Preface

Thermal energy storage (TES) refers to a method that stores energy in thermal forms (heat or cold) and uses the stored thermal energy either directly or indirectly through an energy conversion process when needed. The importance of TES is reflected by at least five aspects: (a) approximately 90% of current global energy budget centres around thermal energy generation, conversion, storage and transmission; (b) thermal energy accounts for over 50% of the world's final energy consumption with only ∼10% currently from renewable sources; (c) the dispatchability of some renewable generation — particularly concentrated solar power — requires TES; (d) TES is one of the most flexible and cost-effective methods for peak-shaving of nuclear power plants; and (e) some of the most advocated emerging energy technologies have low efficiency with respect to primary energy sources, for example, electric vehicles (<∼20%), hydrogen and fuel cell technology (below ∼10%) and carbon capture and storage (<∼70% for compression and transportation) with the rest exhausted as heat. TES therefore has a significant role to play in future low-carbon and even net-zero-carbon energy systems.

TES technologies are usually classified according to the materials used for storing thermal energy. There are three categories, namely sensible heat storage (SHS, based on the temperature change of the TES material), latent heat storage (LHS, based on the phase change of the TES material) and thermochemical storage (TCS, based on sorption and/or reversible chemical reactions). SHS is a relatively mature and already widely deployed technology; LHS has recently been used in industrial applications; while TCS is still at the early stage of fundamental research. TES technologies account for over 50% of global non-pumped hydro installations.

This book covers all three TES technologies, including materials, devices, systems and applications. It is intended for use by senior undergraduates and graduates at Masters and PhD levels as a textbook, as well as researchers and practicing engineers as a reference book. It aims to be distinctive from other TES-related books in terms of the breadth (covering materials, devices, systems and applications), coherence (linking materials properties to system-level performance) and uniqueness (including modelling across length scales, materials formulation, manufacture and quality control).

There are 14 chapters in this book. Chapter 1 introduces the classical thermodynamics concepts and laws relevant to thermal energy storage. Chapter 2 outlines the basic concepts of transport phenomena and associated conservation equations and constitutive relationships, which dictate the rates of transferring mass, momentum and energy in thermal energy storage systems. Chapters 3 and 4 discuss sensible and latent heat storage materials, respectively; whereas Chapters 5 and 6 deal with sorption and reversible chemical reaction-based thermochemical storage materials, respectively. Chapter 7 discusses extensively the manufacturing of thermal energy storage materials, covering formulation, manufacturing processes, scale-up and quality control. This is unique in TES-related books and is one of the two longest chapters of the book. Chapter 8 delves into modelling of thermal energy storage materials at the molecular scale, which is also unique in TES-related books. Chapters 9–11 discuss sensible heat, latent heat and thermochemical storage devices, respectively. Chapter 10 is the second long chapter of this book due to the significant progress in the development of latent heat storage technology over the past decade, particularly commercial deployment of high-temperature composite phase changer materials that started in 2016. Chapter 12 describes modelling of thermal energy storage at the device scale in detail, where all the materials presented are new. Chapter 13 covers thermal energy storage applications through integration and Chapter 14 discusses modelling of thermal energy storage at a system scale including optimisation.

Although each of the 14 chapters were independently written and are therefore self-contained, they can be grouped into four fundamentally related parts: TES fundamentals (Chapters 1 and 2), TES materials (Chapters 3–8), TES devices (Chapters 9–12) and TES systems and applications (Chapters 13 and 14). The interconnection is also reflected in Chapters 8, 12 and 14, which deal with multiscale modelling at the material, device and system scales, respectively. Efforts have also been made to cross reference where appropriate. As a result, this book is not entirely an edited book, but rather lies somewhere between an authored and an edited book.

It would not have been possible to complete this book without the help and support from many people as well as funding agents. I used to take the acknowledgements as a routine duty of authors until all the chapters have been completed and uploaded when I felt this part is what I wanted to write most. Clearly this book builds on the work of others for which the acknowledgements are through references, and the contributors’ own efforts for which I would like to thank them all. Personally, I wish to thank all my current and previous research group members at the University of Birmingham Centre for Energy Storage and at the University of Leeds Institute of Particle Science & Engineering and my collaborators at the Institutes of Engineering Thermophysics and Process Engineering of Chinese Academy of Sciences, and University of Science & Technology Beijing. I thank the UK Engineering and Physical Sciences Research Council, the Royal Academy of Engineering, the UK Department for Business, Energy and Industrial Strategy, the Royal Society and many industrial companies. Particular thanks are due to the Royal Academy of Engineering and Highview Power for a five-year industrial professorship from 2014 to 2019. I also wish to thank the Royal Society of Chemistry for their professionalism and help in producing this well-presented volume. I would like to thank my family and friends for their moral support. Most of all, my thanks go to my wife Huixia and our son Weixuan, for all their help, understanding and tolerance over these long months of putting the book together.

Yulong Ding

Edgbaston

Birmingham