be lowered to produce energy [18]. Figure 2.3 shows the scheme of a S-GES plant. The energy storage capacity of a S-GES can be obtained thanks to Eq. (2.4) [18]: E S−GES = (mghη S−GES ) ·

1 kWh 3.6 · 106 J

Where: E S−GES energy storage capacity of a S-GES plant (kWh) m mass of the block (kg)

(2.4)

2.2 Gravity Energy Storage (GES): How Gravity Can Store Energy

15

Fig. 2.3 Scheme of a S-GES plant

h η S−GES

effective height of the block (m) output efficiency of the S-GES plant (%)

In turn, the effective height of the block is calculated as follows, Eq. (2.5) [18]: h = HS − h M

(2.5)

Where: HS depth of the shaft (m) h M height of the block, with respect to the shaft surface (m) In this technology, to have a larger energy storage capacity, it is necessary to have a considerable height difference and mass weight [18]. This technology has a 80–90% efficiency, an energy storage capacity of 1–20 MWh, an estimated lifetime of 50 years and a lower LCOE much lower than other energy storage technologies such as lithium-ion batteries [18]. According to the British company Gravitricity, the mines deeper than 300 m are suitable for installing S-GES plants and there are almost 14,000 potential installations in the world [18]. Furthermore, that same company built, in April 2020, a 250 kW prototype at Eddinburgh (with the support from UK government) with a height of 15 m, a load capacity of 50 tons and is able of operating at rated power for 1 s [18]. In 2021, Gravitricity launched a 4 MW project and claimed to launch a 8 MW commercial project in the Czech Republic in 2022 for building applications [18].

16

2 Mechanical Storage

Among the benefits of this type of GES technology, it can be found that this it has a high efficiency (due to small friction losses), it is a safety technology (due to its simplicity and maturity) and that it has a fast response (which allows this technology to be used for auxiliary services). On the other hand, among the drawbacks of that type of GES technology, it can be found that it is a very difficult expandable technology (due to that it is made of just one block), it is severely restricted to geographical conditions (due to the need of a deeper than 300 m shaft) and it has not a high lifetime compared to other GES technologies [10].

2.2.3 Piston GES (P-GES) A P-GES plant, containing a water circuit and a gravity piston, has the following operation: an unit that can act as both pump and turbine pumps water to the lower end of the gravity piston (which is placed in a water-filled sealed vessel in a hole under the surface) at times of energy surplus, causing it to rise vertically (thus converting electrical energy into potential); while at times of energy deficit, the piston is dropped vertically to convert potential energy into electrical energy [18]. The scheme of a P-GES plant is shown in Fig. 2.4. The energy storage capacity of a P-GES plant can be obtained thanks to Eq. (2.6) [18]: ( ) E P−GES = Δρπr P2 h P gη P−GES (HC − h P ) ·

1 kWh 3.6 · 106 J

(2.6)

Where: E P−GES rp hP η P−GES HC

energy storage capacity of a P-GES plant (kWh) radius of the gravity piston (m) height of the gravity piston (m) output efficiency of a P-GES plant (%) height of the container (m)

As a result of the floatability of water, Δρ is obtained thanks to Eq. (2.7) [18]: Δρ = ρ P − ρw

(2.7)

Where: ρ P density of the gravity piston (kg/m3 ) ρw density of the water (kg/m3 ) This technology can increase its energy capacity storage by using pistons made of denser materials. On the other hand, one of the challenges this technology faces is to reduce the slide friction, what can be done with a steel shell [18].

2.2 Gravity Energy Storage (GES): How Gravity Can Store Energy

17

Fig. 2.4 Scheme of a P-GES plant

For this GES technology, the US company Gravity Power is considered to be its advocate. Some of their studies indicate that the energy storage capacity of a P-GES plant can reach tens of MWh, that this technology is capable of going from 0 to nominal power in a matter of seconds, of providing a power of 5 MW continuously for 4 h, has an efficiency of between 75–80% and an estimated useful life of about 40 years [18]. The German company Heindl Energy, on the other hand, has proposed to increase the energy storage capacity and reduce the height of the container by storing gravitational energy through the lifting of giant rocks. In this way, the energy storage capacity could range from 1 to 10 GWh (to obtain a storage capacity of 8 GWh, the diameter of the piston, the giant rock, would have to be 250 m), the efficiency would be around 80% and the estimated lifetime would be about 60 years [18]. Among the advantages of this GES technology, it can be found that it has a good scalability (and it is hardly limited to geographical conditions), is a safe technology (because of its simplicity), has a fast response and has a high lifespan, compared

18

2 Mechanical Storage

to other GES technologies [10]. However, this technology has disadvantages such as not having high efficiency and not being as easily expandable as other GES technologies [10].

2.2.4 Compressed Air Piston GES (CAP-GES) This GES technology is similar to P-GES technology, with the difference that, on top of the gravity piston, an air chamber is placed which, in turn, is connected to a highpressure vessel (which in turn is connected to an air compressor) [18]. Figure 2.5 shows the scheme of a CAP-GES plant. In this technology, energy is stored in the following way: in moments of energy surplus, water is pumped (thanks to the pumpturbine unit) to the lower part of the piston, so that the piston rises, transforming electrical energy into gravitational potential energy (in the same way, it is done in a P-GES plant), but, in addition, when the piston rises, the air chamber above the piston is compressed, so that electrical energy is transformed into elastic potential energy. On the other hand, in moments of energy deficit, the compressed air expands, transforming the elastic potential energy into electrical energy and pushing down the gravity piston; thus, the piston descends, transforming the gravitational potential energy into electrical energy [18]. In this technology, pressurized air (thanks to the use of some equipment used in CAES systems) is placed over the gravity piston in order to increase the energy density of a CAP-GES plant. On the other hand, the return pipe used to contain the expelled water has no connection to the top of the gravity piston, contrary to a P-GES plant [18]. In a CAP-GES plant, the energy storage capacity is given by Eq. (2.8) [18]: E CAP-GES = E A + E P−GES

(2.8)

Where: E CAP−GES energy storage capacity of a CAP-GES plant (kWh) EA energy stored in the compressed air (kWh) E P−GES , which has been previously introduced, can be obtained from Eq. (2.4), while the term E A can be obtained thanks to Eq. (2.9) [18]: ⎛ E A = ⎝η A

∫V2 V1

⎞ PAP d VC ⎠ ·

1 kWh 3.6 · 106 J

Where: ηA

circulation efficiency of isothermal compressed air (%)

(2.9)

2.2 Gravity Energy Storage (GES): How Gravity Can Store Energy

19

Fig. 2.5 Scheme of a CAP-GES plant

PAP air pressure in the container over the gravity piston (Pa) VC volume of the air container (m3 ) Thanks to Eqs. (2.6) and (2.9), Eq. (2.8) can be expressed as, Eq. (2.10) [18]: ⎛ E CAP−GES = ⎝η A

∫V2 V1

⎞ Pd VC + Δρπr P2 h P gη P−G E S (HC − h P )⎠ ·

1 kWh 3.6 · 106 J (2.10)

This type of GES was proposed by Berrada et al. [20], and the simulations carried out by this group of researchers point out that gravity storage with a height of 500 m can storage the same amount of energy (20 MWh) that a 375 m height compressed air gravity storage, i.e., a CAP-GES plant has a higher energy density. Among the benefits of this GES technology, this type of GES has a good scalability, is hardly limited to geographical restrictions, has a higher energy density, has a fast response and has a high lifetime, compared to other GES technologies [19]. On the

20

2 Mechanical Storage

other hand, this technology has drawbacks such as not having a high cycle efficiency, not having a high safety (as a result of using a more complex equipment) and not being a modular technology [19].

2.2.5 Rope-Hoisting Piston GES (RP-GES) This GES technology is quite similar to the P-GES technology, with the difference that, in this technology, the gravity piston is connected at its upper end to a rope which, after passing through a fixed pulley, is connected to a motor-generator unit [18]. Figure 2.6 shows the scheme of a RP-GES plant. In this technology, the operating mode is as follows: in moments of energy surplus, water is pumped to the lower part of the piston and the motor is driven to pick up the rope, both actions aiming at raising the piston, transforming electrical energy into potential energy. On the other hand, in moments of energy deficit, the piston is dropped to transform the potential energy into electrical energy thanks to both the pump-turbine unit and the motor-generator unit [18]. In a RP-GES plant, the energy storage capacity is given by Eq. (2.11) [18]:

Fig. 2.6 Scheme of a RP-GES plant

2.2 Gravity Energy Storage (GES): How Gravity Can Store Energy

E RP−GES = E R +

) ( Fr E P−GES g− g mP

21

(2.11)

Where: E RP−GES energy storage capacity of a RP-GES plant (kWh) ER energy storage capacity of the rope and its drive motor (kWh) mP mass of the piston (kg) The term E P−GES has been slightly modified, as a result of the force exerted by the rope on the gravity piston. The term E R , in turn can be expressed as, Eq. (2.12) [18]: ⎛ E R = ⎝η R

∫h 2

⎞ Fr d Hc ⎠ ·

h1

1 kWh 3.6 · 106 J

(2.12)

Where: η R output efficiency of the rope and its motor-drive mechanism (%) Fr rope pulling force (N) Hc height of the container Thanks to Eqs. (2.6) and (2.12), Eq. (2.11) can be expressed as, Eq. (2.13) [18]: ⎛ ⎜ E R P−G E S = ⎝η R

(

∫h 2 Fr dh + Δρπr P2 h P h1

⎞ ) Fr 1 kWh ⎟ g− η P−G E S (HC − h P )⎠ · mP 3.6 · 106 J

(2.13) The RP-GES technology, still under conceptual phase, was proposed by Emrani and other researchers [21], and the simulations carried out by this group of researchers point out that the peak power, as a result of simultaneous operation of the motorgenerator and the pump-turbine units, increases and the energy storage capacity of a GES with a hoisting system was obtained to be almost the double of the energy storage capacity without a hoisting system [18, 21]. Among the advantages of this technology, it can be found that it has a good scalability (i.e., it has a good potential for energy storage capacity), is quite independent of the geographical conditions, has a fast response and a high lifetime, compared to other GES technologies [19]. On the other hand, among the disadvantages of this technology, it has not a high cycle efficiency (due to friction losses), it has not a high safety (due to that it is a more complex and an immature technology) and it is not a modular technology (compared to other GES technologies) [18].

22

2 Mechanical Storage

2.2.6 Mountain Mine-Car GES (MM-GES) An MM-GES plant works as follows: in times of energy surplus, a loaded mine car (thanks to a motor-generator unit) is lifted from a lower stacking platform to an upper stacking platform by means of chains, transforming electrical energy into gravitational potential energy in the process. On the other hand, in times of energy deficit, the mine car is slowly lowered from the upper platform to the lower platform, in the process, the mine car will rotate the motor through the chains, transforming gravitational potential energy into electrical energy in the process [18]. Figure 2.7 shows the scheme of a MM-GES plant. This GES technology, which has a higher safety and controllability as a result of the control of the speed of the mine-car, need to use cheap materials (for example, concrete blocks or gravel) as heavy loads to reduce the correspondent cost of this part and needs high requirements for the chain mechanical-strength (which will be used to haul the mine-cars) [18]. In addition, to improve the operation of the MMGES plant, a moderate slope (for the ascent and descent of the mine cars) should be selected (between 6 and 25º): too gentle a slope will imply lower efficiency and too steep a slope will imply greater demands on the equipment [18]. In a MM-GES plant, the energy storage capacity is given by Eq. (2.14) [18]: ( E MM−GES = ηMM−GES

n MM ∑ i=1

) m MM−i gΔh MM−GES ·

1 kWh 3.6 · 106 J

Where: E MM−GES ηMM−GES n MM m MM−i

energy storage capacity of a MM-GES plant (kWh) output efficiency of a MM-GES plant (%) number of mountain mine-cars total mass of the single mine-cars with their loads (kg)

Fig. 2.7 Scheme of a MM-GES plant

(2.14)

2.2 Gravity Energy Storage (GES): How Gravity Can Store Energy

23

Δh MM−GES altitude difference between the two stacking platforms of the MM-GES system (m) This technology is mainly represented by the US company Advanced Rail Energy Storage (ARES), whose energy storage equipments consist of multiple tracks with a 5 MW rated power (that can increased up to 1 GW if geographical conditions are available); furthermore, due to the scalability of this technology, its energy storage capacity can range from several MWh to dozens of GWh if changes in the number of mine-cars and in the slope length and gradient are made [18]. ARES is currently undertaking a 50 MW MM-GES plant project in Pahrump, Nevada, USA. This plant has a fast response time (a matter of seconds), has a 78% cycle efficiency and an estimated lifespan of 40 years. The primary purpose of this plant project will be to provide ancillary services to the California Independent System Operator (CAISO) [18]. Among the benefits of this GES technology, it has a good scalability, a high safety, a fast response and is a modular technology. However, on the other hand, it presents several drawbacks such as a low cycle efficiency (as a result of considerable friction losses), a low lifetime and is subject to certain geographical restrictions [19].

2.2.7 Mountain Cable-Car GES (MC-GES) This GES technology has a similar mode of operation to the MM-GES technology, with the difference that it uses a ropeway to transport the load from the lower platform to the upper platform, in order to adapt the system for steeper slopes [18]. At times of energy surplus, the motor-generator unit is used to lift the ropeway from a point on the lower platform to a point on the upper platform (transforming electrical energy into potential energy); while at times of energy deficit, the loads are lowered to produce electricity (from the generator) by transforming gravitational potential energy into electrical energy [18]. Figure 2.8 shows the scheme of a MC-GES plant. In a MC-GES plant, the energy storage capacity is given by Eq. (2.15) [18]: ( E MC−GES = ηMC−GES

n MC ∑ i=1

) m MC−i gΔh MC−GES ·

1 kWh 3.6 · 106 J

(2.15)

Where: E MC−GES ηMC−GES n MC m MC−i Δh MC−GES

energy storage capacity of a MC-GES plant (kWh) output efficiency of a MC-GES plant (%) number of cable-cars in the MC-GES plant mass of the cable-car with its load (kg) height difference between the two platforms (m)

This GES technology has largely been started by the U.S. company Energy Cache, which built a prototype in California in 2012, demonstrating higher efficiency than

24

2 Mechanical Storage

Fig. 2.8 Scheme of a MC-GES plant

PHES technology and 40% lower cost (also the cost of this technology reduces as the height difference between platforms increases) [18]. The energy storage capacity of this GES technology is generally less than 20 MWh, but it can be increased if geological conditions allow it (due to the good scalability of this technology) and its cycle efficiency is around 85% [18]. The MC-GES technology offers advantages such as high safety, a good scalability (but limited to geographical conditions) and its modularity. On the other hand, it has several disadvantages such as slow response, a low lifetime, a poor ability to adapt to geographical conditions and a low cycle efficiency, compared to other GES technologies [19].

2.2.8 Linear Electric Machine-Based GES (LEM-GES) The LEM-GES technology, which was proposed in 2019 by Botha et al., transforms electrical energy into gravitational potential energy (and vice versa) from pistons (which have an integrated linear motor and corresponding power electronics) moving between a lower and upper platform via a guideway [18, 22]. Furthermore, this technology does not require the use of a rope to raise or lower the piston, but the vertical movement is executed by the electromagnetic traction provided by the linear motor [18, 22]. In moments of energy surplus, the piston is lifted up to the upper platform (transforming electrical energy into potential energy) and, in moments of energy deficit, the piston is dropped to the lower platform (transforming electrical

2.2 Gravity Energy Storage (GES): How Gravity Can Store Energy

25

Fig. 2.9 Scheme of a LEM-GES plant

energy into gravitational potential energy) [18]. Figure 2.9 shows the scheme of a LEM-GES plant. In this technology, thanks to the use of linear motors (as opposed to rotary motors), electricity can be transformed into linear motion. Therefore, if a vertical guide (made of ferromagnetic materials) is included, the linear motor will be able to raise or lower the pistons, without the need for a transmission equipment (as has been previously said) [18]. In a LEM-GES plant, the energy storage capacity is given by Eq. (2.16) [18]: ( E LEM−GES = ηLEM−GES

n∑ LEM i=1

) m LEM−i gΔh LEM−GES ·

1 kWh 3.6 · 106 J

(2.16)

Where: E LEM−GES ηLEM−GES n LEM m LEM−i Δh LEM−GES

energy storage capacity of a LEM-GES plant (kWh) output efficiency of a LEM-GES plant (%) number of LEM pistons mass of the LEM piston (kg) height difference between the platforms of the LEM-GES system (m)

The LEM-GES technology, currently in the conceptual phase, is classified into two types: surface and underground. In addition, the guideway is usually hexagonal in shape (as well as the pistons inside the guideway) in order to make better use of

26

2 Mechanical Storage

space [18]. In a study carried out by Botha et al. [18, 23], it was found that due to the fact that in the underground, kilometers deep wells can be drilled (so, unlike surface sites, the height difference between platforms is considerable), the energy storage capacity of LEM-GES technology in the subsurface is much higher than that of the surface (being able to store the same energy in an iron piston in a subsurface site as in several pistons equal to the first one in a surface site). For this technology, the energy storage capacity depends on the platforms design and the cycle efficiency is determined by the efficiency of a linear motor, i.e. about 95% [18]. Among the benefits of this technology, it has a good scalability, has a high cycleefficiency (due to that friction losses are practically negligible), is largely independent of specific geographic conditions if the site is on the surface, has a high lifespan (as a result of almost no friction losses) and is a modular technology (which allows it to increase its energy storage capacity) [19]. On the other hand, for this technology, different drawbacks can be found: it has the slowest response (compared to other GES technologies), is not a safety technology (as a result of its complexity and its immaturity) and is severely restricted to geographic conditions if the site is on the underground [19].

2.3 Flywheel Energy Storage (FES): The Power of Speed to Store Energy Until now, the MESS studied stored energy in the form of gravitational potential energy (both the PHES and the various GES technologies). Apart from the previously described methods seen above, other MESS can be found. Thus, flywheel energy storage (FES) systems store mechanical energy (more specifically, kinetic energy) in a rotating flywheel, which is confined with vacuum (state which is achieved by a vacuum pump connected to the container), partial or absolute, to reduce or eliminate, respectively, the aerodynamic losses. The mentioned stored energy is then converted into electrical energy by the action of an electrical machine [24]. Furthermore, as conventional mechanical bearings are a source of energy losses, FES systems make use, totally or partially, of magnetic bearings, which allows to reduce maintenance and to avoid friction losses. Lastly, the bidirectional converter transforms direct current into alternating current (therefore, it is sometimes referred to as an inverter) [24]. To give the reader a clear picture, Fig. 2.10 shows the scheme of a FES system. The use of flywheels as energy storage is not a new concept. Several centuries ago, purely mechanical flywheels were used exclusively to keep machines running from cycle to cycle, which was indispensable in the industrial revolution [25, 26]. Although, during that time, different shapes and designs were implemented [25], it was not until 1917 that Dr. A. Stodola first performed an actual analysis of flywheel rotor shapes and rotational stress [26]. The next major milestone in this technology came in the 1970s, when flywheel energy storage was proposed for use in vehicles

2.3 Flywheel Energy Storage (FES): The Power of Speed to Store Energy

Fig. 2.10 Scheme of a FES system

Fig. 2.11 Scheme of a CAES plant

27

28

2 Mechanical Storage

and for stationary backup power [25, 26]. In the years immediately following, the U.S. company Flywheel Systems, together with other companies, built and tested in the laboratory composite fiber rotors, which have the advantage over metal rotors in that they can withstand higher speeds (up to 100,000 revolutions per minute, r.p.m., as opposed to the 10,000 rpm that a metal rotor can withstand) and can withstand greater mechanical stress [26, 27]. However, it was not until the 1980s that magnetic bearings and motor-generators appeared, a fact that would mark a turning point in this technology [26]. So much so that the following decade, it was demonstrated that the also called “mechanical” batteries could be more useful than chemical batteries in several applications [26]. In a FES system, the energy stored is given by Eq. (2.17) [27]: ( E FES =

) 1 kWh 1 2 J ωFES · 2 3.6 · 106 J

(2.17)

Where: E FES energy storage capacity of a FES system (kWh) J moment of inertia of rotor (kg·m2 ) ωFES angular velocity of the rotor of the FES system (rad·s-1 ) To store the energy, it is necessary to convert mechanical energy to electrical energy and viceversa, so it is necessary an electrical machine to achieve that purpose [27]. To achieve that purpose, different electrical machines can be found in a FES system: an induction machine (IM), a permanent magnet synchronous machine (PMSM), a synchronous homopolar machine (SHM) and a switched reluctance machine (SRM) [27]. Of these machines, IMs can be used in low-speed applications and can be made with low cost and high-strength materials, PMSMs can be used for high and ultrahigh-speed applications (because it has a high efficiency of about 95%), SHMs are made from robust materials, can be used in high-speed applications and have an average efficiency of 83%, lastly, SRMs can be used for high-speed applications, are more robust than IMs and have less production cost than PMSMs [27]. Among the advantages of FES systems, they have a high efficiency of 85–95% [28], >85% [24], 85–90% [29], about 85% [27], 90–95% [30], 70–95% [14]; they have a high lifetime of about 20 years [27, 28], > 20 years [24], ≈ 25 years [30], 15–20 years [14]; they have a high specific power of 400–1500 W/kg [28], 400–500 W/kg [14], 400–30,000 [12]; they have a non-negligible specific energy of 5–80 Wh/ kg [14], 5–200 Wh/kg [12], 10–80 Wh/kg [28]; they have an energy density of 20–80 Wh/L [8], 0.25–424 Wh/L [12]; they have a power density of 1000–5000 W/L [8], 40–2000 [12]; it is easy to know the state of charge, SOC, of a FES system (it is only necessary to know the flywheel spinning speed) [24]; they are an environmentally friendly technology [29, 31]; they have lower periodic maintenance [29, 31]; and they are not temperature sensitive [24, 29]. On the other hand, they have high capital costs [14, 29, 30]; they present safety issues as a result of the rotor high speed (what could end up with the possibility of breaking) [29, 32]; they have a short discharge

2.4 Compressed Air Energy Storage (CAES): How to Store Energy in the Air?

29

time (from seconds to minutes) [14, 29]; a high mechanical stress and fatigue [29] and they have an unavoidable self-discharge [30]. FESS can be used in several applications, such as uninterruptible power supply (UPS) (as a replacement or a complement to batteries), transport (to assist hybrid and electric vehicles when harsh acceleration is needed), RES integration (improving RES stability and balancing the grid frequency due to that this technology has a fast response), flexible AC transmission systems (FACTS) (as a result of that FES high speed and response allow FACTS to have a good performance and to improve over power flow and long distance AC transmission line), marine (in future shipboards, FES systems are expected to promote applications such as UPS or bulk storage, among others), space (because this ESS, compared to NiMH batteries, reduces the solar array area, i.e., fewer PV panels are needed to store the same amount of energy) and power smoothing and frequency regulation (due to its fast response and its low energy density) [33]. In fact, there are different FES systems currently working: for example, in the LA underground Wayside Energy Storage System (WESS), there are 4 flywheel units with an energy storage capacity of 8.33 kWh and a power rating of 2 MW; while the company Active Power Inc., for its part, has developed a series of flywheels with an energy storage capacity of 2.8 kWh and a power rating of 675 kW for UPS applications [31]. However, this technology presents important challenges for its future implementation: such as reducing the costs of the technology, increasing the flywheel speed, efficiency, specific energy and investigating its modular application (i.e., the possibility of having several flywheel rotors simultaneously). In this way, the stability of the power system is expected to be improved [27].

2.4 Compressed Air Energy Storage (CAES): How to Store Energy in the Air? Among the MESS, the latest ESS that will be described will be the compressed air energy storage (CAES) system. A CAES system, which is one of the most promising technologies to be combined with RES (because they have a high potential to compensate for the fluctuating nature of RES; in fact, CAES plants can regenerate up to 80% electricity production to support the development of RES based plants) [34]. The mode of operation of a CAES plant is as follows: at times of low energy demand, excess energy from the main grid or from renewable energies is used to compress air (thanks to a compressor) and, by means of a pump, convey it to a sealed subway cavern or to a pressurized storage tank. On the other hand, when there is an energy requirement, this pressurized air is released and used to drive a turbine to produce electricity [34]. In the process of using electricity to compress air (and vice versa), electrical energy is transformed into potential energy (commonly referred to exergy) and vice versa [35, 36].

30

2 Mechanical Storage

The idea of compressing air to store electrical energy dates back to the early 1940s, when the patent application “Means for Storing Fluids for Power Generation” was submitted to the US Patent Office by Gay [35]. However, it was not until the 1960s that CAES systems were developed at either the industrial or scientific research level, which changed in the mentioned decade when appeared an economic interest to store low-cost off-peak power from baseload generation to be used for peak-load hours [35]. When possible, PHES systems were used to achieve that purpose, however these storage systems are severely restricted to geographical conditions; this reason led, in 1969 in northern Germany, to the decision of developing a CAES plant in this region, which was supported by suitable geological formations that allowed to store compressed gas in underground caverns [35]. The mentioned plant was put into operation in 1978 under the name of Huntorf CAES plant. As a curious fact, this storage technology was initially known by another name: the company Nordwestdeutsche Kraftwerke (NKW), which built the Huntorf plant, called this technology Air Storage System Energy Transfer (ASSET); while the technology supplier Brown, Boveri & Company (BBC) used the term Gas Turbine Air Storage Peaking Plant (GTASPP) (because CAES derived from gas turbine technology and served as a peak load capacity) [35]. Depending on the focus of the study, CAES systems can be classified into different types. Thus, if only the energy storage capacity is taken into account, CAES can be divided into large-scale (>50 MW), small-scale (about 10 MW) and micro-scale ( 10 MWh energy storage capacity plant in Goderich, Ontario, Canada, which has a discharge power rate of 1.75 MW and a charge power rate of 2.2 MW. On the other hand, to provide the required high heat transfer efficiencies, there also the so-called Advanced ACAES technologies (which are available since recently, in which ceramic heat exchangers are used to achieve that purpose [36, 38]. – Isothermal CAES (I-CAES): This type of CAES, currently under development, stores the previously compressed air at near-ambient temperatures, to avoid the problems associated with temperature control (if necessary, the isothermal uses electrical energy to reach the required temperature, what makes this process much greener). This technology has a higher round-trip efficiency, compared to other CAES systems. The temperature increase produced during compression and the temperature decrease produced during expansion are deduced from heat transfer (with the aid of the humidity in the air; it is possible that two-phase movement of air and the droplets help this phenom occur). Furthermore, this process has a lower thermodynamic work during expansion and compression as a result of the isothermal process and during the isothermal expansion, process that is carried out when power is needed, electricity can be delivered without the need of an external heat source (and, therefore, of fossil fuels) [34, 36]. To give an overview of CAES technology, this technology has advantages such as the fact that it can be integrated with renewable energies (which contributes to more sustainable energy), that it can use the subsoil to store compressed air, which means that this technology has fewer geographic restrictions than other technologies such as PHES (in fact, it is estimated that 80% of US soil is suitable for the implementation of this technology) [36], can be used in large-scale energy storage applications [12] and in long-term storage applications (this technology has a discharge time of 1– 24 h) [14], has a higher specific energy and power than PHES (i.e., the other ESS that can be used for large-scale applications), 3.2–60 versus 0.3–1.33 Wh/kg [12], 30–60 versus 0.5–1.5 Wh/kg [14] and 2.2–24 versus 0.01–0.12 W/kg, respectively [12]; has a higher energy density compared to PHES 0.4–20 versus 0.5–1.33 Wh/L [12]; and has a high lifetime (20–50 years [14], 20–60 years [8]). On the other hand, CAES systems presents several drawbacks such as the need of heating the air (for the D-CAES and A-CAES technologies) during the expansion process, that may result in the need of burning fossil fuels (in the case of the D-CAES technology) [36], it has not a high cycle efficiency (40–80% [14], 57–89% [12], 42% efficiency for the CAES plant in Huntorf and 57% efficiency for the CAES plant in McIntosh) [38]. Among the challenges this storage technology presents, it is necessary to increase the cycle efficiency (that is currently low, as a result of the heat dissipation during

32

2 Mechanical Storage

Table 2.1 Technical comparison of the MESS Parameters

PHES

GES

FES

CAES

Efficiency (%)

65–87

75–95

70–95

40–89

Lifetime (years)

20–80

30–50

15–25

20–60

Specific energy (Wh/kg)

0.3–1.5

–

5–200

3.2–60

Discharge time

1–24 h

1–4 h [14]

≈ sec-min

1–24 h

compression and the cool dissipation during expansion), which can be done with the incorporation of polygeneration (using the heat produced during compression for some process industrial heating applications and the cool produced during expansion for some air-conditioning applications); and to extend CAES in the field of underwater CAES and smart-grids (thus enabling the large-scale implementation of this technology) [34]. This section has described in detail the different MESS. However, in order to condense the main characteristics of each of the systems, so that the reader can make a quick mental sketch of which is the best method of mechanical energy storage depending on the required application, Table 2.1 presents a technical comparison of the different technologies that have been previously explained.

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Chapter 3

Thermal Energy Storage (TES): The Power of Heat

The use of thermal storage systems is not new; ancient civilizations already used this method for different purposes. Thus, there are documents dating from 350 years ago in Persia that emphasized the importance of ice or snow (which could be collected near lakes, rivers or mountains) for the preservation of food or cold drinks [1]. However, this thermal storage methods are far from current thermal energy storage technologies. Current thermal energy storage systems are used based on the following principle: as a result of the solar energy intermittency, it is necessary to use an energy storage system so that the excess energy produced by the mentioned renewable energy source is stored [2]; that weakness was identified by Willsie [3], who (taking that principle into account) built two plants in 1904: one in Saint Louis, Missouri (of 6 horsepower) and the other one in Needles, California (of 15 horsepower); which could operate during night with the solar heat stored during the day: Willsie had made the first thermal energy storage system (in the way it is currently conceived) [3]. On the other hand, to integrate solar thermal energy, in concentrated solar power (CSP) plants, whose first plant, “Solar Engine One” was commissioned in 1913 in Egypt [3], thermal energy storage (TES) systems are used to store heat during high solar intensity periods periods to be released during the periods of weak or no solar irradiation [2]. In Fig. 3.1, it is shown the scheme of a CSP plant with a TES system as backup. The mode of operation of a CSP plant is as follows: the sunlight is reflected towards the central tower by the heliostats and heats a fluid; that heat will be stored later in a TES system and, afterwards, will be used to produce electricity through a turbine [4]. This storage technology, which has a high potential to store energy in heat form over a significant period of time to be used to generate electricity through heat when needed, is a promising technology to reduce the dependence on fossil fuels [5]. The TES systems, which store energy by cooling, melting, vaporizing or condensing a substance (which, in turn, can be stored, depending on its operating temperature range, at high or at low temperatures in an insulated repository) [4] can store heat energy of three different ways. Based on the way TES systems store heat © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 J. M. Andújar Márquez et al., Energy Storage Systems: Fundamentals, Classification and a Technical Comparative, Green Energy and Technology, https://doi.org/10.1007/978-3-031-38420-2_3

35

36

3 Thermal Energy Storage (TES): The Power of Heat

Fig. 3.1 Scheme of a CSP plant with a TES system

energy, TES can be classified into three types: sensible heat storage (SHS), latent heat storage (LHS) and thermochemical heat storage (TCHS) [6]. Next, a detailed description of the three types of TES systems is done.

3.1 Sensible Heat Storage (SHS) Sensible heat storage systems, considered the simplest TES system [6], store energy by varying the temperature of the storage materials [7], which can be liquid or solid materials and which does not change its phase during the process [8, 9]. In the case of heat storage in a solid material, a flow of gas or liquid is passed through the voids of the solid material, which will be porous [8, 9]. Solid materials for SHS, which may include rock, stone, brick, concrete, wood or earth, are used for heating applications [10]. On the other hand, among liquid materials, which are widely used for cooling and heating purposes, water is the best material to be employed due to its high specific heat capacity, availability and low cost [10]. In a mass of material, the amount of energy stored by sensible heat is given by Eq. (3.1) [9]: ⎛ Q SHS = ⎝

T2

T1

⎞ m · c p · dT ⎠ ·

1 kWh 3.6 · 106 J

Where: Q SHS energy stored by sensible heat in a material (kWh) m mass of the material (kg) specific heat at constant pressure (J/(kg °C)) cp

(3.1)

3.1 Sensible Heat Storage (SHS)

T1 T2

37

initial temperature of the storage material (°C) final temperature of the storage material (°C)

If the considered temperature range is too small, the dependence of cp on temperature can be neglected, so Eq. (3.4) can be rewritten as, Eq. (3.2) [9]:   Q SHS = m · c p · T ·

1 kWh 3.6 · 106 J

(3.2)

Where: T temperature variation (°C) This technology can store heat to later generate electricity or to later supply the stored heat. On the one hand, if heat is used to produce electricity through a turbine, a molten salt thermal energy storage (MSTES) system can be used. In this technology, the molten salt (which results of a liquid formed by the fusing of an inorganic salt), is used to store sensible heat at temperatures exceeding the 100 °C, so it can be used later to produce electricity through a turbine. A CSP system, as shown in Fig. 3.4, is the ideal technology for integrating MSTES systems. Currently, different MSTES systems can be found, among which the following can be highlighted: the NOOR I plant, in Morocco, with a rated power capacity of 150 MW and the Solar two plant, in USA, with a rated power capacity of 105 MW [4]. This technology presents the challenge that a molten salt are corrosive in nature, as well as that its operating temperature has not reached 565 °C, which limits plant efficiency and increases levelized electricity costs [11]. On the other hand, if heat is stored to be supplied later, this technology can be classified into 5 different types [9]: Aquifer thermal energy storage (ATES): Dating back to the mid 1960s, this technology uses an underground aquifer to store sensible heat thanks to the use of at least two hydraulically connected wells (one for cold water and the other one for hot water) and a heat exchanger that are used for groundwater extraction and injection [4]. Figure 3.2 shows the scheme of an ATES system (where the water flow direction depends on if the ATES system is used for cooling or heating purposes). For this technology, around 3000 ATES plants have been installed worldwide (more of 90% of them are located in the Netherlands), among which the following can be highlighted: the 20 MW plant located in the University of Technology in Eindhoven (commissioned in 2002), the 2 MW plant of Anova Verzekering Co. Building, located in Amersfoort, Netherlands (commissioned in 1996) and the 5 MW plant in the Copenhagen Airport (commissioned in 2015) [4]. This method of heat energy storage presents a serious challenge, because even at depths greater than 200 m, the ground water is at temperatures below 25 °C (insufficient to provide heat); to correct this problem, water can be pumped to the surface during the summer and, through solar panels, heated and stored underground again to be used, for domestic use, during winter [11].

38

3 Thermal Energy Storage (TES): The Power of Heat

Fig. 3.2 Scheme of an ATES system

Hot water thermal energy storage (HWTES): This established technology, which is widely used on a large scale for seasonal storage of solar thermal heat, stores hot water (a commonly used storage material because of its high specific heat) inside a concrete structure, which is wholly or partially buried in the ground, to increase the insulation of the hot water [4]. Figure 3.3 shows a scheme of a HWTES system. Currently, the HWTES plant in Friedrichshafen-Wiggenhausen, Germany (commissioned in 1996), can be highlighted [4]. Cavern thermal energy storage (CTES): This technology, which is currently rarely employed (because of its expensive construction or installation) makes use of a natural or man-made cavern to store thermal energy. In CTES systems, during the charging cycle, excess heat is used to heat up the water inside the storage tank (and the hot water, during the discharging cycle, is taken from the top of the tank and used for heating purposes) [4]. Figure 3.4 shows the scheme of a CTES system. In Sweden, two examples of CTES systems can be found: the Avesta cavern TES system (built in 1981 to store heat from an incineration plant and which has a storage volume of 1.5 · 104 m3 ) and the Lyckebo TES system (commissioned in 1983, with a storage volume of 1.15 · 105 m3 and a maximum operation temperature of 90 °C) [4]. Gravel water thermal energy storage (GWTES): A waterproof and insulated pit is buried in the ground close to the surface of the soil, between 5 and 15 m. This technology, which usually store a gravel and water mixture (although it can store a sand and water mixture or a soil and water mixture), can reach a maximum storage temperature of 90 °C. In a GWTES system, heat can be charged and discharged through plastic pipes carrying a fluid installed at different layers inside the storage

3.1 Sensible Heat Storage (SHS)

39

Fig. 3.3 Scheme of a HWTES system

Fig. 3.4 Scheme of a CTES system

system [4]. Figure 3.5 shows the scheme of a GWTES system. Different examples of GWTES systems can be found: in Marstal, Denmark, there is a 6000 MWh heat storage capacity plant (commissioned in 2011), while in Dronninglund, Denmark, there is a 5400 MWh heat storage capacity, which was commissioned in 2013 [4].

40

3 Thermal Energy Storage (TES): The Power of Heat

Fig. 3.5 Scheme of a GWTES system

Borehole thermal energy storage (BTES): this technology, which dates back from 1977 when a 42 borehole TES was built in Sigtuna, Sweden, stores large amounts of heat (which will be charged or discharged by vertical borehole heat exchangers) underground to be used during winter, transferred to the underground mainly by conductive flow carrying a liquid fluid through a series of closely spaced boreholes [4]. Figure 3.6 shows the scheme of a BTES system. Among the different BTES systems that can be found, the Brædstrup District Heating, in Denmark (commissioned in 2013), with a heat storage capacity of 616 MWh and the Crailshem, Germany BTES system (commissioned in 2007), with a heat storage capacity of 1135 MWh, can be highlighted [4]. Regarding the technical parameters of the SHS technology, it presents an efficiency of 50–90% [4, 12], a lifetime of 10–30 years [4], a small volumetric density of 50 kWh/m3 [13] or a small specific energy of 10–50 Wh/kg [12], 20–30 Wh/kg [13]. Among the advantages of the SHS TES, it has a simpler design than other TES technologies, has low operation costs associated, has a high specific heat capacity, has a good thermal conductivity and a good adaptability to its container [9, 10], an unlimited cycle lifetime, a completely reversible charging and discharging [4]. On the other hand, it presents several disadvantages such as not being able to store or deliver energy at a constant temperature, a low specific energy, high space requirements, a high self-discharge [9, 10] and the high initial capital investment [4]. Although the different SHS TES systems present different challenges, all of them have one

3.2 Latent Heat Storage (LHS)

41

Fig. 3.6 Scheme of a BTES system

challenge in common: the need of a storage medium which can maintain an structured layer, so the warmest water is at the top of the storage medium, while the coldest water is at the bottom of the storage medium [9].

3.2 Latent Heat Storage (LHS) Latent heat storage (LHS) systems, whose use is gradually expanding because of its ability to store large amounts of heat energy (because this technology has a high specific energy compared to a SHS system) in small temperature ranges [10, 14], uses the heat applied to the material to induce a phase change from solid to liquid (in this case, the heat would be stored as latent heat of fusion) or from liquid to gas (in this case, the heat would be stored as latent heat of vaporization) [4, 9, 11]. Among the materials used for LHS, it is common to find solid-liquid phase change materials (PCMs) for building applications, such as organic compounds (paraffins or fatty acids), inorganic compounds (salt hydrates) or a mixture of inorganic and/or organic compounds known as eutectics mixtures [10]. Normally, inorganic materials have almost double volumetric heat storage capacity than the organic ones [15]. In a mass of a solid material of a material that is first heated from a temperature T1 to the melting temperature and then heated to the ebuillition temperature and then heated again to a temperature T2 , the amount of energy stored by latent heat is given by Eq. (3.3) [9]:

42

3 Thermal Energy Storage (TES): The Power of Heat

⎛

Q LHS

⎡T A TB = ⎝m · ⎣ C ps (T )dT + qt + C pl (T )dT T1

T2 + qi + TB

⎤⎞

TA

C pv (T )dT ⎦⎠ ·

1 kWh 3.6 · 106 J

(3.3)

Where: Q LHS m T1 TA C pl TB C ps T2 C pv

energy stored in a latent heat storage system (kWh) mass of the material (kg) initial temperature of the storage material (°C) melting temperature of the phase change material (°C) specific heat at constant pressure of the material in solid phase (J/(kg °C)) boiling temperature of the phase change material (°C) specific heat at constant pressure of the material in liquid phase (J/(kg °C)) final temperature of the storage material (°C) specific heat at constant pressure of the material in vapor phase (J/(kg °C))

In a LHS system, in order to select the best PCM, different technical properties are taken into account: among the thermal properties, a material with a good heat transfer, a high latent heat of transition and a suitable phase-transition temperature (in order to reduce the size of the heat store) is sought; among the physical properties, a material with a favorable phase equilibrium, a high density, a small volume change and a low vapor pressure is sought (in order to obtain a smaller size of the storage container); among the kinetic properties, a material with no supercooling (so it is not necessary to freeze that material under the fusing temperature to make it change phase) and with sufficient crystallization rate is sought; among the chemical properties, a material with long-term chemical stability, compatible with materials of construction, no toxicity and no fire hazard is required (in order to reduce the degradation of the system); on the other hand, regarding the economic aspects, an abundant, cost effective and available material is sought [15]. The LHS technology presents a higher specific energy than SHS technology: 50– 150 Wh/kg [12], 50–100 Wh/kg [13], a higher volumetric energy density than SHS systems: 100 kWh/m3 [13], a lifetime of 10–30 years [4], or a 70–90% efficiency (which can only be competitive against solid SHS systems [13]). Among the benefits of the LHS technology, the advantages of LHS technology are that the phase change enthalpy of PCMs is much higher than the sensible heat, the specific energy of the materials used for this technology are 14 times greater than the SHS materials one, the volume required to store the same amount of energy is much smaller for a LHS system than for a SHS system (in the case of a LHS system using a parraffin wax, a 70% less volume is required than for a SHS system using rocks) and due to that the involved mass is low, a LHS system can avoid seasonal overheating problems [12]. On the other hand, this technology presents several disadvantages such as its low thermal conductivity, the supercooling phenom (that

3.3 Thermochemical Heat Storage (TCHS)

43

occurs in some materials when changing from a liquid to a solid phase), the low thermal stability after a great number of cycles, the corrosiveness, the high costs, the flammability that presents a LHS system [10, 12], its complicated technical maintenance [12] or its limited commercial availability (which is only for certain materials and temperatures) [16]. This technology has a wide variety of applications, among which are the use in CSP plants (using as a TES system a LHS system instead of a SHS system) [16], the use in building heating and cooling, in thermal control or for industrial waste heat storage [12]. However, as a result of the high costs of this technology, the applications in which it is used require a small storage size, a small range of temperature and a minimum weight or volume [9]. LHS technology presents a series of challenges, such as reducing the corrosion faced with high temperature PCMs (so, in a future, PCMs with high thermal conductivity and high melting temperatures can be further used, which will lead to the integration of these materials in CSP plants), the phase segregation or incongruent melting and solidifications of PCMs materials made of different components (to correct this problem, eutectics can play a major role), to get PCMs with unaltered termo-physical properties at high temperatures or to obtain commercial distribution of this technology [16].

3.3 Thermochemical Heat Storage (TCHS) Termochemical heat storage (TCHS) systems use heat to induce a completely reversible chemical reaction and/or sorption process [10, 15] (in the case of heat storage in a sorption process, the heat is stored by breaking the binding force between the sorbent and the sorbate in terms of chemical potential) [17]. According to Yu et al. [10, 17], TCHS can be divided into chemical reaction (or more precisely, chemical reaction without sorption) and sorption (whose term, first proposed by McBain, is a general term that refers to both adsorption and absorption). In this technology, the heat is applied, during the thermal charging process, to provoke an endothermic reaction (which would occur inside an endothermic reactor) or to provoke the desorption process [14, 17]; while during the thermal discharging process, the heat is released in an exothermic reaction (which would occur inside an exothermic reactor) or in the adsorption process [14, 17]. Furthermore, the materials that react will be stored in different tanks (in the case of the chemical reaction TCHS technology, the material A, which results from the exothermic reaction, will be stored inside a tank, while the materials B and C, which results from the endothermic reaction will be stored inside another tank) [13]. For a chemical reaction TCHS system, Fig. 3.7 shows a simplified scheme. The reactions that take place can be written as, Eq. (3.21) [14, 17]: A + H eat  B + C

(3.4)

44

3 Thermal Energy Storage (TES): The Power of Heat

Fig. 3.7 Scheme of a chemical reaction TCHS system

Although TCHS technology can potentially store more energy per unit of volume than SHS or LHS technologies as a result of the heat of the reaction [18] or as a result of the large amount of heat involved in the desorption or the sorption processes [17] (in fact, the volume required to store 1850 kWh of thermal energy is 34 m3 for a SHS system using water, 20 m3 for a LHS, while for a sorption TCHS, the volume is 10 m3 and for a chemical reaction TCHS, the volume required is 1 m3 ) [17], it is the least investigated TES technology [18] (this technology is still at a very early stage of development, in fact, most of the studies are done at laboratory scale; furthermore, large technical and economic investments are required before this technology becomes commercially available) [13]. In the case of a chemical reaction TCHS system, the amount of heat that can be stored (which is stored in a chemical reaction which, in turn, depends on the heat of reaction and the extent of conversion) is given by, Eq. (3.5) [15, 18]: Q TCHS = (ar mh r ) ·

1 kWh 3.6 · 106 J

(3.5)

Where: Q TCHS ar m h r

heat stored in the TCHS system (kWh) fraction of reagents which reacted total mass in the chemical reaction (kg) heat of reaction per unit mass (J/kg)

In a chemical reaction TCHS system (although this technology is far from being implemented), different potential materials for use can be found: manganese oxide, calcium hydroxide, magnesium oxide or iron carbonate, among others [18].

3.3 Thermochemical Heat Storage (TCHS)

45

According to Wentworth and Chen [13, 19], the criteria to select the proper materials for a TCHS system is as follows: the endothermic reaction (to store heat energy) should occur at temperatures lower than 1273 K, while the exothermic reaction (to recover the stored energy) should occur at temperatures higher than 773 K; both reactions should have large enthalpies of reaction (so that the storage capacity can be maximized), be completely reversible (so that the materials can be used for long periods of time) and fast enough to carry out quickly the adsorption of solar energy and regeneration of the heat; the products of the reaction should have a small molar volume so that the storage volume can be minimized and be separated before the storage for an uncatalyzed reaction or its mixture must be stable for during the storage for a catalyzed reaction; and finally, the materials to be used in the reactions should be able to be handled without complex equipment, should not be highly reactive towards water or oxygen (because these elements are difficult to be completely excluded from any closed system) and should be commercially available at low costs [13, 19]. Among the properties sought for potential materials, a high specific energy or a high thermal conductivity can be found [18]. Furthermore, a chemical reaction TCHS system presents as technical parameters a high specific energy of 120–250 Wh/kg [12], which rises to 500–1000 Wh/kg in the case of the specific energy of the reactant materials (instead of the system) [13] or a high efficiency of 75–100% [12]. The TCHS technology has different benefits such as a high energy density (for chemical reaction TCHS system) [10, 13, 16, 18], negligible heat losses [10, 16], the latter allows a long term storage capacity [10, 16], the possibility of long distance transport [16] or a higher efficiency compared to other TES technologies [12]. However, on the other hand, this technology presents several disadvantages, for example, a TCHS system can also present a poor energy density if it is a sorption TCHS system [17], it presents high investment costs [10, 16], it is a complex and non-mature technology (it is only available at laboratory scale) [10, 13, 16, 17], the materials used for TCHS have a high and inappropriate operation temperature (over 500 °C) [10, 20], the ability of mass transfer in a chemical reaction TCHS system [10, 17] or restrictions that results from the reaction kinetics [18]. On the other hand, the TCHS technology has a series of challenges to be faced in the future, such as improving the system energy density (which is much lower than the energy density of the materials used in this technology) [10], reducing the complexity of a TCHS system [17], correcting the crystallization problem at high concentrations in a sorption TCHS system by subjecting them to a treatment [17], improving heat transfer (which can be achieved by extending the surface of a heat exchanger) [17], reducing heat losses (which can be done by using separated reactors for charging/discharging reactions) [17] or reducing its current high costs [10, 17] (in the case of a sorption TCHS system, it can be achieved by adopting modular reactors, which, in addition, would entail a simpler and more compact design) [17]. Before this technology becomes commercially available, these challenges must be addressed so, in a near future, the TCHS technology can become available for building or CSP plants.

46 Table 3.1 Technical comparison of the TES technologies

3 Thermal Energy Storage (TES): The Power of Heat

Parameters

SHS

LHS

TCHS

Efficiency (%)

50–90

70–90

75–100

Lifetime (years)

10–30

10–30

*

Specific energy (Wh/kg)

10–50

50–150

120–250

* The lifetime of TCHS systems, not available, will depend on the reactant degradation and side reactions [21]

In this section, the different technologies of TES have been described. To make it easier for the reader to make a mental sketch of which is the best method of thermal energy storage depending on the required application, in Table 3.1 a technical comparison is made thanks to the data previously provided.

References 1. Morofsky E (2007) History of thermal energy storage. Therm Energy Storage Sustain Energy Consum 3–22. https://doi.org/10.1007/978-1-4020-5290-3_1 2. Pelay U, Luo L, Fan Y, Stitou D, Rood M (2017) Thermal energy storage systems for concentrated solar power plants. Renew Sustain Energy Rev 79:82–100. https://doi.org/10.1016/j.rser. 2017.03.139 3. Ragheb M (n.d.) Solar thermal power and energy storage historical perspective 4. Mitali J, Dhinakaran S, Mohamad AA (2022) Energy storage systems: a review. Energy Storage Sav. https://doi.org/10.1016/J.ENSS.2022.07.002 5. Thaker S, Olufemi Oni A, Kumar A (2017) Techno-economic evaluation of solar-based thermal energy storage systems. Energy Convers Manag 153:423–434. https://doi.org/10.1016/j.enc onman.2017.10.004 6. Mahon H, O’Connor D, Friedrich D, Hughes B (2022) A review of thermal energy storage technologies for seasonal loops. Energy 239:122207. https://doi.org/10.1016/j.energy.2021. 122207 7. Li G (2016) Sensible heat thermal storage energy and exergy performance evaluations. Renew Sustain Energy Rev 53:897–923. https://doi.org/10.1016/J.RSER.2015.09.006 8. Haselbacher A (2015) An overview of thermal energy storage 9. Socaciu LG (2012) Thermal energy storage: an overview. Acta Tech Napocensis Ser Appl Math Mech Eng 55 10. Lizana J, Chacartegui R, Barrios-Padura Á, Valverde JM (n.d.) Characterization of thermal energy storage materials for building applications. In: Proceedings of the 3rd international congress on sustainable construction and eco-efficient solutions, vol 30. Charact. Thermal energy storage materials in building applications 11. Sadeghi G (2022) Energy storage on demand: thermal energy storage development, materials, design, and integration challenges. Energy Storage Mater 46:192–222. https://doi.org/10.1016/ J.ENSM.2022.01.017 12. Mabrouk R, Naji H, Benim AC, Dhahri H (2022) A state of the art review on sensible and latent heat thermal energy storage processes in porous media: mesoscopic simulation. Appl Sci 12. https://doi.org/10.3390/app12146995 13. Pardo P, Deydier A, Anxionnaz-Minvielle Z, Rougé S, Cabassud M, Cognet P (2014) A review on high temperature thermochemical heat energy storage. Renew Sustain Energy Rev 32:591– 610. https://doi.org/10.1016/j.rser.2013.12.014

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14. Shabgard H, Rahimi H, Naghashnejad M, Acosta PM, Sharifi N, Mahdavi M et al (2022) Thermal energy storage in desalination systems: state of the art, challenges and opportunities. J Energy Storage 52:104799. https://doi.org/10.1016/J.EST.2022.104799 15. Sharma A, Tyagi VV, Chen CR, Buddhi D (2009) Review on thermal energy storage with phase change materials and applications. Renew Sustain Energy Rev 13:318–345. https://doi.org/10. 1016/j.rser.2007.10.005 16. Opolot M, Zhao C, Liu M, Mancin S, Bruno F, Hooman K (2022) A review of high temperature (≥ 500 °C) latent heat thermal energy storage. Renew Sustain Energy Rev 160:112293. https:/ /doi.org/10.1016/J.RSER.2022.112293 17. Yu N, Wang RZ, Wang LW (2013) Sorption thermal storage for solar energy. Prog Energy Combust Sci 39:489–514. https://doi.org/10.1016/j.pecs.2013.05.004 18. Kuravi S, Trahan J, Goswami DY, Rahman MM, Stefanakos EK (2013) Thermal energy storage technologies and systems for concentrating solar power plants. Prog Energy Combust Sci 39:285–319. https://doi.org/10.1016/J.PECS.2013.02.001 19. Wentworth WE, Chen E (1976) Simple thermal decomposition reactions for storage of solar thermal energy. Sol Energy 18:205–214. https://doi.org/10.1016/0038-092X(76)90019-0 20. Prieto C, Cooper P, Fernández AI, Cabeza LF (2016) Review of technology: thermochemical energy storage for concentrated solar power plants. Renew Sustain Energy Rev 60:909–929. https://doi.org/10.1016/J.RSER.2015.12.364 21. Abedin AH, Rosen MA (2011) A critical review of thermochemical energy storage systems. Open Renew Energy J 4:42–46

Chapter 4

Electrical Storage

Electrical energy storage systems (EESS) are the best method to directly store electricity (i.e., the energy storage is given in a pure format). Although this storage systems have a fast response and a high power density, they present several drawbacks such as a high self-discharge rate and a low energy density [1, 2]. In this section, the two different EESS will be described in order to let the reader know the best option based on its application.

4.1 Superconducting Magnetic Energy Storage (SMES): A Magnetic Field to Store Energy Superconducting magnetic energy storage (SMES) systems are based on the concept of the superconductivity of some materials, which is a phenomenon (discovered in 1911 by the Dutch scientist Heike Kamerlingh) that occurs to some materials when are cooled down under the so called critical temperature, at which point they begin to exhibit zero electrical resistance [2]. SMES is the only known technology that stores electrical energy into electric current: in this technology, a direct current passes through an inductor (more accurately, a coil), which is made from a circular (so that the current can circulate continuously with practically no losses) superconducting material to store electrical energy [3] (which will be in the form of a direct current that flows along the superconductors and is conserved inside a direct current magnetic field [2]). As a superconducting material (usually made of niobium-titanium) needs to be under a critical temperature (which is a very low temperature), to maintain it in its superconducting state, the material needs to be cooled down (which is usually done by immersing it in liquid helium at 4.2 K, in super fluid helium at 1.8 K, in both cases contained in a vacuum-insulated cryostat) [3] or in liquid nitrogen in the case of high temperature superconductors [2]. Furthermore, a SMES system needs a power conversion system (to bidirectionally convert the electrical energy connected © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 J. M. Andújar Márquez et al., Energy Storage Systems: Fundamentals, Classification and a Technical Comparative, Green Energy and Technology, https://doi.org/10.1007/978-3-031-38420-2_4

49

50

4 Electrical Storage

Fig. 4.1 Scheme of a SMES plant

between the inductor and the grid/load) [3]. In order to make easier to understand how a SMES system works, Fig. 4.1 shows the scheme of a SMES plant. The first concept of a SMES system was brought up by Ferrier in 1969, who proposed to build a large toroidal coil capable of supplying diurnal storage of electrical energy for the whole of France (however, because of the high costs, the idea was discarded) [4]. Two years later, in 1971, a research to understand the fundamental interaction between an energy storage system and an electrical system was started at the University of Wisconsin, US [2, 4], what resulted in the creation of the first SMES system after a successful charging and discharging process [5]. The success of this experiment led to the start of the design and development of SMES for utility applications in 1979 (thus, in 1981, Los Alamos National Laboratory first commercially installed a SMES designed for preventing low frequency oscillations of Wester US Power System; while years later, American Super Conductor started to develop and market different SMES for different commercial purposes, which has led to a worldwide research to improve the quality of this technology and to reduce its costs) [5]. Although the first SMES systems were built with low temperature superconductors (LTS), which have a typical operating temperature at 4.2 K [6], the discovery of high temperature superconductors (HTS), which have an operating temperature over 40 K, led to their commercialization in the late 1990s [2, 6]. In fact, American Super Conductor produced the first HTS-SMES in 1997, and afterwards, it was connected to a larger grid in Germany [2]. Currently, different SMES systems can be found for different purposes: China has developed small and medium scale SMES plants to enhance voltage stability, Korea has developed for power quality improvement, power system stability and synchronization control of smart micro power grid; on the other

4.1 Superconducting Magnetic Energy Storage (SMES): A Magnetic Field …

51

hand, Super Power Inc. (in partnership with ABB Inc., Brookhaven National Laboratory and the Texas Center for Superconductivity at University of Houston) is developing an advanced 20 kW HTS-SMES with an energy storage capacity of 2 MJ [5]. The energy stored in a SMES system is given by Eq. (4.1) [3, 6]:  E SMES =

 1h 1 kW 1 2 · LI · 2 SM 3600 s 1000 W

(4.1)

Where: E SMES energy stored in a SMES system (kWh) L inductance of the superconducting material (H) ISM current flowing through the superconducting material (A) Among the benefits of this technology, it has a very high energy storage efficiency (as a result of practically no losses) of ≥ 97% [1, 3], 95% [5], > 95% [7], 95–98% [2]; has a long lifetime of > 20 years [7], 30 years [1, 5], 20–30 years [8], 20–40 years [2]; a cycle life of > 100,000 cycles [7], 10,000–100,000 cycles [8]; has a fast response [2] of few milliseconds [1, 3]; and has a high specific power [2] of 500–2000 W/kg [7], 500–15,000 W/kg [8], 500–5000 W/kg [2]. On the other hand, it presents several drawbacks such as a very low specific energy [2] of 0.5–5 Wh/kg [2, 7], 0.27–75 Wh/kg [8], a high self-discharge rate [2, 3], the need of continuous cooling [2, 3], a short discharge time [2] of milliseconds to seconds [7], the strong magnetic field that is generated [1, 2] and high capital costs [1]. This technology faces different challenges to be solved in the future, such as research in the area of additional protection to solve the current problem energy losses or inductor damage in case of a failure in the inductor [2], to improve the structure of the SMES system to handle the Lorentz force during charging and discharging processes (because of the excessive vibrations produced by it in the system) [2], more research to implement better and more robust controllers [2], to reduce the period of cooling a superconducting material from ambient temperature to critical temperature (currently 4 months), a further research of the application of liquid helium as the cooling medium (so the performance of a SMES system can be improved) [2] and to make the superconducting material to operate at higher currents to reduce its length (with the respective cost savings it would imply) [2]. Finally, doors are opening in the applications of SMES technology, such as hybridization with other energy storage technologies: for example, hybridization with liquid hydrogen (which would be the cooling medium) could be possible [2].

52

4 Electrical Storage

4.2 Supercapacitor Energy Storage (SCES): Just Stored Electricity A capacitor is the most direct method to store electrical energy [1, 3]. Capacitors, which can be charged much faster than batteries, consists of, in its simplest form, of two metal plates (which are separated by a nonconducting layer, i.e., a dielectric) and its mode of operation is as follows: when a plate is charged with direct-current electricity, the other one will induce in it a charge of the opposite sign [3]. Nevertheless, a capacitor has as its main drawback its very low energy density, which led to the development of devices with a much greater capacitance and energy density: the supercapacitors [1, 3]. Supercapacitors, also denoted as ultracapacitors, are a type of electrochemical capacitors that consists of electrolytes, current collectors and electrodes, which stores energy electrochemically by using a polarized electrolyte [9] and which can be considered a viable energy storage system because, compared to batteries, supercapacitors have a specific power in several orders of magnitude higher and a comparable specific energy [9]. This technology differs from a conventional capacitor in the electrodes materials (which is based on carbon technology for supercapacitors) [10]. The concept of double-layer architecture was established when the phenomenon of electrostatic attraction and osmotic repulsion of charged electrodes submerged in electrolyte solutions was discovered by the German physicist Hermann von Helmholtz in 1853 [11]. A hundred years later, in 1957, H.I. Becker, at General Electric Company, proved and patented the double-layer capacitance and its charging/ discharging mechanism in a cell [11] (which will be introduced later). Later, in 1968, Standard Oil Company, Cleveland, Ohio (SOHIO) invented an early cell which was composed of two layers of activated carbon separated by a thin porous insulator; that cell was the basis for the development of the supercapacitor technology now known as electrochemical double layer capacitors (EDLC). However, three years later, in 1971, because of commercialization problems, SOHIO licensed their invention to the Japanese company NEC, which named their recent acquisition as supercapacitors (which is the common name used for this technology in the Asian area) and used it as a backup power to maintain computer memory [9–11]. Then, in 1979, NEC started to produce supercapacitors for electric vehicles ignition systems [9]. Around that time, more specifically in 1978, the Panasonic company created the Gold Capacitor, i.e., a supercapacitor which used activated carbon as an electrode and an organic electrical solution [9, 10] and, in 1987, the ELNA company developed the Dynacap (however, the three mentioned supercapacitors were only suitable for low power applications) [10]. On the other hand, in 1982, the Pinnacle Research Institute (PRI) developed high-power devices to be used in in military applications and named them ultracapacitors (which is the common name for this technology in North America) [10, 11]: those devices, commonly known as pseudo-capacitors, used ruthenium oxide in their electrodes [11]; around that time, the Maxwell Company developed the EDLCs for electric vehicles (also named by them as ultracapacitors) [10]. Regarding hybrid and assymmetric supercapacitors, they were developed in the 1990s decade [11]. Since

4.2 Supercapacitor Energy Storage (SCES): Just Stored Electricity

53

their introduction to the market, supercapacitors have been receiving a lot of attention. Currently, NESS, Panasonic, EPCOS, NEC and Maxwell companies lead the way in research and development of supercapacitors, which are mainly developed in the United States, Japan and Russia [9]. Supercapacitors can be classified into three main types: EDLCs, pseudocapacitors and hybrid supercapacitors [9]. Next, a description of each type of supercapacitors is done: Electrochemical double layer capacitor (EDLC): this supercapacitor stores the charge electrostatically and make use of high surface area carbon materials. The mode of operation of this type of supercapacitor is as follows: when the electrode is immersed in the electrolyte, during the charging process (when the supply source is connected to the electrodes), two opposite charges are formed at the electrode/ electrolyte interface, forming a charge layer of one polarity (positive or negative) on the surface of the electrode and a charge layer of the opposite polarity in the electrolyte solution, both separated by a formed layer of solvent or by a water layer (this layer would be the dielectric), which prevent the charge flow between electrode and electrolyte when the supercapacitor is charged [12]. Figure 4.2 shows the scheme of the operating mode of an EDLC supercapacitor during the charging and discharging processes. The electrochemical double layer created during the charging process is used to store energy (furthermore, the energy stored in the supercapacitor can be increased by applying a higher voltage). Among the characteristics of this kind of supercapacitors, its electrostatic storage of energy is linear with respect to the stored charge (which corresponds to the concentration of the absorbed ions) and a very high lifetime as a result of that there is no chemical changes taking place within the electrode or electrolyte [12]. Finally, in an EDLC the energy stored is given by Eq. (4.2) [11]:  E EDLC SCES =

 1h 1 2 CSC VSC · 2 3600 s

(4.2)

Where: E EDLC SCES energy stored in an EDLC supercapacitor (kWh) CSC capacitance of the supercapacitor (F) VSC voltage of the supercapacitor (V) Pseudocapacitors: this technology, which is faradaic in origin (i.e., non electrostatic) depends on fast and reversible electrochemical redox reactions (which take place on the surface of the electrode, avoiding structural changes and providing improved stability) and the energy is stored by means of electron transfer between the electrolyte and the electrodes. Compared to EDLCs, because of fast reversible charge transfer reaction, pseudocapacitors have a higher energy density [12]. In this technology, the charged atoms move towards the charged electrodes with opposite polarity; the charge is stored in the two double layers formed between the electrode (which is made from a metal oxide or a conducting polymer material) and the

54

4 Electrical Storage

Fig. 4.2 Scheme of the operating mode of an EDLC supercapacitor during charging and discharging processes

electrolyte. The charge transfer between the electrolyte and the electrode from the dissolved ion, which does not react with the atoms of the electrode (there is only charge transfer), is what causes the pseudocapacitance [12]. The two layers which are formed are called the inner and the outer Helmholtz layers, respectively. The inner Helmholtz layer, given by the center of the inner layer (consisting of solvent, ions and undissolved molecules fully adsorbed to the electrode surface), is closest to the dissolved ions, which interact with the electrode surface and are adsorbed by it. On the other hand, the outer Helmholtz layer has the highest charge density and from it begins the diffusion layer; in this layer the long-range electrostatic forces dominate, since the dissolved ions interact with the charged metal ions (therefore, this double layer formed affects the structure of the electrode and that of the electrolyte layer itself) [12]. Figure 4.3 shows a schematic diagram of the mode of operation of a pseudocapacitor. In a pseudocapacitor, the energy stored is given by (4.3) [11]:  E pseudo SCES =

  2  1h 1 2 CSC Vrated SC − Vmin SC · 2 3600 s

Where: E pseudo SCES C Vrated SC Vmin SC

energy stored in a pseudocapacitor (kWh) capacitance of the supercapacitor (F) rated voltage of the supercapacitor (V) minimum voltage of the supercapacitor (V)

(4.3)

4.2 Supercapacitor Energy Storage (SCES): Just Stored Electricity

55

Fig. 4.3 Schematic diagram of the mode of operation of a pseudocapacitor

Hybrid capacitors: this supercapacitor technology is made of assymmetric electrodes, one of them has electrostatic capacitance and the other one has electrochemical capacitance, i.e. an electrode has a high amount of double layer capacitance and the other one has a high amount of pseudocapacitance. As a result of the asymmetry of the electrodes, this technology achieves higher specific energy and specific power [12]. The supercapacitors technology presents several advantages such as this technology is maintenance free, environmentally friendly, has a minimal explosion risk, can operate in a wide range of temperatures without significative changes in the parameters of this technology, a low impedance compared to batteries (what allows this technology to withstand high pulses of energy without lifetime deterioration [10], a high cycle lifetime of about 100,000 cycles [7], 500,000 cycles [9, 10], more than 106 cycles [11]; a high efficiency of 75–95% [7], 60–95% [2], 85–98% [9, 10]; a high specific power of 104 W/kg [10], 500–10,000 W/kg [9], 500–5000 W/kg [7],

56 Table 4.1 Technical comparison of the EES technologies

4 Electrical Storage

Parameter

SMES

SCES

Efficiency (%)

95–98

60–98

Lifetime (cycles)

104 –105

105 –106

Specific power (W/kg)

500–15,000

500–10,000

Discharge time

Milisec-sec

Sec-min

500–2000 W/kg [2]; and a low charging time (in the order of seconds to minutes) [9]. On the other hand, this technology also presents several drawbacks such as a high self-discharge rate, it is not possible to use it for some applications (because during discharging time, its voltage decreases exponentially) [10], it has high costs associated [9], a low rated voltage of 2.7–3 V for EDLC cells (which forces to connect in series a high number of cells if it is desired to use this technology for high voltage applications) [10, 11], a low specific energy of 1.5–2.5 Wh/kg [7], 2.5–15 Wh/kg [2], 1–10 Wh/kg [9], ≈ 10 Wh/kg [11] and a short discharge time (in the order of second to minutes) [9]. Among the possible applications of the supercapacitors technology, it can be used in applications such as transmission lines (due to its ability to adapt to significant power demand variations) [10], uninterruptible power supply (UPS) applications (as an emergency power supply) [9, 10], telecommunications and aircrafts (due to its fast response) [9, 10], aerospace or hybrid electric vehicles (because of its high specific power) [9, 10]. Although supercapacitors have a great potential to be used in many industries in a near future, this technology must face different challenges before this purpose can be achieved, such as to use low cost materials to make supercapacitors, to increase the specific energy of this technology or to reduce their self-discharge rate [9]. In this section, the different electrical energy storage technologies have been introduced. In order to make it easier for the reader to understand and know which is the best technology depending on the required application, in Table 4.1 a technical comparison is made.

References 1. Zakeri B, Syri S (2015) Electrical energy storage systems: a comparative life cycle cost analysis. Renew Sustain Energy Rev 42:569–596. https://doi.org/10.1016/J.RSER.2014.10.011 2. Adetokun BB, Oghorada O, Abubakar SJ (2022) Superconducting magnetic energy storage systems: prospects and challenges for renewable energy applications. J Energy Storage 55. https://doi.org/10.1016/J.EST.2022.105663 3. Chen H, Cong TN, Yang W, Tan C, Li Y, Ding Y (2009) Progress in electrical energy storage system: a critical review. Prog Nat Sci 19:291–312. https://doi.org/10.1016/j.pnsc.2008.07.014 4. Molokac S, Grega L, Rybar P, Rybarova M (2009) SMES MRI device-alternative for ecological energy storage. Clean Technol

References

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5. Mukherjee P, Rao VV (2019) Design and development of high temperature superconducting magnetic energy storage for power applications—a review. Phys C Supercond Its Appl 563:67– 73. https://doi.org/10.1016/j.physc.2019.05.001 6. Amaro N, Pina JM, Martins J, Ceballos JM (2012) Superconducting magnetic energy storage: a technological contribute to smart grid concept implementation. In: SMARTGREENS 2012— Proceedings of 1st international conference on smart grids green IT Systems, pp 113–20. https:/ /doi.org/10.5220/0003978301130120 7. Mitali J, Dhinakaran S, Mohamad AA (2022) Energy storage systems: a review. Energy Storage Sav. https://doi.org/10.1016/J.ENSS.2022.07.002 8. Sabihuddin S, Kiprakis AE, Mueller M (2015) A numerical and graphical review of energy storage technologies. Energies 8:172–216. https://doi.org/10.3390/en8010172 9. Yaseen M, Khattak MAK, Humayun M, Usman M, Shah SS, Bibi S et al (2021) A review of supercapacitors: materials design, modification, and applications. Energies 14:7779. https:// doi.org/10.3390/EN14227779 10. Moftah A, Shetiti A Al (2019) Review of supercapacitor technology 11. Zhao J, Burke AF (2021) Review on supercapacitors: technologies and performance evaluation. J Energy Chem 59:276–291. https://doi.org/10.1016/j.jechem.2020.11.013 12. Joshi PS, Sutrave DS (2019) Supercapacitor: basics and overview

Chapter 5

Electrochemical Energy Storage (EcES). Energy Storage in Batteries

Electrochemical energy storage (EcES), which includes all types of energy storage in batteries, is the most widespread energy storage system due to its ability to adapt to different capacities and sizes [1]. An EcES system operates primarily on three major processes: first, an ionization process is carried out, so that the species involved in the process are charged, then, the mentioned charged species are transported and, finally, the charge is recombined [1, 2]. When talking about an EcES system, batteries are implicitly mentioned, which are electrochemical devices that convert chemical energy into electrical energy [1]. On the other hand, batteries can be classified into two basic types: primary and secondary. The first one is not rechargeable, while the second one can be recharged. According to scientific records, which can be considered the first battery was invented in 1799 by Alessandro Volta, who reported his invention to the Royal Society in London in 1800 [3]. However, the first rechargeable battery, based on lead-acid chemistry, would take years to arrive. In fact, it was not discovered until 1860 by Gaston Planté [4]. This battery, as well as those developed subsequently, contained a liquid electrolyte and it was not until 1881 when Carl Gassner developed the first commercially successful dry cell battery [5]. The following battery to be invented was the Nickel-Cadmium battery (by the Swedish Chemist Waldemar Jungner in 1899) [5], which used caustic KOH as its electrolyte. Many of these systems are still the basis of commercially available batteries today—such is their relevance that most of the single-use (primary) batteries, are based on the alkaline dry cell that was originally invented by Gassner [5]. Afterwards, new designs have been successively appearing, giving name to the different technologies. Thus, in addition to conventional batteries, it is possible to find Molten Salt, Redox Flow and the most recent technology, Metal Air batteries (Fig. 5.1). The emergence of new types of batteries has led to the use of new terms. Thus, the term battery refers to storage devices in which the energy carrier is the electrode, the term flow battery is used when the energy carrier is the electrolyte and the term fuel cell refers to devices in which the energy carrier is the fuel (whose chemical energy © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 J. M. Andújar Márquez et al., Energy Storage Systems: Fundamentals, Classification and a Technical Comparative, Green Energy and Technology, https://doi.org/10.1007/978-3-031-38420-2_5

59

60

5 Electrochemical Energy Storage (EcES). Energy Storage in Batteries

Fig. 5.1 General classification of battery technologies

is converted into electrical energy) [1]. However, some terms can be misleading. In this sense, scientific references, such as [6], consider metal/air batteries as a hybrid between batteries and fuel cells (more specifically, the air cathode battery is considered a fuel cell). Following, a detailed study of existing battery technologies is made with the aim of helping to understand their features and potential applications.

5.1 Conventional Technology Batteries 5.1.1 Fundamental Principles In this group, the batteries included are the most common and the most extended in the market, such as Lead-Acid, Nickel-Cadmium (Ni-Cd) and Lithium-ion (Li-ion) batteries. All of these batteries have in common a redox reaction in which one of the electrodes releases electrons, which are used to supply the load in the external circuit and, after that, are carried to the other electrode. The electrode that releases electrons becomes positively charged (and will release cations to the other electrode through the electrolyte), while the electrode that receives electrons becomes negatively charged (and will release anions to the other electrode through the electrolyte) (Fig. 5.2) [7, 8]. The chemical characteristics and some manufacturers of the three types of batteries that have a cell configuration similar to this conventional design are shown in Table 5.1. Rechargeable lead-acid battery was invented in 1860 [15, 16] by the French scientist Gaston Planté, by comparing different large lead sheet electrodes (like silver, gold, platinum or lead electrodes) immersed in diluted aqueous sulfuric acid; experiment from which it was obtained that in a cell with lead electrodes immersed in the acid, the secondary current that flowed through it was the highest and flowed for the longest period of time. Although that first battery did not have a large capacity, it

5.1 Conventional Technology Batteries

61

(a)

(b)

Fig. 5.2 Cell configuration of a conventional battery during: a charge, b discharge Table 5.1 Conventional batteries. Characteristics and manufacturers Battery

Cell reaction

Manufacturer

Lead-Acid

Anode: Pb + HSO4 − ⇌ 4Pb(II)SO4 + H+ + 2e− Cathode: Pb(IV)O2 + 3H+ + HSO4 − + 2e− ⇌ Pb(II)SO4 + 2H2 O Overall cell: PbO2 + Pb + 2H2 SO4 ⇌ 2PbSO4 + 2H2 O

MK Powered (Anaheim, USA), Exide (Milton, USA), Electro source (Canada), Clarios (Milwaukee, USA), Leoch (China) [9, 10]

NiCd

Anode: Cd + 2OH− ⇌ Cd(OH)2 + 2e− Cathode: 2NiO(OH) + 2H2 O + 2e− ⇌ 2Ni(OH)2 + 2OH− Overall cell: 2NiO(OH) + Cd + 2H2 O ⇌ 2Ni(OH)2 + Cd(OH)2

SAFT (France), ALCAD (Irun, Spain), Raytalk (China), Enersys (Reading, USA), Mouser (Mansfield, USA), HAWKER GmbH (Germany), GAZ (Russia) [10–13]

Li-ion

Anode: Lix C6 ⇌ xLi+ + C6 + xe− Cathode: Li1−x XXO2 + xLi+ + xe− ⇌ LiXXO2 Overall cell: Lix C6 + Li1−x XXO2 ⇌ LiXXO2 + C6

Panasonic (Osaka, Japan), LG Chem, SK Innovation (Seoul, South Korea), A123 Systems (Michigan, USA), Samsung SDI (Yongin, South Korea), CATL (Ningde, China), Toshiba (Tokyo, Japan), AESC (China), Bisco (Anaheim, USA) [10, 14]

62

5 Electrochemical Energy Storage (EcES). Energy Storage in Batteries

attracted the interest of scientists such as Fauré (who coated lead plates with a paste of water, sulfuric acid and red lead oxide), Volckmar (who replaced the lead sheet with a lead grid) or Sellon (who used lead-antimony grids instead of pure lead grids), so the capacity of these batteries was increased. Nowadays, as a result of the rapid development of the automobile after Second World War, which led to an exponential increase in the production of lead-acid batteries, these are used in various vehicles such as aircraft, submarines or hybrid electric vehicles. Nevertheless, these batteries are still under study and present different challenges such as increasing their power performance or their specific energy [15, 16]. On the other hand, the rechargeable Nickel-cadmium (NiCd) battery was created in 1899 by the Swedish chemist Waldemar Jungner. Compared to lead-acid batteries, this battery has drawbacks such as its high initial cost. However, it has other advantages over lead-acid battery such as a lower maintenance, due to higher corrosion resistance [17]. This battery is currently used for portable electronics applications, but one of its major drawbacks is that it is made of toxic materials, so proper management and recycling of those materials is a current challenge for this technology [18]. As for the last group of conventional batteries, experiments for lithium-ion batteries began in 1912, but it was not until 1980 that John B. Goodenough created rechargeable lithium-ion batteries, such as those used in electronic devices around the world [19, 20]. Lithium-ion batteries replaced zinc-mercury batteries used up to the moment in medical devices, such as pacemakers, extending the replacement time from two to five years, and improving the survival rate from 75 to 100% [21].

5.1.2 Mathematical Model Considering charge and discharge models for conventional batteries, in the battery model described by Tremblay et al. (that can be used for lead-acid, NiCd, lithiumion and nickel-metal hydride batteries, for both charge and discharge cycles), the controlled voltage source is described by Eq. (5.1) [22]: V = V0 − K ·

∫ Q ∫ − Relec i + Ae−B idt Q − idt

where: V V0 K Q Relec i A B

battery voltage (V) no-load battery voltage (V) polarization voltage (V) battery capacity (Ah) internal resistance (Ω) battery current (A) exponential zone amplitude (V) inverse of the charge at the end of the exponential zone (Ah)−1 .

(5.1)

5.1 Conventional Technology Batteries

63

In an attempt to obtain the mathematical model based on experimental data, it is first necessary to know V0 , K , A and B. In Fig. 5.3, it is possible to identify the indicated points and obtain their values [22]. With the points in Fig. 2.1 identified, previous parameters will be calculated thanks to Eqs. (5.2)–(5.5). A = V f ull − Vex p B=

3 Q ex p

( ) (V f ull − VNOM + A e−B Q NOM − 1 )(Q − Q NOM ) K = Q NOM V0 = V f ull + K + Relec i − A

(5.2) (5.3)

(5.4) (5.5)

where: V f ull Vex p Q ex p VNOM Q NOM

fully charged battery voltage (V) voltage at the end of exponential zone (V) battery capacity at the end of exponential zone (Ah) voltage at the end of nominal zone (V) battery capacity at the end of nominal zone (Ah).

Based on the above, Table 5.2 shows the typical parameters values for each of the conventional battery types studied in this paper [22].

Fig. 5.3 Typical conventional battery discharge curve

64

5 Electrochemical Energy Storage (EcES). Energy Storage in Batteries

Table 5.2 Conventional batteries-controlled voltage source parameters Battery

Lead-acid (12 V, 1.2 Ah)

NiCd (1.2 V, 1.3 Ah)

Li-ion polymer battery (3.6 V, 1 Ah)

Parameter V0 (V)

12.65

1.25

3.73

R(Ω)

0.25

0.023

0.09

K (V)

0.33

0.0085

0.0088

0.66

0.14

0.47

2884.61

5.77

3.53

A(V) B(Ah)−1

5.1.3 Technical Comparison Currently, the battery industry relies on lithium for its most efficient batteries, but this element is expensive and geographically unsustainable, as most of the current lithium mines are not in ideal locations for the US or Europe. This may be the reason why sodium batteries (see Sect. 5.2.2) are slowly being developed to have the same energy capacity as their lithium counterparts, as these batteries are much cheaper, and the required sodium can simply be extracted from the ocean or practically anywhere, given that it is the sixth most common element in the Earth’s crust [23]. In the beginning, lithium batteries were tested out with a bunch of different cathodes, before settling on the first commercial cathode: magnesium dioxide. Now that both anode and cathode materials have reached a plateau of sorts, the challenge is to further improve the specific energy of batteries and make them more affordable, which will require a lot of effort [24]. From a technical point of view, Li-ion batteries can reach a high lifetime of 1000–10,000 cycles [25, 26], ~ 8000 cycles [27], ~ 10,000 cycles [28], while NiCd batteries can reach a lifetime of > 2000 cycles [25], 2000–2500 cycles [26, 28] and, on the other hand, lead-acid batteries can only reach a lifetime of 500–1500 cycles [26], < 2000 cycles [27], ~ 2500 cycles [28]; Li-ion batteries have the greatest specific energy (80–200 Wh/kg [25], 75–200 Wh/kg [26, 27], ~ 200 Wh/kg [28], 100–265 Wh/kg [29]), compared to lead-acid batteries (30–50 Wh/kg [26], ~ 50 Wh/kg [28], 30–40 Wh/kg [29]) and NiCd batteries (50–75 Wh/kg [25, 29], 45– 80 Wh/kg [26], 55–75 Wh/kg [28]); and Li-ion batteries exhibit higher average round-trip efficiency (< 97% [25], 85–95% [26], 90–95% [27, 30], 85–90% [28], 92–95% [29]) than lead-acid batteries (80% [25], 60–95% [26], ~ 80% [27], 80– 82% [29], 70–90% [30]) and NiCd batteries (60–91% [26], 72% [29]). Furthermore, Li-ion batteries have higher specific power (500–2000 W/kg [25], 400–1200 W/kg [26], 150–3000 W/kg [30]) than Ni-Cd batteries (150–300 W/kg [26]) and lead-acid batteries (75–300 W/kg [26, 30]); and for Li-ion batteries a wider power range can be found (0–50 MW [26], 0–100 MW [30] for Li-ion batteries, compared to 0–40 MW [26] for NiCd batteries and 0–20 MW [26], 0–40 MW [30] for lead-acid batteries) although these three batteries can have a wide power range. Regarding the possible applications of conventional batteries, for lead-acid batteries applications such as

5.2 Molten Salt Batteries

65

Table 5.3 Comparison of the main technical parameters of the different conventional batteries Parameters

Lead-acid

Li-ion

NiCd

Efficiency (%)

60–95

85–97

60–91

Life cycles

500–2500

1000–10,000

2000–2500

Specific energy (Wh/kg)

30–50

75–265

45–80

household Uninterruptible Power Supply (UPS) of the order of few Wh or such as submarine power or load-levelling of the order of several MWh can be found [31], while for Li-ion batteries applications such as portable electronic devices or electric vehicles (EVs) can be found [32] and finally for NiCd batteries applications such as aviation safety, telecommunication network or off-grid PV can be found [33]. Table 5.3 shows a summary of a technical comparison between the different conventional batteries. Table D.1 from Appendix D.1 shows different commercial models for each kind of conventional batteries.

5.2 Molten Salt Batteries 5.2.1 Fundamental Principles Molten salt batteries (ZEBRA batteries and sodium sulphur batteries) are designed to take advantage of the conductivity of sodium ions, higher than 0.2 S/cm at 260 °C and with a positive temperature gradient. Consequently, they are used in applications where the temperature varies between 270 and 350 °C. As for the history of molten salt batteries, ZEBRA batteries were invented in South Africa and were first applied in 1978. For two decades, it was developed by Daimler-Chrysler and its current production depends on MES-DEA [34]. A few years after the appearance of ZEBRA, in 1983, Tokyo Electric Power Company (TEPCO) and NGK Insulators, Ltd. introduced sodium sulphur (NAS) batteries [35]. Both batteries proposals share the cylindrical design which characterizes this kind of batteries and, in both of them, a ceramic electrolyte made from β-Al2 O3 (alumina) transfers the sodium ions between the positive and negative electrodes (Fig. 5.4). In this kind of batteries, there is no side reaction, so there is no charge loss due to the ceramic electrolyte and, consequently, their efficiency is high. The two mentioned proposals can be used in different energy storage applications such as electric vehicles [34, 35]; however, both present a series of disadvantages that are a challenge for the development of both technologies. In the case of ZEBRA batteries, due to the high operation temperature, the development of ZEBRA batteries for automotive applications has been affected, since they present self-discharge issues. In this sense, the combination of ZEBRA batteries with Electrochemical Double Layer Capacitors (EDLCs) is being studied as a possible solution

66

5 Electrochemical Energy Storage (EcES). Energy Storage in Batteries

Fig. 5.4 Cell configuration of molten salt batteries

[36]. On the other hand, NAS battery also presents a high operation temperature that reduces its efficiency, moreover, the solid electrolyte can become brittle and break during operation, which can result in an increased risk of fire and explosion due to the penetration of molten sodium through the cell. In this sense, the use of a ceramic electrolyte and molten electrodes in this kind of batteries presents different challenges such as increasing the safety of their operation or reducing their operating temperature, which limit the applications of this technology [37]. Despite their drawbacks, these kinds of batteries have lifetime and specific energy three and four times respectively, as higher as conventional batteries. In addition, they can provide power peaks in less than 30 s, so they are used in applications where the quality of the power supply is the main decision factor.

5.2.2 Technical Comparison From a technical point of view, ZEBRA batteries can reach a lifetime from 2600 cycles [28] to 4000 cycles [38], while NAS batteries can reach a lifetime of 2500– 4000 cycles [26], 2500–4500 cycles [28, 30]; both batteries have similar operating temperature (265–350 °C [38], 270–350 °C [28] for ZEBRA batteries and 250– 350 °C [25], 300–350 °C [39] for NAS batteries) and high specific energy that is higher for NAS batteries (150–240 Wh/kg [25, 26], 100–240 Wh/kg [30]) than for

5.3 Redox Flow Batteries

67

Table 5.4 Molten salt batteries. Characteristics and manufacturers Battery

Cell reaction

Manufacturer

ZEBRA Anode: Molten MES-DEA (Switzerland), Eurobat (Brussels, Belgium), sodium (Na) FIAMM Sonick (Switzerland), General Electric (Boston, Cathode: Ni and NaCl USA) [10, 34] impregnated with NaAlCl4 Overall cell: NaAlCl4 + 3Na ⇌ 4NaCl + Al NAS

Anode: Sodium (Na) Cathode: Sulfur (S) Overall cell: 2Na + xS ⇌ Na2 Sx

Table 5.5 Comparison of the main technical parameters of the different molten salt batteries

NGK Insulators (Tokyo, Japan), ABB (Zürich, Switzerland), Silent Power (Switzerland), BASF (Ludwigshafen am Rhein, Germany) [10, 35]

Parameters

ZEBRA

NAS

Efficiency (%)

70.7–80.9

75–90

Life cycles

2600–4000

2500–4500

Specific energy (Wh/kg)

100–120

100–240

ZEBRA batteries (approximately 100–120 Wh/kg [33, 38]). However, NAS batteries have a higher round-trip efficiency than ZEBRA batteries (80–90% [25], 75–90% [26], 75–85% [28, 30] versus 70.7–80.9% [38]). On the other hand, NAS batteries present slightly higher specific power (150–230 W/kg [25], 100–230 W/kg [30]) than ZEBRA batteries (150–200 W/kg [25]). Regarding the applications of these types of batteries, ZEBRA batteries can be used in electric and hybrid electric vehicles or energy storage applications, while NAS batteries can be used for wind power integration or high-value grid services [39]. The main features of this kind of batteries are shown in Table 5.4, while a summary of a technical comparison between the different molten salt batteries is shown in Table 5.5. Table D.2 in Appendix D.2 shows molten salt batteries models.

5.3 Redox Flow Batteries 5.3.1 Fundamental Principles The two groups of batteries presented so far have well-defined applications based on their cell structure (conventional batteries for portable applications and molten salt batteries for applications requiring high quality power supply). Nevertheless, none of these previous batteries accomplishes the requirements of the large-scale grid. First, at the grid connection line (a huge physical infrastructure,

68

5 Electrochemical Energy Storage (EcES). Energy Storage in Batteries

with almost no storage capability) grid storage is vital because it must uncouple oscillating customer demand from generation, which has a clear fluctuating character in the case of renewable energy sources. Additionally, grid storage must be able to separate power from energy, tolerate a high number of charge/discharge cycles, to have good round-trip efficiency, to exhibit fast response to load or input changes, and all at reasonable capital costs [40]. Based on the above, a new cell design (Redox Flow Batteries, RFBs are also called Regenerative Fuel Cells, RFBs) was thought of where the reactants are not stored inside the electrode itself (as in previous battery designs), but are dissolved in the electrolyte solution and stored in external tanks (Fig. 5.5) [41]. Then, additional balance-of-plant devices (pump, level sensors, etc.) are needed to make the liquid electrolyte flow. In addition, an Ion Exchange Membrane (IEM) separates the anolyte and catholyte solutions and allows for the transport of charge-carrying species. Furthermore, the IEM can act as an effective barrier to prevent permeation of active species and improve the ionic selectivity of the system by reducing the crosstalk of active species and addressing important drawbacks such as self-discharge or loss of capacity [42]. Additionally, thanks to the fact that there is no physical transfer of material across the electrode/electrolyte interface, the lifetime of this type of batteries is not directly influenced by the depth-of-discharge (DOD), as it is the case in conventional rechargeable batteries. In this type of batteries, the power is determined by the

Fig. 5.5 Cell configuration of redox flow batteries (“Me” refers to reactant dissolved in the electrolyte solution)

5.3 Redox Flow Batteries

69

number of stacked cells and the stored energy depends on the reactants: their nature, their concentration, and the size of tanks. In addition, for one of the batteries of this technology (Zinc Bromide battery), one of the potential risks is the formation of zinc dendrites, which will start their growth if the critical potential value is reached (at that moment, the equilibrium state will be broken and the growth of zinc dendrites will start). Furthermore, the growth of zinc dendrites will be accelerated in case the current density at the electrode surface is high and non-uniform [43]. There are three different electrolytes that form the basis of existing flow batteries designs, currently in demonstration or in development of large-scale projects, which are: Iron-Chromium (IC), Vanadium (VRB) and Zinc Bromide (ZNBR). Within the ZNBR batteries, it is possible to find other variants such as Polysulphide Bromide (PSB), in which the role played by zinc in the anode side is replaced by polysulphide. The main features of the three types of batteries classified as RFB are shown in Table 5.6. As for the history of RFBs, ICBs were pioneered and studied extensively by NASA in the 70s–80s and by Mitsui in Japan [49]. However, the conceptual design of flow batteries was introduced in 1933 in a patent by Pissoort, who described the use of a vanadium redox couple. In the late 1970s, NASA studied flow batteries and considered the Fe-Cr and Fe-Ti redox pair to be the most promising systems. Later, in 1978, Pellegri and Spaziante patented the idea of using vanadium redox salts (without relevant developments), but it was not until 1986 that a group of Australian scientists at the University of New South Wales led by Skyllas-Kazacos achieved the first successful demonstration of a commercial vanadium cell, followed in 1989 by the development of vanadium redox batteries. As for ZNBR batteries, their concept appeared more than a hundred years ago; however, it was not until 1970–1980 when Exxon and Gould brought the first proposals to practical use [45]. Table 5.6 Redox flow batteries. Characteristics and manufacturers Battery

Cell reaction

ICB

Anode: ⇌ + 1e− Cathode: Fe3+ + 1e− ⇌ Fe2+

NASA (Washington D.C., USA), Mitsui Engineering & Shipbuilding Co. Ltd. (Tokyo, Japan), Sumitomo Electric Industries Ltd. (Osaka, Japan) [44]

VRB

Anode: V4+ ⇌ V5+ + 1e− Cathode: V3+ + 1e− ⇌ V2+

University of South Wales (Cardiff, U.K.), UniEnergy Technologies (Mukilteo, USA), Rongke Power (Dalian, China), Kashima-Kita Electric Power Group (Japan), Kansai Electric Company (Osaka, Japan), Hokkaido Electric Power Company (Sapporo, Japan), Fraunhofer Institute (Münich, Germany) Sumitomo Electric Industries, Mitsubishi Chemicals (Tokyo, Japan) [44–46]

ZNBR

Anode: Zn ⇌ Zn2+ + RedFlow (Brisbane, Australia), Jofemar Energy (Peralta, 2e− Spain) [47, 48] Cathode: Br2 + 2e− ⇌ 2Br−

Cr2+

Manufacturer/developer Cr3+

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5 Electrochemical Energy Storage (EcES). Energy Storage in Batteries

Table 5.7 Comparison of the main technical parameters of the different RFBs

Parameters

ICB

VRB

ZNBR

Efficiency (%)

76.3–79.6

65–90

60–85

Life cycles

–

100,000–18,000 2000–10,000

Specific energy 15.8 Wh/L 20–70 Wh/L 10–50 Wh/kg

30–85 Wh/L 30–50 Wh/kg

5.3.2 Technical Comparison From a technical point of view, ZNBRs present the highest specific energy (30– 85 Wh/L [25], 30–60 Wh/L [30], 30–50 Wh/kg [26, 30]) compared to VRBs (10– 50 Wh/kg [25], 10–35 Wh/kg [26], 10–30 Wh/kg [30], 20–70 Wh/L [30]) and ICBs (15.8 Wh/L [50]); ICBs present lower round-trip efficiency (76.3–79.6% [51]) than VRBs (75–85% [25], 85–90% [26], 65–85% [30]) and slightly higher than ZNBRs (65–70% [25], 65–85% [26], 60–65 % [28], 70–80% [30]) and a higher operating temperature (40–60 °C) than VRBs and ZNBRs (10–40 °C) [45, 52]. Finally, redox flow batteries present a high lifetime: 10,000–16,000 cycles [25], 12,000–18,000 cycles [26], > 13,000 cycles [28], 10,000–13,000 cycles [30] for VRBs and > 2000 cycles [26], 2000–10,000 cycles [30] for ZNBRs. Regarding the applications of these batteries, examples can be found such as UPS, interseasonal storage, load levelling function or electric and hybrid vehicles, especially those of large dimensions (due to the low specific energy) [46]. Table 5.7 shows a summary of a technical comparison between the different RFBs. Concerning current trends in redox flow batteries, RFBs can be found to present challenges such as research on the flow management and parameter estimation [46]. Furthermore, the possibility of modifying VRB systems in order to increase the density of the active material and, above all, to find replacements for vanadium, a relatively rare material, is currently being studied [45]. Another challenge faced by redox flow batteries are the limitations associated with IEMs, such as their high costs, safety concerns due to the evolution of toxic intermediates, or temperature limitations due to corrosive gases released at temperatures above 150 °C [53]. Table D.3 in Appendix D.3 shows different commercial models of redox flow batteries.

5.4 Metal–Air Batteries 5.4.1 Fundamental Principles In order to achieve batteries with higher specific energy and lower maintenance than conventional rechargeable batteries, metal-air batteries were developed. These batteries have an open cell structure, i.e., on the one side the electrode is a metal

5.4 Metal–Air Batteries

71

(lithium or zinc) and, on the other side, the electrode is oxygen (regarding the different designs of the cell structures studied along the paper, this last group of metal-air batteries have a cell design that likely approach to fuel cells design), taken from the air, for the reaction to take place. Air is introduced through a channels-based structure and a catalyst ensures oxygen reduction. The intermediate electrolyte allows the flow of ions, and its nature establishes the type of battery: aqueous, non-aqueous, hybrid and solid-state metal–air batteries. In the case of aqueous and hybrid electrolyte, a metal ion conducting polymer membrane is required [54]. The configuration of the different metal–air batteries is shown in Fig. 5.6. Although, there are primary (nonrechargeable) metal–air batteries, such as aluminium–air (Al-air) or magnesium–air (Mg–air) batteries, our study will be focused on secondary (rechargeable) batteries: lithium–air (Li–air) and zinc–air batteries (Zn–air) [55] as shown in Table 5.8. Metal– Air batteries cell configuration.

Fig. 5.6 Metal–air batteries cell configuration

Table 5.8 Metal–air batteries. Characteristics and manufacturers Battery

Cell reaction

Manufacturer

Li-Air

Anode: Li ⇌ + American Chemical Society (Washington, DC., Cathode: Li+ + 1e− + O2 ⇌ LiO2 USA)

Zn-Air

Anode: Zn + 4OH− ⇌ Zn(OH)4 2− + 2e− Cathode: 1/2O2 + H2 O + 2e− ⇌ 2OH−

Li+

1e−

NantEnergy (Scottsdale, USA), Cegasa (Vitoria, Spain), ReVolt (USA), Energizer (Saint Louis, USA)

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5 Electrochemical Energy Storage (EcES). Energy Storage in Batteries

Table 5.9 Summary of the technical parameters of the batteries studied in the paper Comparison of battery storage technologies Characteristics

Conventional batteries

Molten salt batteries

RFBs

Metal–air batteries

Efficiency (%)

60–97

70.7–90

60–90

75

Life cycles

500–10,000

2500–4000

2000–18,000

875 bar) for refuelling fuel cell vehicles [48, 49].

6.2.4 Physisorption The physisorption of gas molecules, Fig. 6.5, onto the surface of a solid, is the result of resonant fluctuations of charge distributions (i.e., Van der Waals interactions, composed of two terms: an attractive and a repulsive one, which decrease with distance, d, in a ratio of d −6 and d −12 , respectively). For this reason, physisorption is weak, and significant physisorption can only be observed at low temperatures (< 273 K) [38]. Porous materials are a potentially promising storage technology for absorbing hydrogen, since they can reach a high capacity and can release the gas reversibly [28, 50]. Among all porous materials, porous carbon materials and

6.2 Hydrogen Storage. Energy Stored in an Invisible Fuel

89

Fig. 6.5 Physisorption process

Metal Organic Frameworks (MOFs) are known to be promising. This technology has advantages such as low cost of materials, high surface area, faster charging and discharging processes or the possibility of mitigating thermal management issues. However, the need for low pressure and temperature, the weight of carrier materials and low gravimetric and volumetric density make the application of this technology difficult. These disadvantages have meant that experiments with this technology have been unsatisfactory; and it is far from be widely used, being only possible to find applications in small-scale experiments [50].

6.2.5 Complex Hydrides Storage Complex hydrides are generally solid ions composed of cations bonded to complex anion groups (centered on Al, B or N, among others), such as AlH4 − , NH2− or NH2 − , through a covalent bond, in which hydrogen participates. Due to slow kinetics reactions, decomposition of complex metal hydrides take place at high temperatures (in the case of LiBH4 , it takes place at 500 °C), while hydriding reaction take place at high pressures (up to 200 MPa) because of a faster reaction rate [51]. Figure 6.6 shows physical process of complex hydrides.

Fig. 6.6 Complex hydrides process

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6 Chemical Energy Storage (CES): How to Store Energy Inside a Fluid

Although complex hydrides are known since 19th century (there is a report [52] on metal amides from 1809), it was not until the 1960s when they were started to be studied as potential hydrogen storage materials [52]. Many years later [53], in the mid-nineties, Bogdanovic discovered hydrogen uptake and release for sodium alanate, NaAlH4 , at moderate conditions. Later, in 2002 [53], P. Chen discovered reversible nitrogen-based complex hydrides and, in 2003, A. Züttel, and co-workers were the first to start investigating tetrahydridoboranates, such as LiBH4 , [53]. For this technology, high volumetric and gravimetric densities can be found (which will be different based on the material used). For example, for ammonia borane, NH3 BH3 , a 19.6 wt.% and a 150 g/L gravimetric and volumetric densities, respectively, are found [54], while for Mg2 FeH6 , a 5.5 wt.% and a 150 g/L gravimetric and volumetric densities, respectively, are found [55]. Furthermore, this technology has a long lifetime, with more than 5000 adsorption/desorption cycles [53]. Although these densities made complex hydrides storage a serious option to store large amounts of hydrogen (up to 700 kg [53]), this technology has to cope with issues such as thermal management (heat removal at several hundred of degrees) during refuelling [54]. This technology can be used in different applications such as on-board hydrogen storage, stationary storage, or portable power [51].

6.2.6 Alkalimetal + H2 O This technology combines a particular case in complex hydrides (which it is made, for this hydrogen storage technique, from alkali or alkaline earth cations bonded to the complex anions introduced above) with water to cause a simple reaction in which hydrogen is obtained as a product [56]. Figure 6.7 shows the physical process of this technology. This technology is far from be implemented, as it is still in the development phase. It was in 2003 that Li et al. generated hydrogen from a reaction between sodium borohydride (NaBH4 ), with a gravimetric density of 10.6 wt.%, and water at an operating temperature of 60 °C [57].

Fig. 6.7 Alkalimetal + H2 O physical process

6.2 Hydrogen Storage. Energy Stored in an Invisible Fuel

91

The materials that can be used for this technique have a wide range for both volumetric and gravimetric densities, varying from 25.86 g/L for CsH to 138.08 g/L for BeH2 in the case of volumetric density, and from 0.75 wt.% for CsH to 18.39 wt.% for LiBH4 in the case of gravimetric density [56]. Furthermore, an advantage of this technology over complex hydrides is a lower operating temperature, for example, the decomposition temperature of NaBH4 to obtain hydrogen is 565 °C [56], while for the reaction of this material with water, the operating temperature is just 60 °C [57]. Due to their higher gravimetric and volumetric densities, together with a higher stability of borohydrides, some of the most promising materials in this technology (still under research), LiBH4 , NaBH4 or Ca(BH4 )2 , among others [56], can be found. Once the different hydrogen storage techniques have been analysed, a comparison has been made between gravimetric and volumetric densities for the different hydrogen storage alternatives, Fig. 6.8 (where alkali metals are treated as a particular case of complex hydrides, but in the case of a reaction with water, the operating temperature is much lower). In addition, Table 6.1 gives a technical comparison between the different commercial hydrogen storage technologies discussed in the paper. Finally, similar to the conventional path of energy production, transmission and distribution shown in Fig. 1.3, in Fig. 6.9, an alternative path is shown, but for green hydrogen production, transmission, storage and final use, with the purpose of highlighting the applications of the currently commercial hydrogen storage technologies. Table E.1 in Appendix E shows commercial examples for hydrogen storage solutions.

Fig. 6.8 Alternatives for hydrogen storage: technical comparative

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6 Chemical Energy Storage (CES): How to Store Energy Inside a Fluid

Table 6.1 Summary of technical parameters of commercial hydrogen storage technologies Technology

Lifetime

Efficiency (%)

Volumetric density (g/L)

Compressed hydrogen storage

20 years

90–95

30

Liquid hydrogen storage 30 years (2025 DOE target)

75–80

70.8

Metal hydrides storage

10 years

85–90

100

Complex hydrides storage

30 years

–

150

Fig. 6.9 Alternative path for green hydrogen production, transmission, storage and use

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Chapter 7

Discussion of Storage Technologies. Keys to Select the Suitable Energy Storage System for Each Use

According to the comprehensive analysis developed along the book, there are different alternatives to energy storage depending on the application required. While it is true that PHES technology currently dominates the energy storage market (in fact, by 2023, the installed capacity for this technology worldwide is expected to be 179 GW [1]), other alternatives are becoming increasingly relevant, although they currently have a much lower installed capacity than PHES technology. Among them, battery storage technology stands out (it is expected to have a global installed capacity of 27 GW by 2023 [1]). Although it is obvious that batteries are widely used (in computers, mobile phones, vehicles), other storage technologies can play a key role in different applications: for example, hydrogen storage can be used in heavy transport (trucks, buses, railways, submarines or spy-planes), or renewable sources-based microgrids. In order to know the use that can be given to different energy storage technologies, in Fig. 7.1, a comparison of the rated power vs the energy stored and the discharge time of different ESS that have been previously introduced in this book is made thanks to the data extracted from [2, 3]; while in Fig. 7.2, a comparison of the applicable power ranges of the storage technologies and the discharge time at rated power is made thanks to the data extracted from [2, 4]. Taking into account Figs. 7.1 and 7.2, it is obvious that there is not a perfect energy storage technology, but there will be more or less suitable technologies depending on the application to be given to them. Thus, although supercapacitors, flywheels and SMES systems offer a high efficiency and a high lifetime, they all have in common that they have a short discharge time and store large amounts of power, but not energy (that is the reason why, although they are commonly named as energy storage technologies, they should be named as power storage technologies); so, these 3 technologies are not available for long term storage (and their application field is severely restricted). On the other hand, technologies such as PHES or CAES can store large amounts of energy and can be used in high power applications (although they present disadvantages such as geographical restrictions in the case of PHES and a reduced efficiency in the case of CAES); so they can be used in large-scale storage © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 J. M. Andújar Márquez et al., Energy Storage Systems: Fundamentals, Classification and a Technical Comparative, Green Energy and Technology, https://doi.org/10.1007/978-3-031-38420-2_7

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Fig. 7.1 Comparison of the different storage technologies based on their rated power, energy stored and discharge time

Fig. 7.2 Comparison of the applicable power ranges and the discharge times at rated power of the different energy storage technologies

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and long term applications (in the case of TES systems, although they can store large amounts of energy and be used in high power applications, they cannot store as much energy as PHES and CAES technologies, on the one hand, and, on the other hand, they present a high self-discharge, due to heat losses). Finally, in recent years it has become clear that the workhorse of energy storage will be between energy storage in batteries and hydrogen storage; therefore, it is not uncommon to find different press headlines [5–8] or journal articles [9, 10] that make mention of it and compare both energy carriers, both for use in transport systems and for use in storage in the electricity grid. For this reason, this section will focus on the comparison of these two energy storage systems, in order to make the reader a clearer picture of what is offered by the so-called energy storage systems of the future. In order to select the best choice of the two energy storage options, the first comparison to be made is the lifetime of the storage systems. For example, for a hydrogen storage system, a lifetime of 5122 cycles can be found for a type III compressed hydrogen tank [11], which is a longer lifetime than most of the batteries (only redox flow batteries and some lithium-ion batteries can present better behaviour in terms of lifetime), while for a metal hydride tank, the lifetime is up to 1500 cycles [12], which is only competitive against some battery technologies such as metal-air batteries or lead-acid batteries. Furthermore, hydrogen storage technologies can be used for long-term storage, because of a negligible self-discharge, which is not the case for batteries (although there are batteries such as Li-ion batteries which have a low self-discharge rate, it is not completely negligible), which are considered as an option for shortmedium term storage [13]. On the other hand, regarding storage systems round trip efficiency, for metal hydride tanks, efficiencies of 88% can be found [14]. Although some batteries can be found with higher round-trip efficiency, this storage system is competitive against battery ones. However, contrary to battery storage systems (which convert electrical energy into electrochemical energy to store energy in the charging process and, in the discharging process, batteries convert electrochemical energy into electrical energy), a hydrogen storage system does not convert the electrical energy into chemical energy in the charging process by itself (as well as it does not convert chemical energy into electrical energy in the discharging process), since a device is needed to produce hydrogen from electrical energy. If green hydrogen (the one obtained via renewable powered electrolysis) is required to be produced, it is necessary to use an electrolyser to produce hydrogen. For an alkaline electrolyser (the most developed electrolysis technology) this process has efficiencies between 43–66% [15]. Furthermore, once the hydrogen is stored in the tank, to obtain electrical energy from it, another device is needed; if that device is a polymeric electrolyte membrane fuel cell, for example, its efficiency will be up to 60% [16]. In this sense, for the whole process (production, storage and conversion into electricity), even if the energy losses associated with storage process (which in the case of metal hydride tanks, are about 12% of the stored energy), the overall efficiency is 25.8–39.6%, while for battery storage systems, the round-trip efficiency varies from 60 to 95%, i.e., between 2 and 4 times the hydrogen process efficiency (even if the losses associated with storage process are ignored). In addition, since the fuel cell efficiency is lower or equal to 60% (i.e.,

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much lower than the whole round-trip efficiency of battery storage systems), the equivalent energy in a hydrogen storage tank needs to be considerably higher than the energy stored in a battery in order to obtain the same electrical energy. Furthermore, although hydrogen systems (i.e., apart from the hydrogen storage, an electrolyser to produce hydrogen and a fuel cell to convert chemical energy from hydrogen into electric energy are needed) hardly can compete with batteries in terms of overall efficiency, in terms of specific energy density, hydrogen has no rival. Hydrogen has a lower heating value of 33.36 kWh/kg, i.e., more than a hundred times batteries specific energy (moreover other ESS do not even come close to reaching that specific energy). Therefore, this fact also allows hydrogen storage systems to complement batteries and be used in renewable sources-based plants as a long-term storage system, while batteries would act as short and medium-term storage system. In fact, in the future, hydrogen energy and batteries are more likely to specialize in two completely different uses—for example, batteries are practical for small devices such as mobile phones and light transport, while hydrogen storage is suitable for stationary applications and heavy transport. Furthermore, the increase in global energy demand, along with the need to reduce dependence of fossil fuel, makes the integration of RES unavoidable. However, these systems are not always available (for example, solar energy is not available at night, or wind energy is not available when it is not windy). In that sense, ESS can be a solution to integrate RES, to improve power system security (because in case of failure of the main power grid supply, they can guarantee the load energy demand), or as a way to guarantee auxiliary services (such as battery banks in hospitals). Moreover, the different ESS reduce the need of additional resources for transmission. They also improve system efficiency, due to that they allow the system to guarantee the load energy demand when RES are not available, and a better use of existing resources due to a more controlled security and supply and production. Lastly, these systems can reduce the investment costs required for new installations. This book has presented different energy storage systems which can be used in the future, making special emphasis in hydrogen storage technologies and battery storage technologies, offering the technical parameters, the benefits and the drawbacks of the different ESS that have been explained along the book. With that information, the reader is able to know the best energy storage to choose depending on the needed application.

References 1. International Energy Agency (n.d.) Cumulative installed storage capacity, 2017–2023— Charts—Data & Statistics—IEA. https://www.iea.org/data-and-statistics/charts/cumulativeinstalled-storage-capacity-2017-2023. Accessed 2 Mar 2023 2. Hossain E, Faruque HMR, Sunny MSH, Mohammad N, Nawar N (2020) A comprehensive review on energy storage systems: types, comparison, current scenario, applications, barriers, and potential solutions, policies, and future prospects. Energies 13:1–127. https://doi.org/10. 3390/en13143651

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3. Bignucolo F, Caldon R, Coppo M, Pasut F, Pettinà M (2017) Integration of lithium-ion battery storage systems in hydroelectric plants for supplying primary control reserve. Energies 10. https://doi.org/10.3390/EN10010098 4. Sprake D, Vagapov Y, Lupin S, Anuchin A (2017) Housing estate energy storage feasibility for a 2050 scenario. In: 2017 internet technologies and applications (ITA): proceedings of the seventh international conference, pp 137–42. https://doi.org/10.1109/ITECHA.2017.8101925 5. Jones A, Neilson M (2021) Battery electric vs hydrogen—which is the future for electric vehicles? Lexology 6. Fletcher C (2022) Hydrogen vs. electric cars: comparing innovative sustainability. Earth Org Earth 7. Meyer G, Thomas N (2021) Hydrogen: the future of electricity storage? Financial Times 8. Yap L, Thomson L (2022) Is green hydrogen the future of energy storage? AZO Cleantech 9. Ferrario AM, Vivas FJ, Manzano FS, Andújar JM, Bocci E, Martirano L (2020) Hydrogen vs. battery in the long-term operation. A comparative between energy management strategies for hybrid renewable microgrids. Electron 9. https://doi.org/10.3390/electronics9040698 10. Pellow MA, Emmott CJM, Barnhart CJ, Benson SM (2015) Hydrogen or batteries for grid storage? A net energy analysis. Energy Environ Sci 8:1938–1952. https://doi.org/10.1039/C4E E04041D 11. Zhang M, Lv H, Kang H, Zhou W, Zhang C (2019) A literature review of failure prediction and analysis methods for composite high-pressure hydrogen storage tanks. Int J Hydrogen Energy 44:25777–25799. https://doi.org/10.1016/J.IJHYDENE.2019.08.001 12. Bhattacharyya R, El-Emam RS, Khalid F (2022) Multi-criteria analysis for screening of reversible metal hydrides in hydrogen gas storage and high pressure delivery applications. Int J Hydrogen Energy 47:19718–19731. https://doi.org/10.1016/J.IJHYDENE.2021.12.168 13. Marocco P, Novo R, Lanzini A, Mattiazzo G, Santarelli M (2023) Towards 100% renewable energy systems: the role of hydrogen and batteries. J Energy Storage 57. https://doi.org/10. 1016/J.EST.2022.106306 14. Ni M (2006) An overview of hydrogen storage technologies. Energy Explor Exploit 24:197–209 15. Renewable Energy Agency (2021) Making the breakthrough: green hydrogen policies and technology costs 16. Andújar JM, Segura F (2009) Fuel cells: history and updating. A walk along two centuries. Renew Sustain Energy Rev 13:2309–22. https://doi.org/10.1016/j.rser.2009.03.015

Appendix A

Mechanical Energy Storage Technology

In this appendix, different examples of mechanical energy storage systems that are currently under operation can be found (Table A.1). Table A.1 Examples of MESS currently under operation PHES Model: Fengning Pumped Storage Power Station (China) [1] Energy stored: 18 GWh/day Rated power: 3.6 GW Investment: 1.85 billion e (1 e = 1.01 $, 3 August 2022)

Model: Ghatghar Pumped Storage power plant (India) [2, 3] Energy stored: 469.5 GWh/year Rated power: 250 MW Investment: 83 million e (1 e = 137 JPY, 3 August 2022) Storage capacity: 3.21 million m3

(continued)

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 J. M. Andújar Márquez et al., Energy Storage Systems: Fundamentals, Classification and a Technical Comparative, Green Energy and Technology, https://doi.org/10.1007/978-3-031-38420-2

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Table A.1 (continued) Flywheel Model: NASA G2 Flywheel [4] Energy stored: 525 Wh Rated power: 1 kW Speed: 60,000 rpm Dimensions: 305 (F) mm × 762 mm (1 inch = 25.4 mm) Weight: 99 kg (1 pound = 0.45 kg)

Model: AFS-Trinity System [5] Energy stored: 2 kWh Rated power: 200 kW Speed: 40,000 rpm Weight: 540 kg Lifetime: 100,000 cycles

CAES D-CAES [6–9] Model: Huntorf plant Energy stored: 1160 MWh Rated power: 321 MW Total volume: 310,000 m3 Efficiency: 42% Maximum pressure: 100 bar Model: McIntosh plant Energy stored: 2640 MWh Rated power: 110 MW Total volume: 560,000 m3 Efficiency: 54% Maximum pressure: 76 bar A-CAES [10, 11] Model: Goderich, Ontario, Canada plant Energy stored: 7 MWh Rated power: 1.75 MW (discharge), 2.2 MW (charge) Efficiency: > 60%

Appendix B

Thermal Energy Storage Technology

In this section, two examples of TES systems (integrated with a CSP system) currently under operation are found (Table B.1). Table B.1 Examples of CSP systems with TES systems incorporated currently under operation CSP + TES Model: PS10 plant (Sanlúcar la Mayor, Seville, Spain) [12–16] Energy generated: 24.3 GWh/year Energy stored: 20 MWh, 50 min Rated power: 11 MW Solar field: 60 ha Storage material: Pressurized water Cost: 57 million e

Model: PS20 plant (Sanlúcar la Mayor, Seville, Spain) [12, 14, 17] Energy generated: 44 GWh/year Rated power: 20 MW Solar field: 80 ha Storage material: Pressurized water Cost: 90 million e

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 J. M. Andújar Márquez et al., Energy Storage Systems: Fundamentals, Classification and a Technical Comparative, Green Energy and Technology, https://doi.org/10.1007/978-3-031-38420-2

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Appendix C

Electrical Energy Storage Technology

For electrical storage systems, in Table C.1, different commercial examples of the supercapacitor technology (currently commercially available) can be found. Table C.1 Commercial examples of supercapacitors Electrical energy storage SCES Model: CDCL1500C0-002R85STZ Ultracapacitor cell Energy stored: 1.69 Wh Rated power: 240 W Dimensions: 60.8 (F) mm × 85 mm Weight: 342 g Lifespan: 1,000,000 cycles Cost: 48.68 e Supercapacitors technology: EDLC Model SM0165-048-ATH Energy stored: 52.8 Wh Rated power: 46,079 W Dimensions: X-418 mm, Y-198 mm, 180 mm Weight: 14.2 kg Lifespan: 1,000,000 cycles Cost: 861.31 e Supercapacitors technology: EDLC Data provided by the manufacturer

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Appendix D

Electrochemical Energy Storage Technology

Appendix D.1. Conventional Battery Technology The batteries included in this group are the most common and the most extended in the market, like Lead-Acid, Nickel-Cadmium and Lithium-ion batteries. All of them have in common a redox reaction in which one of the electrodes releases ions and the electrolyte carries them to the other side (Table D.1).

Appendix D.2. Molten Salt Battery Technology The batteries included in this group are characterized by their high operating temperature and high specific energy. Both ZEBRA and NAS batteries have in common a cylindrical cell structure where molten salts and alumina are used for electrode and electrolyte respectively (Table D.2).

Appendix D.3. Redox Flow Battery Technology This type of battery is characterized by the fact that the electrolyte is stored in a tank that is separated from the own cell structure. Additionally, there is no material transfer between electrode and electrolyte, so the lifetime is independent of DOD (Table D.3).

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 J. M. Andújar Márquez et al., Energy Storage Systems: Fundamentals, Classification and a Technical Comparative, Green Energy and Technology, https://doi.org/10.1007/978-3-031-38420-2

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Appendix D: Electrochemical Energy Storage Technology

Table D.1 Commercial examples of conventional batteries Lead-acid Model: 6GFMJ-65 Battery capacity: 65 Ah/12 V Lifetime: ≥ 10 years Dimensions: X-350 mm, Y-166 mm, Z-174 mm Weight: 21.4 kg Cost: 57 e Model: EP200-12 Battery capacity: 200 Ah/12 V Lifetime: 3–5 years Dimensions: X-533 mm, Y-250 mm, Z-240 mm Weight: 62.95 kg Cost: 201.87 e (1 | = 0.012 e (3 August 2022)) Nickel–cadmium Model: N-3000CR Battery capacity: 3000 mAh/1.2 V Lifetime: 1 cycle Dimensions: Diameter-26 mm, Height-50 mm Weight: 86 g Cost: 6.86 e Model: VNT D U HC Battery capacity: 4500 mAh/1.2 V Lifetime: ≥ 4 years (55 °C) Dimensions: Diameter-32.15 mm, Height-59.9 mm Weight: 124 g Cost: 25.40 e (1 £ = 1.20 e (3 August 2022)) Lithium-ion Model V-LYP400Ah 3.2 V Stored energy: 1.2 kWh Lifetime: 2000 cycles Dimensions: X-460 mm, Y-285 mm, Z-65 mm Weight: 13.5 kg Cost: 550 e Model: LG Chem RESU10H Energy stored: 9.8 kWh Battery capacity: 189 Ah Lifetime: ≥ 10 years Dimensions: X-452.12 mm, Y-482.6 mm, Z-226.06 mm Weight: 74.9 kg Cost: 5996.3 e (1 $ = 1.01 e (3 August 2022)) Data provided by the manufacturer

Appendix D: Electrochemical Energy Storage Technology Table D.2 Commercial examples of Molten Salt batteries ZEBRA Model ZEBRA Z5278-ML3X-64 Stored energy: 17.8 kWh Lifetime: 3500 cycles Dimensions: X-826 mm, Y-530 mm, Z-295 mm Weight: 182 kg Cost: 1500 e Model: FZSonick ST523 Battery capacity: 38 Ah/620 V Stored energy: 22.5 kWh Lifetime: > 4500 cycles (80% DOD) Dimensions: X-624 mm, Y-406 mm, Z-1023 mm Weight: 256 kg Cost-18,000 e NAS Model: BASF NAS® Battery Stored energy: 1450 kWh Lifetime: 20 years; 4000 cycles Dimensions: X-6058 mm, Y-2438 mm, Z-2591 mm Weight: 21 tons Cost: Non available

Data provided by the manufacturer

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Table D.3 Commercial examples of redox flow batteries ICB Model Enervalut Proyect Nominal power: 250 kW Lifetime: research Weight: tonnes Cost: Investment 4672,900 e ZnBr Model: ZBM2 Stored energy: 10 kWh Lifetime: 10 years Dimensions: X-830 mm, Y-823 mm, Z-400 mm Weight: 240 kg Cost: 7921 e (1 $ = 1.01 e (3 August 2022)) Model: ZBM3 Stored energy: 10 kWh Lifetime: 10 years Dimensions: X-861 mm, Y-747 mm, Z-400 mm Weight: 240 kg Cost: 8713 e (1 $ = 1.01 e (3 August 2022))

VRB Model: RFB40X P1 Nominal power: 40 kW Stored energy: 40 kWh Lifetime: > 20 years Dimensions: X-2300 mm, Y-1400 mm, Z-1900 mm Weight: 3400 kg Cost: 44,780.6 e (1 | = 0.012 e (3 August 2022)) Model: E22 VRB Battery Nominal power: 50 kW Stored energy: 200 kWh Lifetime: > 10,000 cycles; > 20 years Dimensions: X-6000 mm, Y-2400 mm, Z-2600 mm Weight: 24,000 kg Cost: Non available Data provided by the manufacturer

Appendix D: Electrochemical Energy Storage Technology

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Table D.4 Commercial examples of metal-air batteries Li-Air Model Li -Air 500 mAh Samsung Electronics Battery capacity: 500 mAh Lifetime: 7 cycles Dimensions: X-70 mm, Y-10 mm, Z-23 mm Weight: 35 mg Cost: Non available Zn-Air Model DQFC 24/24–125 Stored energy: 2.88 kWh Lifetime: 300 cycles Dimensions: X-410 mm, Y-220 mm, Z-240 mm Weight: 21.8 kg Cost: 300 e Data provided by the manufacturer

Appendix D.4. Metal-Air Technology This type of battery is characterized by an open cathode structure, where air enters and, in the presence of a catalyst, oxygen reacts with the metal-ions. This allows to increase the specific energy with respect to conventional rechargeable batteries (Table D.4).

Appendix E

Chemical Energy Storage: Hydrogen Storage

In this Appendix, authors show commercial examples of hydrogen storage devices. Nowadays, it is possible to find two commercial options for hydrogen storage: compressed hydrogen storage and metal hydride storage (Table E.1). Table E.1 Commercial examples of hydrogen storage Compressed gas hydrogen storage Model B50 Stored energy: 26.7 kWh Vol. H2 : 8900 NL Vol. bottle: 50 L Pressure: 200 bar Dimensions: H-1680 mm, Ø-230 mm Weight: 85 kg Cost: 200 e annual contract Metal hydride storage Model Hbond 5000 L Stored energy: 15 kWh Vol. H2 : 5000 NL Vol. bottle: 98.6 L Pressure: 15 bar Dimensions: H-1100 mm, Ø-169 mm Weight: 76 kg Cost: 10,000 e Data provided by the manufacturer

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© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 J. M. Andújar Márquez et al., Energy Storage Systems: Fundamentals, Classification and a Technical Comparative, Green Energy and Technology, https://doi.org/10.1007/978-3-031-38420-2

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