Heat and Cold Storage, Volume 1 E-Book
142,99 €
Mehr erfahren.
- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Serie: ISTE Consignment
- Sprache: Englisch
Heat and Cold Storage 1 is dedicated to sensible and latent heat storage processes.
Beginning with some theoretical reminders, this book presents the main situations of low-temperature and high-temperature sensible storage for electricity generation. It also analyzes latent storage on phase-change materials (PCMs) from a fundamental standpoint, presenting the mechanisms to prepare PCMs and their integration into heat and cold storage processes. The most promising materials are presented, along with ways of improving the materials studied. Notions of technico-economic profitability are also defined.
Finally, the book looks at heat storage in thermodynamic solar power plants and the wide variety of physical storage principles involved.
Sie lesen das E-Book in den Legimi-Apps auf:
Seitenzahl: 429
Veröffentlichungsjahr: 2024
Ähnliche
Table of Contents
Cover
Table of Contents
Title Page
Copyright Page
Foreword
1 Sensible Heat Storage: Overview
1.1. Introduction
1.2. General principles
1.3. Storage configurations
1.4. Modeling of thermocline storage
1.5. References
2 Low-Temperature Sensible Heat Storage
2.1. Sensible heat storage associated with buildings
2.2. Underground thermal energy storage
2.3. References
3 High-Temperature Heat Storage for Electricity
3.1. Heat storage associated with compressed air electricity storage
3.2. Electricity storage by Carnot batteries
3.3. References
4 Latent Heat Storage: Fundamentals and Most Widely Used Phase Change Materials
4.1. Fundamentals of latent heat storage
4.2. Phase change materials classification and criteria for selection
4.3. Commonly used PCMs
4.4. Tecno-economic evaluation
4.5. Emerging alternative materials
4.6. References
5 Engineering Phase Change Materials to Improve Their Properties and Broaden Applications
5.1. Introduction
5.2. Micro-/nanoencapsulated PCMs
5.3. Shape-stabilized PCMs
5.4. Conclusion
5.5. References
6 Latent Heat Storage Systems: Concepts and Applications
6.1. Introduction
6.2. Types of systems and main components
6.3. Cold storage
6.4. Applications in the building sector
6.5. Applications in industry
6.6. Concentrated solar power plants
6.7. Other domains
6.8. Conclusion
6.9. References
7 Use of Hydrates for Cold Storage and Distribution in Refrigeration and Air-Conditioning Applications
7.1. Introduction
7.2. Hydrate definition and properties
7.3. Hydrate systems for cold storage and distribution
7.4. Criteria for use of hydrates in refrigeration
7.5. Hydrate applications in refrigeration and air-conditioning
7.6. Conclusion
7.7. References
8 Concentrated Solar Power Plants and Storage
8.1. Introduction
8.2. Concentrated solar power plants and storage
8.3. Storage types
8.4. Analysis of systems
8.5. References
List of Authors
Index
Summary of Volume 2
End User License Agreement
List of Tables
Chapter 2
Table 2.1. Thermal characteristics of materials
Table 2.2. Thermal characteristics of rocks and soils
Chapter 3
Table 3.1. Characteristics measured for a range between ambient temperature an...
Table 3.2. Energy stored by tonne in the given conditions
Table 3.3. Characteristics of a thermal pumping system
Chapter 4
Table 4.1. Latent heat storage material classification attending to their chem...
Table 4.2. Main desirable characteristics for a latent heat storage material
Table 4.3. The main characteristic according to the PCM classification (based ...
Table 4.4. Example of the current existing PCM manufacturers and suppliers
Chapter 5
Table 5.1. Frequently encountered problems, consequences and examples of conce...
Table 5.2. Selection of recent reviews on ME-PCMs and SS-PCMs
Table 5.3. Examples of core–shell encapsulated organic PCMs with exceptionally...
Table 5.4. Examples of the effect of paraffin wax’s nano-encapsulation on the ...
Table 5.5. Examples of core–shell nano-encapsulated salt hydrates
Table 5.6. Additional benefits that can be obtained from SS-PCMs compared to b...
Table 5.7. Short description of common porous clay mineral materials
Table 5.8. PCM loading ranges in studied porous clay mineral-based SS-PCMs (PW...
Table 5.9. Silica-based SS-PCMs. Aggregated data from (Mitran et al. 2021): Tm...
Table 5.10. Summary of main assets and disadvantages of commonly used porous s...
Chapter 6
Table 6.1. Comparison of various CTESS (adapted from Wang and Kusumoto (2001))
Table 6.2. Characteristics of latent heat storage technologies depending on se...
Chapter 7
Table 7.1. Characteristics of hydrate structures
Table 7.2. Thermodynamic properties of PCMs suitable for secondary refrigerati...
Table 7.3. Work on the rheology of hydrate slurry; Bold: work on refrigeration...
Table 7.4. Convective heat transfer coefficient (CHTC) for various slurries an...
Chapter 8
Table 8.1. Data on the reactions studied for thermochemical storage at tempera...
Table 8.2. Solid and liquid materials for sensible heat storage
Table 8.3. Materials resulting from waste for sensible heat storage
Table 8.4. Phase change materials for latent heat storage
Table 8.5. Thermochemical materials and reactions
Table 8.6. Costs of materials for the storage system (according to Heller et a...
List of Illustrations
Chapter 1
Figure 1.1. Various sensible heat storage configurations.
Figure 1.2. Dual media heat storage.
Figure 1.3. Lumped heating of a solid by a fluid
Figure 1.4. Charge of a packed granular bed thermocline storage system.
Chapter 2
Figure 2.1. Maxlean combined heating system.
Figure 2.2. ATES closed loop (IEA-DHC 2018). (a) Winter mode; (b) Summer mode.
Figure 2.3. Drake Landing Solar Community storage system: general layout
1
.
Chapter 3
Figure 3.1. Daily consumption of electricity in France
Figure 3.2. France: wind energy output 2017
Figure 3.3. CAES Installation in Huntorf
Figure 3.4. Example of ACAES with two compression stages
Figure 3.5. Layout of caverns and their communications.
Figure 3.6. CLAIRE loop of CEA.
Figure 3.7. Liner inside the cavern.
Figure 3.8. Progression of the thermal front in TES and breakthrough time
Figure 3.9. Modified Brayton cycle during the storage phase
Figure 3.10. Modified Brayton cycle in discharge phase
Figure 3.11. Energy balances of the storage and discharge phases
Figure 3.12. Storage efficiency depending on the maximal temperature and on th...
Figure 3.13. Artist view of a 10 GWh thermal pumping system
Figure 3.14. Brayton cycle variant with liquid exchangers
Chapter 4
Figure 4.1. Examples of transformations involving an enthalpy change
Figure 4.2. Illustration of a first-order phase change, occurring at constant ...
Figure 4.3. Illustration of a second-order phase change, associated with non-c...
Figure 4.4. Latent heat storage materials classification attending to their co...
Figure 4.5. Scheme of temperature levels and its relation to thermal power dur...
Figure 4.6. Scheme of temperature levels and its relation to required heat exc...
Figure 4.7. Main approaches found in literature to enhance the heat transfer i...
Chapter 5
Figure 5.1. Examples of characteristic dimensions and morphologies of PCMs emb...
Figure 5.2. SEM images of spherical-shaped PCM microcapsules (Song et al. 2007...
Figure 5.3. Classification of microencapsulation methods (Peng et al. 2020)
Figure 5.4. Examples of additional functions of ME-/NE-PCMS that can be achiev...
Figure 5.5. Microencapsulated PCMs with micro-nanostructured shells: (a) nanof...
Figure 5.6. Classification of extensively investigated SS-PCMs according to th...
Figure 5.7. 3D porous graphene structures and SS-PCMs. Scheme for the preparat...
Figure 5.8. Confining PCM within CNTS (A). SEM images of empty (right) and inf...
Figure 5.9. Illustration of highly graphitized carbon foam preparation method ...
Figure 5.10. SEM images of EG at different magnifications (Tao et al. 2015)
Figure 5.11. SEM images of (A) calcined diatomite, (B) sepiolite (C) montmoril...
Chapter 6
Figure 6.1. Scientific and technological challenges related to TESS design
Figure 6.2. Classification of various storage systems based on storage concept...
Figure 6.3. PCM families according to temperatures and transition enthalpies.
Figure 6.4A. Schematic representation of various types of cold storage (adapte...
Figure 6.5. Configuration of a Trombe wall with PCM (adapted from Omara and Ab...
Figure 6.6. Operating principle of the system with storage heat exchanger: (a)...
Figure 6.7. Schematic representation of a combined water heating system with h...
Figure 6.8. Schematic representation of a CSP plant integrating a LH-TESS (ada...
Figure 6.9. Storage systems integrated in CSP plants (adapted from Pelay et al...
Figure 6.10. Typical LH-TESS that can be used in a CSP plant (adapted from Pel...
Chapter 7
Figure 7.1. Illustration on a microscopic scale of different kinds of slurry: ...
Figure 7.2. Representation of a gas hydrate (Marum 2009)
Figure 7.3. Structure of a mixed gas + TBAB hydrate (Shimada et al. 2005).
Figure 7.4. Phase diagram (P, T) of water–CO
2
mixture
Figure 7.5. Lw-H-V equilibrium conditions of water-CO2, water-CO2-salt (with s...
Figure 7.6. Dissociation enthalpies of mixed hydrates of CO2 + additive (with ...
Figure 7.7. CFC-12 hydrate-based cool storage system (Mori et al. 1989a)
Figure 7.8. Air-conditioning system by TBAB hydrate slurry for NKK Corporation...
Figure 7.9. Refrigerant hydrate-based refrigeration system (Ogawa et al. 2006)
Figure 7.10. CO2 hydrate-based refrigeration loop (Jerbi et al. 2010b; Dufour ...
Figure 7.11. Management of vapor release in CO2-hydrate-based refrigeration pr...
Figure 7.12. Carbon dioxide hydrate-based vapor-compression refrigeration syst...
Chapter 8
Figure 8.1. Solar concentration principles.
Figure 8.2. Thémis solar tower power plant, Targasonne, Eastern Pyrenees....
Figure 8.3. Main types of concentrated solar power plants.
Figure 8.4. Daily electric production of a solar power plant with thermal stor...
Figure 8.5. Energy model of solar power plant.
Figure 8.6. Map of direct normal irradiation.
Figure 8.7. Solar multiple
Figure 8.8. Relation between the capacity factor and the solar multiple depend...
Figure 8.9. Types of active or passive storage and direct or indirect circulat...
Figure 8.10. Operation of a two-tank active storage system
Figure 8.11. Andasol power plant, Andalusia, Spain.
Figure 8.12. Principle of PS10 power plant, Seville, Spain.
Figure 8.13. Thermocline storage operation.
Figure 8.14. Schematic representation of the latent heat storage prototype – D...
Figure 8.15. Schematic representation of the prototype: (a) sandwich PCM/ grap...
Figure 8.16. Composite configuration with graphite fin
Figure 8.17. Three layer latent/sensible/latent configuration
Figure 8.18. Principle of thermochemical storage.
Figure 8.19. Two-tank thermal storage equipment
Figure 8.20. Shell and tube heat exchanger.
Figure 8.21. Molten salt pump (Sulzer© VEY molten salt pump)
1
Figure 8.22. Horizontal pump for synthetic oil.
Figure 8.23. Storage tank, Gemasolar.
Figure 8.24. Molten salt tank
Figure 8.25. Gemasolar power plant with its two-tank storage.
Figure 8.26. Schematic representation of the Andasol power plant.
Figure 8.27. Fluidized particles storage.
Figure 8.28. Steam accumulator
Figure 8.29. Thermodynamic diagram of water
Figure 8.30. PS10 power plant with its steam accumulators.
Figure 8.31. Power plant with steam accumulator without water circulation.
Figure 8.32. Power plant with steam accumulator with water circulation.
Figure 8.33. Charge of a thermocline storage.
Figure 8.34. Modeling of thermocline storage by filters in series
Figure 8.35. Temperature profiles in a thermocline with various dimensionless ...
Figure 8.36. Thermocline outlet fluid temperature of MicroSol-R (PROMES) power...
Figure 8.37. Output temperature of the thermocline tank of MicroSol-R (PROMES)...
Figure 8.38. Thermal storage with mixed filler materials of Solar One power pl...
Figure 8.39. RHTS design
Figure 8.40. Storage for DSG power plant combining sensible heat and latent he...
Figure 8.41. Two-story storage of DSG power plant in Badaling (China)
Figure 8.42. Distribution of two-tank storage costs
Figure 8.43. Greenhouse gas emissions of two types of thermal storage: two mol...
Guide
Cover Page
Title Page
Copyright Page
Foreword
Table of Contents
Begin Reading
List of Authors
Index
Summary of Volume 2
WILEY END USER LICENSE AGREEMENT
Pages
iii
iv
ix
x
xi
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
SCIENCES
Energy, Field Directors – Alain Dollet and Pascal Brault
Heat and Cold Storage, Subject Head – Philippe Marty
Heat and Cold Storage 1
Sensible and Latent Storage
Coordinated by
Pierre Odru
Elena Palomo del Barrio
First published 2024 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:
ISTE Ltd27-37 St George’s RoadLondon SW19 4EUUKwww.iste.co.uk
John Wiley & Sons, Inc.111 River StreetHoboken, NJ 07030USAwww.wiley.com
© ISTE Ltd 2024The rights of Pierre Odru and Elena Palomo del Barrio to be identified as the authors of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act 1988.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s), contributor(s) or editor(s) and do not necessarily reflect the views of ISTE Group.
Library of Congress Control Number: 2023948927
British Library Cataloguing-in-Publication DataA CIP record for this book is available from the British LibraryISBN 978-1-78945-133-7
ERC code:PE8 Products and Processes Engineering PE8_6 Energy processes engineering
Foreword
Philippe MARTY
LEGI, CNRS, Grenoble INP, Université Grenoble Alpes, Grenoble, France
There has always been an interest in storing heat: prehistoric people heating a stone using fire and then plunging it into a hollow piece of wood filled with water in order to cook their food can be thought of as conducting a first heat storage experiment. As for the Persians, they stored ice in the desert in dome-like buildings with thick clay walls.
Nowadays, heat storage is an important topic of debate on the development of renewable energies. It is generally accepted that massive deployment of these energies should be accompanied by significant storage facilities in order to cope with the irregularity of wind or insolation. Many industrial processes release waste heat. According to a study conducted by ADEME (French Agency for Ecological Transition), nearly 100 TWh of waste heat are released each year, which amounts to approximately one-third of the needs in this sector. In buildings, the currently developed heat storage methods rely essentially on storing water in balloons.
As for the national power grid, the massive solution that is most commonly implemented involves getting water at altitude and then passing it through turbines. Pumped hydroelectric energy storage (PHES) therefore stores electric energy in a gravitational form. This book will not discuss this technology. The same is true for electrochemical storage in batteries or hydrogen vector-based techniques that are the object of other volumes in the SCIENCES series of books published by ISTE.
The two volumes presented here have been written by renowned European experts in the field of heat storage and associated materials. They are exclusively dedicated to heat and cold storage and exhaustively discuss all the possible physical and technical solutions. Sensible heat storage methods, in which the temperature of a body is modified to store or release energy, will be presented. The technique involving phase change will also be presented in detail. Thermochemical or sorption heat storage, which is highly promising due to its larger density, will be dealt with in a separate volume.
Volume 1, Heat and Cold Storage 1: Sensible and Latent Heat Storage, focuses exclusively on these two types of energy transfers. The state of the art on the standard applications of storage for the building industry is presented, and long-term storage is given particular attention. Indeed, in a country with no steady insolation, the energy autonomy of a building depends on long-term storage possibility, which is also known as inter-seasonal storage. Underground storage offers in this respect possibilities that will be discussed.
The storage of electricity in the form of heat is studied in the presentation of new high-temperature processes. This promising technology is considered for very high power installations and can be seen as an alternative to PHES or to the use of hydrogen vector as a solution for the temporary storage of electricity.
Phase change materials (PCMs) are an attractive alternative when the temperature differences between the storage material and the external environment are too small. It is important to recall that the principle is using the phase change, most often solid–liquid, to accumulate or release the heat transferred in latent form. Due to the high value of the enthalpy of phase change of certain materials, compared to their heat capacity, storage density can be increased. A detailed presentation of the available materials is proposed. The wide range of applications of PCM for the storage of both heat and cold is rapidly extending. For example, they can be found in ice slurries in the form of encapsulated materials. The stakes in the micro- or nano-encapsulation process, and also in the impregnation of porous media, are huge, as they involve difficult techniques that are presented in detail in Volume 1. Besides a high mechanical and chemical stability, the thermal conductivity of the synthesized materials must be high enough to allow for reasonable energy transfer times. This requirement leads to the incorporation of highly conductive materials in the PCM in order to enhance their performances. Chapter 8 is dedicated to the applications of these materials in the industry and construction fields, including the particular case of storage integrated in solar power plants.
Cold storage is essential in a considerable number of applications, particularly in the food industry. Among the high-performance solutions, storage on hydrates is a future possibility that will be presented in Chapter 7.
The particularly promising case of concentrated solar power plants is also discussed in Chapter 8. Though current power plants essentially use molten salts, therefore relying on the principle of sensible storage, future developments of latent and thermochemical systems are presented.
Volume 2 is entitled Heat and Cold Storage 2: Thermochemical Storage. Similar to the electrochemical storage being able to sustainably store electrical power, thermochemical or sorption storage is able to store heat or cold over an a priori infinite duration. Unlike sensible or latent storage, this characteristic explains why energy engineers are very much in favor of this technique, which moreover presents a very high energy density that may reach several hundred kWh/m3. This storage method in the form of chemical potential of the energy includes two distinct classes depending on whether the phenomenon in question is physical (van der Walls forces) or chemical (covalent bonds).
This volume introduces first the principles of sorption in a highly didactic manner and defines the criteria for the selection of materials to be implemented. This is followed by a detailed description of how an absorption cycle operates, which will indicate the future stakes of this method. The challenges that the researchers and manufacturers in the field are currently faced with relate to developing new designs of exchanger reactors, devising new cycles, and implementing new materials.
Particular attention is given to adsorption processes: after a review of the principles of this phenomenon and a thorough description of solid–gas adsorption cycles and systems, a large number of examples of prototype installations are presented.
These two volumes are addressed to several communities: researchers will find here a summary of the progress made by various universities in the field of storage, while academics will find a didactic presentation of the processes implemented. Engineers in research centers will find out the current technological stakes. There is room for improvement in many sectors: materials and associated manufacturing and characterization techniques, equipment, heat exchangers, new cycles, etc.
2Low-Temperature Sensible Heat Storage
Pierre ODRU
Previously IFPEN, Paris, France
Unlike fossil fuels that can be easily and indefinitely stored, heat is an energy difficult to store. Solar heat, which can be captured by solar thermal panels as hot water, is essentially available during summer, though it is most needed during winter. The same for cold available during winter. This explains the interest in reliable and large-scale storage solutions that may also allow the collection of significant amounts of heat wasted in industrial processes. Storage directly associated with buildings will be distinguished from underground storage.
2.1. Sensible heat storage associated with buildings
Sensible heat storage associated with buildings stores the heat collected by solar thermal panels over various time scales, from several days to transferring the heat collected during the hot season to the cold season (vice versa for cold). The required properties of the storage material are high specific and volumetric heat capacities, to reduce the necessary masses and volumes, and also good thermal conductivity to facilitate exchanges.
For the temperatures required in building (heating, cooling, domestic hot water), concrete or building materials can be used passively. But water is particularly adapted and can be directly circulated in order to provide domestic hot water or heating. It is moreover economical and neutral to the environment. It may however facilitate corrosion and it has a limited use temperature domain, though well adapted to the building.
Table 2.1.Thermal characteristics of materials
Material
Temperature (°C)
Density (kg/m
3
)
Specific heat capacity (J/kg·K)
Volumetric heat capacity (kJ/m
3
·K)
Thermal conductivity (W/m·K)
Water
0–100
1,000
4,190
4,190
0.63
Ice
<0
920
2,060
1,895
2.1 (0°C)
Concrete
0–150
2,250
1,130
2,542
0.9–1.3
Brick
–
1,700
850
1,400
0.7
The disadvantage of sensible heat storage is its low-energy density, requiring large volumes. This is why standard tanks have limited capacity. Very large capacities require the use of external storage or geological structures, such as aquifers, rocks or soils under certain conditions.
In general, heat extraction must be conducted so that output temperature is maintained as constant as possible. For example, in the case of domestic hot water, if three quarters of a storage at 90°C are used, the user experience is not the same if temperature stays at 90°C or if it is 37°C if the already used hot water is replaced by water at 20°C with mixture. This generally requires temperature stratification, which is difficult to maintain, and increases system complexity.
2.1.1. Short duration storage
Solar heat collected by solar thermal panels is essentially available during the day, and in a temperate country it may be absent for several days in a row. This justifies short duration storage. The principle of these storage facilities is well known. They consist of metallic or fiberglass composite tanks coated with adapted insulation material, glass wool, polystyrene or polyurethane foam. The calculations allowing the dimensioning of these types of tanks are quite standard. The ageing of materials must obviously be known and adapted.
Typically, for a single-family home in Europe (two to five persons), a solar water heater dedicated exclusively to domestic hot water is composed of solar collectors with a total surface of around 4 m2 and a storage tank of 200–300 L. The solar coverage rate of such an installation, the part of water heated by solar energy, ranges between 60 and 90%.
In temperate countries, solar water heaters cannot by themselves meet the needs and must be used in combination with a classic gas or electric water heater, especially if they combine the production of domestic hot water and the underfloor heating of the building during winter. Some manufacturers propose using an auxiliary wood-firing boiler.
Figure 2.1.Maxlean combined heating system.
In some cases, water can be used in an open loop, but the heat from the solar thermal panel is generally transmitted from an exchanger located, for stratification reasons, in the lower (cold) part of the storage tank (Hadorn 2005). The heat is then recovered by a second exchanger bathing in the upper (hot) part of the tank and distributed in the building. As part of the SHC (Solar Heating and Cooling) program of the IEA (International Energy Agency), a combined system design, known as Maxlean concept, was subjected to an advanced energy and economic optimization.
The schematic representation in Figure 2.1 shows the following:
the energy supply zone: solar collectors and classic water heater;
transfer, storage, control and distribution zone;
charge, namely domestic hot water and home heating.
All the processes allowing the optimization and also the sensitivity studies are provided in IEA SHC Program (2008a).
2.1.2. Long duration (seasonal) solar heat storage
Seasonal solar heat storage obviously requires large volumes of water that are heated during summer to be used in winter. Large size tanks have the advantage of reduced surface to volume ratio, which limits thermal losses, but the duration being significant, heat insulation must be important. This storage should be obviously associated with buildings having high-quality insulation and sufficient solar collector surface allowing heat storage to be completed by the end of summer and to last the longest time possible during winter. An additional heating system is however generally needed.
The storage volume has an important place in the design of the building or house. But it can also be placed outside and underground in the case of a building or a group of buildings. It can be made from reinforced concrete with a sealing liner. The soil may play the role of additional insulator, but it will first absorb a part of the heat before the system reaches equilibrium.
Building such a tank obviously requires taking into account average insolation conditions, the efficiency of solar panels, the heat insulation of the buildings and the tank, pumping systems and consumption.
According to a Swiss study (Hadorn 2005), a 200 m2 house with high-quality insulation would only require 15 m2 of collectors to meet the domestic hot water and heating needs of 6,100 kWh/year. However, half of the needs occur during the three winter months when solar heat input is low. Under these conditions, the storage transfer needs would be 1,850 kWh. Only 10 m2 of additional collectors would then be required, without counting heat losses.
For actual examples, please refer to IEA Preheat Programme (2007).
2.1.3. The stratification problem
A storage system with an exchanger consists of an actual storage volume, in which the cold water, heavier, is supplied by the bottom, and the hot water, lighter, is collected at the top. The exchanger bringing the heat from solar panels is at the bottom and heats the cold water that goes up due to the density difference in the tank and accumulates at the top part.
Water stratification, due to the variation of density with temperature, will therefore play a critical role in system efficiency, with an intermediate zone in which heat exchanges take place. The system is all the more efficient as this stratification can be maintained for a longer time and it gives rise to a more significant temperature gradient.
Reaching proper stratification is a difficult task. For efficiency reasons, a high and thin storage tank is preferable. If water flows through the storage tank, hot water can be injected at the most favorable place in order to limit water displacement and thus increase the efficiency of stratification. This can be achieved using a vertical pipe with opening valves at various levels, electronically controlled to open at the desired level (see the Maxlean system). A flexible pipe with a density allowing it to float at the expected level can also be used. There are various methods for calculating stratification in a tank (see for example Haghighat (2013, p. 70) and Chapter 1).
2.2. Underground thermal energy storage
Another method for seasonal heat (or cold) storage for residential or tertiary applications involves the use of large underground storage capacities, which offer free on-site materials and favorable thermal characteristics.
Table 2.2.Thermal characteristics of rocks and soils
Material
Temperature (°C)
Density (kg/m
3
)
Specific heat capacity (J/kg·K)
Volumetric heat capacity (kJ/m
3
·K)
Thermal conductivity (W/m·K)
Water
0–100
1,000
4,190
4,190
0.63
Compact rock
–
2,600
800
2,080
2.5
Dry soil
–
1,300
800
1,050
1.28
Wet soil
<100
1,700
2,000
3,400
0.52
Beyond a certain depth, the basement has a constant temperature, equal to the average of the annual temperature on the site, and it also has significant thermal inertia, coupled with very significant volumes of available materials. Heat and cold can be alternatively stored in it, depending on the season. However, the fact that soils and rocks may contain water generally limits their range of use at temperatures below 100°C.
There are essentially aquifer thermal energy storage (ATES) and borehole thermal energy storage (BTES), which store by conduction in the solid medium, and finally subsurface energy storage, using foundations. The heat transfer fluid used is in general glycol water to eliminate freezing risks.
A geological heat storage system requires three conditions to be met at the same location:
energy resource: solar hot water collected in summer, waste heat from industrial installations, cool water stored in summer, etc.;
energy demand shifted in time: need for heating buildings during winter, need for cooling during summer;
geological and hydrogeological context favorable to underground storage of heat or cold.
Investment is significant and must be economically justified in the long term.
Moreover, the system should have auxiliary heating or cooling systems (heat pumps, classic heating or cooling, etc.). In addition to these, there is an obligation for sustainable management of the environmental impact, including the preservation of the integrity of underground drinking water.
Projects will depend also on the proper evaluation of the heating and cooling demand of the buildings, and on the proper dimensioning of the surface installations: coefficient of performance (COP) of the heat pumps, thermal insulation, proper dimensioning of pipelines, energy efficiency of the pumps, heat exchangers, efficiency of the regulation systems, etc.
Storage is all the more efficient as the losses by thermal diffusion in the underground remain relatively limited, and therefore as it is larger. Thermal equilibrium in the underground is only reached after several years, inducing more significant losses during the first period of operation. There may be a great impact on the return on investment.
2.2.1. Principle of the aquifer thermal energy storage
Aquifer thermal energy storage is possible only if the aqueous phase is not flowing, which requires specific geological conditions and limits the potential. It can compete with other uses.
This system requires at least two distant wells to prevent cold and hot parts from mixing. Exchanges are also possible between distinct aquifers (Reichstag in Berlin), a cold one near the surface and a hot one at depth.
Figure 2.2.ATES closed loop (IEA-DHC 2018). (a) Winter mode; (b) Summer mode.
In the simplest case, cold water is pumped in summer and is heated through an exchanger by a thermal solar source or by cogeneration and is sent to the aquifer. It then heats the building in winter, and once cooled it is sent back to the aquifer. In many cases, cold water pumped during summer can also be used for cooling the building, before receiving the complementary thermal input.
A heat pump may complete the installation, in addition to the classic heating or cooling means.
Reversible heat exchanges are not only convective through water, but also mobilize a diffusive part in the neighboring solid layers. Reaching thermal equilibrium may take several years, which entails the initial loss of significant amounts of heat. Available power depends on the pumped flow rate and on the quantity of stored hot water. Once the equilibrium is reached, the recovered to injected energy ratio may exceed 75%; thermal storage then has a dominant part in the heating balance, or of electric power consumption when cooling is involved.
Basements in the Netherlands are very favorable to the implementation of ATES systems, which allowed a certain number of local enterprises to gain highly competitive know-how. The technology is considered mature. There is fast return on investment in favorable cases.
A well-documented ATES example, from both technical and economic perspective, is that of cold storage conducted at Richard Stockton College in New Jersey (Packsoy et al. 2009). Wells and their installation have considerable costs. These may however be lowered after a learning period. A significant return on investment is expected after 20 years of operation, with a decrease in the carbon footprint of the institution.
A study was conducted in France on off-season recharge of a deep aquifer used in geothermal system with hot water from a household waste incineration plant. The objective was to increase the winter potential and avoid resource depletion (Reveillere et al. 2013).
The Parisian Basin has an interesting geothermal heat potential, which happily coincides with strong local demand. The most interesting and widely exploited geological formation is that of Dogger. Water temperature varies there between 55 and 85 °C for depths ranging between 1,500 and 2,000 m. A 200 m3
