Methods and systems for thermal energy storage

Abstract

A method of storing thermal energy, comprises exposing a first heat transfer medium to thermal energy from a heat source (12), and passing said first heat transfer medium through a first channel (11) which is in heat conductive contact with a thermal energy carrier (10) comprising a thermal energy storage substance in an amount of 40‐50 % by weight, about 50‐60 % by weight, about 60‐70 % by weight, about 70‐80 % by weight, about 80‐90 % by weight, about 90‐95 % by weight or 95‐99.5 % by weight, such that heat is transferred from the first transfer medium to the thermal energy carrier (10). The first heat transfer medium is a gas.

Description

[0001] METHODS AND SYSTEMS FOR THERMAL ENERGY STORAGE

[0002] Technical field

[0003] The present disclosure relates to devices and methods for energy storage, and in particular for thermal energy storage.

[0004] Background

[0005] Thermal energy storage can be used in order to store thermal energy from e.g. solar energy (in particular concentrated solar power plants) or surplus energy from industrial processes. A medium in which the thermal energy is stored should preferably have a high heat capacity, but it should also be stable, such that it does not expand or change form at relevant storage temperatures, as e.g. water does.

[0006] US2013180520A1 suggests to use various molten salts as heat storage medium and as a heat transfer medium. Such systems have proven capable of operating at temperatures of around 700 degC. However, the salts disclosed comprise elements which may be rare, and thus both difficult and costly to obtain.

[0007] Further devices for thermal energy storage are disclosed in CN210952464U W02013020176A1 and in US 20150256119A1.

[0008] As there is a need for energy storage, there is a potential for further development of media for thermal energy storage.

[0009] Summary

[0010] It is an objective of the present disclosure to provide improved devices and methods for thermal energy storage.

[0011] Particular objectives include providing devices and methods which enable efficient and environmentally thermal energy storage.

[0012] The invention is defined by the appended independent claims, with embodiments being set forth in the appended dependent claims, in the following description and in the attached drawings.

[0013] According to a first aspect, there is provided a method of storing thermal energy, comprising exposing a first heat transfer medium to thermal energy from a heat source, and passing said first heat transfer medium through a first channel which is in heat conductive contact with a thermal energy carrier comprising a thermal energy storage substance in an amount of 40-50 % by weight, about 50-60 % by weight, about 60-70 % by weight, about 70-80 % by weight, about 80-90 % by weight, about 90-95 % by weight or 95-99.5 % by weight, such that heat is transferred from the first transfer medium to the thermal energy carrier. In the method, said first heat transfer medium is a gas.

[0014] The thermal energy storage substance may be a phase change material, and operation of the thermal energy carrier may be performed at temperatures which take advantage of such phase change(s).

[0015] In particular, the thermal energy storage substance may be a silicon metal, i.e. silicon in metallic form, or non-passivated silicon. Other thermal energy storage substances are possible, such as metals, metalloids and / or alloys thereof, provided desirable melting and / or boiling points are achieved.

[0016] The thermal energy carrier may comprise the thermal energy storage substance, consist essentially of the thermal energy storage substance, or consist of the thermal energy storage substance.

[0017] It is understood that the heat transfer medium should be a gas at all temperatures and pressures which occur during operation of the system. Preferably, the heat transfer medium should also be a gas at room temperature and atmospheric pressure.

[0018] By using a gas for the heat transfer, it is possible to use a lower cost heat transfer medium, which still is capable of transferring heat at very high temperatures, and which is easier to handle.

[0019] The exchange of heat may take place at a temperature of at about 1000-1100 degC, about 1100-1200 degC, about 1200-1300 degC, about 1300-1400 degC, about 1400-1500 degC, about 1500-2000 degC, about 200-2500 degC, about 2500-3500 degC or about 3000-3500 degC.

[0020] In particular, the heat exchange may take place at a temperature, or in a temperature range, which brings about a phase change of the material of the thermal energy carrier from solid to liquid. For silicon, such a temperature range may advantageously include the melting point of silicon, which is 1414 degC, with the temperature being 1414 degC + / - 100 degs, preferably + / - 50 degs. The heat source may be selected from a group consisting of an electric resistance heater, an induction heater, a concentrated solar energy device, a combustion system and an arc furnace.

[0021] The first heat transfer medium may be guided in the first channel, which is which is immersed in the thermal energy carrier.

[0022] According to a second aspect, there is provided a method of retrieving thermal energy from a thermal energy storage, comprising providing a second heat transfer medium, and passing said second heat transfer medium through a second channel which is in heat conductive contact with a thermal energy carrier comprising a thermal energy storage substance in an amount of 40-50 % by weight, about 50-60 % by weight, about 60-70 % by weight, about 70-80 % by weight, about 80-90 % by weight, about 90-95 % by weight or 95-99.5 % by weight. The second heat transfer medium is a gas.

[0023] The thermal energy storage substance may be a phase change material, and operation of the thermal energy carrier may be performed at temperatures which take advantage of such phase change(s).

[0024] In particular, the thermal energy storage substance may be a silicon metal, i.e. silicon in metallic form, or non-passivated silicon. Other thermal energy storage substances are possible, such as metals, metalloids and / or alloys thereof, provided desirable melting and / or boiling points are achieved.

[0025] The thermal energy carrier may comprise the thermal energy storage substance, consist essentially of the thermal energy storage substance, or consist of the thermal energy storage substance.

[0026] By using a gas for the heat transfer, it is possible to use a lower cost heat transfer medium, which still is capable of transferring heat at very high temperatures.

[0027] The exchange of heat may take place at a temperature of at about 1000-1100 degC, about 1100-1200 degC, about 1200-1300 degC, about 1300-1400 degC, about 1400-1500 degC, about 1500-2000 degC, about 200-2500 degC, about 2500-3500 degC or about 3000-3500 degC.

[0028] In particular, the heat exchange may take place at a temperature which brings about a phase change of the material of the thermal energy carrier from liquid to solid. For silicon, such a temperature range may advantageously include the melting point of silicon, which is 1414 degC, with the temperature being 1414 degC + / - 100 degs, preferably + / - 50 degs.

[0029] The thermal energy carrier may comprise, or preferably consist of, metallurgical grade silicon.

[0030] The thermal energy storage substance may be provided as a cohesive body of the silicon metal.

[0031] The thermal energy storage substance may be provided as particles having a particle size of about 0.1-0.2 mm, about 0.2-0.5 mm, about 0.5-0.7 mm, about 0.7-1 mm, about 1-3 mm, about 3-4 mm or about 4-5 mm.

[0032] In the method, at least one of the first heat transfer medium and the second heat transfer medium may comprise at least one of air, nitrogen, helium, neon, argon, krypton, xenon, or a combination thereof.

[0033] The second heat transfer medium may be guided in the second channel, which is immersed in the thermal energy carrier.

[0034] The second heat transfer medium may be conveyed through a heat exchanger and caused to exchange heat with a working fluid.

[0035] The working fluid may be any type of working fluid, such as for a carnot process or for an organic rankine cycle. In particular, the working fluid may be water.

[0036] The working fluid may be conveyed to a turbine.

[0037] A thermoelectric generator may be used to generate electricity from the second heat transfer medium.

[0038] In the method the first channel may be in fluid connection with the second channel.

[0039] Alternatively, in the method, the first channel may be separated from the second channel.

[0040] The first heat transfer medium may be collected from outside and optionally preheated prior to being subjected to the heat source.

[0041] The first heat transfer medium may be preheated by heat transfer with the second heat transfer medium.

[0042] The thermal energy carrier may be divided into a plurality of cells, each cell containing an amount of said thermal energy storage substance, wherein the channel, and the second channel, if any, is configured to exchange heat with at least some of the cells. The cells may be divided laterally by cell walls, which may be formed of a suitable ceramic material. Moreover, the cells may be downwardly limited by a cell bottom.

[0043] By dividing the thermal energy carrier into cells, it is possible to provide a large volume of material, while controlling the expansion and contraction taking place in connection with the phase change.

[0044] At least some of the cells may have a cell cross section, which increases in a direction away from a cell bottom.

[0045] To this end, at least some of the cell walls may have a thickness which taper in the direction away from a cell bottom over at least part of a cell wall height.

[0046] At least some, preferably all, of the cells may contain an amount of said thermal energy storage substance which has a volume that in a maximum expanded state of the thermal energy storage substance, is less than a volume of the cell.

[0047] The cells may be formed as right prisms, with a polygonal, in particular hexagonal, cross section.

[0048] The cells may be divided into sheets, each sheet comprising a plurality of cells having their base surfaces in a plane parallel with a sheet plane.

[0049] At least one said channel may be arranged to extend in a plane parallel with at least one of the sheets.

[0050] At least one said channel may be arranged to intersect at least two of the sheets.

[0051] According to a third aspect, there is provided a system for storing thermal energy, comprising a thermal energy carrier comprising a thermal energy storage substance in an amount of 40-50 % by weight, about 50-60 % by weight, about 60-70 % by weight, about 70-80 % by weight, about 80-90 % by weight, about 90-95 % by weight or 95-99.5 % by weight, such that heat is transferred from the first transfer medium to the thermal energy carrier, a first channel which is in heat conductive contact with said thermal energy carrier, and a first heat transfer medium, which is conveyed in said first channel. Said first transfer medium is a gas.

[0052] The thermal energy storage substance may be a phase change material, and operation of the thermal energy carrier may be performed at temperatures which take advantage of such phase change(s).

[0053] In particular, the thermal energy storage substance may be a silicon metal, i.e. silicon in metallic form, or non-passivated silicon. Other thermal energy storage substances are possible, such as metals, metalloids and / or alloys thereof, provided desirable melting and / or boiling points are achieved.

[0054] The thermal energy carrier may comprise the thermal energy storage substance, consist essentially of the thermal energy storage substance, or consist of the thermal energy storage substance.

[0055] The first channel may be connected to a heat source, for heating the first heat transfer medium.

[0056] The heat source may be selected from a group consisting of an electric resistance heater, an induction heater, a concentrated solar energy device, a combustion system and an arc furnace.

[0057] The first channel and the thermal energy carrier may be configured to exchange heat at a temperature of about 1000-1100 degC, about 1100-1200 degC, about 1200-1300 degC, about 1300-1400 degC, about 1400-1500 degC, about 1500- 2000 degC, about 200-2500 degC, about 2500-3500 degC or about 3000-3500 degC.

[0058] The system may further comprise a second channel which is in heat conductive contact with said thermal energy carrier, and a second heat transfer medium, which is conveyed in said first channel, wherein the second heat transfer medium is a gas.

[0059] The thermal energy carrier may comprise, or preferably consists of, metallurgical grade silicon.

[0060] The thermal energy storage substance may be provided as a cohesive body of the thermal energy storage substance.

[0061] The system as claimed in any one of claims 25-21, wherein the thermal energy storage substance is provided as particles having a particle size of about 0.1- 0.2 mm, about 0.2-0.5 mm, about 0.5-0.7 mm, about 0.7-1 mm, about 1-3 mm, about 3-4 mm or about 4-5 mm.

[0062] At least one of the first heat transfer medium and the second heat transfer medium may comprise at least one of air, nitrogen, helium, neon, argon, krypton, xenon, or a combination thereof.

[0063] The second heat transfer medium may be guided in the first channel, which is immersed in the thermal energy carrier. The system may further comprise a heat exchanger, which is connected to the second channel, for causing second heat transfer medium to exchange heat with a working fluid.

[0064] The working fluid may be any type of working fluid, such as for a carnot process or for an organic rankine cycle. In particular, the working fluid may be water.

[0065] The working fluid may be conveyed to a turbine.

[0066] The system may further comprise a thermoelectric generator, configured to generate electricity from the second heat transfer medium, or from the working fluid, if any.

[0067] The first channel may be in fluid connection with the second channel.

[0068] Alternatively, the first channel may be separated from the second channel.

[0069] The thermal energy carrier may be divided into a plurality of cells, each cell containing an amount of said thermal energy storage substance, wherein the channel, and the second channel, if any, is configured to exchange heat with at least some of the cells.

[0070] The cells may be separated by cell walls, and at least some of the cell walls may have a thickness which taper in a direction away from a cell bottom over at least part of a cell wall height.

[0071] At least some, preferably all, of the cells may contain an amount of said thermal energy storage substance which has a volume that in a maximum expanded state of the thermal energy storage substance, is less than a volume of the cell.

[0072] The cells may be formed as right prisms, with a polygonal base surface.

[0073] The cells may be divided into sheets, each sheet comprising a plurality of cells having their base surfaces in a plane parallel with a sheet plane.

[0074] At least one said channel may be arranged to extend in a plane parallel with at least one of the sheets.

[0075] At least one said channel may be arranged to intersect at least two of the sheets.

[0076] Fig. 1 is a schematic diagram of a system for storing and recovering thermal energy. Fig. 2 is a schematic diagram of a system for storing and recovering thermal energy.

[0077] Figs 3a-3b schematically illustrate an architecture for a system for storing and recovering thermal energy.

[0078] Figs 4a-4b schematically illustrate an alternative, or supplementary, architecture for a system for storing and recovering thermal energy.

[0079] Detailed description

[0080] Fig. 1 schematically discloses a system for storing and recovering thermal energy in a thermal energy storage substance in the form of non-passivated silicon. The system comprises a thermal energy carrier 10, which may be provided in an insulating enclosure 101. This insulating enclosure may be hermetically sealed, such that any gas present therein does not communicate with an outside.

[0081] A first channel 11 is provided immersed in the thermal energy carrier 10, such that heat can be transferred from the first channel 11 to the thermal energy carrier 10.

[0082] The first channel 11 is connected to a heat source 12.

[0083] In the first channel 11, there is provided a first heat transfer medium, which may be caused to circulate in a loop, which may be closed, from the heater 12 to the thermal energy carrier 10 and back to the heater 12.

[0084] A second channel 13 is provided immersed in the thermal energy carrier 10, such that heat can be transferred from the thermal energy carrier 10 to the second channel 13.

[0085] The second channel 13 is connected to a heat exchanger 14.

[0086] In the second channel 13, there is provided a second heat transfer medium, which may be caused to circulate in a loop, which may be closed, from the heater thermal energy carrier 10 to the heat exchanger 14 and back to the thermal energy carrier 10.

[0087] The heat exchanger 14 may, in turn be configured for exchanging heat from the first heat transfer medium to a working medium, which may be used in a heat cycle process, e.g. to generate electric energy through a turbine 15 or any other converter for converting thermal energy into electric energy. The thermal energy carrier 10 comprises a thermal energy storage substance, in particular non-passivated silicon, which may be present in an amount of 40-50 % by weight, about 50-60 % by weight, about 60-70 % by weight, about 70-80 % by weight, about 80-90 % by weight, about 90-95 % by weight or about 95-99.5 % by weight. The thermal energy storage substance may be provided as a cohesive block of material. Alternatively, the thermal energy storage substance may be provided as pellets or grains with a particle size of about 0.1-0.2 mm, about 0.2-0.5 mm, about 0.5-0.7 mm, about 0.7-1 mm, about 1-3 mm, about 3-4 mm or about 4-5 mm.

[0088] The first channel 11 may be formed of tubes of a high-temperature ceramic material, or even of so-called "ultra high temperature ceramic". The first channel 11 may be configured along a meandering or helical path through the thermal energy carrier 10. Alternatively, the first channel may be provided as a plurality of parallel channels through the thermal energy carrier 10 with manifolds at upstream and downstream portions of the thermal energy carrier 10.

[0089] The heat source 12 may be selected from a group consisting of an electric resistance heater, an induction heater, a concentrated solar energy device, a combustion system and an arc furnace.

[0090] The heat generated at the heat source and transferred to the first heat transfer medium may be sufficient to cause the first heat transfer medium to exchange heat with the thermal energy carrier 10 at a temperature of at about 1000-1100 degC, about 1100-1200 degC, about 1200-1300 degC, about 1300-1400 degC, about 1400-1500 degC, about 1500-2000 degC, about 200-2500 degC, about 2500-3500 degC or about 3000-3500 degC. In particular temperatures above the melting point of silicon, which is about 1414 degC, are particularly interesting, as this allows for the phase change of the silicon to be used to enhance its heat storage capacity. In addition, it is preferable to remain below the boiling point of silicon, which is about 3265 degC. It is also preferable to keep the amount of impurities in the thermal energy carrier as low as possible, in order to reduce the risk of pressure increases due to impurities that boil at lower temperature than the silicon. Such impurities may incur a need for the enclosure to be hermetically sealed to prevent such impurities from escaping from the enclosure.

[0091] The first heat transfer medium may comprise, or consist of, at least one of air, nitrogen, helium, neon, argon, krypton, xenon. An enclosure 101 for storing a metal or metalloid undergoing a phase change while using ceramic material in the walls and in the heat pipes inside the material, and accommodating volume changes can be provided as follows.

[0092] A high-temperature-resistant ceramic material can be selected, which can withstand the heat generated during the metal's phase change process.

[0093] A sufficient thickness of ceramic walls of the enclosure 101 is selected to provide structural integrity and thermal stability. The design may be configured such that it allows for expansion and contraction without compromising the enclosure's integrity.

[0094] It is possible to provide expansion joints, by integrating flexible joints or gaps in the ceramic walls to accommodate volume changes without causing stress or cracking.

[0095] For thermal insulation, materials like ceramic fiber blankets or refractory bricks ma y be provided between the ceramic walls and the metal to maintain temperature uniformity and minimize heat loss.

[0096] One or more pressure relief valves or vents may be implemented to release excess pressure that may build up due to volume changes during the phase transition.

[0097] The flow in the channels 11, 13 may be used to regulate temperature. An auxiliary channel (not shown) may be provided for additional heat removal, in order to control heat in the thermal energy carrier 10.

[0098] It may be desirable to provide a monitoring system (not shown), including sensors for temperature, pressure, and volume changes within the enclosure 101, and to connect these sensors to a monitoring system for real-time data tracking and alerts for any anomalies.

[0099] High-temperature seals or gaskets may be used to prevent leakage and maintain an airtight environment within the container.

[0100] The second channel 13 may be provided in the same manner as the first channel, i.e. from tubes of a ceramic material. The second channel may be arranged to follow e.g. in parallel with, the path of, the first channel 11.

[0101] The heat exchanger 14 may be provided as a conventional heat exchanger having capability of handling the temperatures received from the second heat transfer medium emerging from the thermal energy carrier 10. The heat exchanger 14 may be connected to any type of heat consuming system 15, such as a carnot process, an organic rankine cycle, a turbine, or the like.

[0102] The working medium heated by the heat exchanger 14 may be cycled through the heat consuming system, or it may be captured upstream of the heat exchanger 14 and released downstream of the heat consuming system.

[0103] Fig. 2 schematically illustrates a system which corresponds to the system illustrated in fig. 1, but where the first heat transfer medium is collected from outside air at 17 and where a preheater 16 is provided for preheating such collected air prior to it being fed to the heat source 12 where it is caused to pick up heat and then conducted in the first channel 11 to heat the thermal energy carrier 10.

[0104] The first heat transfer medium which has transferred heat to the thermal energy carrier may be released to surrounding atmosphere or be recycled, optionally to be mixed with added medium in the form of outside air.

[0105] One or more thermoelectric generators may be provided for picking up residual heat at places in the system where such may be at hand.

[0106] For example, a first thermoelectric generator 18a may be provided to pick up residual heat from the second channel 13 upstream of the thermal energy carrier 10.

[0107] As another example, a second thermoelectric generator 18b may be provided to pick up residual heat from the first channel 11 downstream of the thermal energy carrier 10.

[0108] As another example, a third thermoelectric generator 18c may be provided to pick up residual heat from the first channel enclosure 101.

[0109] As another example, a fourth thermoelectric generator 18d may be provided to pick up residual heat from the heat source 12.

[0110] In order to manage the fact that the metal will expand and contract as it undergoes a phase change, which may give rise to substantial forces, both on the enclosure and on any channels 104, 105 used for conducting the heat transfer fluid in the metal, it is possible to divide the metal into a plurality of individual cells 103, each of which providing sufficient space for the expansion / contraction. The cells may be laterally limited by a cell wall and downwardly limited by a cell bottom. Hence, each cell 103 may enclose a coherent body of the thermal energy storage substance and / or an amount of thermal energy storage substance particles, as described above. At least some, preferably all, of the cell walls may have a thickness which taper in a direction away from a cell bottom. Hence, cell walls may taper in a direction upwardly. Such taper may be continuous along the entire cell wall, or the taper may increase or decrease with increasing distance from the cell bottom.

[0111] In particular, cell thickness may be determined in accordance with the forces expected from the expanding / contracting the thermal energy storage substance enclosed in the cells.

[0112] Coherent blocks of the thermal energy storage substance or the thermal energy storage substance powder may be pre-fabricated to fit the individual cells.

[0113] Figs 3a-3b schematically illustrate a first concept for forming such a structure 102, wherein cells 103 are given a hexagonal shape in one plane, such that each cell 103 forms an essentially right prism having a hexagonal base surface. The cells 103 may in turn be divided into sheets 1011, 1011a, 1011b, 1011c, with channels 104 provided between sheets 1011, 1011a, 1011b, 1011c, and in particular in contact with the underside of an associated sheet 1011, 1011a, 1011b, 1011c.

[0114] Fig. 3b is a sectional view taken along the line A-A in fig. 3a.

[0115] A plurality of such sheets 1011, 1011a, 1011b, 1011c may be enclosed in the enclosure 101.

[0116] The size of each sheet 1011, 1011a, 1011b, 1011c, the thickness of the sheet (i.e. the height of the prisms, and the number of sheets 1011, 1011a, 1011b, 1011c may be selected to provide a desired capacity.

[0117] Alternatively, or as a supplement, as illustrated in figs 4a-4b, channels 105 may be provided in a direction normal to the sheet planes, such that the channels 105 intersect the sheets 1011, 1011a, 1011b, 1011c. Fig. 4b is a sectional view taken along the line B-B in fig. 4a.

[0118] With the sheet design, a modular system can be provided, which will allow the production of different capacity thermal energy carriers having different capacities from a limited number of parts. In this context, it is noted that several sheets may be arranged in the same plane to form a layer, with the thermal energy carrier being made up of a plurality of layers rather than merely a plurality of sheets.

[0119] Individual sheets or layers may be replaceable.

[0120] The number and size of channels 104, and their density (channel volume in relation to cell 103 volume, may be determined as desired. It is possible to provide a single set of channels 104, 105 which is used both to introduce heat into the thermal energy carrier. Such a set 104, 105 may be controllable by valves.

[0121] In particular with the design as per figs 4a-4b, it is possible to stack a plurality of sheets 1011, 1011a, 1011b, 1011c, such that they are held in place by the channels 105.

[0122] Alternatively, separate sets of channels 104, 105 may be used for introduction of heat into the thermal energy carrier and for extraction of heat from the thermal energy carrier, respectively.

[0123] The cell structure 102 (including e.g. cell walls, cell bottom, possible cell cover) may be formed of a ceramic material having suitable thickness and which may be selected to provide an appropriate combination of (or trade-off between) thermal conductivity (preferably as high as possible) and strength (also preferably as high as possible).

[0124] It is noted that in the event it is desired to operate the thermal energy carrier at temperatures where one or more of the material(s) in which thermal energy is stored, such as the thermal energy storage substance or any impurities present in the thermal energy storage substance, then it may be necessary to provide for the management of the ensuing pressure increase.

[0125] Hence, it will be of importance generally to select the right ceramic material(s), in particular a high-temperature-resistant ceramic material that can withstand the heat generated during the metal's phase change process.

[0126] It will also be important to select and adapt wall thickness and design, e.g. by opting for a sufficient thickness of ceramic walls to provide structural integrity and thermal stability. For example, there may be provided a design that allows for expansion and contraction without compromising the container's integrity.

[0127] To this end, one or more expansion joints may be provided in the form of integrated flexible joints or gaps in the ceramic walls to accommodate volume changes without causing stress or cracking.

[0128] Moreover, insulation materials may be used that provide thermal insulation, such as ceramic fiber blankets or refractory bricks between the ceramic walls and the metal to maintain temperature uniformity and minimize heat loss. Pressure regulation may also be used to mitigate effects of phase change, e.g. by the implementation of pressure relief valves or vents to release excess pressure that may build up due to volume changes during the phase transition.

[0129] Temperature control may be provided by installing heating or cooling elements to regulate the temperature inside the container and ensure a controlled environment for the phase change process.

[0130] A monitoring system may be provided, which includes sensors for temperature, pressure, and volume changes within the thermal energy carrier and connect these sensors to a monitoring system for real-time data tracking and alerts for any anomalies.

[0131] High-temperature seals or gaskets may be used to prevent leakage and maintain an airtight environment within the container.

[0132] While the concept has been described and illustrated with reference to silicon, and in particular to non-passivated silicon, it is understood that the concepts disclosed herein may be used also with other thermal energy storage substances, including elements or compositions having suitable heat capacity, melting point and / or boiling point, with in particular Cu, Fe, B, Ga, Ge, Au, Hf, Ni, Ti, W, Mo, Ta, As, Sb, Te, including alloys of two or more of these elements, as non-limiting examples.

[0133] Channels used for heat tranfer to or from the thermal energy carrier may be formed such that they essentially meander or zig-zag in two or three dimensions through the thermal energy carrier. For example, channels may be formed so as to extend helically through the thermal energy carrier.

Claims

CLAIMS1. A method of storing thermal energy, comprising: exposing a first heat transfer medium to thermal energy from a heat source (12), and passing said first heat transfer medium through a first channel (11) which is in heat conductive contact with a thermal energy carrier (10) comprising a thermal energy storage substance, such as silicon, in an amount of 40-50 % by weight, about 50-60 % by weight, about 60-70 % by weight, about 70-80 % by weight, about 80-90 % by weight, about 90-95 % by weight or 95-99.5 % by weight, such that heat is transferred from the first transfer medium to the thermal energy carrier (10), characterized in that said first heat transfer medium is a gas.

2. The method as claimed in claim 1, wherein said exchange of heat takes place at a temperature of at about 1000-1100 degC, about 1100-1200 degC, about 1200-1300 degC, about 1300-1400 degC, about 1400-1500 degC, about 1500- 2000 degC, about 200-2500 degC, about 2500-3500 degC or about 3000-3500 degC.

3. The method as claimed in claim 1 or 2, wherein the heat source is selected from a group consisting of an electric resistance heater, an induction heater, a concentrated solar energy device, a combustion system and an arc furnace.

4. The method as claimed in any one of the preceding claims, wherein the first heat transfer medium is guided in a heat supply channel immersed in the thermal energy carrier (10).

5. A method of retrieving thermal energy from a thermal energy storage, comprising: providing a second heat transfer medium, and passing said second heat transfer medium through a second channel (13) which is in heat conductive contact with a thermal energy carrier (10) comprising thethermal energy storage substance in an amount of 40-50 % by weight, about 50-60 % by weight, about 60-70 % by weight, about 70-80 % by weight, about 80-90 % by weight, about 90-95 % by weight or 95-99.5 % by weight, characterized in that said second heat transfer medium is a gas.

6. The method as claimed in claim 9, wherein said exchange of heat takes place at a temperature of at about 1000-1100 degC, about 1100-1200 degC, about 1200-1300 degC, about 1300-1400 degC, about 1400-1500 degC, about 1500- 2000 degC, about 200-2500 degC, about 2500-3500 degC or about 3000-3500 degC.

7. The method as claimed in any one of the preceding claims, wherein the thermal energy carrier (10) comprises, or preferably consists of, metallurgical grade silicon.

8. The method as claimed in any one of the preceding claims, wherein the thermal energy storage substance is provided as a cohesive body of the silicon metal.

9. The method as claimed in any one of claims 1-7, wherein the thermal energy storage substance is provided as particles having a particle size of about 0.1- 0.2 mm, about 0.2-0.5 mm, about 0.5-0.7 mm, about 0.7-1 mm, about 1-3 mm, about 3-4 mm or about 4-5 mm.

10. The method as claimed in any one of the preceding claims, wherein at least one of the first heat transfer medium and the second heat transfer medium comprises at least one of air, nitrogen, helium, neon, argon, krypton, xenon, or a combination thereof.

11. The method as claimed in any one of claims 5-10, wherein the second heat transfer medium is guided in a heat retrieval channel system immersed in the thermal energy carrier (10).

12. The method as claimed in any one of claims 5-11, wherein the second heat transfer medium is conveyed through a heat exchanger and caused to exchange heat with a working fluid.

13. The method as claimed in claim 12, wherein the working fluid is conveyed to a turbine.

14. The method as claimed in any one of claims 5-13, wherein a thermoelectric generator is used to generate electricity from the second heat transfer medium.

15. The method as claimed in any one of claims 5-14 in conjunction with any one of claims 1-4, wherein the first channel (11) is in fluid connection with the second channel (13).

16. The method as claimed in any one of claims 5-14 in conjunction with any one of claims 1-4, wherein the first channel (11) is separated from the second channel (13).

17. The method as claimed in any one of the preceding claims, wherein the first heat transfer medium is collected from outside and optionally preheated prior to being subjected to the heat source.

18. The method as claimed in claim 17, wherein the first heat transfer medium is preheated by heat transfer with the second heat transfer medium.

19. The method as claimed in any one of the preceding claims, wherein the thermal energy carrier (10) is divided into a plurality of cells, each cell containing an amount of said thermal energy storage substance, wherein the first channel (11), and the second channel (13), if any, is configured to exchange heat with at least some of the cells.

20. The method as claimed in claim 20, wherein at least some of the cells have a cell cross section, which increases in a direction away from a cell bottom.

21. The method as claimed in claim 19 or 20, wherein at least some, preferably all, of the cells contain an amount of said substance which has a volume that in a maximum expanded state of the substance, is less than a volume of the cell.

22. The method as claimed in any one of claims 19-21, wherein the cells are formed as right prisms, with a polygonal cross section.

23. The method as claimed in any one of claims 19-22, wherein the cells are divided into sheets, each sheet comprising a plurality of cells having their base surfaces in a plane parallel with a sheet plane.

24. The method as claimed in claim 23, wherein at least one said channel (104)is arranged to extend in a plane parallel with at least one of the sheets (1011, 1011a, 1011b, 1011c).

25. The method as claimed in claim 23 or 24, wherein at least one said channel (105) is arranged to intersect at least two of the sheets (1011, 1011a, 1011b, 1011c).

26. A system for storing thermal energy, comprising: a thermal energy carrier (10) comprising a thermal energy storage substance in an amount of 40-50 % by weight, about 50-60 % by weight, about 60-70 % by weight, about 70-80 % by weight, about 80-90 % by weight, about 90-95 % by weight or 95-99.5 % by weight, such that heat is transferred from the first transfer medium to the thermal energy carrier, a first channel (11) which is in heat conductive contact with said thermal energy carrier (10), and a first heat transfer medium, which is conveyed in said first channel (11), characterized in thatsaid first transfer medium is a gas.

27. The system as claimed in claim 26, wherein the first channel (11) is connected to a heat source (12), for heating the first heat transfer medium.

28. The system as claimed in claim 27, wherein the heat source (12) is selected from a group consisting of an electric resistance heater, an induction heater, a concentrated solar energy device, a combustion system and an arc furnace.

29. The system as claimed in any one of claims 26-28, wherein the first channel (11) and the thermal energy carrier (10) are configured to exchange heat at a temperature of about 1000-1100 degC, about 1100-1200 degC, about 1200-1300 degC, about 1300-1400 degC, about 1400-1500 degC, about 1500-2000 degC, about 200-2500 degC, about 2500-3500 degC or about 3000-3500 degC.

30. The system as claimed in any one of claims 26-29, further comprising: a second channel (13) which is in heat conductive contact with said thermal energy carrier (10), and a second heat transfer medium, which is conveyed in said second channel (13), wherein said second heat transfer medium is a gas.

31. The system as claimed in any one of claims 26-30, wherein the thermal energy carrier (10) comprises, or preferably consists of, metallurgical grade silicon.

32. The system as claimed in any one of claims 26-31, wherein the thermal energy storage substance is provided as a cohesive body of the thermal energy storage substance.

33. The system as claimed in any one of claims 26-31, wherein the thermal energy storage substance is provided as particles having a particle size ofabout 0.1-0.2 mm, about 0.2-0.5 mm, about 0.5-0.7 mm, about 0.7-1 mm, about 1-3 mm, about 3-4 mm or about 4-5 mm.

34. The system as claimed in any one of claims 26-33, wherein at least one of the first heat transfer medium and the second heat transfer medium comprises at least one of air, nitrogen, helium, neon, argon, krypton, xenon, or a combination thereof.

35. The system as claimed in any one of claims 26-34, wherein the second heat transfer medium is guided in a the second channel which is immersed in the thermal energy carrier (10).

36. The system as claimed in any one of claims 26-35, further comprising a heat exchanger (14), which is connected to the second channel (13), for causing second heat transfer medium to exchange heat with a working fluid.

37. The system as claimed in claim 36, wherein the working fluid is conveyed to a turbine (15).

38. The system as claimed in any one of claims 26-37, further comprising a thermoelectric generator (18a), configured to generate electricity from the second heat transfer medium, or from the working fluid, if any.

39. The system as claimed in any one of claims 26-38, in conjunction with claim 23, wherein the first channel (11) is in fluid connection with the second channel (13).

40. The system as claimed in any one of claims 26-38, in conjunction with claim 23, wherein the first channel (11) is separated from the second channel (13).

41. The system as claimed in any one of claims 26-40, wherein the thermal energy carrier (10) is divided into a plurality of cells (103), each cell (103) containing an amount of said thermal energy storage substance, wherein the firstchannel (11, 104, 105), and the second channel (13, 104, 105), if any, is configured to exchange heat with at least some of the cells (103).

42. The method as claimed in claim 41, wherein at least some of the cells have a cell cross section, which increases in a direction away from a cell bottom.

43. The system as claimed in claim 41 or 42, wherein at least some, preferably all, of the cells (103) contain an amount of said thermal energy storage substance which has a volume that in a maximum expanded state of the thermal energy storage substance, is less than a volume of the cell.

44. The system as claimed in any one of claims 41-43, wherein the cells (103) are formed as right prisms, with a polygonal base surface.

45. The system as claimed in any one of claims 41-44, wherein the cells (103) are divided into sheets (1011, 1011a, 1011b, 1011c), each sheet (1011, 1011a, 1011b, 1011c) comprising a plurality of cells (103) having their base surfaces in a plane parallel with a sheet plane.

46. The system as claimed in claim 45, wherein at least one said first or second channel (11, 13, 104, 105) is arranged to extend in a plane parallel with at least one of the sheets (1011, 1011a, 1011b, 1011c).

47. The system as claimed in claim 45 or 46, wherein at least one said first or second channel (11, 13, 104, 105) is arranged to intersect at least two of the sheets (1011, 1011a, 1011b, 1011c).

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