A vessel unit for storing and transferring heat

Abstract

The invention relates to a vessel unit for storing and transferring heat comprising a first inner heat storage vessel configured for heat storage and a second vessel at least partially surrounding the first inner heat storage vessel. The invention also relates to a system for storing and transferring heat comprising at least one vessel unit. The invention further relates to a method for storing and transferring heat.

Description

[0001] Title: A vessel unit for storing and transferring heat

[0002] Description:

[0003] The invention relates to a vessel unit for storing and transferring heat comprising a first inner heat storage vessel configured for heat storage and a second vessel at least partially surrounding the first inner heat storage vessel.

[0004] The invention also relates to a system for storing and transferring heat comprising at least one vessel unit.

[0005] The invention further relates to a method for storing and transferring heat.

[0006] WO2023 / 073334 discloses a vacuum insulated thermal store with a vessel unit for storing and transferring heat, wherein the vessel unit comprises a first inner heat storage vessel configured for heat storage and a second vessel surrounding the first inner heat storage vessel. The inner vessel is containing a solid sensible heat storage material with electric heating elements and a heat exchanger each embedded in the sensible storage material, wherein between the inner vessel and the outer vessel a vacuum insulation space is provided. The embedded electric heating elements and the heat exchanger in the sensible storage material provide safety challenges that necessitate advanced engineering solutions providing a relatively complex vessel unit, in particular where the electric heating elements are relatively close to pipes associated to the heat exchanger. In addition, these solutions contribute to higher overall costs due to the need for specialized materials, robust safety mechanisms, regular maintenance, and comprehensive system design and testing.

[0007] It is an object of the present invention to provide an improved and / or robust vessel unit.

[0008] This object is achieved with the vessel unit as defined in claim 1.

[0009] The vessel unit for storing and transferring heat comprises:

[0010] - a first inner heat storage vessel configured for heat storage;

[0011] - a second vessel at least partially surrounding the first inner heat storage vessel, wherein between the first inner heat storage vessel and the second vessel a heat transfer space is provided, wherein the heat transfer space is configured to transfer heat originating from the first inner heat storage vessel outside the vessel unit; - a third outer vessel surrounding the second vessel, wherein between the second vessel and the third outer vessel a thermal insulation space is provided.

[0012] The vessel unit comprises an inner vessel and an outer vessel and a vessel between the inner and the outer vessel. These three vessels define three fluidly separated spaces or rooms, i.e. an inner heat storage space, the heat transfer space and the thermal insulation space. The inner heat storage space is designed for heat storage, such as by means of solid heat storage material filling the inner heat storage space defined by the first inner vessel. The heat transfer space is designed for transferring internal heat from the inner vessel to the outside of the vessel unit and the outer thermal insulation space is designed for thermal insulation. In the heat transfer space a fluid may be present, wherein the fluid can be heated by means of the outer side of the first vessel wall. The thermal insulation space ensures that the stored heat is retained for longer periods, maintaining a stable temperature within the inner vessel and simultaneously ensures that heat loss in the transfer space is reduced to a minimal. By assigning different functions to each of the three vessels, it is possible to provide a relatively robust construction of the vessel unit allowing a long term (for example longer than a week) energy storage. The three different functions associated to each vessel are heat storage in the first vessel, heat transfer by means of a heat transfer space provided by the second vessel and thermal insulation by means of the thermal insulation space provided by the third vessel. Each vessel can be made from a metal or an alloy, i.e. there is no need for specialized materials. As a result a cost effective and robust vessel unit can be realized. In addition, the effective insulation provided by the third outer vessel minimizes thermal stresses due to high internal temperature differences with respect to ambient surrounding, reducing wear and tear and reduces the need for frequent maintenance.

[0013] By means of the vessel unit it is possible to store energy, in particular heat, for a relatively long period of time. By storing energy in the vessel unit in the summer, where there is normally a surplus of energy, for example provided by sustainable energy sources, and / or at times where energy is relatively cost friendly, the vessel unit is configured to provide minimal energy storage loss for a relatively long time, such as weeks or even months. At times, for example in the winter period, where the costs of energy are normally higher, the system further has an improved configuration to transfer the energy, in particular heat, out of the system. The vessel unit is configured to transfer internal heat in a relatively efficient manner externally with a relatively low impact on the total heat energy stored in the inner vessel and with drastically reduced heat loss during transfer.

[0014] In one aspect, the thermal insulation space is configured as a vacuum space. Vacuum technology is used in the system to engineer high-performance thermal insulation to prevent conductive and convective thermal leakage, i.e. to reduce heat loss from the first inner heat storage by providing a vacuum or at least a partial vacuum of for example 10-10000 Pa.

[0015] In one further aspect, at least a portion of a side of a wall of the first inner heat storage vessel defining the heat transfer space is provided with a heat transfer structure designed for providing a maximal heat transfer area in the heat transfer space and / or with a corrugated and / or textured outer first inner heat storage vessel wall surface designed for providing a maximal heat transfer area in the heat transfer space. Such a heat transfer structure can for example by heat conductive ribs providing a larger heat transfer area than for example a flat outer wall portion of the first vessel. In other words by means of the heat transfer structure or a corrugated I textured outer first inner heat storage vessel wall surface the surface area for transferring heat from the inner vessel into a fluid in the transfer space can be maximised.

[0016] The first inner heat storage vessel may comprise a wall with an outer side provided with spacers adapted to be not in contact with an inner side of the second vessel in an unexpanded state of the first inner heat storage vessel. In use of the vessel unit, the first inner heat storage vessel may thermally expand towards the relatively stationary second vessel, wherein in some situations contact cannot be prevented in a thermally expanded state of the first vessel. Uncontrolled direct contact or local contact between the wall of the first inner vessel (with or without surface area enlarging measures such corrugations or heat transfer structure as mentioned above) and the wall of the second vessel is undesired, because such contact may result in damage and in a less robust vessel unit. Hence, the outer side of the wall of the first inner vessel is provided with multiple spacers, preferably spacers equi-spaced around the circumference of this outer wall and / or in a vertical arrangement, such that controlled contact by means of the spacers is possible to absorb thermal expansion of the first vessel in an expanded state to provide a relatively robust vessel unit. The spacers may be electrically insulated, such that in case there is contact between the first vessel and the second vessel by means of the spacers, the contact provides no electrical leakage between these vessels. Such electrical insulation enhances safety and reliability of the vessel unit, in particular if the first vessel comprises electrical heating members (electrodes) for heating the solid material inside the storage space of the first vessel.

[0017] In a further aspect, the third outer vessel is surrounding the first inner heat storage vessel and the second vessel. In this configuration, the first and the second vessel have no contact with the ambient surroundings which ensures maximal thermal insulation. In another aspect, the first inner heat storage vessel is configured to be electrically insulated with respect to the heat transfer space and / or the first inner heat storage vessel is configured to be electrically insulated with respect to the thermal insulation space. Such electrical insulation further enhances safety and reliability to provide a relatively robust vessel unit, in particular if the first vessel comprises electrical heating members (electrodes) as mentioned above.

[0018] The system for storing and transferring heat comprises at least one vessel unit of this disclosure, and a heat exchanger which is in fluid communication with the heat transfer space. The heat exchanger may be external of the at least one vessel unit. The heat exchanger may use a fluid, such as a gas for example air, being pumped by means of a pump through the transfer space in order to retrieve heat originating from the first inner heat storage vessel. In other words, the heat originating from the first inner heat storage vessel will be transferred by means of the fluid from the transfer space to the outside of the vessel unit. As a result a cost effective and robust system can be realized, i.e. an improved system for storing and transferring heat.

[0019] The system may further comprise at least one controller configured for:

[0020] - operating a heat transfer mechanism including the heat exchanger; and / or

[0021] - operating a vacuum pump for providing a vacuum insulation space in the thermal insulation space; and / or

[0022] - operating an energy introduction unit for introducing heat in the first inner heat storage vessel of the vessel unit.

[0023] The method for storing and transferring heat comprises at least the following steps: A- storing heat in a first inner heat storage vessel;

[0024] B- providing a thermal insulation space between a second vessel surrounded by a third outer vessel and the third outer vessel;

[0025] C- transferring heat from a heat transfer space between the first inner heat storage vessel and the second vessel which is at least partially surrounding the first inner heat storage vessel.

[0026] The disclosure also discloses a computer program product, comprising a computer readable storage medium storing instructions which, when executed on at least one processor of the controller of the system, cause said at least one processor to carry out the method steps of this disclosure.

[0027] It is to be understood that both the foregoing general description and the following detailed description present various embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed.

[0028] The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification.

[0029] The apparatus and method will now be explained in more detail with reference to the appended drawings, in which:

[0030] Figures 1a,b show a schematic view of a system and method for storing and transferring heat;

[0031] Figures 2 shows a perspective view of a vessel unit for storing and transferring heat;

[0032] Figures 3a, b show details of the vessel unit shown in figure 2.

[0033] Like reference numbers refer to like elements throughout the various drawings.

[0034] The vessel unit, system and method for storing and transferring heat will now be described more fully hereinafter with reference to the accompanying drawings in which exemplary embodiments of the invention are shown. However, the invention may be embodied in many different forms and should not be construed as limited to the representative embodiments set forth herein. The exemplary embodiments are provided so that this disclosure will be both thorough and complete, and will fully convey the scope of the invention and enable one of ordinary skill in the art to make, use and practice the invention. The figures show a vessel unit 1 for storing and transferring heat comprising:

[0035] - a first inner heat storage vessel 10 configured for heat storage, for example the first inner heat storage vessel 10 is configured for receiving solid material in a storage space 15 defined by the vessel 10;

[0036] - a second vessel 20 at least partially surrounding the first inner heat storage vessel 10, wherein between the first inner heat storage vessel 10 and the second vessel 20 a heat transfer space 25 is provided, wherein the heat transfer space 25 is configured to transfer heat originating from the first inner heat storage vessel 10 outside the vessel unit 1 ;

[0037] - a third outer vessel 30 surrounding the second vessel 20, wherein between the second vessel 20 and the third outer vessel 30 a thermal insulation space 35 is provided.

[0038] The inner heat storage vessel 10 is configured for receiving solid material in a storage space 15 defined by the vessel 10 for storing heat energy over a long period of time (for example at least weeks). The solid material in the first inner heat storage vessel 10 is capable to be heated to a temperature between 150-1000°C, preferably between 250-750°C, without significant chemical reactions or melting. Solid material in the first inner heat storage vessel to store energy for long term heat storage beneficial from efficiency and safety perspective, in particular solid materials having no phase change in temperature ranges between 100-1000 degrees. The solid material may be capable to be heated to a temperature between 150-1000°C, preferably between 250-750°C, without significant chemical reactions or melting. The solid material is a stationary heat storage medium. Solid storage material may include natural rocks, sandstone, granite, sand, salts, oxides ceramics, castable cements, concrete, basalt, steel slag or elements such as carbon / graphite, silicon, or iron. It is also possible to use mixtures of the mentioned solid materials. Using solid storage material in the vessel unit 1 has advantages from an efficiency and safety perspective. The first inner heat storage vessel 10 is provided with electrical heating members 82a, b designed for heating solid material in the first inner heat storage vessel 10. The electrical heating members 82a, b comprise electrodes which may be at least partly positioned inside the solid material in the first vessel 10.

[0039] The second vessel 20 is provided with at least one inlet 21 for introducing a fluid into the heat transfer space 25 and with at least one outlet 23 for discharging the fluid from the heat transfer space 25. The second vessel 20 is provided with an upper part 20a and a lower part 20b, wherein the upper part 20a is provided with the at least one inlet 21 for introducing a fluid into the heat transfer space and the lower part 20b is provided with the at least one outlet 20b for discharging the fluid from the heat transfer space 25.

[0040] The third outer vessel 30 is provided with a port 31 in its vessel wall 33. The port 31 is provided to provide a thermal insulation space 25 configured as a vacuum space. In the vessel unit 1 there are no fluid other inlets / outlets / ports than the inlet 21 I outlet 23 in second vessel wall 22 defining the heat transfer space 25 and the port 31 in the outer vessel wall 33 defining the thermal insulation space. The three spaces 15, 25, 35 are fluidly separated with respect to each other by means of the vessel walls. In other words, the three spaces are fluidly closed with respect to each other, such that there is no fluid communication between the spaces, i.e. there is no fluid communication between the solid material in the first space 15, the fluid in the second heat transfer space 25 and the fluid in the third thermal insulation space 35. It is possible to use other techniques than vacuum insulation in the thermal insulation space 35, such that outer vessel wall 32 has no port 31 , wherein such a vessel unit (not shown) only comprises the inlet 21 I outlet 23 in second vessel wall 22.

[0041] The volume of the heat transfer space 25 is smaller than the volume of the thermal insulation space 35. In fact, the volume of the heat transfer space 25 is the smallest volume of the three spaces 15, 25, 35 of the vessel unit. For heat transfer a compact transfer space and a relatively large heat transfer surface are advantageous for efficient and / or maximal heat transfer. The volume of the first inner heat storage vessel is at least 2 cubic meter, preferably, at least 5 cubic meter, more preferably, at least 10 cubic meter. As shown in the figures, the third outer vessel 30 is surrounding the first inner heat storage vessel 10 and the second vessel 20. The outer vessel wall 33 of the third outer vessel 30 is in contact with the ambient surroundings and prevents contact between the ambient surroundings and the vessel wall 12 of the first inner vessel 10 and the vessel wall 22 of the second vessel 20.

[0042] The system 100 of this disclosure is shown in figure 1a. The system 100 for storing and transferring heat comprises the vessel unit 1 and a heat exchanger 60 which is in fluid communication with the heat transfer space 25. The heat exchanger 60 is in fluid communication by means of a heat transfer mechanism which comprises fluid lines 63, 64, 65 and a pump 67 for pumping fluid through fluid line 65 and the inlet 21 into the heat transfer space 25 and to the heat exchanger 60 by means of the outlet 23 and the fluid line 63. The fluid lines 63, 65 extend through the wall 33 of the third outer vessel 30, through the thermal insulation space 35 and are connected to the inlet 21 and outlet 23 of the second vessel wall 22 to provide a fluid connection between the heat transfer mechanism including the heat exchanger 60 and the heat transfer space 25. In the variant shown, the exit of the heat exchanger 60 is in fluid communication with the pump 67 by means of the fluid line 64 to provide a closed fluid circuit. Such a closed circuit further reduces heat losses of the system 100. By means of the heat exchanger heat energy is transferred from the system 100, in particular from the heat transfer space, in particular by means of a fluid flowing through the heat transfer space 25. The fluid in the heat transfer space 25 is heated by means of the first vessel 10 configured for heat storage, in particular the fluid is heated by the outer surface of the first vessel 10 in the heat transfer space 25. This heat energy can be used by means of the heat exchanger 60 in for example a conventional heating system for buildings or other energy heat demanding appliances or converted to other forms such as mechanical work or electricity.

[0043] The system 100 is further provided with a vacuum pump 70 configured to provide at least a partial vacuum in the thermal insulation space 35 by means of at least one port 31 in the wall 33 of the third outer vessel 30. As shown, a fluid line 71 provides the fluid connection between the vacuum pump 70 and the port 31. Optionally an exit fluid line 73 may be connected to the vacuum pump 70.

[0044] The system 100 further comprises an energy introduction unit 80 for storing heat energy in the first inner heat storage vessel 10 by converting electrical energy into heat energy by means of electrical heating members 82a, b provided in the first inner heat storage vessel 10. The energy introduction unit 80 of the system 100 for storing heat energy in the first inner heat storage vessel 3 comprises an electrical network 84 connected to the electrical heating members 82a, b to be heated with electricity for heating the solid material in the first inner heat storage vessel 3. The electrical network 84 is for example connected or connectable to solar panels (not shown) or to the electrical grid as a power source.

[0045] The system 100 also comprises at least one controller 90 configured for: - operating the heat transfer mechanism including the heat exchanger 60 and / or the pump 67; and / or

[0046] - operating the vacuum pump 70; and / or

[0047] - operating the energy introduction unit 80.

[0048] As shown in figure 1a by means of the dotted lines the controller 90 is communicating with the heat exchanger 60, the pump 67, the vacuum pump 70 and / or the energy introduction unit 80. The pump (not shown) can be integrated in the heat exchanger 60.

[0049] The controller 90 is adapted to operate the energy introduction unit 80 by monitoring the temperature inside the first vessel 10 at various locations and / or controlling the charging of the system depending on the monitored temperatures and depending on electricity price. If the electricity price monitored by the controller 90 is relatively low, for example falls below a predetermined limit value, and the controller 90 monitors a charging demand, the control will instruct the energy introduction unit 80 to charge the solid material in the first vessel 10. The controller 90 is further adapted to control the discharge of heat depending on the heat need by switching on or off or adjusting the speed of the pump 67 and / or the heat exchanger 60. The pump 67 may be configured as an air pump or ventilator. The controller is further adapted to control the vacuum, for example in a vacuum range between 10 and 10000 Pa in the vacuum insulation space 35 to achieve the optimal insulation value to minimize heat losses in the vessel unit 1

[0050] Figure 1 b shows the method steps of the method of this disclosure. The method for storing and transferring heat comprises the following steps:

[0051] A- storing heat in a first inner heat storage vessel 10;

[0052] B- providing a thermal insulation space 35 between a second vessel 20 surrounded by a third outer vessel 30 and the third outer vessel 30;

[0053] C- transferring heat from a heat transfer space between the first inner heat storage vessel and the second vessel which is at least partially surrounding the first inner heat storage vessel.

[0054] In step B at least a partial vacuum is provided in the thermal insulation space 35. A vacuum or at least a partial vacuum of for example 10-10000 Pa in the thermal insulation space 35 may be provided by the vacuum pump 70. In step c, heat from the heat transfer space 25 is transferred to a heat transfer mechanism including the above described heat exchanger 60.

[0055] By means of the energy introduction unit 80, solid heat storage material is heated to a temperature between 150-1000°C, preferably between 250-750°C, without significant chemical reactions or melting as mentioned above.

[0056] The vessel unit 1 is also shown in figure 2, wherein details of the vessel unit 1 are shown in figures 3a, b. The vessel unit 1 is carried with respect to the underground 4 on a support comprising pillars 3. These pillars 3 carry the three vessel 10, 20, 30, wherein the vessel wall 33 is the outer wall of the vessel unit 1 surrounding the second vessel 20 and the first inner heat storage vessel 10 completely.

[0057] The first inner heat storage vessel 1 is configured to be electrically insulated with respect to the heat transfer space 25. The first inner heat storage vessel 1 is further configured to be electrically insulated with respect to the thermal insulation space 35. The electrical insulation of the vessels 10, 20, 30 is for example provided by means of the pillars 3 and / or other vessel support structures in the vessel unit 1 , wherein the pillars 3 and / or the support structures comprise electrical insulation (not shown), for example alumina insulators. Electrical leakage between these vessels 10, 20 is prevented by electrical insulation such that the safety and reliability of the vessel unit is enhanced.

[0058] The fluid lines 63, 65 are only partially shown in figure 2. In addition, the port 31 of the vessel unit 1 to be connected to the vacuum pump 70 is shown.

[0059] Fig. 3a shows a cross-section through the vessel unit 1 approximately halfway through the total height of the vessel unit 1 and figure 3b shows an enlarged view indicated with C in figure 3a of the cross-section.

[0060] From the enlarged view, it can be seen that at least a portion of a side of a wall of the first inner heat storage vessel 10 defining the heat transfer space 25 is provided with a heat transfer structure 90 designed for providing a maximal heat transfer area in the heat transfer space 25. The heat transfer structure 90 is an integral part of the at least one portion of the outer side of the wall 12 of the first inner heat storage vessel 10. Optionally, it is also possible that the heat transfer structure is positioned against or fixated to the at least one portion of the outer side of the wall 12 of the first inner heat storage vessel 10. The heat transfer structure 90 is made of a heat conductive material. The heat transfer structure 90 may be made of the same metal or alloy as the wall 12 or the outer side of the wall 12 of the first inner heat storage vessel 10. Other configurations to obtain a relatively large heat transfer area in the heat transfer space 25 are possible such as a corrugated and / or textured outer first inner heat storage vessel wall surface (not shown).

[0061] As shown in figure 3b, the first inner heat storage vessel 10 comprises a wall 12 with an outer side provided with spacers 96 adapted to be not in contact with an inner side of the wall 22 of the second vessel 20 in an unexpanded state of the first inner heat storage vessel. Figure 3b shows the unexpanded state of the first inner heat storage vessel 10. Each spacer 96 has a spacer end facing the wall of the second vessel 20. In the unexpanded state of the first inner heat storage vessel 10 there is an air gap between this spacer end and the wall of the second vessel 20.

[0062] In use of the vessel unit 1 and the system 100, the first inner heat storage vessel 10 may thermally expand towards the relatively stationary second vessel 20, The spacers 96 prevent uncontrolled contact between the wall 12 of the first inner vessel 1 and the wall 22 of the second vessel 20. Controlled contact due to thermal expansion by means of the spacers 96 does not provide any damage or at least reduces any damage drastically. In other words, the spacers 96 provide a more robust vessel unit. The outer side of the wall 12 of the first inner vessel is provided with multiple spacers 96. Each spacer 96 extends transversely or radially away from the outer side of the wall 12 of the first inner vessel 10. The spacers 96 are equi-spaced around the circumference of the outer side of the wall 12, such that controlled contact by means of the spacers 96 is possible to absorb thermal expansion of the first vessel 10 to provide a relatively robust vessel unit. In a cylinder configuration of the vessels as shown, six spacers 96 can be provided around the circumference at a certain height of the vessel 10, wherein two adjacent spacers enclosed an angel of 60 degrees with the center of the cylindrical vessel 10. In a vertical direction multiple sets of six spacers 96 may be provided on the outer side of the wall 12. The spacers 96 are electrically insulated by means of an insulator for example an alumina insulator 97, such that in case there is contact between the first vessel 10 and the second vessel 20 by means of the spacers 96, the contact provides no electrical leakage between these vessels 10, 20. Such electrical insulation enhances safety and reliability of the vessel unit.

[0063] In the thermal insulation space radiation shields 98 are provided. The radiation shields 98 are mounted against an inner side of the wall 33 of the third outer vessel 30 in an arrangement surrounding the second vessel 20. Each radiation shield 98 mainly extends along the second vessel 20 or the first vessel 10 in a vertical direction. Other configurations of the radiation shields are possible, such as for example multiple parallel extending radiation shields in a vertical direction. The radiation shields 98 are arranged at a distance from an outer wall side of the second vessel 20 and at a distance from the inner wall side of the third outer vessel 30 as can be seen in figure 3b. The radiation shields 98 may comprise a single layer or a multi-layer, wherein at least one layer is made from an appropriate metal or alloy, in particular aluminium or an aluminium alloy, or stainless steel or a steel alloy.

Claims

CLAIMS1. A vessel unit for storing and transferring heat comprising:- a first inner heat storage vessel configured for heat storage;- a second vessel at least partially surrounding the first inner heat storage vessel, wherein between the first inner heat storage vessel and the second vessel a heat transfer space is provided, wherein the heat transfer space is configured to transfer heat originating from the first inner heat storage vessel outside the vessel unit;- a third outer vessel surrounding the second vessel, wherein between the second vessel and the third outer vessel a thermal insulation space is provided, wherein the first inner heat storage vessel is configured to be electrically insulated with respect to the heat transfer space.

2. The vessel unit according to claim 1 , wherein at least a portion of a side of a wall of the first inner heat storage vessel defining the heat transfer space is provided with a heat transfer structure designed for providing a maximal heat transfer area in the heat transfer space and / or with a corrugated and / or textured outer first inner heat storage vessel wall surface designed for providing a maximal heat transfer area in the heat transfer space.

3. The vessel unit according to claim 1 or 2, wherein the second vessel is provided with at least one inlet for introducing a fluid into the heat transfer space and with at least one outlet for discharging the fluid from the heat transfer space.

4. The vessel unit according to claim 3, wherein the second vessel is provided with an upper part and a lower part, wherein the upper part is provided with the at least one inlet for introducing a fluid into the heat transfer space and the lower part is provided with the at least one outlet for discharging the fluid from the heat transfer space.

5. The vessel unit according to any of the preceding claims, wherein the volume of the heat transfer space is smaller than the volume of the thermal insulation space.

6. The vessel unit according to any of the preceding claims, wherein the thermal insulation space is configured as a vacuum space.

7. The vessel unit according to any of the preceding claims, wherein the first inner heat storage vessel is configured to be electrically insulated with respect to the thermal insulation space.

8. The vessel unit according to any of the preceding claims, wherein the first inner heat storage vessel comprises a wall with an outer side provided with spacers adapted to be not in contact with an inner side of the second vessel in an unexpanded state of the first inner heat storage vessel.

9. The vessel unit according to claim 8, wherein the spacers are electrically insulated.

10. The vessel unit according to any of the preceding claims, wherein the third outer vessel is surrounding the first inner heat storage vessel and the second vessel.

11. The vessel unit according to any of the preceding claims, wherein the first inner heat storage vessel is configured for receiving solid material for storing heat energy, wherein the solid material in the first inner heat storage vessel is capable to be heated to a temperature between 150-1000°C, preferably between 250-750°C, without significant chemical reactions or melting, and / or the volume of the first inner heat storage vessel is at least 2 cubic meter, preferably, at least 5 cubic meter, more preferably, at least 10 cubic meter, and / or the first inner heat storage vessel is provided with electrical heating members designed for heating solid material in the first inner heat storage vessel and / or in the thermal insulation space one or more radiation shields are arranged.

12. A system for storing and transferring heat comprising at least one vessel unit according to any of the preceding claims, and a heat exchanger which is in fluid communication with the heat transfer space.

13. The system according to claim 12, wherein the system is provided with a vacuum pump configured to provide at least a partial vacuum in the thermal insulation space by means of at least one port in the third outer vessel.

14. The system according to claim 12 or 13, wherein the system further comprises an energy introduction unit for storing heat energy in the first inner heat storage vessel, for example by converting electrical energy into heat energy by means of electrical heating members provided in the first inner heat storage vessel.

15. The system according to any of the preceding claims 12-14, wherein the system comprises at least one controller configured for:- operating a heat transfer mechanism including the heat exchanger; and / or- operating the vacuum pump; and / or- operating the energy introduction unit.

16. A method for storing and transferring heat comprising at least the following steps:A- storing heat in a first inner heat storage vessel;B- providing a thermal insulation space between a second vessel surrounded by a third outer vessel and the third outer vessel;C- transferring heat from a heat transfer space between the first inner heat storage vessel and the second vessel which is at least partially surrounding the first inner heat storage vessel, wherein the first inner heat storage vessel is configured to be electrically insulated with respect to the heat transfer space.

17. The method according to claim 16, wherein in step B at least a partial vacuum is provided in the thermal insulation space.

18. The method according to claim 16 or 17, wherein heat from the heat transfer space is transferred to a heat transfer mechanism including a heat exchanger.

19. The method according to any of the preceding claims 16-18, wherein the first inner heat storage vessel comprises solid material for storing heat energy, wherein the solid material is heated to a temperature between 150-1000°C, preferably between 250-750°C, without significant chemical reactions or melting.

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