Thermal energy store

Abstract

The invention relates to a thermal energy store (2) comprising a heat storage medium (34) and one or more pipes (12) extending through the heat storage medium (34) and through which a heat transfer fluid can be conducted, such that heat stored in the heat storage medium (34) can be transferred from the heat storage medium (34) through pipe walls (18) of the one or more pipes (12) to the heat transfer fluid. The one or more pipes (12) are designed as one or more electrical resistance heating elements into which electrical power can be introduced, which can be transferred as heating power from the one or more pipes (12) to the heat storage medium (34). Furthermore, the invention relates to a system comprising one or more electrical power sources and such a thermal energy store (2).

Description

[0001] The invention relates to a thermal energy storage device, comprising a heat storage medium and one or more pipes which extend through the heat storage medium and through which a heat transfer fluid can be passed, so that heat stored in the heat storage medium can be released from the heat storage medium through pipe walls of the one or more pipes to the heat transfer fluid.

[0002] Such thermal energy storage systems can be used, for example, to temporarily store surplus energy. With decentralized energy sources, for example, particularly when they are also or exclusively set up for island operation, there can sometimes be overproduction or availability of power in several time windows, which however is not used during these time windows due to a lack of demand from the connected consumers. In the case of decentralized electricity production that is not capable of providing base load, it can often happen that potentially available power is not used at the same time by the decentralized consumers on site. Conversely, there is often a demand for electrical power from locally connected electrical consumers in time windows in which the volatile electrical energy source can only produce less.Intermediate storage is in principle possible in such a way that electrical power can be called up at a later time, for example using electrochemical storage devices such as accumulators. However, these are expensive to provide and are subject to significant wear and tear due to charging and discharging cycles, at least in the long term. Thermal energy storage devices, on the other hand, are easier and cheaper to manufacture and require less maintenance and are less prone to failure. Thermal energy storage devices also require some expensive components. These include, for example, a heat storage medium, which can disadvantageously entail high acquisition and processing costs, and sometimes also costs for the acquisition and maintenance of a suitable container, for example if it must be particularly chemically resistant, pressure-resistant or liquid- and / or gas-tight.The same applies to components for introducing and removing thermal energy into such a thermal energy storage system.

[0003] The invention is based on the object of improving a thermal energy storage device of the type mentioned at the outset, in particular of overcoming the disadvantages mentioned, and further in particular of providing a particularly simple and / or cost-effective possibility of temporarily storing overproduced electrical energy.

[0004] The problem is solved by a thermal energy storage device of the type mentioned above, in which one or more pipes are designed as one or more electrical resistance heating elements into which electrical power can be introduced, which can be transferred as heating power from the one or more pipes to the heat storage medium. The heating power that can be introduced over a period of time can thus be stored as heat in the heat storage medium.

[0005] This provides a thermal energy storage device that is particularly simple and cost-effective to manufacture and requires particularly little maintenance over its operating life. In particular, the thermal energy storage device according to the invention no longer necessarily requires a separate electrical heating device. This is achieved by structurally integrating an electrical heating device into the pipe(s).

[0006] For this purpose, the pipeline or pipelines are connected, for example, to a first electrical supply line at a first electrical connection point and to a second electrical supply line at a second electrical connection point. These electrical connection points are arranged in such a way, and the pipeline or pipelines therebetween are designed in such a way that an electrical resistance is formed between the connection points by the electrically conductive pipeline or pipelines. In particular, the pipeline or pipelines can be made of an electrically conductive material, in particular of metal or a material comprising metal.The electrical resistance between the connection points is dimensioned and matched to a connectable electrical power source for heating the thermal energy storage device in such a way that the electrical power source enables continuous electrical resistance heating of the pipeline. The level of electrical resistance can be adjusted, for example, by adjusting the wall thickness, length, and the specific electrical resistance of the material of the pipeline(s).

[0007] Thus, electrical power can be converted into thermal heating power along the pipeline(s) and thereby introduced into the thermal energy storage device, or is converted into thermal heating power in a thermal storage process and thereby introduced into the thermal energy storage device. With such electrical heating, the pipeline(s) are heated directly in the sense of an electrical heating element. The power that can be introduced or is introduced is transferred from the thereby heated pipeline to the heat storage medium. Depending on the heat storage medium, any cavities, and material properties, the transfer to the heat storage medium can occur through a contribution from heat conduction, heat radiation, and heat convection.

[0008] The inventive design of the pipeline or pipelines thus enables a simple and cost-effective conversion of electrical power into thermal power directly in the thermal energy storage device according to the invention. This results in particular simplicity of construction, mechanical robustness, and low maintenance. The pipeline thus has a dual function. A first function is as a heating device for converting electrical power into thermal power, including its transfer to the heat storage medium. A second function is as a flow channel for the heat transfer fluid to pass through the heat storage medium. This allows thermal energy to be absorbed by the heat storage medium and extracted from the thermal energy storage device using the heat transfer fluid.Depending on the heat storage medium, any cavities within it, and its material properties, the transfer of thermal energy from the heat storage medium to the heat transfer fluid can occur through thermal conduction, thermal radiation, and thermal convection. It is understood that thermal energy transfer from the heat storage medium to the heat transfer fluid is possible provided the heat transfer medium has a higher temperature than the heat transfer fluid.

[0009] In a first mode of charging, the thermal energy storage device can be operated in such a way that, within a time window, the full electrical power is delivered to the electrically conductive material of the pipeline and from there completely to the heat storage medium and stored there. In this case, it is possible that, within the time window, no heat is supplied to the heat transfer fluid in the thermal energy storage device. In a second mode of operation, the thermal energy storage device can be operated in such a way that, within a time window, the full electrical power is delivered to the electrically conductive material of the pipeline, with a first part of this power being delivered to the heat storage medium and stored therein, and with a second part of this power being supplied to the heat transfer fluid and taken from the thermal energy storage device.In the second operating mode, a first portion of the power is stored in the heat storage medium, and at the same time, the fluid flow of the heat transfer fluid is heated with a second portion of the power, thereby providing continuous flow heating of the heat transfer fluid. In a third operating mode, the thermal energy storage device can be operated such that, within a specific time window, the entire electrical power is delivered to the electrically conductive material of the pipe and from there to the heat transfer fluid. It is possible for no heating power to be supplied to the heat storage medium during this time window. The third operating mode enables the thermal energy storage device to be operated as a continuous flow heater without simultaneously storing any electrical power.

[0010] The heat transfer fluid can, in particular, be a liquid or a gas. The liquid or gas can also be loaded with particles, droplets, or gas bubbles. In particular, the heat transfer fluid can be water or an oil. The heat transfer fluid can also be in a supercritical state.

[0011] The invention makes it possible to convert electrical power or electrical energy into thermal energy in a structurally simple and cost-effective manner and to store it immediately for further use as thermal power or energy. This further use can occur, for example, as heat for heating. Alternatively or in parallel, energy conversion of a portion of the stored thermal energy to provide mechanical or electrical power is possible using suitable energy conversion techniques. The invention thus opens up a broad spectrum of applications. In particular, the energy storage device according to the invention is suitable for cost-effectively storing excess electrical power available over certain time windows as thermal energy.The strength of the invention lies in particular in the dispensability of technically more complex, financially more investment-intensive and more maintenance-intensive technologies, such as combined heat and power engines.

[0012] The problem is also solved by a system comprising one or more electrical power sources and a thermal energy storage device as mentioned above or below.

[0013] The system consisting of an electrical power source and an energy storage system enables greater utilization of the electrical power provided by the electrical power source by temporarily storing excess power, often unneeded at a given moment, with low investment costs and low maintenance. For example, in isolated electrical power sources, the system can improve the utilization of electrical power or energy that is provided unevenly over time.However, even in cases where the system's electrical power source is used as a local electrical power source in addition to a grid connection, the system can make a technically and economically viable contribution. For example, in cases where the power provided by the electrical power source is not capable of meeting base load requirements, but can be used more economically than the power from the grid connection when available. In these cases, it is certainly technically possible to feed this surplus power into the grid connection's grid during periods of available and unused surplus power from the electrical power source.

[0014] Depending on the sometimes very low or non-existent remuneration of the network operator of the grid connection, the system according to the invention opens up a more economical use by keeping the surplus power within the sphere of influence of the system operator as thermal energy and remaining fully or partially usable.

[0015] The invention is therefore particularly suitable for applications where the supply of electrical power is uneven and has limited predictability. Most of the aforementioned advantages are particularly evident when the electrical power source is one of the so-called "renewable energies" that are often not suitable for baseload. In particular, it is possible for the system's electrical power source to be a photovoltaic system, a wind turbine, and / or a hydropower plant.

[0016] Advantageous further developments of the invention will become apparent from the dependent claims and from the following description including exemplary embodiments and associated drawings.

[0017] In a further development of the invention, it is provided that the heat storage medium comprises or consists of one or more mineral materials, in particular concrete, for example old concrete and / or recycled concrete, building rubble, dolomite, limestone, sand, gravel and / or stones.

[0018] On the one hand, these materials particularly well meet the requirement for effective storage, namely a high specific heat capacity relative to mass and volume. At the same time, these materials are inexpensive to obtain. In particular, old concrete, recycled concrete, and construction rubble can contribute to the realization of the advantages of the invention with low investment costs, as they are particularly inexpensive to obtain or can even be advantageously included in the investment cost balance, since the production of a thermal energy storage device according to the invention can simultaneously involve the disposal of these materials, provided they previously accrued as waste subject to disposal at a cost.

[0019] In a further development of the invention, the heat storage medium is provided in bulk form, in particular in the form of a heap of pieces, for example, fragments, or consists of such a heap. This allows the heat storage medium to be provided logistically easily and cost-effectively. In particular, this eliminates the complex and cost-intensive production of, for example, a cast mass as a heat storage medium.

[0020] In a further development of the invention, it is provided that the heat storage medium comprises two or more materials or material mixtures, of which a first material or a first material mixture has a higher thermal conductivity than a second material or a second material mixture. In this way, depending on the geometry of the thermal energy store and in particular the arrangement of the heat storage medium, an optimization of the heat transfer processes within the heat storage medium can be achieved. In particular, it is possible for the first material or the first material mixture to be arranged in regions with particularly high heat flow densities and temperature gradients that occur during storage or withdrawal, and the second material or the second material mixture in other regions. In this way, when different materials orMaterial mixtures enable particularly rapid storage or removal of thermal energy into or from the thermal energy storage system.

[0021] In a further development of the invention, the materials are arranged around the pipes in such a way that, in the radial direction away from a region of the pipe's outer surface, a first partial region of the heat storage medium adjacent to the pipe's outer surface has a higher thermal conductivity than a second partial region of the heat storage medium arranged at a radial distance from the pipe's outer surface. This enables particularly effective thermal storage of energy or power. In particular, the introduction of a certain power from the pipe or pipes into the heat storage medium is hereby possible with lower temperature gradients and lower maximum temperatures of the pipe or pipes. Accordingly, while maintaining a maximum temperature, particularly rapid transfer of heat from the pipe or pipes is possible.the pipes into the heat storage medium. Particularly high heat outputs can also be achieved when extracting heat using the heat transfer fluid.

[0022] For example, it is possible for the first material or the first material mixture to be arranged in a ring-shaped manner around a pipeline in cross-sectional terms. If this is the case on a straight section of the pipeline, this corresponds to a cylindrical sleeve shape of the first material or the first material mixture adjacent to the cylindrical outer surface of the pipeline, which is surrounded by the second material or the second material mixture.

[0023] In a further development of the invention, the thermal energy storage device comprises a housing, in particular a silo housing, in which the heat storage medium and a portion of the one or more pipes are arranged. This allows the thermal energy storage device to be implemented simply and cost-effectively. For example, the silo can be added to a property to be heated. The thermal energy storage device can be designed with a silo diameter and a silo height. The silo diameter can, for example, be the largest main dimension in the horizontal direction, in particular the circle diameter in the case of a circular base area.

[0024] These advantages are particularly evident when the thermal energy storage device supplements an existing property connected to a non-base-load decentralized electrical power source, such as a photovoltaic system or a wind turbine, as an energy source, to form a system according to the invention. For example, the thermal energy storage device can be designed as a cylindrical body, in particular as an annex to a property or real estate complex to be heated. Designs in which the thermal energy storage device is designed to be mobile are also possible. For example, it is possible for the thermal energy storage device to be arranged in or attached to a transport container, in particular an ISO container, or to be structurally integrated with such a container.

[0025] In a further development of the invention, the housing has an outer wall comprising a thermal insulation layer, in particular a high-temperature-resistant insulation layer, for example comprising or consisting of one or more of the following insulating materials: perlite, foam glass, ceramic fibers, glass fibers, rock wool. This improves the energy efficiency of the thermal energy storage device and the system. Furthermore, the suitability of the thermal energy storage device and the system for storing energy for particularly volatile electrical power sources is improved, especially over a particularly long period of time.

[0026] In a further development of the invention, the heat storage medium is divided into several storage areas. This makes it possible, for example, to heat the thermal energy storage device to different temperature levels in the different storage areas or to cool it to different temperature levels when removing heat.

[0027] For example, it is possible to separate the storage areas from each other by an insulating material. This allows temperature differences between the storage areas to be maintained for a particularly long time. Alternatively or additionally, it is possible to create storage areas by one or more cavities or a higher void ratio in one or more of the fill. This can be implemented in a particularly simple and cost-effective manner.

[0028] In a further development of the invention, it is provided that various pipes designed as electrical resistance heating elements extend through or adjacent to various storage areas. In particular, this can be achieved in that the storage areas can be heated partially or completely independently of one another and / or in that heat can be released from the storage areas to a or the heat transfer fluid partially or completely independently of one another.

[0029] This allows the storage areas to be heated differently by different circuits. Likewise, if the temperatures in the different storage areas differ, heat transfer fluid at different temperature levels can be drawn from the different pipes. In one embodiment, two or more of the pipes are interconnected in a mixing device of the thermal energy storage system in such a way that individual heat transfer fluid streams emerging from the pipes at different temperatures are mixed into a combined fluid stream, resulting in a mixed fluid temperature. The mixing device may include actuators.In particular, it is possible for the actuators to be controlled by means of a control device, in particular a control device of a system according to the invention described below, and thus for the mixing temperature to be automatically controlled. This has the advantage that heat consumers with specific operating points, in particular with specific temperature requirements, can be operated particularly reliably and energy-efficiently.

[0030] In a further development of the invention, the plurality of pipes comprises at least three pipes configured as three electrical resistance heating elements. This has the advantage that three resistance heating elements can be supplied with three-phase alternating current in a star connection.

[0031] For example, the three pipes are designed as three resistance heating elements with identical electrical properties, e.g., identical electrical resistances. This has the further advantage that only a neutral conductor potential is present at the star point of the star connection. For example, this allows fluid inlet or outlet connections for the heat transfer fluid to be implemented at the star point of the electrical star connection with particularly low electrical hazards.

[0032] In a further development of the invention, it is provided that in the system at least one of the one or more electrical power sources has or is an electrical power source that is independent of the power grid, for example a solar system, a hydroelectric power plant and / or a wind turbine. The system has a control system for providing electrical power by means of the one or more electrical power sources for electrical consumers outside the system. The control system is configured such that, in time windows in which the electrical power that can be provided by means of the electrical power source that is independent of the power grid exceeds the electrical power demanded by the electrical consumers by an electrical surplus power, it feeds this surplus power, in whole or in part, into the thermal energy storage device as the electrical heating power.

[0033] The control system can, for example, be a control electronics unit to which the electrical power source is connected and configured to distribute the available electrical power of the electrical power source to one or more electrical consumers that are also connected to the control electronics. To distribute the power, the control system or control electronics unit can have one or more switching devices for opening or closing electrical circuits. These can be, for example, electromechanical relays, semiconductor relays, or thyristors.

[0034] One of the consumers could, for example, be the thermal energy storage device. Other electrical consumers could be other components of the system itself, i.e., components that serve the system's own function, such as switching devices, display devices, measuring devices, or transmitting devices. Electrical consumers outside the system are consumers that do not serve the system's own function. In isolated operation of the system, i.e., without a connection to the electrical grid, the electrical consumers outside the system can be supplied with power via the system.

[0035] The available electrical power of the electrical power source often varies over time. This is particularly the case when the electrical power source is a photovoltaic system or a wind turbine.

[0036] This makes it possible, depending on the operating status—in particular, the current capacity of the electrical power source combined with the current electrical power drawn by electrical consumers outside the system—to provide surplus power that could also be drawn by consumers but is not currently being drawn. In cases where the system is connected to an electrical power grid, this surplus power can be fed into the electrical power grid, in particular the public electrical power grid, during time windows in which such surplus power can be provided.

[0037] In the technical and economic reality, however, such feed-in is often associated with very limited, and sometimes completely nonexistent, economic benefits due to low to nonexistent remuneration from many public electricity grids. As a result, in many scenarios, feeding into an electricity grid is economically unattractive or even unattractive for investors and operators of such an electricity source.

[0038] In the system, such surplus power can be introduced wholly or partially as electrical heating power into the thermal energy storage device. In this case, the advantages of the thermal energy storage device according to the invention, with its simple to implement and cost-effective design in terms of both investment and maintenance, come into play in particular. The surplus power generated within a certain time window introduces a quantity of thermal energy into the thermal energy storage device, which can be withdrawn in whole or in part at a later time in a simple and cost-effective manner, as required, within different time windows. For withdrawal, the heat transfer fluid can flow through one or more pipes, whereby the heat transfer fluid is heated to a higher temperature when heat is withdrawn from the thermal energy storage device than the temperature at which it is introduced into the thermal energy storage device.When extracting heat energy from the thermal energy storage system, one or more pipes act as a continuous flow heater for the heat transfer fluid.

[0039] In a further development of the invention, at least one of the one or more electrical power sources is a power grid withdrawal point of a power grid. The power grid withdrawal point can be provided alternatively or in addition to the aforementioned possible electrical power sources. The power grid is, for example, a public power grid from which electrical power can be drawn. In addition, electrical power can also be fed into the power grid.

[0040] The system comprises a control system or the control system for providing electrical power to electrical consumers outside the system using one or more electrical power sources. The control system can be designed as an integral unit or as distributed components. In cases where one or more of the aforementioned off-grid electrical power sources are present, the control system can also be the same control system as the control system in question.

[0041] The control system is configured to extract electrical power from the power grid withdrawal point during initial selectable time windows and feed it into the thermal energy storage system as electrical heating power or as part of the electrical heating power. The initial selected time windows can be determined according to various criteria. These could, for example, be time windows during which the costs incurred for withdrawing power from the power grid are particularly low. A possible design is for the control system to be configured to automatically and logically evaluate the time-varying costs for withdrawing power and to determine a start and end of the initial selected time windows based on one or more cost limit values.This enables particularly cost-effective charging of the thermal energy storage system and contributes to a particularly ecological and economic overall balance of the electricity grid.

[0042] In a further development of the invention, it is provided that the system is coupled to at least one heat consumer, in particular a heating system, for example a building heating system, in such a way that heat that can be released or released by the heat storage medium to the heat transfer fluid can be or is supplied in whole or in part to the at least one heat consumer, in particular can be or is transferred from the heat transfer fluid to the heat consumer by means of at least one heat exchanger.

[0043] As a result, the energy stored in the thermal energy storage device can be used in later time windows, regardless of the time windows in which the excess electrical power was generated. The system according to the invention can be implemented particularly advantageously, for example, in buildings requiring heating that have an aforementioned electrical power source, in particular a photovoltaic system or a wind turbine. As a result, in time windows in which any excess electrical power is generated, this energy can be temporarily stored as heat energy in the thermal energy storage device and withdrawn from the thermal energy storage device in later time windows, in particular to meet the building's heating energy requirements. As a result, in particular, the degree of self-sufficiency in the energy supply from the grids for the provision of electrical energy and heating energy in a building can be increased in a straightforward and cost-effective manner.

[0044] As an alternative to use as heating energy, e.g. by transferring it to a heating system, the thermal energy temporarily stored in the thermal energy storage device can be fed to an energy conversion device, in particular a thermal power plant, and converted therein. In particular, the thermal power plant can be a turbine in conjunction with an electric generator. This can result in a phase change of the heat transfer fluid in the pipeline or pipelines, in particular evaporation from the liquid state to a gaseous state, being or being achieved. For example, the heat transfer fluid can be pumped into the pipeline or pipelines by means of a feed pump, so that the heat transfer fluid leaves the pipeline or pipelines at a volume flow rate greater than that with which it entered the pipeline or pipelines.This allows mechanical power or work to be generated using the heat transfer fluid in a heat engine connected to the pipeline(s). The resulting mechanical power or work can be converted into electrical power by a generator, which converts the mechanical power or work into electrical power or work.

[0045] In a further development of the invention, it is possible for the heat consumer to have or be at least one heat engine. The heat engine is designed to convert a portion of the emitted heat into electrical power. For example, the heat engine is a turbine driving a generator. This enables a portion of the energy stored in the thermal energy storage device to be reconverted into electrical power. The operation of the heat engine can be controlled and monitored, for example, in one of the aforementioned control systems, in particular control electronics. Furthermore, it is possible for the or a portion of the electrical power generated by the heat engine and the generator to be or be supplied by the control device, in particular the control electronics, to one of the several consumers outside the system. In particular, the control device is configured to control this automatically.

[0046] The invention is explained by way of example with reference to the following embodiments and the accompanying drawings. They show: Fig. 1: a perspective transparent line drawing of a thermal energy storage device, Fig. 2: a transparent side view as a line drawing of the thermal energy storage device from Figure 1 , Fig. 3: a representation of an electrical connection point of the thermal energy storage device with a fluid connection point.

[0047] Figure 1 shows an embodiment of a thermal energy storage device 2 as a perspective, transparent line drawing. The thermal energy storage device 2 has a housing 4. The housing 4 is cylindrical, i.e., has a circular base 6. The housing has outer walls 8, wherein the outer walls 8 delimit the thermal energy storage device 2 to the outside, toward the environment 9, and to the inside, delimit an interior space 10.

[0048] A pipeline 12 is arranged in the interior space 10. The pipeline 12 extends with several straight sections 14 and several bent sections 16. For the sake of clarity, identical components—here, for example, the several straight sections 14 and the several bent sections 16—are not individually identified in the figures, but are shown only once or a few times as examples.

[0049] The pipe 12 is designed as an electrical resistance heating element. This includes the pipe 12 being made of or comprising an electrically conductive material. In its function as an electrical resistance heating element, the pipe 12 can be heated by an electrical current flowing through a pipe wall 18 or a portion of the pipe wall 18 of the pipe 12 in the axial direction 20 of the pipe 12, thereby generating heat at the ohmic resistance of the electrically conductive material, which heats the pipe 12. In this sense, the electrical current flows through an annular cross-section in the axial direction 20 of the pipe 12.

[0050] For its function as an electrical resistance heating element, the pipe 12 is provided with electrical connections through which the pipe 12 becomes part of an electrical circuit. The pipe 12 has a (in the Figures 1 and 2only schematically indicated) first electrical connection point 22. The first electrical connection point 22 is a (in the Figures 1 and 2 not shown) first electrical supply line 24. Furthermore, the pipeline 12 has a (in the Figures 1 and 2 only schematically indicated) second electrical connection point 26. The second electrical connection point 26 is a (in the Figures 1 and 2The first electrical connection point 22 is electrically connected to the second electrical supply line 28 (not shown). By applying an electrical voltage difference to the first electrical connection point 22 and the second electrical connection point 26, a current can flow through the pipeline 12 and thus the heating of the thermal energy storage device 2. In the present exemplary embodiment, the first electrical connection point 22 is arranged at a first end section 30 of the pipeline 12. The second electrical connection point 26 is arranged at a second end section 32 of the pipeline 12.

[0051] The interior space 10 is filled with a heat storage medium 34 in the form of a bed of concrete fragments. This can be realized particularly cost-effectively using recycled or old concrete. The bed or fragments are not shown in the figures for clarity.

[0052] To prevent undesirable temperature equalization between the interior 10 and the environment 9, the outer walls 8 comprise a high-temperature-resistant insulating material. This insulating material is applied in the form of an insulating layer (not shown in the figures) on the side of the outer walls 8 facing the interior 10 and, in the case of a charged thermal energy storage device 2 and thus in the case of a hot interior 10, reduces heat conduction from the interior 10 to the colder environment 9.

[0053] The bed of the heat storage medium 34 has a void fraction of between 0% and 50%, in particular between 10% and 40%, further in particular between 20% and 35%. The void fraction is that portion of the volume of the bed which is not formed by the material of the heat storage medium 34 itself, but by gas, for example air, located therebetween. A smaller void fraction can result in a greater heat capacity and thus a better storage option for thermal energy. A larger void fraction can offer the advantage of a bed as the heat storage medium 34 which is often particularly inexpensive to produce, in particular with little preparatory work.

[0054] By applying electrical power to the pipe 12, which is designed as a heating element, the pipe 12 itself can be heated, so that the temperature of the pipe 12 rises. As a result of the temperature rise of the pipe 12 to a temperature level that exceeds the temperature level of the heat storage medium 34 in the area adjacent to the pipe 12, heat is transferred from the pipe 12 to the heat storage medium 34.

[0055] This heat transfer during heating of the thermal energy storage device 2, i.e., during charging, comprises, as described below, the heat transfer mechanisms of thermal radiation, convective heat transfer, and thermal conduction. The thermal radiation is emitted by the hot pipe 12, which impinges on the fragments of the heat storage medium 34 located within line of sight and heats them. Convective heat transfer involves the freely moving gas present in the hollow portion of the heat storage medium 34 being heated upon contact with the pipe 12. Due to the resulting heating and reduction in its density, the gas rises against gravity, causing a continuous convective movement of the gas.When the already heated gas comes into contact with fragments of the heat storage medium 34 that have a lower temperature than the already heated gas, heat is in turn transferred from the hot gas to these fragments. Within the fragments of the heat storage medium 34, heat conduction also occurs, whereby, for example, heating of the outer layer of a fragment of the heat storage medium 34 results in the heating of the outer layer leading to heat conduction into the interior of the fragment, where a lower temperature exists. These heat transfer mechanisms typically occur in combination when heating the thermal energy storage device 2.

[0056] The amount of heat introduced into the thermal energy storage device 2 by charging can be stored for an extended period of time. Thus, the stored thermal energy can be retained for later use over this period. During the storage period, an increasingly homogenizing temperature field develops throughout the entire heat storage medium 34 in the interior 10 of the thermal energy storage device 2 due to the aforementioned heat transfer mechanisms.

[0057] Heat stored in the thermal energy storage device 2 can in turn be extracted from it. For this purpose, a heat transfer fluid can be passed through the pipeline 12. As it flows through the pipeline 12, the heat transfer fluid absorbs heat from the pipeline 12, which heat is in turn transferred to it by the heat storage medium 34. This requires that at least some areas of the heat storage medium 34 have a higher temperature than the heat transfer fluid fed into the pipeline 12, so that the heat transfer fluid has a higher temperature when flowing out of the thermal energy storage device 2 than when flowing in. The heat transfer fluid is conveyed through the pipeline 12 and thus through the heat storage medium 34 by a conveying device, in particular a pump.

[0058] This heat transfer during the removal of heat from the thermal energy storage device 2, i.e., during discharging, also includes the heat transfer mechanisms of thermal radiation, convection heat transfer, and heat conduction. Thermal radiation is emitted from the surfaces of the fragments of the heat storage medium 34. The thermal radiation impinges on parts of the pipe wall 18 of the pipe 12 that are in line of sight and heats them. Convection heat transfer involves the freely moving gas present in the hollow portion of the heat storage medium 34 being cooled upon contact with the pipe 12. Due to the resulting increase in its density, the gas sinks in the direction of gravity, causing a continuous convection movement of the gas.When the cooled gas comes into contact with fragments of the heat storage medium 34 that have a higher temperature than the already cooled gas, heat is in turn transferred from these fragments to the hot gas. In the process, the edge region of the affected fragments cools down. Heat conduction also occurs within the fragments of the heat storage medium 34. For example, cooling of the outer layer of a fragment of the heat storage medium 34 as described above results in the higher temperature inside the fragment leading to heat conduction from the interior of the fragment to its edge region, where a lower temperature exists due to the cooling that has already taken place. These heat transfer mechanisms usually occur in combination when the thermal energy storage device 2 is discharged.

[0059] In the exemplary embodiment, the heat storage medium 34 comprises two materials. The first material has a higher thermal conductivity than the second material. In principle, it is possible for the first material and the second material to be present in the interior 10 without any special sorting or other geometric features. In the present exemplary embodiment, the first material and the second material are arranged in the interior 10 such that the first material is arranged on the outer surface 38 of the pipes 12, and the second material is arranged around the first material.Thus, in the radial direction away from a region of the pipe outer surface 38 of the pipes 12, a first partial region of the heat storage medium 34 in the form of the first material, adjacent to the pipe outer surface 38, has a higher thermal conductivity than a second partial region of the heat storage medium 34 in the form of the second material, arranged at a radial distance from the outer wall. With a uniform arrangement of the first material around the pipe outer surface 38 of the pipe 12, i.e. with the same applied material thickness of the first material, the radial distance by which the second partial region of the heat storage medium 34 is spaced from the pipe outer surfaces 38 corresponds to this applied material thickness of the first material.Such an arrangement can, for example, have the advantage that, particularly during transient processes such as charging or discharging the thermal energy storage device 2, lower temperature peaks occur in the heat storage medium 34 and / or higher heat flux densities are enabled. This expands the range of applications and partially increases the durability and service life of components of the thermal energy storage device 2.

[0060] Various designs of the aforementioned type are also possible with other materials or material mixtures, provided that the first material or the first material mixture has a higher thermal conductivity than the second material or the second material mixture and an arrangement in partial areas as mentioned above is given.

[0061] In a further embodiment, the heat storage medium 34 is divided into several storage areas. For example, it is possible for two pipes 12 to be arranged one above the other in a correspondingly higher housing. Each area of ​​the interior space around one of the two pipes designed as heating elements represents a storage area in this sense. These storage areas can be separated, for example, by a partition wall made of insulating material. Alternatively, they can be separated by an intermediate area with a particularly high void ratio.Alternatively, the storage areas can be designed without any particular mechanical separation, but rather simply result as separate storage areas in that the areas of the interior that are arranged closer to a first pipe than to a second pipe or a further pipe are regarded as part of a corresponding first storage area. In various exemplary embodiments, it is possible for different pipes designed as electrical resistance heating elements to extend through or adjacent to different storage areas. This can in particular be designed such that the storage areas can be heated partially or completely independently of one another and / or that heat can be extracted from the storage areas partially or completely independently of one another by means of a heat transfer fluid.The better the storage areas are thermally insulated from each other, the greater this independent charging and discharging capability.

[0062] In a particular further embodiment, the thermal energy storage device has three pipes designed as three electrical resistance heating elements. The three pipes have the same electrical properties, in particular the same electrical resistance. Each of the pipes has its own first electrical connection point and its own second electrical connection point. In this embodiment, the three pipes are electrically connected to one another in a star connection. All first electrical connection points of the pipes are electrically connected to a star point. Each of the three second electrical connection points of the three pipes is connected to a different one of the three outer conductors of a three-phase alternating current electrical power source or can be connected by means of an aforementioned control system.The star point is therefore at the neutral conductor potential of the three-phase alternating current if the electrical resistances of the three pipelines are the same.

[0063] Figure 3shows an exemplary possible implementation for introducing the heat transfer fluid into a pipeline 12 and / or for leading it out of a pipeline 12 in conjunction with introducing and leading out the electrical current for introducing the electrical power for heating the thermal energy storage device 2. This implementation is implemented in all of the aforementioned embodiments for the one or more pipelines 12. The thermal energy storage device 2 has a current transfer device 36 for this purpose. The current transfer device 36 establishes a galvanic connection between the pipe outer surface 38 and a first electrical supply line 24 or a second electrical supply line 28, in particular a power cable. The first electrical supply line 24 and / or second electrical supply line 28 has a cable lug 41, with which the supply line 24 28 is electrically conductively connected to the current transfer device 36.Each pipe 12, which is designed as a resistance heating element, has a first current transfer device 36 at one or its first electrical connection point 22 and a second current transfer device 36 at its second electrical connection point 26. By applying an electrical potential difference between the first current transfer device 36 and the second current transfer device 36, an electrical current can be effected between them through the pipe 12 and the electrical power can be introduced into the pipe 12. The galvanic connection of the one or more current transfer devices 36 to the pipe outer surface 38 and thus also to the electrical supply line 24 28 is formed at a current transfer section 42 of the current transfer device 36. The current transfer section 42 has an inner surface 44.The dimensions of the inner surface 44 correspond to the dimensions of the pipe outer surface 38 in such a way that the inner surface 44 and the pipe outer surface 38 form a flat, electrically conductive connection through which the electrical current flow of the heating power can be conducted. Not necessarily, but usually, the pipe outer surface 38 and, correspondingly, the inner surface 44 are cylindrical and have the same diameters. At the current transfer section 42, the electrically conductive connection has such a large area that, during a current transfer, the electrical current densities present are significantly lower than the current density occurring in the pipe 12 in the axial direction 20 between the current transfer devices 36. Furthermore, the current transfer device 36 can have an insulating section 46 in which there is no electrically conductive connection between the pipe outer surface 38 and the current transfer device.This can be achieved by an insulating gap 48 present along the insulating section 46 between the pipe outer surface and the inner surface 44, which is designed to be thermally and / or electrically insulating.

[0064] By means of one or more of the current transfer devices 36, the heating power can be introduced into a pipeline 12, whereby only in the areas of the pipeline between the current transfer devices 36 do such high current densities occur in the pipeline 12 that a significant heating of the pipeline 12 occurs there, in the sense of a resistance heating element. The current transfer device 36 is thus suitable for establishing a current transfer between the power supply lines 40 and the pipelines 12 and for ensuring that the strongly heated area of ​​the pipeline lies outside the current transfer device 36.

[0065] The current transfer device 36, in particular the current transfer section 42 and, if present, the insulating section 44, extends entirely or partially through the outer wall 8 of the thermal energy storage device 2. Thus, the electrical supply lines 24, 28 are connected to the current transfer device outside the outer walls 8 and thus remain subject to little thermal stress. Each current transfer section 36 extends through openings, in particular holes, in the outer walls 8 up to the interior space 10 or into the interior space 10. Thus, the heated region of the pipes 12 is arranged entirely within the interior space 10.

[0066] The heat transfer fluid is guided into or out of the pipe 12 through an insulating element 50. The insulating element 50 comprises or consists of an electrically insulating material. In the present embodiment according to Figure 3The insulating element is a ceramic tube. The insulating element 50 connects a fluid supply line 52 in a fluid-conducting manner to an end section 30 32 of the pipeline 12. The pipeline 12, in particular its end section 30 32, and the fluid supply line 52 are electrically insulated from one another by means of the insulating element 50.

[0067] The thermal energy storage device 2 is designed for storing thermal energy at temperatures of more than 700°C, preferably more than 800°C. Accordingly, it is provided that the thermal energy storage device in the interior 12 comprises only structural components with such thermal fatigue strength.

[0068] In a further exemplary embodiment, the thermal energy storage device 2 is part of a system which, in addition to the thermal energy storage device, has several electrical power sources (not shown in the figures). These can be electrical power sources independent of the power grid with unevenly available power, for example a solar system, a wind turbine, or a hydroelectric power plant. If this unevenly available power is not used or not fully used by consumers within a time window, the power provided exceeds the used power by an excess power. In the system, this excess power is supplied to the thermal energy storage device 2 as heating power. Thus, within the time window, the excess power that arises is supplied to the thermal energy storage device 2, and thermal energy is stored therein.Thus, on the one hand, consumers who are not part of the system can be supplied with electrical energy from the grid-independent electrical power sources, whereby electrical power not currently required by the consumers can be used as heating power and temporarily stored in the thermal energy storage system.

[0069] Thermal energy stored in the thermal energy storage device 2 can be extracted as needed. For this purpose, the heat transfer fluid is conveyed through one or more pipes 12 and heated by heat dissipation from the heat storage medium 34. The heated heat transfer fluid emerging from the pipe(s) 12 can either be fed directly to a heat consumer as a heat-dissipating medium, where it can dissipate heat. Alternatively, the heat from the heat transfer fluid can be transferred to a heat exchanger, which can then be further conducted by means of another heat transfer fluid.

[0070] A control system is connected to the electrical power sources and is designed to distribute the time-dependent electrical power to the electrical consumers and to feed any surplus power to the thermal energy storage device 2.

[0071] In a further embodiment, the system alternatively or additionally comprises a heat consumer (not shown in the figures) in the form of a building heating system. The heat consumer is coupled to the thermal energy storage unit via a heat exchanger such that heat transferred to the heat transfer fluid can be supplied to a building to be heated to adjust the indoor climate.

[0072] In a further embodiment, the system alternatively or additionally comprises a heat consumer (not shown in the figures) in the form of a re-electricity generation device. The re-electricity generation device comprises a heat engine in the form of a turbine, which drives an electric generator. The electrical power generated by the generator is fed to the control system and can be supplied to the electrical consumer(s).

[0073] If the thermal energy storage device 2 has multiple pipes 12 and different streams of the heat transfer fluid at different temperature levels can be drawn from them, the system can include a mixing device for mixing the streams into a single stream. This allows one or more thermodynamic properties of the single stream to be maintained in a manner that is particularly well-adapted to a heat consumer and more stable over time than without such a mixing device.

[0074] The control system is configured so that charging and discharging of the thermal energy storage device 2 can be carried out automatically over a temperature range between 150 °C and at least 600 °C averaged in the interior space (10).

[0075] In some preferred embodiments, in particular in embodiments in a system with a building heating system and / or a heat engine as a heat consumer, the heat storage medium (34) has a heat capacity with which a thermal energy of at least 100 MWh, in particular at least 200 MWh, for example 1 GWh, can be stored by increasing the temperature averaged in the interior 8 from 150 °C to 700 °C.

[0076] The thermal energy storage system 2 makes the system feasible with low investment and allows for long-term, cost-effective operation with low maintenance. Existing off-grid electrical power systems can also be easily and cost-effectively supplemented with a thermal energy storage system 2. Reference symbol:

[0077] 2 thermal energy storage 4 housing 6 base area 8 outer walls 9 surroundings 10 interior 12 pipe 14 straight section 16 bent section 18 pipe wall 20 axial direction 22 first electrical connection point 24 first electrical supply line 26 second electrical connection point 28 second electrical supply line 30 first end section 32 second end section 34 heat storage medium 36 current transfer device 38 pipe outer surface 40 current supply line 41 cable lug 42 current transfer section 44 inner surface 46 insulating section 48 insulating gap 50 insulating element 52 fluid supply line

Claims

1. Thermal energy storage device, comprising a heat storage medium (34) and one or more pipes (12) which extend through the heat storage medium (34) and through which a heat transfer fluid can be passed, so that heat stored in the heat storage medium (34) can be released from the heat storage medium (34) through pipe walls (18) of the one or more pipes (12) to the heat transfer fluid, characterized in that the one or more pipes (12) are designed as one or more electrical resistance heating elements into which electrical power can be introduced, which can be delivered as heating power from the one or more pipes (12) to the heat storage medium (34).

2. Thermal energy storage device according to claim 1, characterized in thatthe heat storage medium (34) comprises or consists of one or more mineral materials, in particular concrete, for example old concrete and / or recycled concrete, building rubble, dolomite, limestone, sand, gravel and / or stones.

3. Thermal energy storage device according to claim 1 or claim 2, characterized in that the heat storage medium (34) has a bulk material form, in particular a heap of pieces, for example fragments, or consists of this.

4. Thermal energy storage device according to one of the preceding claims, characterized in that the heat storage medium (34) comprises two or more materials or material mixtures, of which a first material or a first material mixture has a higher thermal conductivity than a second material or a second material mixture.

5. Thermal energy storage device according to claim 4, characterized in thatthe materials are arranged around the pipes (12) in such a way that, in the radial direction away from a region of the pipe outer surface (38), a first partial region of the heat storage medium (34) adjacent to the pipe outer surface (38) has a higher thermal conductivity than a second partial region of the heat storage medium (34) arranged at a radial distance from the pipe outer surface (38).

6. Thermal energy storage device according to one of the preceding claims, characterized in that the thermal energy storage device (2) has a housing (4), in particular a silo housing (34), wherein the heat storage medium (34) and a part of the one or more pipes (12) are arranged in the housing (4).

7. Thermal energy storage device according to claim 6, characterized in thatthe housing (4) has an outer wall (8) which has a thermal insulating layer, in particular a high-temperature-resistant insulating layer, for example comprising or consisting of one or more of the following insulating materials: perlite, foam glass, ceramic fibers, glass fibers, rock wool.

8. Thermal energy storage device according to one of the preceding claims, characterized in that the heat storage medium (34) is divided into several storage areas.

9. Thermal energy storage device according to claim 8, characterized in that various pipes (12) designed as electrical resistance heating elements extend through or adjacent to various storage areas, in particular in such a way that the storage areas can be heated partially or completely independently of one another and / or that heat can be released from the storage areas to a or the heat transfer fluid partially or completely independently of one another.

10. Thermal energy storage device according to one of the preceding claims, characterized in that the plurality of pipes (12) comprise at least three pipes which are designed as three electrical resistance heating elements, in particular as three resistance heating elements with the same electrical properties, for example with the same electrical resistances.

11. System comprising one or more electrical power sources and a thermal energy storage device according to one of claims 1 to 10.

12. System according to claim 11, characterized in thatat least one of the one or more electrical power sources comprises or is an electrical power source that is independent of the power grid, for example a solar system, a hydroelectric power plant and / or a wind power plant, wherein the system comprises a control system for providing electrical power by means of the one or more electrical power sources for electrical consumers outside the system, wherein the control system is configured such that, in time windows in which the electrical power that can be provided by means of the electrical power source that is independent of the power grid exceeds the electrical power called up by the electrical consumers by an electrical surplus power, it introduces this surplus power in whole or in part as the electrical heating power into the thermal energy storage device.

13. System according to claim 11 or claim 12, characterized in thatat least one of the one or more electrical power sources is a power grid withdrawal point of a power grid, wherein the system comprises a or the control system for providing electrical power by means of the one or more electrical power sources for electrical consumers outside the system, wherein the control system is configured such that it withdraws electrical power from the power grid withdrawal point in first selectable time windows and introduces it into the thermal energy store (2) as the electrical heating power or as part of the electrical heating power.

14. System according to one of claims 11 to 13, characterized in thatthe system is coupled to at least one heat consumer, in particular a heating system, for example a building heating system, in such a way that heat that can be released or released by the heat storage medium (34) to the heat transfer fluid can be or is fully or partially supplied to the at least one heat consumer, in particular can be or is transferred from the heat transfer fluid to the heat consumer by means of at least one heat exchanger.

15. System according to claim 14, characterized in that the heat consumer has or is at least one heat engine which is designed to convert part of the heat emitted into electrical power, for example a turbine driving a generator.

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