CALORIC STORE

Abstract

A heat store (10) for an energy storage system includes a solid body (20) comprising a solid thermally conductive matrix (22) with a solid thermal filler material (21) embedded therein. The solid thermally conductive matrix (22) forms a thermally conductive pathway to the solid thermal filler material (21) distributed within the solid thermally conductive matrix (22). The heat store (10) for the energy storage system also includes a thermal transfer element (30).

Claims

1. A heat store for an energy storage system, comprising: a solid body comprising a solid thermally conductive matrix with a solid thermal filler material embedded therein, the solid thermally conductive matrix forming a thermally conductive pathway to the solid thermal filler material distributed within the solid thermally conductive matrix; and a thermal transfer element.

2-5. (canceled)

6. A heat store according to claim 1, wherein the thermal transfer element comprises: electrical heating coil embedded within the solid thermally conductive matrix and operative during a charging phase of the heat store to act as a heat input; and a heat exchanger embedded within the solid thermally conductive matrix and operative during a discharging phase of the heat store to transfer thermal energy from the solid body to the heat transfer fluid.

7. A heat store according to claim 1, wherein: the solid thermal filler material has a melting point that is higher than the melting point of the solid thermally conductive matrix such that the thermal filler material will remain solid during operation of the heat store as the heat store is thermally cycled between upper and lower temperature levels of a temperature range; and the body is housed in a container configured to provide structural support for the body during at least a part of the temperature range.

8. A heat store according to claim 1, wherein the solid thermally conductive matrix comprises a solid aluminum matrix.

9. (canceled)

10. (canceled)

11. A heat store according to claim 1, wherein the solid thermally conductive matrix material has a substantially higher thermal conductivity than the solid thermal filler material.

12. A heat store according to claim 1, wherein the solid thermal filler material comprises a plurality of discrete elements interspersed within the solid thermally conductive matrix.

13. A heat store according to claim 12, wherein the plurality of discrete elements comprise irregularly-shaped particles.

14. A heat store according to claim 12, wherein the plurality of discrete elements comprise stacked blocks.

15-25. (canceled)

26. An energy storage system comprising a heat store as defined in claim 1.

27. (canceled)

28. A method of forming a heat store for an energy storage system, comprising: combining molten thermally conductive matrix material with solid thermal filler material in a mould; allowing the thermally conductive matrix material to solidify to form a solid body comprising a solid thermally conductive matrix with the solid thermal filler material embedded therein; and providing a thermal transfer element in thermal connection to the solid thermally conductive matrix; wherein the thermal transfer element is actively cooled during the casting process.

29. A method according to claim 28, wherein the solid thermal filler material is provided as a plurality of discrete elements.

30. A method according to claim 29, wherein the plurality of discrete elements comprise irregularly-shaped particles.

31. A method according to claim 29, wherein the plurality of discrete elements comprise blocks.

32. A method according to claim 28, wherein the thermal transfer element comprises one or more of: electrical heating coil; and a heat exchanger operative to transfer thermal energy between the solid body and a heat transfer fluid.

33. (canceled)

34. A method according to claim 28, wherein the step of providing the thermal transfer element comprises providing the thermal transfer element in the mould prior to adding the molten thermally conductive matrix material to the mould.

35. A method according to claim 28, wherein the thermal transfer element is provided with a protective coating to protect the thermal transfer element from the molten thermally conductive matrix material.

36. A method according to claim 28, wherein the method comprises positioning the thermal transfer element within the mould and then subsequently adding the solid thermal filler material to the mould.

37. (canceled)

38. (canceled)

39. A method according to claim 28, wherein the method further comprises heating the thermal transfer element and solid thermal filler material and adding the molten thermally conductive matrix material.

40. A method according to any of claim 28, wherein the solid body is cast in a plurality of stages such that the solid body is built up in layers.

41. A heat store for an energy storage system, comprising: a solid body comprising a solid thermally conductive matrix with a solid thermal filler material embedded therein, the solid thermally conductive matrix forming a thermally conductive pathway to the solid thermal filler material distributed within the solid thermally conductive matrix; and a thermal transfer element, wherein the solid body forms a stove surface for cooking.

Description

[0124] Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

[0125] FIG. 1 is a schematic illustration of an energy storage system incorporating a heat store in accordance with the present invention;

[0126] FIG. 2 is a schematic cross-sectional view of a heat store for use in the energy storage system of FIG. 1 in accordance with a first embodiment of the invention;

[0127] FIG. 3 is a schematic perspective view of the heat store of FIG. 2 showing its constituent parts;

[0128] FIG. 4 is a schematic cross-sectional view of the heat store of FIG. 2 forming part of a series of heat stores;

[0129] FIGS. 5a and 5b are a schematic perspective views of a heat store for use in the energy storage system of FIG. 1 in accordance with a second embodiment of the invention;

[0130] FIG. 5c is a schematic perspective view of a heat store for use in the energy storage system of FIG. 1 in accordance with a third embodiment of the invention;

[0131] FIG. 6 is a schematic perspective view of a heat store for use in the energy storage system of FIG. 1 in accordance with a fourth embodiment of the invention;

[0132] FIG. 7 is a schematic cross-sectional view of a heat store for use in the energy storage system of FIG. 1 in accordance a fifth embodiment of the invention;

[0133] FIG. 8 is a schematic cross-sectional view of a heat store for use in the energy storage system of FIG. 1 in accordance a sixth embodiment of the invention;

[0134] FIG. 9 is a schematic cross-sectional view of a heat store for use in the energy storage system of FIG. 1 in accordance a seventh embodiment of the invention;

[0135] FIG. 10 is a schematic cross-sectional view of a heat store for use in the energy storage system of FIG. 1 in accordance an eighth embodiment of the invention; and

[0136] FIG. 11 is a schematic cross-sectional plan view of a heat store for use in the energy storage system of FIG. 1 in accordance with a ninth embodiment of the invention.

[0137] FIG. 1 shows an energy storage system 1 comprising a heat generation stage 5 and a heat store 10.

[0138] The energy storage system 1 may be a power generation system (e.g. system operative to convert power into heat for storage during a charging phase and operative to convert stored heat into power (e.g. electrical power) during a discharging phase—such as an electricity storage system) or may be part of an industrial process or a domestic heating system. The heat generation stage 5 may take a variety of forms depending upon the type of energy storage system 5.

[0139] In the case of a power generation system, the heat generation stage 5 may comprise a working fluid cycle operative to compress a working fluid during the charging phase and operative to expand a working fluid during the discharging phase to generate power. The heat store 10 may be operative to receive thermal energy from the working fluid cycle during the charging phase and operative to transfer thermal energy to the working fluid cycle during the discharging phase.

[0140] One example of such a process is an adiabatic compressed air energy storage system, such as the system described in the 2006 paper titled “Adiabatic Compressed Air Energy Storage for the Grid Integration of Wind Power” by Stefan Zunft, Christoph Jakiel, Martin Koller and Chris Bullough. This paper describes using a pressurised store and transferring the heat directly between the air (working fluid) and the solid storage media. The design and manufacture of the pressure vessel at this scale and temperature is technically extremely challenging and the potential cost made the proposed system uneconomic using conventional heat store technology. Other types of electricity storage systems include concentrating solar power plants with molten salt, pumped heat energy storage system and liquid air energy storage systems.

[0141] FIGS. 2 and 3 show a first embodiment of a sensible heat thermal storage system 10 comprising a solid metal composite block 20, and an embedded coiled heat exchanger 30, a heat transfer fluid inlet 40, and a heat transfer fluid outlet 50.

[0142] As illustrated in FIG. 2, in this example the solid metal composite block 20 is made up of a solid aluminium matrix 22 surrounding (low-cost) irregularly-shaped solid magnetite particles 21 embedded in the matrix. Solid metal composite block 20 is formed by casting molten aluminium over the magnetite particles 21 whilst coiled heat exchanger 30 is in place to form a solid block with good heat storage and good heat transfer properties. The solid magnetite particles 21 have a higher melting point than the solid aluminium matrix 22 and therefore remain solid both during the casting process and during operation of the thermal storage system 10.

[0143] When charging the thermal storage, hot heat transfer fluid enters through inlet 40 and is cooled as it passes through heat exchanger 30 before leaving the thermal storage via outlet 50. The thermal energy is transferred from the heat transfer fluid via heat exchanger 30 to solid metal composite block 20. Solid metal composite block 20 has good thermal conductivity as has been previously described and hence the heat flows rapidly from the heat exchanger 30 to all parts of the solid metal composite block 20.

[0144] When discharging the thermal storage, cool heat transfer fluid enters in reverse through outlet 50 and is heated as it passes through heat exchanger 30 before leaving the thermal storage via inlet 40. The thermal energy is transferred to the heat transfer fluid via heat exchanger 30 from solid metal composite block 20. Solid metal composite block 20 has good thermal conductivity as has been previously described and hence the heat flows rapidly from all parts of the solid metal composite block 20 to the heat exchanger 30.

[0145] FIG. 4 shows a version of sensible thermal storage system 10 comprising a plurality of solid metal composite blocks 20 connected in series with insulation 60 provided around the blocks 20. The provision of insulation breaks between blocks allows for a temperature front to be generated in multiple blocks. Due to the high thermal conductivity of the aluminium any individual block will tend to settle at an average temperature when not charging or discharging. The use of multiple blocks with insulation will tend to reduce the temperature difference between the thermal fluid and the solid metal composite block 20. It is analogous to a thermal front travelling through a packed bed and can improve the efficiency of the heat transfer process.

[0146] FIGS. 5a and 5b show an alternative heat store 10′ based on heat store 10 shown in FIG. 2, heat store 10′ comprising a solid metal composite block 20′ formed in accordance with blocks 20 of heat store 10, an external heat exchanger 30′, heat transfer fluid inlet 40′ and outlet 50′. In this case the solid metal composite block 20′ is cast as a block with flat sides and the external heat exchanger 30′ is bonded or otherwise attached to one face of the block 20′. FIG. 5a shows the heat exchanger 30′ separate from the solid metal composite block 20′ prior to attachment.

[0147] FIG. 5c shows heat store 10′ with an additional solid metal composite block 20′ is attached to the other side of heat exchanger 30′. The blocks could be welded to the heat exchanger. Alternatively the heat exchanger channels could be cast into the blocks. The inlet and outlet pipes could be welded to one block and then both blocks welded together. In this way the heat exchanger is low cost and integral to the blocks.

[0148] FIG. 6 shows an alternative arrangement based on the embodiment of FIG. 3 (features in common are labelled accordingly) in which the coiled heat exchanger 30″ is mounted externally of a cylindrical solid metal composite block 20″. In one embodiment, the coiled heat exchanger 30″ may be a flexible heat exchanger wrapped around the outside of the block. The heat exchanger may be held in place by tensioning straps or else bonded to the surface of the block. If held in place with tensioning straps this can allow for differing thermal expansions.

[0149] FIG. 7 shows an alternative embodiment of a heat store 10′″ comprising a plurality of solid metal composite blocks 20′″ (each formed in accordance with block 20 of heat store 10) and a heat exchanger 30′″ comprising a container 33 filled with a heat transfer fluid 32, an inlet 40′″ and an outlet 50′″. As illustrated, the plurality of solid metal composite blocks 20′″ are stacked within container 33 and surrounded by heat transfer fluid 32.

[0150] When charging the thermal storage, hot heat transfer fluid enters through inlet 40′″ and is cooled as it passes around solid metal composite blocks 20′″ before leaving the thermal storage via outlet 50′″. The thermal energy is transferred from the heat transfer fluid 32 to solid metal composite blocks 20″. Solid metal composite blocks 20′″ have good thermal conductivity as has been previously described. The blocks 20′″ are stacked in such a way that the fluid passes evenly around the different blocks.

[0151] When discharging the thermal storage, cool heat transfer fluid 32 enters in reverse through outlet 50′″ and is heated as it passes solid metal composite blocks 20′″ before exiting via inlet 40′″. The thermal energy is transferred to the heat transfer fluid 32 from solid metal composite blocks 20′″.

[0152] FIG. 8 shows a further embodiment of the invention of a sensible heat thermal store 10″″ comprising a solid metal composite block 20″″ (formed in accordance with block 20 of heat store 10), and a heat exchanger 30″″ comprising a first embedded heat exchanger 30A having a first heat transfer fluid inlet 41 and a first heat transfer fluid outlet 51, and a second embedded heat exchanger 30B having a second heat transfer fluid inlet 42 and a second heat transfer outlet 52.

[0153] When charging the thermal storage, a hot heat transfer fluid enters through inlet 41 and is cooled as it passes through first heat exchanger 30A before leaving the thermal store 10″″ via outlet 51. The thermal energy is transferred from the heat transfer fluid via first heat exchanger 30A to solid metal composite block 20″″. Solid metal composite block 20″″ has good thermal conductivity as has been previously described and hence the heat flows rapidly from the first heat exchanger 30A to all parts of the solid metal composite block 20″″.

[0154] When discharging the thermal storage, a cool heat transfer fluid, which can be different to the heat transfer fluid used for charging, enters through inlet 42 and is heated as it passes through second heat exchanger 30B before leaving the thermal store 10″″ via outlet 52. The thermal energy is transferred to the heat transfer fluid via second heat exchanger 30B from solid metal composite block 20″″. Solid metal composite block 20″″ has good thermal conductivity as has been previously described and hence the heat flows rapidly from all parts of the solid metal composite block 20″″ to second heat exchanger 30B.

[0155] FIG. 9 shows a further embodiment of the invention of a sensible heat thermal store 10′″″ comprising a solid metal composite block 20′″″ (formed in accordance with block 20 of heat store 10), an embedded heat exchanger 30′″″, heat transfer fluid inlet 42′ and outlet 52′ and an embedded electric heating element 70.

[0156] Electric heating element 70 is embedded within the matrix of solid metal composite block 20′″″ but electrically isolated from the block 20′″″ (e.g. by means of an electrically insulative coating) such that when an electrical current passes through electric heating element 70 the current does not pass through the block. When charging the thermal storage electricity is passed through the electric element 70, which heats the electric heating element 70. Typically heating is achieved via resistive heating. The thermal energy is transferred to the solid metal composite block 20′″″ and hence the heat flows rapidly from the electric heating element 70 to all parts of the solid metal composite block 20′″″.

[0157] When discharging the thermal storage, a cool heat transfer fluid enters through inlet 42′ and is heated as it passes through heat exchanger 30′″″ before leaving the thermal storage via outlet 52′. The thermal energy is transferred to the heat transfer fluid via heat exchanger 30′″″ from solid metal composite block 20′″″.

[0158] FIG. 10 shows a further embodiment of the invention of a sensible heat thermal storage system 10″″″ comprising a solid metal composite block 20″″″ (formed in accordance with block 20 of heat store 10) and an electric heating element 70′ embedded within the matrix of solid metal composite block 20″″″.

[0159] When charging the thermal storage electricity is passed through the electric heating element 70, which heats the electric heating element 70. The thermal energy is transferred to the solid metal composite block 20 and hence the heat flows rapidly from the electric heating element 70 to all parts of the solid metal composite block 20.

[0160] When discharging the thermal storage either a cool gas or solid object is put in contact with the solid metal composite and heat is transferred from the solid metal composite to the gas or solid object. For example the gas could be air that needs to be warmed and is blown over the solid metal composite. Alternatively, the solid metal composite might supply heat to a stove surface or even be the stove surface for cooking.

[0161] FIG. 11 shows a yet further embodiment of a sensible heat thermal storage system 110 comprising a solid metal composite block 120, an embedded (e.g. straight) heat exchanger pipe 130, a heat transfer fluid inlet 140, and a heat transfer fluid outlet 150.

[0162] In this example the solid metal composite block 120 is made up of a solid aluminium matrix 122 surrounding an ordered arrangement of magnetite bricks 121 embedded in the matrix. Block 120 includes a thicker solid aluminium section 122A in which heat exchanger pipe 130 is embedded. Solid metal composite block 120 is formed by casting molten aluminium over the magnetite bricks 121 whilst heat exchanger 130 is in place to form a solid block with good heat storage and good heat transfer properties. The solid magnetite bricks 121 have a higher melting point than the solid aluminium matrix 122 and therefore remain solid both during the casting process and during operation of the thermal storage system 110.

[0163] FIG. 11 is a view from above and shows how the magnetite bricks 121 are arranged within the matrix such that each face of each brick may be exposed to the matrix 122. In one embodiment, the magnetite bricks 121 are a 230 mm×190 mm×50 mm in size and 7.5 kg in weight (per brick), equivalent to a volume of around 2200 cm.sup.3 per brick. This corresponds to a commercially available magnetite storage heater bricks. Of course, other sizes of bricks (smaller or larger) may be used.

[0164] When charging the thermal storage, hot heat transfer fluid enters through inlet 140 and is cooled as it passes through heat exchanger 130 before leaving the thermal storage via outlet 150. The thermal energy is transferred from the heat transfer fluid via heat exchanger 130 to solid metal composite block 120. Solid metal composite block 120 has good thermal conductivity as has been previously described and hence the heat flows rapidly from the heat exchanger 130 to all parts of the solid metal composite block 120.

[0165] When discharging the thermal storage, cool heat transfer fluid enters in reverse through outlet 150 and is heated as it passes through heat exchanger 130 before leaving the thermal storage via inlet 140. The thermal energy is transferred to the heat transfer fluid via heat exchanger 130 from solid metal composite block 120.