ENHANCED HOMOGENOUS CATALYZED REACTOR SYSTEMS

Abstract

An energy storage system is provided. The energy storage system includes a vessel made of a refractory material and containing a phase change material, a thermally insulating cover at least partially surrounding the vessel, an emitter, made of a refractory material, having a first side arranged to be heated by the phase change material and a second side intended to radiate thermal power, at least one photovoltaic cell arranged to receive the thermal power emitted by the second side of the emitter, and electric means for heating the phase change material.

Claims

1. An energy storage system, comprising: a vessel made of a refractory material and containing a phase change material; a thermally insulating cover at least partially surrounding the vessel; an emitter, made of a refractory material, having a first side arranged to be heated by the phase change material and a second side intended to radiate thermal power; at least one photovoltaic cell arranged to receive the thermal power emitted by the second side of the emitter; and an electric means for heating the phase change material.

2. The energy storage system according to claim 1, wherein the phase change material is selected from the group comprising: silicon, ferrosilicon, steel, copper, iron, aluminum, manganese, nickel, chromium, boron, B.sub.4C, Si.sub.3N.sub.4 and Al.sub.2O.sub.3.

3. The energy storage system according to any of the previous claims, wherein the electric means for heating comprises a metallic coil surrounding the thermally insulating cover and means for generating an alternating electric current through the metallic coil.

4. The energy storage system according to any of the previous claims, wherein the electric means for heating the phase change material uses resistive heating to heat the phase change material.

5. The energy storage system according to claim 4, wherein the electric means for heating the phase change material comprises a plurality of resistive heaters arranged at least partially surrounding an outer wall of the vessel.

6. The energy storage system according to claim 5, wherein the plurality of resistive heaters are composed of a material selected from the group comprising: tungsten, tantalum, molybdenum, graphite, WC, WSi.sub.2, TiSi.sub.2, MoSi.sub.2, TaSi.sub.2, Pt, Pd, Ir, Rh, Os, Re, WRe, WThO.sub.2, WMo, AKSW, WNiCu, WNiFeCo, WMoNiFe and FeCrAlNi alloys.

7. The energy storage system according to any of the previous claims, wherein the electric means for heating the phase change material comprises a plurality of electrodes provided within the vessel.

8. The energy storage system according to claim 7, wherein the plurality of electrodes are composed of a material selected from the group comprising: tungsten, tantalum, molybdenum, graphite, WC, WSi.sub.2, TiSi.sub.2, MoSi.sub.2, TaSi.sub.2, Pt, Pd, Ir, Rh, Os, Re, WRe, WThO.sub.2, WMo, AKSW, WNiCu, WNiFeCo, WMoNiFe and FeCrAlNi alloys.

9. The energy storage system according to any of the previous claims, further comprising a transparent protective window provided between the emitter and the at least one photovoltaic cell.

10. The energy storage system according to claim 9, wherein the protective window is composed of a material selected from the group comprising: pure quartz, vycor quartz, CaF, MgF, BaF.sub.2, Y.sub.2O.sub.3, AlN, BN, Al.sub.2O.sub.3, TiO.sub.2, MgO, SiC, LaF.sub.3, GaP, Si.sub.3N.sub.4, ZnS, ZnSe, Al.sub.23O.sub.27N.sub.5, MgAl.sub.2O.sub.4, SrTiO.sub.3, Y.sub.3Al.sub.5O.sub.12 and BaTiO.sub.3.

11. The energy storage system according to claim 9 or 10, comprising a sealed cavity formed between the emitter and the protective window, wherein an inert atmosphere is created within the cavity.

12. The energy storage system according to any of the previous claims, comprising a sealed cavity formed between the emitter and the at least one photovoltaic cell, wherein an inert atmosphere is created within the cavity.

13. The energy storage system according to any of the previous claims, wherein an inert atmosphere is created within the vessel and at least partially surrounds the phase change material.

14. The energy storage system according to any of the previous claims, wherein the emitter is cylindrical cup-shaped, the cup-shape of the emitter forming an emitter cavity that receives the at least one photovoltaic cell, wherein an outer surface of the cylindrical cup-shaped emitter is arranged to be heated by the phase change material and an inner surface of the cylindrical cup-shaped emitter is intended to radiate thermal power towards the at least one photovoltaic cell, and the vessel comprises an open hole in which the emitter is received.

15. The energy storage system according to claim 14, further comprising a plurality of photovoltaic cells provided on each side of a polyhedral-shaped photovoltaic device.

16. The energy storage system according to any of the previous claims, wherein at least part of a wall of the vessel is configured as the emitter.

17. The energy storage system according to any of the previous claims, further comprising at least one shutter located between the emitter and the at least one photovoltaic cell, such that in a closed position of the shutter the passage of radiation from the emitter to the at least one photovoltaic cell is hindered and in an open position of the shutter the passage of radiation from the emitter to the at least one photovoltaic cell is permitted.

18. The energy storage system according to any of claims 1-13 or 16, wherein the emitter is configured as an upper wall of the vessel, the energy storage system comprises at least one photovoltaic cell facing towards the emitter, and the energy storage system further comprises a shutter located between the emitter and the at least one photovoltaic cell, such that in a closed position of the shutter the passage of radiation from the emitter to the at least one photovoltaic cell is hindered and in an open position of the shutter the passage of radiation from the emitter to the at least one photovoltaic cell is permitted.

19. The energy storage system according to any of claims 1-13 or 16, wherein the emitter is located at a bottom part of the vessel, such that the phase change material is located over the emitter, the energy storage system comprises at least one photovoltaic cell facing towards the emitter, and the energy storage system further comprises a shutter located between the emitter and the at least one photovoltaic cell, such that in a closed position of the shutter the passage of radiation from the emitter to the at least one photovoltaic cell is hindered and in an open position of the shutter the passage of radiation from the emitter to the at least one photovoltaic cell is permitted.

20. The energy storage system according to any of the previous claims, further comprising a mechanism to move the at least one photovoltaic cell towards or away from the emitter.

21. The energy storage system according to any of the previous claims, further comprising a conduit suitable for carrying a fluid and arranged at least partially surrounding the vessel, between the vessel and the thermally insulating cover.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The various embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:

[0041] FIG. 1 shows an energy storage system according to an exemplary embodiment of the present disclosure.

[0042] FIG. 2 shows an energy storage system according to an exemplary embodiment of the present disclosure.

[0043] FIG. 3 shows a perspective view of a photovoltaic array according to the embodiment of FIG. 2.

[0044] FIG. 4 shows another view of the photovoltaic array of FIG. 3.

[0045] FIG. 5 shows an energy storage system according to an exemplary embodiment of the present disclosure.

[0046] FIG. 6 shows an energy storage system according to an exemplary embodiment of the present disclosure.

[0047] FIG. 7 shows an energy storage system according to an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

[0048] The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses of the present disclosure. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

[0049] FIG. 1 shows an energy storage system according to one exemplary embodiment of the present disclosure. In this embodiment the energy storage system includes a phase change material (1) contained in a containment vessel (2). In this embodiment part of the vessel walls comprises a thermal emitter (3) which is heated by the melted material, namely an upper wall of the vessel is configured as the emitter in this embodiment. A thermally insulating cover (4) surrounds the remaining walls of the vessel. A photovoltaic device (7) including one or several photovoltaic cells is arranged facing the emitter (3). In this embodiment, a transparent protective window (5) is provided between the emitter (3) and the photovoltaic device (7), covering the emitter (3). A shutter (6) is arranged between the window (5) and the photovoltaic device (7), which can be opened to release the energy stored in the phase change material (1). During the power production mode of operation the shutter (6) is open and the phase change material begins to solidify at a nearly constant temperature. The phase change material heats the side of the emitter most proximate to the phase change material and the side of the emitter facing the photovoltaic cells radiates thermal power. Energy is thereby released by means of the radiation from the emitter (3) towards the photovoltaic device (7), which directly produces electricity. During the storage mode of operation, the thermal power emitted by the emitter is turned back to the emitter due to the presence of a closed shutter, thus maintaining the phase change material in the melted phase and hindering the radiation from the emitter to reach the photovoltaic device.

[0050] With continued reference to the energy storage system of FIG. 1, the photovoltaic device (7) is bonded to a highly thermally conductive substrate (8) which is mounted on a heat sink (9). The energy storage system of this embodiment further comprises a mechanism to move the photovoltaic device (7) towards and away from the emitter (3). When the shutter (6) opens, the photovoltaic device (7) is thus moved close to the emitter by actuating on pumps (10) that hold the heat sink. Similarly, the photovoltaic device (7) is moved away from the emitter when the shutter (6) is closed. The cavity (11) formed in between the surface of the phase change material (1), the vessel (2) and the emitter (3) is sealed and filled with an inert gas. Also, the cavity (12) formed in between the emitter (3) and the window (5) is sealed and filled with a protective atmosphere that prevents the oxidation of the emitter (3). In various embodiments, sealing rubbers (13) are used for sealing each of these cavities. In various embodiments highly reflective walls (14) are used in the lateral sides of the optical cavity formed by the photovoltaic device (7), the protective window (5) and the emitter (3) for thermal radiation confinement.

[0051] Finally, in the embodiment of FIG. 1 the electric means for heating the phase change material are implemented as a water-cooled copper coil (15) which surrounds the thermally insulating cover (4). When an alternating current is passed through this coil (15) an electromagnetic field is created that generates the so-called Eddy currents within the electrically conductive phase change material (1), which in turn heats up the phase change material by Joule effect until melting.

[0052] In various embodiments, the phase change material (1) is metallurgical-grade silicon, which has a very high latent heat of fusion of about 1800 kJ/kg, high thermal conductivity of up to 150 W/m-C and a melting point of 1400 C. In various embodiments doping materials, such as boron or phosphorous or magnetic materials, such as iron or nickel, are added to silicon to increase its electrical conductivity and its magnetic permeability, respectively, and thereby enhance the inductive heat transfer. In various embodiments, other materials with a high latent heat of fusion and melting point that are used as phase change material are steel, copper, iron, aluminum, manganese, nickel, chromium and boron.

[0053] In various embodiments the vessel (2) is made of a refractory material which is electrically isolating to avoid its direct heating by inductive electromagnetic fields. In various embodiments, Si.sub.3N.sub.4 is used. Alternatively, other materials such as SiC, B.sub.4C, TiB.sub.2, saphire, steatite, cordierite, mullite, boron carbide, boron nitride, aluminum nitride, alumina, spinel or zirconia may be used, as well as ceramic matrix or fiber reinforced composites, which provide a superior thermal cycle resistance.

[0054] In various embodiments, however, an electrically conductive vessel is used. This can be done in combination with either an electrically isolate or conductive phase change material, e.g. silicon. In the former case, the phase change material is heated indirectly by first heating the conductive vessel. In one example, tungsten is used in this case for manufacturing the vessel. Other possible options for the vessel material are: graphite, refractory metals such as tantalum, molybdenum, niobium, and rhenium; refractory metals silicides such as WSi.sub.2, TiSi.sub.2, MoSi.sub.2 and TaSi.sub.2 and other refractory metal alloys such as WC, WRe, WThO.sub.2, WMo, AKSW, tungsten heavy alloys such as WNiCu, WNiFeCo and WMoNiFe. In these embodiments, electrically isolating phase change materials may be used in addition to the electrically conductive materials already mentioned. Among them, boron may be used due to its extremely high latent heat of fusion of 4600 kJ/kg and its melting point of 2077 C. Alternatively, other materials such as B.sub.4C, Si.sub.3N.sub.4 or Al.sub.2O.sub.3 may be used.

[0055] In various embodiments, the thermally insulating cover (4) is made of a refractory electrically isolating material with a low thermal conductivity and low thermal mass. Besides, a highly reflective material is desirable for the inner surface of the thermally insulating cover (4). In one embodiment, the insulating walls are made of Al.sub.2O.sub.3. Alternatively, other materials with the lowest thermal conductivity, such as Mullite, Cordierite, Zirconia and Steatite, may be also used for the thermally insulating cover (4). Ceramic fibers may be also used instead or in combination with the aforementioned materials as the thermally insulating cover (4). In one example, ceramic fibers made of Al.sub.2O.sub.3SiO.sub.2 are ideal for low weight and low thermal mass insulation.

[0056] In various embodiments, the emitter (3) is made of a highly thermally conductive refractory material with low vapor pressure and high emissivity in its second side. Any of the materials specified for the vessel (2) are also usable for building the emitter (3). Generally, those materials having the lowest vapor pressure at high temperatures may be employed, such as tungsten, graphite, molybdenum, tantalum, platinum, hafnium carbide, tungsten carbide, zirconium carbide, zirconium oxide, hafnium oxide, yttrium oxide, holmium oxide, erbium oxide, aluminum oxide and ytterbium oxide.

[0057] In various embodiments, materials allowing operation in air, thus avoiding the use of a protective atmosphere are chosen for the emitter. This is the case of most of the oxide-based ceramics and other refractory materials such as Si.sub.3N.sub.4, MoSi.sub.2, SiC and FeCrAlNi alloys such as Inconel and Kanthal. For the latter compounds, the main concern is the rate of emitter evaporation own to their high vapor pressure. Other materials, such as Pt, Pd, Ir, Rh, Os, Re and their alloys show a very low vapor pressure and can also be operated in air.

[0058] When the emitter is made of a metallic material, it may be covered by a thin film of an oxide, such as hafnium oxide, to provide some degree of spectral selective emission, the layer thickness being generally in the range of about 100 nm to about 500 nm, depending on the desired cut-off wavelength. Alternatively, a two-dimensional photonic crystal may be manufactured on the second surface of the emitter to enhance the emissivity in the spectral band of interest for photovoltaic conversion. In this embodiment, a protective atmosphere is required in the cavity (12) for preventing the metal oxidation. In one embodiment, this atmosphere comprises a vacuum. Alternatively, a regenerative halogen cycle, mostly based on iodine, may be used to return evaporated metal from the window to the emitter.

[0059] In various embodiments a protective atmosphere of inert gas is used within the vessel cavity (11) to avoid the oxidation of the phase change material (1). In one embodiment, argon is used.

[0060] In various embodiments, the shutter (6) is made of alumina, which has a very high reflectivity in the infrared range. Several consecutive shutters may be placed one after the other to provide enhanced thermal insulation during the storing time.

[0061] In various embodiments the photovoltaic device comprises several photovoltaic cells integrated in a highly dense packed array. This array may be formed, for example, according to International Pub. No. WO 2009149505 A1 or International Pub. No. WO 2001099201 A1, which are each incorporated herein by reference.

[0062] In various embodiments, the photovoltaic cells comprise single p-n junctions made of InGaAsSb semiconductor grown on a GaSb substrate and comprise a back surface reflector. Alternatively, multijunction cells or monolithic interconnected modules, such as those described in U.S. Pat. No. 6,162,987, which is also incorporated herein by reference, may be used.

[0063] FIG. 2 shows an energy storage system according to an embodiment of the present disclosure. The energy storage system according to this embodiment includes a phase change material (1) within a containment vessel (2), and a thermally insulating cover (4) surrounding the vessel (2). Both the vessel (2) and the thermally insulating cover (4) have an open hole adapted to receive a cylindrical cup-shaped emitter (3). The cylindrical cup-shaped emitter (3) is thus arranged to be heated from its first surface (i.e. the surface of the emitter most proximate to the phase change material, which in this case is the outer surface of the cylindrical cup-shape) by the melted phase change material. A cylindrical cup-shaped transparent window (5) is provided concentrically to the emitter (3) and covers the inner side of the emitter. The cup-shape of both the emitter and the protective window configure an emitter cavity capable of receiving one or several photovoltaic cells. In this embodiment, the energy storage system includes a plurality of photovoltaic cells conforming a photovoltaic device. The photovoltaic device (16) is configured to be polyhedral-shaped and is introduced within the emitter cavity, thereby producing electricity from the thermal power emitter by the inner side of the cylindrical cup-shaped emitter, due to the heating of the outer side of the emitter by the energy released from the melted material (1). Each side of that polyhedron contains a string (17) of series or parallel connected photovoltaic cells (20).

[0064] With continued reference to the embodiment of FIG. 2, a cavity (11) formed between the phase change material (1), the vessel (2) and the emitter (3) is sealed and filled with an inert gas. A second cavity (12) formed between the emitter (3) and the protective window (5) is sealed and filled by a protective atmosphere. In this embodiment sealing rubbers (13) are used for sealing each of these cavities. Finally, a water-cooled copper coil (15) surrounds the walls of the thermally insulating cover (4). When an alternating current is passed through this coil, it generates an electromagnetic field that generates the so-called eddy currents within the phase change material, which in turn heat up the phase change material (1) by Joule effect until melting. In this embodiment, the energy storage system includes a mechanism to move the photovoltaic device away from the emitter cavity during the heating process of the phase change material by the electric means for heating, in order to avoid the melting of the photovoltaic cells in the storage mode of operation of the system. In the storage mode of operation of the energy storage system, the inner surface of the emitter radiates towards the same surface due to the emitter shape, thus turning thermal power emitted by the emitter back to the emitter. In the power production mode of operation of the system, the mechanism is actuated to move the photovoltaic device towards the emitter, thus placing the photovoltaic device within the emitter cavity. In this position of the photovoltaic device, the photovoltaic cells receive the thermal power emitted by the emitter, as previously described.

[0065] In the embodiment of FIG. 2, the emitter (3) is in one example, made of an electrically isolate material, in order to avoid its direct heating by the electromagnetic fields. However, an electrically conductive emitter may be also used if its melting point is much higher than the melting point of the phase change material. In one embodiment, SiC is used due to its high thermal conductivity and low vapor pressure.

[0066] In one embodiment, a vacuum is created within the cavity (12) for minimizing the convective heat transfer from the emitter (3) to the protective window (5). Alternatively, a noble gas, such as argon, may be used.

[0067] FIGS. 3 and 4 show a photovoltaic device according to the embodiment of FIG. 2. The photovoltaic device comprises several photovoltaic cell strings (17), one string provided on each side of a polyhedron holder (18). Each string is mounted on a flat highly thermally conductive Direct Bonded Copper (DBC) substrate (19) that provides thermal conductivity and the adequate thermal expansion coefficient. The polyhedron holder (18) is made of copper and has an inner circuit (21) where water is introduced for active cooling of the photovoltaic cells. Each string (17) comprises several interconnected photovoltaic cells (20). Each photovoltaic cell (20) has both positive and negative contacts in the front side of the cell and the cells are interconnected by bonding wires (22) to electrically conductive paths (23) that are deposited on top of the photovoltaic cells. The final photovoltaic cell of a string is connected to an electrically conductive path (24) that is connected to an external circuit. The uncovered string area is plated with highly reflective material, such as gold, to reflect back to the emitter the radiative power not absorbed by the photovoltaic cells.

[0068] Alternatively, the photovoltaic cells may have positive and negative contacts in opposite sides of the device and be interconnected according to International Pub. No. WO 2001099201 A1, which is incorporated herein by reference.

[0069] FIG. 5 shows an energy storage system according to an embodiment of the present disclosure where Joule heating is used for melting the phase change material. At least two electrodes (25) are used in this embodiment as electric means for heating for passing a high current through the phase change material (1). The phase change material is thus melted by means of Joule effect. In one embodiment, the electrodes are made of tungsten. Other refractory and electrically conductive materials such as tungsten carbide, tantalum, molybdenum, graphite, WSi.sub.2, TiSi.sub.2, MoSi.sub.2, TaSi.sub.2, Pt, Pd, Ir, Rh, Os, Re and their alloys, may be used. In this embodiment, the vessel walls (2) may be made of either electrically isolate or conductive material, so that a broad range of materials may be used, including the aforementioned ones for manufacturing the electrodes.

[0070] FIG. 6 shows an energy storage system according to one embodiment of the present disclosure where Joule heating is used for heating the vessel walls (2) that subsequently heat the phase change material (1). In this embodiment, the electric means for heating include resistive heaters (26) arranged in contact with the vessel walls. The vessel walls must be electrically isolating and the resistive heaters (26) must be made of an electrically conductive refractory material such as tungsten, tantalum, molybdenum, graphite, tungsten carbide, WSi.sub.2, TiSi.sub.2, MoSi.sub.2, TaSi.sub.2, Pt, Pd, Ir, Rh, Os, Re and their alloys and FeCrAlNi alloys such as Inconel and Kanthal.

[0071] FIG. 7 shows an energy storage system according to one embodiment of the present disclosure. In this embodiment, the emitter (3) is arranged at the bottom part of the vessel (2), such that the phase change material (1) is located over the emitter. The remaining elements are analogous to those described in connection with the embodiment of FIG. 1. In the embodiment of FIG. 7, the phase change material starts solidifying from the bottom part of the vessel and therefore, the creation of a solid layer on top of the phase change material is avoided.

[0072] Also, where a phase change material is used the density of which is lower in the solid phase than in the liquid phase (such as silicon), arrangement of the emitter below the phase change material avoids the potential fracture of the vessel due to thermal stress occurring during the expansion of the phase change material during the solidifying process. This is because the liquid phase has always a volume available in the upper side of the vessel for its expansion during the solidifying process.

[0073] While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the present disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the present disclosure as set forth in the appended claims and their legal equivalents.