GB2486204A

GB2486204A - Thermal store and method of storing thermal energy

Info

Publication number: GB2486204A
Application number: GB1020620.9A
Authority: GB
Inventors: Vincent Arthur Smedley; Laurence A Steijger
Original assignee: EAST MIDLANDS RENEWABLE ENERGY Ltd
Current assignee: EAST MIDLANDS RENEWABLE ENERGY Ltd
Priority date: 2010-12-06
Filing date: 2010-12-06
Publication date: 2012-06-13
Also published as: GB201020620D0

Abstract

The thermal store comprises: a thermally insulating housing 12 defining an internal volume 11; a solid material (9, figure 3), such as a rock-based aggregate, disposed within the internal volume; a first heat exchanger 84; a drive 86; and a guide arrangement disposed within the internal volume. The drive is for driving a fluid about the heat exchanger and the solid material in order to transfer heat energy from the heat exchanger to the solid material. Preferably, the fluid is air and the drive is a fan. The guide arrangement may comprise a divider 40 and/or baffles 41-42, the baffles having a plurality of holes to increase air turbulence for improved heat transfer. The housing may include an air inlet 20 and air outlet 22 interconnected by a conduit 80 so that the fan re-circulates the air into the aggregate continuously. A second heat exchanger 88 may be provided at the air outlet to selectively draw thermal energy from the air for use in domestic hot water or central heating. The second heat exchanger may comprise an air source heat pump. The first heat exchanger may be connected to a solar collector to charge the thermal store.

Description

TITLE

Apparatus for storing thermal energy and associated method

TECHNOLOGICAL FIELD

Embodiments of the present invention relate to an apparatus for storing thermal energy. In particular, they relate to an apparatus for storing thermal energy for subsequent transfer to one or more buildings.

BACKGROUND

The energy demand of a building varies depending upon the season. For example, lower temperatures in the winter, as compared with the summer, mean that energy demand in the winter is much higher than in the summer.

Many buildings comprise a heating system that burns a fossil fuel, such as natural gas, to produce heating. Demand for such fossil fuels is therefore very high during winter.

The Earth's fossil fuel reserves are rapidly being depleted. Furthermore, the burning of fossil fuels produces carbon dioxide. Production of carbon dioxide is considered by many scientists to contribute to global warming.

BRIEF SUMMARY

According to some, but not necessarily all, embodiments of the invention there is provided an apparatus for storing thermal energy for subsequent transfer to one or more buildings, comprising: a housing, defining an internal volume, configured to thermally insulate the internal volume from the outside environment; and solid material, situated within the internal volume of the housing, for storing thermal energy.

According to some, but not necessarily all, embodiments of the invention there is provided an apparatus for storing thermal energy for subsequent transfer to one or more buildings, comprising: a housing, defining an internal volume, configured to thermally insulate the internal volume from the outside environment; solid material, situated within the internal volume of the housing, for storing thermal energy; a heat exchanger; a drive for driving a fluid about the heat exchanger and about the solid material, to transfer thermal energy from the heat exchanger to the solid material; and a guide arrangement, situated within the internal volume of the housing, for guiding the fluid around the internal volume of the housing.

According to some, but not necessarily all, embodiments of the invention there is provided a method, comprising: driving a fluid about a heat exchanger and about a 1 0 solid material, to transfer thermal energy from the heat exchanger to the solid material, wherein the solid material is situated within an internal volume defined by a thermally insulating housing; and guiding the fluid around the internal volume of the thermally insulating housing, using a guide arrangement situated within the internal volume of the thermally insulating housing.

According to some, but not necessarily all, embodiments of the invention there is provided an apparatus for storing thermal energy for subsequent transfer to one or more buildings, comprising: a housing, defining an internal volume, configured to thermally insulate the internal volume from the outside environment; solid material, situated within the internal volume of the housing, for storing thermal energy; and means for controlling the transfer of thermal energy from a heat exchanger to the solid material, in dependence upon actual or expected weather conditions.

According to some, but not necessarily all, embodiments of the invention there is provided an apparatus for storing thermal energy and for transferring stored thermal energy to one or more buildings, comprising: a housing, defining an internal volume, configured to thermally insulate the internal volume from the outside environment; solid material, situated within the internal volume of the housing, for storing thermal energy; and means for controlling the transfer of thermal energy from the solid material to the one or more buildings, in dependence upon actual or expected user energy demand.

According to some, but not necessarily all, embodiments of the invention there is provided an apparatus for storing thermal energy and for transferring stored thermal energy to one or more buildings, comprising: a housing, defining an internal volume, configured to thermally insulate the internal volume from the outside environment; and solid material, situated within the internal volume of the housing, for storing thermal energy, wherein the apparatus is situated at least partly beneath ground level and the housing provides at least part of the building foundations for supporting at least one of the one or more buildings.

According to some, but not necessarily all, embodiments of the invention there is provided an apparatus for storing thermal energy for subsequent transfer to one or more buildings, comprising: a housing, defining an internal volume, configured to 1 0 thermally insulate the internal volume from the outside environment; and aggregate material, situated within the internal volume of the housing, for storing thermal energy.

BRIEF DESCRIPTION

For a better understanding of various examples of embodiments of the present invention reference will now be made by way of example only to the accompanying drawings in which: Fig. I illustrates a housing for use in storing thermal energy; Fig. 2 illustrates an isometric view of the housing; Fig. 3 illustrates a first vertical cross sectional view of the housing; Fig. 4 illustrates a horizontal cross sectional view of an apparatus comprising the housing; Fig. 5 illustrates a flow chart of a method; Fig. 6 illustrates a flow chart depicting the flow of thermal energy to the apparatus, within the apparatus, and from the apparatus; Fig. 7 illustrates a second vertical cross sectional view of the housing; and Fig. 8 illustrates a control system of the apparatus;

DETAILED DESCRIPTION

The Figures illustrate an apparatus 10 for storing thermal energy for subsequent transfer to one or more buildings 100, comprising: a housing 12, defining an internal volume II, configured to thermally insulate the internal volume 11 from the outside environment; solid material 9, situated within the internal volume 11 of the housing 12, tar staring thermal energy; a heat exchanger 84; a drive 86 tar driving a fluid 70 abaut the heat exchanger 84 and abaut the saud material 9, ta transfer thermal energy fram the heat exchanger 84 ta the saud material 9; and a guide arrangement 40, situated within the internal valume 11 af the hausing 12, far guiding the fluid 70 araund the internal valume 11 af the hausing 12.

Fig. I illustrates a hausing 12 af an apparatus 10 far staring thermal energy far subsequent transfer ta ane ar mare buildings 100. In the illustrated example, the whale af the hausing 12 is situated beneath graund level 30. The hausing 12 may 1 0 pravide at least part af the building faundatians far supparting the ane ar mare buildings 100. In same implementatians, the hausing 12 is situated directly beneath a single building (such as a hause) and pravides at least part at the building faundatians far that building.

In ather examples af the inventian, the whale ar part af the hausing 12 may be situated abave graund level 30.

A ca-ardinate system 75 is illustrated in Fig. 1. The x and z axes af the ca-ardinate system 75 are parallel ta the plane af the page in Fig. 1. The y axis is directed inta the page. The ca-ardinate system 75 is referred ta below ta explain the arientatian af the hausing 12 and ather items in the subsequent figures.

Fig. 2 illustrates an isametric view af the hausing 12. The housing may be cuboidal in shape. In the illustrated example, the housing 12 is a rectangular prism. The housing 12 comprises a front face 51, side faces 52, 53, a rear face 54, an upper face 55 and a lower face 56.

The height of the housing 12 is parallel to the z-axis of the ca-ordinate system 75 in Figs I and 2. The width of the housing 12 is parallel to the y-axis and the length of the housing 12 is parallel to the x axis in Figs. I and 2.

The housing 12 comprises a base 13, a plurality of walls 14, a lid 15 and an internal insulating layer 16 (not shown in Fig. 1). The front face 51 of the housing 12 comprises a fluid entrance (aperture) 20 and a fluid exit (aperture) 22. The functions of the fluid entrance 20 and the fluid exit 22 will be described in further detail below.

In the illustrated example, the height of the fluid entrance 20 is lower than the height of the fluid exit 22.

The housing 12 is hollow. It defines an internal volume 11 (not shown in Fig. 1) for storing a solid material 9. The solid material 9 is wholly encased by the housing 12.

The solid material 9 is for storing thermal energy for subsequent transfer to the building(s) 100. The thermal energy may, for example, be used to heat water for use in providing at least one of: domestic hot water and central heating.

The solid material may 9 be an aggregate material, such as a rock based aggregate material. In some embodiments of the invention, the solid material 9 is a rock based aggregate material comprising irregularly-shaped pieces of aggregate, each of which has a diameter that is (approximately) between 20 and 40 millimeters.

When the apparatus 10 is constructed, the aggregate may be poured into the internal volume 11 before the lid 15 is placed in its final position. Once the aggregate has been poured into the internal volume 11, gaps will be present between the pieces of aggregate due to the irregular shapes of the pieces.

In some embodiments of the invention, the solid material 9 occupies 40-70% of the internal volume 11. Preferably, the solid material 9 occupies 50-60% of the internal volume 11. In one such example, the solid material 9 occupies 55% of the internal volume 11.

The housing 12 is configured to thermally insulate the internal volume 11 and the solid material 9 from the outside environment. In some embodiments of the invention, the thermal transmittance U of each of the base 13, the waIls 14 and the lid 15 is 0.5 WK1m2 or less. Preferably, the thermal transmittance U of each of the base 13, the waIls 14 and the lid is 0.2WK1m2 or less. In one such embodiment, the thermal transmittance of the base 13 is 0.138 WK1m2, the thermal transmittance of the walls 14 is 0.078 WFC1m2 and the thermal transmittance of the lid 14 is 0.084 WFC1m2.

Fig. 3 illustrates a vertical cross section of the housing 12. Fig. 3 shows the solid material 9 situated within the internal volume 11 of the housing 12.

The base 13 and the lid 15 of the housing 12 may, for example, be made from concrete. The walls 14 may, for example, be made from insulated concrete form. The insulated concrete form may, for example, comprise first and second insulating layers 24, 26, with a structural concrete layer 25 sandwiched between them. The insulating layers 24, 26 may, for example, comprise expanded polystyrene.

In the example illustrated in Fig. 3, one or more insulating materials 16 cover part or the whole of the internal surface defined by the base 13, walls 14 and lid 15. The insulating material(s) 16 may, for example, be one or more polystyrene materials.

Fig. 4 illustrates a horizontal cross section of the apparatus 10. In addition to the housing 12 and the solid material 9, the apparatus 10 illustrated in Fig. 4 further comprises a guide arrangement 40, a filter 82, first and second heat exchangers 84, 1 5 88, a drive 86 and a conduit 80. The solid material 9 situated in the internal volume 11 is not illustrated in Fig. 4 for clarity reasons.

A method according to embodiments of the invention will now be described, referring in particular to Figs. 4 to 8. Fig. 5 illustrates a flow chart of the method. Fig. 6 illustrates thermal energy flow in the method.

Blocks 94 and 95 in Fig. 5 relate to a "charging mode" of the apparatus 10. In the charging mode, thermal energy is transferred to the solid material 9 situated within the housing 12 for storage. Blocks 96 to 97 of Fig. 5 relate to a "discharging mode" of the apparatus 10. In the discharging mode, thermal energy is transferred from the solid material 9 to the one or more buildings 100. The charging mode and the discharging mode are distinguished by a dotted line 200 in Fig. 5.

At block 94 of Fig. 5, thermal energy collected by one or more thermal energy collectors 90 and transferred from the first heat exchanger 84. The one or more thermal energy collectors 90 may, for example, comprise one or more solar thermal collectors that store liquid for solar heating. The solar thermal energy collector(s) may be situated on the one or more buildings 100 (for example, on the roof(s)).

The first heat exchanger 84 is arranged to receive a heat transport fluid (such as a heated liquid) from the one or more thermal energy collectors 90, resulting in thermal energy being transferred by the one or more thermal energy collectors 90 to the first heat exchanger 84. This is depicted by the arrow 201 in Fig. 6.

At least part of the first heat exchanger 84 may be positioned in the fluid entrance 20, as shown in Fig. 4.

At block 95 of Fig. 5, the drive 86 drives a heat transport fluid 70 about the first heat 1 0 exchanger 84 and about the solid material 9 situated in the internal volume 11. The heat transport fluid 70 driven by the drive 86 is different to the heat transport fluid received by the first heat exchanger 84 from the thermal energy collector(s) 90. In some embodiments of the invention, these two heat transport fluids are in different states. For example, the heat transport fluid 70 may be a gas, such as air, whereas 1 5 the heat transport fluid for transferring thermal energy from the collector(s) 90 to the first heat exchanger 84 may be a liquid.

Embodiments of the invention are described below in which the fluid 70 is air.

However, in other embodiments of the invention, the fluid 70 may be a different gas from air, or may be a liquid rather than a gas.

The drive 86 may be a fan which draws air 70 from within the internal volume 11 in order to drive that air 70 about the first heat exchanger 84. In this example, the drive 86 is arranged to draw air 70 from internal volume 11 and pass it through the first heat exchanger 84, causing thermal energy to be transferred from the (heated fluid in the) first heat exchanger 84 to the air 70. This is indicated by the arrow 202 in Fig. 6.

The filter 82 is positioned between the air 70 being drawn from the internal volume 11 and the drive 86, to prevent any solid material that is drawn with the air 70 from damaging the drive 86. In the example illustrated in Fig. 4, the filter 82 is positioned in the fluid exit aperture 22 of the housing 12.

The conduit 80 connects the fluid entrance 20 to the fluid exit 22. The conduit 80 may, for example, be an insulated pipe. The conduit 80 is arranged to direct the air drawn by the drive 86 through the first heat exchanger 84 and back into the housing 12 (via the fluid entrance 20).

In this example, the air 70 passes through a second heat exchanger 88 prior to exiting the housing 12. Fig. 4 illustrates at least part of the second heat exchanger 88 being positioned in the fluid exit 22 of the housing 12. Alternatively, it could be positioned inside the housing 12 or inside the conduit 80.

The second heat exchanger 88 is arranged to extract thermal energy from the air 70, 1 0 for transfer to the building(s) 100. The second heat exchanger 88 may be a part of a device for transferring the thermal energy to the building(s) 100, such as an air source heat pump. Thermal energy that is not extracted by the second heat exchanger 88 is transferred to the solid material 9 for storage.

In this example of the method, the apparatus 10 is in its "charging mode" and it is not desired to transfer thermal energy to the building(s) 100 at the present time. In such a scenario, it may be desirable to deactivate the second heat exchanger 88 (or the device that it is part of) so that thermal energy is not transferred to the second heat exchanger 88 and/or transferred to the building(s) 100.

When the air 70 enters the housing 12, the guide arrangement 40 guides it around the internal volume 11 of the housing 12 in at least two dimensions. In some embodiments of the invention, the guide arrangement 40 guides the air 70 around the internal volume 11 of the housing 12 in three dimensions.

The illustrated guide arrangement 40 comprises one or more baffles 41, 42 and an internal divider 44. The baffles 41, 42 are situated within the solid material 9 that is positioned in the internal volume 11. In the illustrated embodiment, each baffle 41, 42 is substantially planar in nature. Each baffle 41, 42 may comprise a plurality of apertures that increase the turbulence of fluid directed towards it. Each baffle 41, 42, may, for example, be a perforated metal sheet or a wire mesh.

The internal divider 44 is arranged to divide a first region 111 of the internal volume 11 of the housing 12 from a second region 113 of the internal volume 11. In the illustrated example, the internal divider 44 does not extend across the whole of the length of the housing 12. That is, there is a gap between the internal divider 44 and the portion of the insulating layer 16 that covers the wall providing the rear face 54.

Fig. 7 illustrates the fluid 70 entering the housing 12. The first heat exchanger 84 is not illustrated for clarity reasons. The fluid entrance 22 is situated relatively low down in the front face 51, in a position that is closer to the lower face 56 of the housing 12 than the upper face 55. Advantageously, this enables thermal energy to be transferred from the hot air 70 to solid material 9 efficiently (in particular to the parts of the solid material 9 that are closer to the base 13 than the lid 15), because the hot 1 0 air 70 will have a natural tendency to rise within the housing 12.

Upon entry into the housing 12, the air 70 begins to move around the solid material 9 in the second region 113 of the internal volume 11. The air 70 meets the (planar) first baffle 41. The first baffle 41 is angled downwardly with respect to the vertical (the z- 1 5 axis) and acts to constrain upward movement of the air 70. This enables thermal energy to be distributed around the solid material 9 (for example, to lower portions of the solid material 9) more effectively. Some of the air 70 that meets the first baffle 41 will pass through the apertures in the first baffle 41, increasing the turbulence of the air 70 (as shown in Fig. 7) and improving thermal energy transfer to the solid material 9.

The outline path of the air within the housing 12 is illustrated by the line designated with the reference numeral 70. The air 70 travels from the second region 113 of the internal volume 11, around the internal divider 44, and into the first region 111 of the internal volume 11 where the turbulence of the fluid is increased by the second baffle 42, before exiting the housing via the fluid exit 22.

The internal divider 44 guides the air 70 around the internal volume 11 of the housing 12 in the x and y dimensions.

The second baffle 42 is positioned closer to the fluid exit 22 than the fluid entrance (see Fig. 4). The air 70 in the upper regions of the housing 12 will be at a higher temperature than the air 70 in the lower regions, due to stratification of the heat stored in the solid material 9. The second baffle 42 is arranged to cause air 70 to be drawn preferentially from a higher (z-axis) position in the housing 12 through the exit 22. This advantageously enables efficient extraction of thermal energy from the solid material 9 when the apparatus 10 is in its discharging mode. The second baffle 42 may, for example, be situated at a higher (z-axis) position in the housing 12 than the first baffle 41.

The guide arrangement 40 causes the air 70 to follow a longer path around the solid material 9 than it would otherwise take if the guide arrangement 40 were not present.

Advantageously, this enables thermal energy to be transferred from the air 70 to the solid material 9 more effectively. The arrow 203 in Fig. 6 depicts thermal energy 1 0 being transferred from the air 70 to the solid material 9.

The drive 86 may continuously drive the fluid 70 around the endless loop defined by the internal volume 11 of the housing 12 and the conduit 80 for the purpose of transferring thermal energy to the solid material 9 for storage. Thermal energy may 1 5 be stored by the solid material on a short term basis (for example hours or days) or on a long term basis (for example, months).

The apparatus 10 enters the discharging mode at block 96 of Fig. 5. The apparatus may enter the discharging mode because a user in a building 100 demands thermal energy. For example, the user may demand thermal energy for use in providing central heating or domestic hot water.

During the discharging mode, the drive 86 drives the air 70 around the endless loop defined by the internal volume 11 of the housing 12 and the conduit 80, as shown in Fig. 4. The air 70 passes around the solid material 9 situated in the internal volume 11 of the housing 12 in the manner described above in relation to the charging mode.

Passing the air 70 around the solid material 9 causes thermal energy to be transferred from the solid material 9 to the air 70. This is depicted in Fig. 6 by the arrow 204.

When the apparatus 10 enters the discharging mode, the second heat exchanger 88 is activated to enable thermal energy to be transferred from the fluid 70 to the building(s) 100.

Thermal energy is transferred from the fluid 70 to the second heat exchanger 88 when the air 70 passes through the second heat exchanger 88. This is depicted by arrow 205 in Fig. 6. At block 97 of Fig. 5, thermal energy is transferred from the second heat exchanger 88 to the building(s) 100. For example, as mentioned above, the second heat exchanger 88 may be a part of an air source heat pump which transfers the thermal energy to the building(s). The transfer of thermal energy from the second heat exchanger 88 to the building(s) 100 is depicted by the arrow 206 in Fig. 6.

1 0 The drive 86 may therefore drive the fluid around the endless loop defined by the internal volume 11 of the housing 12 and the conduit 80 for the purpose of transferring thermal energy from the solid material 9 to the building(s) 100.

In some embodiments of the invention, it is possible for the apparatus 10 to be in the 1 5 charging mode and the discharging mode at the same time. When the apparatus 10 is simultaneously in the charging mode and the discharging mode, thermal energy is transferred from the thermal energy collector(s) 90 to the fluid 70. Thermal energy carried by the fluid 70 is transferred both to the solid material 9 (for storage) and to the second heat exchanger 88 (for transfer to the building(s) 100).

Fig. 8 illustrates a control system of the apparatus 10 which comprises a controller 46 and a memory 32. The controller 46 may, for example, be processing circuitry.

The controller 46 is configured to read from the memory 32 (and potentially also configured to write to the memory 32). The memory 32 is illustrated in Fig. 8 as storing a computer program 34. The computer program 34 comprises computer program instructions 35 which provide the logic and routines that enable the controller 46 to perform its functions.

The controller 46 is configured to control the charging and discharging of the apparatus 10 by controlling the drive 86.

The thermal energy collector(s) 90 may be likely to be more collect more thermal energy at certain times than others. For example, if the thermal energy collector(s) 90 are solar thermal collector(s), varying weather conditions will cause the amount of thermal energy that is collected to vary.

The controller 46 may be configured to control the drive 86 in dependence upon actual or expected weather conditions. For instance, the controller 46 may control the drive 86 to drive the fluid 70 at times when the thermal energy collectors 90 are providing (or are expected to be providing) significant thermal energy to the first heat exchanger 84 for transfer to the solid material 9. Advantageously, this enables the apparatus 10 to be more energy efficient than if the drive 86 were constantly operational.

The controller 46 may, for instance, control the drive 86 to drive the fluid 70 for longer periods of time during the summer than in the winter, because better weather conditions in the summer are expected to lead to an increased quantity of thermal 1 5 energy being collected by the collector(s) 90.

In some embodiments of the invention, the controller 46 may control the drive in dependence upon a weather forecast. The apparatus 10 may, for instance, comprise a receiver for receiving a weather forecast as electronic data. The weather forecast may, for example, be provided to the apparatus 10 via the internet. The controller 46 may be configured to control the drive 86 in dependence upon the weather forecast.

In some embodiments of the invention, the apparatus 10 may comprise one or more devices for determining current weather conditions (such as, for instance, a thermometer and/or one or more photovoltaic cells). The controller 46 may be configured to control the drive 86 in dependence upon one or more inputs from the device(s).

The controller 46 may be configured to control the drive 86 in dependence upon actual or expected user thermal energy demand. For example, the drive 86 may be activated in the mornings in the expectation that a user will demand thermal energy (for instance, for showering). Alternatively or additionally, the controller 46 may control the drive 86 in dependence upon actual demand for thermal energy. For example, the controller 46 may control the drive 86 in response to user activation of a device (for instance, a hot water shower) which requires thermal energy.

Embodiments of the invention advantageously provide an efficient way to store thermal energy, on a short or long term basis, for future use. Solar thermal energy may be collected and stored by the apparatus 10, enabling the occupants of the building(s) 100 to reduce (and possibly eliminate) their use of fossil fuels.

The illustration of a particular order to the blocks in Figs. 5 and 6 does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible 1 0 for some blocks to be omitted.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the 1 5 scope of the invention as claimed. For example, the fluid 70 for transferring thermal energy to and from the solid material 9 need not be a gas and could, for example, be a liquid. In such embodiments, the drive 86 may be a pump rather than a fan.

The first heat exchanger 84 need not be positioned in the fluid entrance 20. In other implementations, it may be positioned in the internal volume 11 or the conduit 80.

The second heat exchanger 88 need not be positioned in the fluid exit 22. In other implementations it may be positioned in the internal volume 11 or the conduit 80.

In some of the embodiments of the invention described above, the thermal transmittance of the base 13 of the housing 12 is 0.5 WFC1m2 or less. In other embodiments of the invention, the thermal transmittance of the base 13 might be (much) greater than this. In these embodiments, thermal energy is transferred through the base 13 to the ground, which may be recovered later for transfer to the building(s) 100.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS1. An apparatus for storing thermal energy for subsequent transfer to one or more buildings, comprising: a housing, defining an internal volume, configured to thermally insulate the internal volume from the outside environment; solid material, situated within the internal volume of the housing, for storing thermal energy; a heat exchanger; 1 0 a drive for driving a fluid about the heat exchanger and about the solid material, to transfer thermal energy from the heat exchanger to the solid material; and a guide arrangement, situated within the internal volume of the housing, for guiding the fluid around the internal volume of the housing.

1 5

2. An apparatus as claimed in claim 1, wherein the guide arrangement is arranged to guide the fluid in at least two dimensions around the internal volume of the housing.

3. An apparatus as claimed in claim I or 2, wherein the guide arrangement is arranged to guide the fluid in three dimensions around the internal volume of the housing.

4. An apparatus as claimed in claim 1, 2 or 3, wherein the guide arrangement includes one or more baffles.

5. An apparatus as claimed in claim 4, wherein at least one baffle includes a plurality of apertures for increasing the turbulence of the fluid.

6. An apparatus as claimed in any of the preceding claims, wherein the housing comprises a fluid entrance and a fluid exit, and the drive is arranged to drive the fluid about the heat exchanger prior to the fluid entering the housing via the fluid entrance.

7. An apparatus as claimed in any of the preceding claims, wherein the guide arrangement includes at least one divider that is arranged within the internal volume such that when the fluid is driven into the housing via the fluid entrance, the fluid travels around the internal divider before exiting the housing via the fluid exit.

8. An apparatus as claimed in any of the preceding claims, further comprising a conduit connecting the fluid entrance and the fluid exit, for enabling the fluid to flow in an endless loop.

9. An apparatus as claimed in claim 8, wherein the drive is arranged, in use, to continuously re-circulate the fluid around the endless loop.

10. An apparatus as claimed in any of the preceding claims, wherein the heat exchanger is arranged to store a heated liquid and, when the fluid is driven about the heat exchanger, thermal energy is transferred from the heated liquid to the fluid.

11. An apparatus as claimed in claim 10, further comprising: one or more solar thermal collectors arranged to enable solar heating of a liquid and arranged to transfer the heated liquid to the heat exchanger.

12. An apparatus as claimed in any of the preceding claims, wherein the drive is arranged to transfer thermal energy from the solid material to a further heat exchanger, for subsequent transfer to the one or more buildings.

13. An apparatus as claimed in claim 12, wherein the further heat exchanger is provided by an air source heat pump.

14. An apparatus as claimed in claim 13, wherein the air source heat pump is arranged to transfer heat from the fluid to water to provide hot water for the one or more buildings.

15. An apparatus as claimed in claim 14, wherein the hot water is for use in providing at least one of: domestic hot water and central heating.

16. An apparatus as claimed in any of the preceding claims, further comprising a controller configured to control the drive to drive the fluid about the heat exchanger to transfer thermal energy to the solid material.

17. An apparatus as claimed in claim 16, wherein the controller is configured to control the drive to drive the fluid about the heat exchanger to transfer thermal energy to the solid material, in dependence upon actual or expected weather conditions.

18. An apparatus as claimed in claim 16 or 17, when dependent upon claim 12, wherein the controller is arranged to control the drive to drive the fluid about the solid material to transfer thermal energy to the further heat exchanger.

19. An apparatus as claimed in claim 18, wherein the controller is arranged to control the drive to transfer thermal energy from the soUd material to the further heat exchanger, in dependence upon actual or expected user energy demand.

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20. An apparatus as claimed in any of the preceding claims, wherein the fluid is a gas.

21. An apparatus as claimed in any of the preceding claims, wherein the fluid is air.

22. An apparatus as claimed in claim 20 or 21, wherein the drive is a fan.

23. An apparatus as claimed in any of the preceding claims, wherein the solid material is an aggregate material.

24. An apparatus as claimed in claim 23, wherein the aggregate material is a rock based aggregate material.

25. An apparatus as claimed in any of the preceding claims, wherein at least part of the apparatus is situated beneath ground level.

26. An apparatus as claimed in claim 25, wherein the housing provides at least at least part of the building foundations for supporting at least one of the one or more buildings.

27. A method, comprising: driving a fluid about a heat exchanger and about a solid material, to transfer thermal energy from the heat exchanger to the solid material, wherein the solid material is situated within an internal volume defined by a thermally insulating housing; and guiding the fluid around the internal volume of the thermally insulating housing, using a guide arrangement situated within the internal volume of the thermally insulating housing.

28. An apparatus for storing thermal energy for subsequent transfer to one or more buildings, comprising: 1 0 a housing, defining an internal volume, configured to thermally insulate the internal volume from the outside environment; solid material, situated within the internal volume of the housing, for storing thermal energy; and means for controlling the transfer of thermal energy from a heat exchanger to the 1 5 solid material, in dependence upon actual or expected weather conditions.

29. An apparatus for storing thermal energy and for transferring stored thermal energy to one or more buildings, comprising: a housing, defining an internal volume, configured to thermally insulate the internal volume from the outside environment; solid material, situated within the internal volume of the housing, for storing thermal energy; and means for controlling the transfer of thermal energy from the solid material to the one or more buildings, in dependence upon actual or expected user energy demand.

30. An apparatus for storing thermal energy and for transferring stored thermal energy to one or more buildings, comprising: a housing, defining an internal volume, configured to thermally insulate the internal volume from the outside environment; and solid material, situated within the internal volume of the housing, for storing thermal energy, wherein the apparatus is situated at least partly beneath ground level and the housing provides at least part of the building foundations for supporting at least one of the one or more buildings.

31. An apparatus for storing thermal energy for subsequent transfer to one or more buildings, comprising: a housing, defining an internal volume, configured to thermally insulate the internal volume from the outside environment; and aggregate material, situated within the internal volume of the housing, for storing thermal energy.