Heat storage device with heat storage cassette

Abstract

A thermal storage device for storing electrical energy in the form of thermal energy comprises at least one electric heating device (40) for converting electrical energy into thermal energy, and a plurality of thermal storage cassettes (10). Each thermal storage cassette (10) comprises one cassette frame (20) and a plurality of thermal storage rods (30) held within the cassette frame (20). Each thermal storage cassette (10) comprises a holder (22) for holding the thermal storage rods (30) in place, and at least one end (31) of each thermal storage rod (30) remains unfixed, thereby allowing free thermal expansion of the thermal storage rods (30) in the longitudinal direction (L) of the thermal storage rods (30) inside the cassette frame (20).

Description

Technical Field

[0001] The present disclosure relates to a heat accumulator for storing electric energy in the form of heat energy and a method for manufacturing the heat accumulator.

Background Art

[0002] The temporary storage of energy is playing an increasingly important role in the efficient generation and utilization of energy. More electric energy is being generated by wind power plants and solar power plants, and the storage of electric energy is desired especially because the energy demand fluctuates and because the amount of power generation at a given time fluctuates. Under such circumstances, electrochemical batteries are being used, but these have relatively high manufacturing costs. Pumped storage systems are also common, but these are only used in geographically suitable areas and have raised environmental concerns. Heat accumulators that convert electric energy into heat energy for storage represent a further possibility for energy storage. The heat energy can be taken out of the heat accumulator and used for power generation and / or heat supply.

[0003] Various materials are used for heat storage, but high-temperature heat accumulators using metals (e.g., steel) for heat storage have important advantages. Since metals can store energy at relatively high temperatures, the power generation efficiency using the extracted heat energy is improved. Also, the dimensions of a heat accumulator using a metal can be made relatively small, which is particularly important in urban areas. Furthermore, a heat accumulator having a metal body for heat storage can have the modules of the heat accumulator at least partially assembled before being transported to the installation site. This can be an advantage for assembly and can also be an advantage in terms of manufacturing costs.

[0004] A heat accumulator comprising an electric heating device and a heat storage metal body (particularly a metal rod) is described by the applicant, in particular in European Patent No. 3708923, European Patent No. 3647677, European Patent No. 3633303, European Patent No. 3655631, and European Patent Publication No. 4033191. Compared to other shapes, metal rods have a large surface area and therefore high thermal conductivity. The importance of thermal expansion is particularly great when the metal rod used is heated to temperatures exceeding several hundred degrees Celsius during operation, and the shape of the rod also increases. Given the considerable longitudinal expansion and the unavoidable temperature differences within the heat accumulator during operation, mechanical stability and prevention of material stress are important design aspects. In European Patent No. 3647677, European Patent No. 3633303, and European Patent No. 3655631, the applicant discloses designs intended to reduce material stress, which may increase the thermal expansion of the metal rods and reduce the impact of this expansion on other components. International Publication No. 2016099289 and European Patent Application Publication No. 3247963 describe a thermal storage device in which a frame holds several horizontal thermal storage rods. Several such frames with thermal storage rods can be stacked. International Publication No. 2010070704 discloses a thermal storage device with several vertically arranged thermal storage rods. Chinese Patent Application Publication No. 105757982 describes a latent heat storage device in which several elongated thermal storage elements are held in a frame.

[0005] The present invention aims to significantly prevent material stress caused by thermal expansion throughout the entire heat accumulator, while simultaneously keeping the manufacturing process of the heat accumulator as simple as possible and ensuring high stability in the overall structure of the heat accumulator. [Overview of the project]

[0006] The object of the present invention is to provide a heat accumulator and a method for manufacturing a heat accumulator for storing electrical energy in the form of thermal energy, and it is thought that this heat accumulator and manufacturing method are intended to enable high mechanical stability with a simple manufacturing method and to prevent excessive material stress due to thermal expansion.

[0007] This objective is addressed by a heat storage device and method having the features of an independent claim.

[0008] A thermal storage device according to the present invention for storing electrical energy in the form of thermal energy comprises at least one electric heating device for converting electrical energy into thermal energy, and a plurality of thermal storage cassettes. Each thermal storage cassette comprises one cassette frame and a plurality of thermal storage rods held within the cassette frame. Each thermal storage cassette is provided with a holder for holding the thermal storage rods in place, and at least one end of each thermal storage rod is left unfixed so as to allow free thermal expansion of the thermal storage rods in the longitudinal direction of the thermal storage rods inside the cassette frame.

[0009] Optionally, the ends of each heat storage rod are placed on the base of the heat storage cassette so that the heat storage rods can support their own weight. This eliminates the need for each auxiliary fixing structure to be fastened or firmly connected to each heat storage rod. Protection against tilting of the heat storage rods and reliable positioning of the heat storage rods are achieved by a retainer according to the present invention, which is connected to the cassette frame and consists of lower, middle and / or upper guide rails, which will be described in detail later. This retainer can significantly reduce the number of essential parts and the manufacturing costs required to ensure stability within the system. The guide rails can hold all of the heat storage rods of the heat storage cassette in place, and the number of retained heat storage rods may be quite small (e.g., 5 to 10 heat storage rods) or quite large (e.g., 15 to 30 heat storage rods).

[0010] By allowing free expansion of the thermal storage rod in the longitudinal direction, mechanical stress within the thermal storage rod is avoided, and its impact on adjacent components is reduced. The holder of the thermal storage cassette also plays an important role in minimizing material stress on adjacent components. The holder simply supports or holds the thermal storage rod in a specific position, and by avoiding rigid fastening between the holder and the thermal storage rod, such as welding, soldering, bonding, screwing, or riveting, material strain and mechanical stress in the holder can be greatly avoided. At the same time, the thermal storage cassette improves overall stability and handling. Combining multiple thermal storage rods in the cassette into a stable unit facilitates assembly at the installation site of the thermal storage unit. The thermal storage cassette can be pre-assembled and transported as a prefabricated unit (especially as a module consisting of more cassettes, e.g., 6 to 15 cassettes). Overturning or undesirable movement of the thermal storage rod is reliably prevented by this cassette, as well as by combining them in the form of the module. Furthermore, because the cassette separates the heat storage rod to some extent from other components, undesirable heat transfer to other components and / or material stress on other components due to the heated heat storage rod are significantly reduced. The heat storage unit optionally has only a few outwardly protruding members, in which case only the electrical contacts / connections (contacts for sensor systems for connecting to PLCs or other components, cables which are generally essential for technical measurement and control systems) and the cooling section of the heating element have an interface with the outside. This efficiently prevents heat from escaping, minimizing heat loss and improving the overall efficiency of the storage and containment system.

[0011] A method for manufacturing a thermal accumulator according to the present invention for storing electrical energy in the form of thermal energy provides at least one electric heating device for converting electrical energy into thermal energy. To form each of a plurality of thermal accumulator cassettes, the process begins with a cassette frame whose cross section is closed on three sides and open on a fourth side. Retainers are provided on the cassette frame to hold the thermal accumulator rods in place. The plurality of thermal accumulator rods are inserted into each cassette frame on the open fourth side, and the thermal accumulator rods are held in place by the retainers. The cassette frames are then closed on the fourth side, leaving at least one end of each thermal accumulator rod unfixed (i.e., not fastened to another adjacent element), thereby allowing free thermal expansion of the thermal accumulator rods in the longitudinal direction within the cassette frame.

[0012] Any optional embodiment Modifications of the heat storage device and the method according to the present invention are the subject of the dependent claims and will be described in the following detailed description.

[0013] Free thermal expansion inside the cassette frame The cassette frame is made of metal and may have a rectangular shape, for example. This cassette frame surrounds multiple or all of the heat storage rods held by it. The cassette frame is open at both the front and the rear so that the heat transfer fluid can enter from the front, flow along the heat storage rods, and exit from the cassette frame at the rear.

[0014] When the thermal storage cassette is fully assembled, each cassette frame is closed in the longitudinal direction of the held thermal storage rod, and as a result, it is impossible for the thermal storage rod to extend longitudinally from the cassette frame. To allow free longitudinal thermal expansion of the thermal storage rod inside the cassette frame, the space in each cassette frame in the longitudinal direction of the held thermal storage rod is greater than the length of the thermal storage rod. If the frame portion of the cassette frame has a receiving hole for the thermal storage rod, this space should be understood to include a space extending into the receiving hole so that this space covers the entire length of the thermal storage rod. If the cassette frame does not have a receiving hole for the thermal storage rod, the space extends between opposing portions of the cassette frame.

[0015] This creates a (longitudinal) gap between at least one end of the heat storage rod and the cassette frame. This gap is sized to be greater than or equal to the thermal expansion length of the held heat storage rod when the heat storage rod is heated over a predetermined design temperature range of the condenser. This design temperature range depends on the materials used in the condenser and can cover, for example, a range of 0 to 1000°C. The actual operating temperature range of the condenser, i.e., the maximum and minimum temperatures during the continuous filling and releasing phases of the condenser, is within the design temperature range and covers, for example, a range of 200°C to 550°C or 180°C to 600°C. For this design temperature range, the minimum temperature may correspond to the lowest expected ambient temperature (e.g., 0°C during maintenance phases or system startup). The maximum temperature within the design temperature range may be at least 50 to 100°C higher than the maximum operating temperature, for example, as a safety measure.

[0016] An upper limit can be set on the dimensions of the gap between the heat storage rod and the cassette frame, for example, so that at the maximum design temperature of the heat storage unit, this gap is at most 5 cm or at most 1 cm. Avoiding unnecessarily large gaps increases stability and reduces undesirable movement of the heat storage rod, especially during transport of the heat storage cassette. By planning and calculating the distances between individual steel rods, cassettes, modules, and the intervening spaces, the essential / desired (heat transfer) performance and residence time can be directly adjusted through the resulting flow profile of the heat transfer fluid (air / gas, hot oil / liquid), which is caused by increasing or decreasing the flow velocity of a blower, compressor, or pump, thereby precisely generating and / or providing system-related target parameters for consumers or power-consuming components of the energy generation system. This last statement applies to all design variations of the storage system described within the framework of this patent.

[0017] Guide rails for heat storage cassettes The cassette frame may have at least one guide rail, which may be made of a perforated plate in particular and form part of the retainer. Each guide rail extends perpendicular to the longitudinal direction of the heat storage rod (the direction in which it extends the longest). Each guide rail also has several holes, through which one of the heat storage rods extends. The holes in the guide rail thus restrict the freedom of movement of the heat storage rod in a plane perpendicular to the longitudinal direction of the heat storage rod, and thus hold the heat storage rod. However, since the guide rail does not hinder the longitudinal movement of the heat storage rod, thermal expansion of the heat storage rod is permitted without generating relative stress with respect to the guide rail. Thus, the heat storage rod is not rigidly fixed in the hole, and is not immobilized in particular by welding, soldering, or screws. The diameter of the hole can be slightly larger than the diameter of the heat storage rod to be received, for example, by a maximum of 0.5 cm or 1 cm, or by 1% to 7% of the diameter of the heat storage rod.

[0018] The guide rails may extend between two opposing sides (side walls) of the cassette frame that are parallel to the longitudinal direction of the heat storage rods, and the guide rails may be fastened to these sides, for example, by welding, screwing, or locking them in place.

[0019] The holes in the guide rail are arranged along a single row. Therefore, the heat storage rods of the heat storage cassette are arranged adjacent to and parallel to each other along the row. Since the heat storage cassette can have exactly one row of heat storage rods, the problem of potentially non-uniform temperature distribution in the direction perpendicular to this row and in the direction perpendicular to the longitudinal direction of the heat storage rods does not lead to relevant material stress within the heat storage cassette. In principle, it is also possible for one heat storage cassette to hold two or three rows of heat storage rods, and for this purpose the guide rail can have two or three rows of holes, however, the number of rows should not be too large due to potential temperature-related stresses.

[0020] If a single cassette frame has multiple guide rails, they can be arranged parallel to each other and spaced apart along the longitudinal direction of the heat storage rod.

[0021] The guide rail can be formed as a single unit. Alternatively, it can be designed as a two-part or multi-part system. In a two-part design, each rail component can form the edge portion of the guide rail containing each hole, and these holes are closed only in the circumferential direction by both rail components (except for an optional gap between the rail components). With this two-part design, during assembly, it is possible to close the holes in the guide rail by first fastening one rail component to the cassette frame, then placing the heat storage rods in the cassette frame, and then fastening the second rail component to the cassette frame.

[0022] To reliably hold the thermal storage rods inside the cassette frame, each thermal storage rod should be held in at least two or at least three places. Holding means restricting the movement of the thermal storage rod in a direction perpendicular to the longitudinal direction. Holding in at least two places can be achieved by using a corresponding number of guide rails. Alternatively, receptacles for holding the thermal storage rods can be formed at one end of the cassette frame or at both opposing ends, as described below.

[0023] Receptacle for heat storage rod at the end of cassette frame Each cassette frame has a frame base side and an opposing frame end side. These two sides can extend transversely or perpendicularly to the longitudinal direction of the heat storage rod. The cassette frame may have at least one frame portion on the base side and / or end side, which may be hollow and, for example, have a rectangular cross-section.

[0024] The base and / or end frame portions may be provided with receiving holes or recesses for supporting the heat storage rod, thus forming part of the aforementioned retainer. The receiving holes may be identical in shape and diameter to the holes in the guide rails. The receiving holes or recesses are located on the side of the frame portion facing the inside of the cassette frame. No holes are provided on the opposing outer side of the frame portion that define the outer extent of the cassette frame, through which the heat storage rod can exit the cassette frame. In this way, the two frame portions, the base and the end, define the extent of the available space inside the cassette frame in the longitudinal direction for the heat storage rod. This space is determined by the expected maximum thermal expansion (+ tolerance) of the heat storage rod. The space provided by the receiving holes / recesses forms part of the available space, which extends into the (hollow) frame portion. As explained above, this clearance is dimensioned to be large enough so that, at the maximum design temperature of the accumulator, the thermal expansion of the accumulator rod does not cause it to press against both the base and end sections of the frame. The aforementioned design temperature can be higher than the maximum operating temperature and is related to the dimensioning of the distance between the guide rail receiving holes, while on the other hand it is related to the limit of the upper frame section representing the maximum possible extension of the accumulator rod. Production-related tolerances, as well as part-specific tolerances, material-specific tolerances, and safety-related tolerances, are taken into consideration in this dimensioning. Process-related design parameters to be calculated (such as pressure curves, temperature curves, and / or flow profiles) are also related to the aforementioned dimensioning. The accumulator rod can be erected on the base of the frame oriented vertically so that it supports its own weight. Holes that may be provided in one or both sections of the frame provide additional support perpendicular to the longitudinal direction. To reduce heat loss into the ground, it is also possible to use a support surface in the form of a ceramic layer or an insulating base plate made of a material with low thermal conductivity.

[0025] In principle, the heat storage rod can be fixed to the base side, but based on the embodiments described herein, it is advantageous that the fixing can be omitted.

[0026] In principle, the holder for holding the heat storage rod consists only of a frame portion on the base side and a frame portion on the end side, that is, it may not have a guide rail. However, in order to facilitate assembly and enhance stability, it may be preferable to additionally provide at least one guide rail. When the heat storage rod is oriented in the vertical direction, this can prevent a potentially dangerous tilting torque. As a result of the periodic heating and cooling of the heat storage device, slight deformations that may occur within the heat storage device member can also be effectively reduced or eliminated.

[0027] Heat storage rod The heat storage rod can be made of metal or metal alloy. In principle, various metals and metal alloys are possible, but steel may be particularly suitable in terms of robustness, heat capacity, high availability and service life, as well as in terms of very good reusability. Each heat storage rod can consist of one piece in order to avoid stresses that may occur at the contact points of the parts to be connected (e.g., material joining in the form of a welding seam or an adhesive). The plurality of heat storage rods held in the cassette frame can have the same shape and the same dimensions. If they are cylindrical, there is no risk of unwanted contact between the heat storage rods due to thermal expansion, and in a simple way, a plurality of heat storage rods can be held in the cassette frame close to and adjacent to each other. In principle, the heat storage rod can have any cross-sectional shape. For easy insertion of the heat storage rod into the holes of the guide rail and into the receiving holes of the cassette frame, a round or circular cross-sectional shape may be preferred. A more complex shape, such as a T-shaped or double-T-shaped shape, may be preferred in order to increase the surface area and thereby enable faster heat transfer. The shape of the holes in the guide rail can be made to match the cross-sectional shape of the heat storage rod. The cross-sectional shape can also form, for example, an N-sided polygon with three, four, five, six or more corners. Depending on the cross-sectional shape, an increase in the (heat) transfer capacity can be achieved, but this advantage has to be weighed against disadvantages such as the pressure loss in the heat transfer fluid (which is a function of the cross-sectional shape of the heat storage rod), the increase in the required space, and thus the resulting additional costs and construction expenses.

[0028] Thermal storage module The heat storage unit may comprise multiple heat storage modules. Each heat storage module comprises a module frame, which is configured to hold multiple heat storage cassettes. Optionally, the module frame is configured to hold at least one electric heating device. This holding is done without fixing, in particular, without welding, soldering, screwing, or riveting the heat storage cassettes or electric heating devices to the module frame. This prevents material stress that may occur between the module frame and the heat storage cassettes or electric heating devices due to temperature differences or thermal expansion of the components.

[0029] By using multiple thermal storage modules, each with its own modular frame, it is possible to minimize the mechanical stress in the module frames caused by temperature differences within the entire thermal storage unit. Furthermore, the multiple module frames are not fixed to each other, i.e., they are not fixed in place by welding or screws. At least some of the thermal storage modules can be arranged in a front-to-back configuration so that the heat transfer fluid flows through them sequentially, and their module frames are not rigidly fixed to each other.

[0030] The thermal storage cassette has a length substantially determined by the length of the thermal storage rod. Therefore, the thermal expansion of the thermal storage cassette is generally greater in the longitudinal direction than in the direction perpendicular to the longitudinal direction. Thus, the retention of the thermal storage cassette in the thermal storage module should allow for thermal expansion in the longitudinal direction without stress. For this purpose, each module frame is provided with multiple receiving grooves on two opposing sides, each for one of the projections or edges of the thermal storage cassette. In this way, the thermal storage cassette is held in the two opposing receiving grooves, i.e., protected from tipping over. These grooves extend parallel to the longitudinal direction of the thermal storage rod. While these grooves ensure retention in a plane perpendicular to the longitudinal direction, they do not restrict the longitudinal movement (due to thermal expansion) of the thermal storage cassette with the thermal storage rod. The width of the module frame (i.e., the distance between the two opposing grooves) and the depth of the grooves are selected taking into account the thermal expansion of the thermal storage cassette. The distance between the grooves is small enough that the edges of the thermal storage cassette still protrude into the grooves even at the lowest operating temperature. The groove depth is also selected to be large enough that, even when the thermal storage cassette expands due to thermal expansion at the highest operating temperature, the cassette does not come into contact with the bottom surface of one or both of the two opposing grooves. This dimensional design ensures reliable retention across the entire operating temperature range without generating mechanical stress between the module frame and the thermal storage cassette due to thermal expansion.

[0031] To hold the electric heating device, each module frame may be provided with at least one heating device support groove on two opposing sides for each edge portion of the electric heating device. The above description of the support groove for the heat storage cassette can also be applied mutatis mutandis to the support groove for the heating device. The shape and dimensions of the heating device support groove may be the same as or different from those of the support groove for the heat storage cassette.

[0032] In a heat storage module, multiple heat storage cassettes can first be arranged one behind the other, then an electric heating device can be placed between them, and then multiple heat storage cassettes can be placed between them. This allows for more uniform heating compared to when no electric heating device is placed between the heat storage cassettes.

[0033] The aforementioned edge portions protruding into the groove can be designed, for example, as projections or protruding rails. The edge portions and grooves may extend over substantially the entire length of the heat storage rod (e.g., at least 80% or at least 90% of the length). Alternatively, the grooves and / or edge portions may be provided only along one or more short portions, for example, not exceeding 10% or 15% of the length of the heat storage rod.

[0034] It is also possible to reverse the receiving grooves and the edge portions that protrude into them. In this case, each heat storage cassette has two opposing outer grooves, into which the protrusions of the module frame protrude. The electric heating device may also have two opposing outer grooves, into which the protrusions of the module frame protrude.

[0035] Some or all of the heat storage modules may include temperature sensors. The heat storage modules may be equipped with temperature sensors at different heights and at different points along the flow direction through the heat storage module, for example, between two heat storage cassettes or immediately next to an electric heating device.

[0036] Upright arrangement of heat storage modules Multiple or all of the heat storage cassettes can be arranged upright such that the longitudinal direction of the heat storage rod is vertical. In this case, the heat storage rod is erected on the cassette frame base so that it can expand freely in the vertical direction, i.e., upward. The cassette frame base can be the aforementioned frame portion on the base side, and this frame portion may optionally be provided with receiving holes / recesses.

[0037] One advantage of vertical placement is that it reduces the risk of the heat storage rod bending and compromising the overall stability of the heat storage unit. The length of the heat storage rod can be, for example, 5m to 10m, which places a correspondingly large demand on the retainer. In the case of vertical placement, the retainer prevents the heat storage rod from tilting, but it does not bear the weight of the heat storage rod. Therefore, the load on the retainer is reduced, and the retainer can be designed more simply.

[0038] When using the thermal storage module described here, the vertical orientation applies to each thermal storage module, i.e., to all thermal storage cassettes held within it. The thermal storage cassettes of such a thermal storage module are erected on the base plate of the thermal storage module, so that the base plate bears the weight of the thermal storage cassettes. The base plate and the module frame are fastened together, for example, by welding, screwing, or soldering. On the other hand, the base plate and the thermal storage cassettes are not fastened together to avoid material stress due to thermal expansion. The thermal storage cassettes are prevented from tipping over by their edges, which protrude into the receiving grooves on the thermal storage module side.

[0039] The heat storage modules that make up the heat storage unit can be arranged so that they are all upright, partially upright, partially horizontal, or all horizontal.

[0040] Horizontal arrangement of thermal storage modules The thermal storage module can be positioned horizontally such that the longitudinal direction of the thermal storage rods of the thermal storage module is oriented horizontally. Two different horizontal configurations are possible for the thermal storage module. The difference between these two configurations is whether the thermal storage cassette lies flat (with the rows of held thermal storage rods at the same height) or whether the thermal storage cassette is erected on its side walls (the longitudinal direction of the thermal storage rods is also horizontal, but the held thermal storage rods of the thermal storage cassette are aligned vertically).

[0041] In a horizontal configuration, the holder supports the weight of the heat storage rods. The holder supports each heat storage rod at least in two places without fixing the rods in place, in order to ensure the free thermal expansion of the heat storage rods in the longitudinal direction.

[0042] The vertical dimensions of the heat storage cassette can be lower in a horizontal configuration than in a vertical configuration. This height is related to the flow of the heat transfer fluid through the heat storage cassette. Since heated heat transfer fluid rises, excessive height can lead to uneven heat transfer. This problem is practically avoided in a horizontal configuration. By using the upper wall in conjunction with the lower plate, a clearly defined (flow) space can be determined. In a horizontal configuration, the height difference between the upper wall and the lower plate is so small that there is no significant temperature difference in the steel between the upper and lower steel supports.

[0043] Flow of heat transfer medium The heat transfer fluid can be a gas or a mixture of gases. A blower, pump, or other device can be provided to transport the heat transfer fluid so that it flows through the heat storage module (along the heat storage rod). Generally, liquids can also act as heat transfer fluids.

[0044] As the heat transfer fluid flows along the heated heat storage rod, it can absorb heat from the rod, and this heat can be extracted from the accumulator. For this purpose, a heat exchanger can be used, for example. Depending on the design of the accumulator, the heat transfer fluid can also be used to supply thermal energy to the heat storage rod. For example, the heat transfer fluid can be heated by an electric heating device, and the absorbed thermal energy can then be released to the heat storage rod. Heat transfer during the filling phase can be based primarily on convection heat transfer from a high-temperature electric heating element to the heat transfer fluid and steel components / steel heat storage rod. During the release of the accumulator, the steel rod and heating element release heat to the fluid. It is also possible to perform the filling and release of the accumulator simultaneously. In principle, the electric heating device can also directly generate thermal energy in the heat storage rod. In this case, during the pure filling phase, the heat transfer fluid contributes little to, or largely nothing, to heat transfer to the heat storage rod.

[0045] Electric heating device In principle, at least one electric heating device can be designed in any way to convert electrical energy into thermal energy. This can be done, for example, using resistance heating, in which heat is generated by the electrical resistance of the material through which the current flows.

[0046] An electric heating device may comprise multiple conductors through which an electric current flows, generating heat. In some embodiments, a heat transfer fluid may be flowed along these conductors to absorb heat from them, and then the heat may be released to a heat storage rod. In some embodiments, the sole function of the heat transfer fluid is to extract heat from the heated heat storage rod.

[0047] In various modified embodiments, the electric heating device is positioned between two heat storage cassettes. However, more generally, the electric heating device can also be positioned anywhere else along the flow path or circuit of the heat transfer fluid. In principle, at least one electric heating device can be positioned in a separate circuit, where the heated fluid dissipates heat to the heat transfer fluid via a heat exchanger. Thus, the fluid itself in the electric heating device does not come into contact with the heat storage rod. Such a separate circuit can also act as a preheater and can be combined with other electric heating devices within the heat transfer fluid circuit.

[0048] For uniform heat supply, it is preferable that multiple or all heat storage modules each have at least one electric heating device. When forming multiple relatively small heat storage modules, having just one electric heating device can be advantageous because it minimizes material stress caused by temperature differences inside the modules.

[0049] The conductor of the electric heating device can be extended in a meandering manner so as to cover a surface area substantially corresponding to the internal surface area of ​​the heat storage cassette, or a substantial portion of this surface area, for example, at least 70%. For this purpose, the conductor of the electric heating device can extend over the length of the heat storage rod, or at least 80% of this length. The meandering shape of the conductor also extends in the width direction (i.e., in a direction perpendicular to the longitudinal direction and parallel to the main direction of the guide rail) over at least 80% of the width of the heat storage cassette.

[0050] Both the heat storage cassette and the electric heating device can have an overall plate shape (especially rectangular), meaning their length and width are at least five times greater than their depth. The relatively shallow depth is important for maximizing the surface area and thus heat exchange, while also avoiding the problem of greater thermal expansion or mechanical stress in the depth direction.

[0051] The electric heating device may include a support rod held or supported by a module frame. This support rod may protrude beyond the surface area of ​​the conductor, which meanders in the width direction. This support rod may also be located at one end of the module frame, adjacent to the end of the heat storage rod. This conductor extends from the support rod into the interior of the module frame, i.e., into the area enclosed by the module frame. The electrical supply conductor, on the other hand, extends on the opposite side of the support rod. The electrical supply conductor is electrically connected to the conductor used for heating, but is not designed for heating purposes itself. Therefore, the electrical supply conductor has lower electrical resistance than the conductor. The electrical supply conductor leads to a connection box containing electrical connection points for connecting cables. Because the connection box is located away from the interior of the module frame, the connection points within the connection box and the cables connected to the connection points can be largely protected from the high temperatures that may occur inside the module frame. Through the cables, a connection is established to a programmable logic controller (PLC), which includes electronic components for controlling or monitoring the electric heating device and optionally other components of the heat storage device. For example, this PLC may also include electronic components for evaluating temperature measurement data, and in particular, it can detect failure conditions based on temperature rise, such as when an electric heating device continues to heat while a blower, compressor, or pump has failed. Since the PLC is located away from the heating area of ​​the accumulator, both the power supply conductors and connecting cables, as well as the PLC, are protected from excessive temperatures. The (power) cables of the heating elements used for mains power connection / connection to the power grid can be connected to the junction box, while, for example, the cables of thermal sensors and pressure sensors can be connected directly to the PLC at a distance of several meters. In the assembled state of the accumulator module, only the power supply conductors and junction box protrude outward from the module frame, while the conductors of the accumulator cassette and heating device are located inside the module frame. Thermal insulation material can be provided between the junction box and the module frame.

[0052] Assembly of heat storage cassettes and heat storage units As partially described, the starting point for assembly can be a cassette frame with three sides closed. These three sides can be called the base side and the two side walls. The fourth side of the cassette frame (i.e., the upper frame portion) is not closed until later. In this way, the thermal storage rods can be inserted from this open fourth side by lifting them, for example, with a crane or other lifting device. During this process, a retainer prevents the thermal storage rods from tipping over. Preferably, while the fourth side is open, each thermal storage rod is held in place by the retainer at least in two places, thereby ensuring accurate positioning and reliable retention. Then, as described above, the upper frame portion, which may have receiving holes for the thermal storage rods, is placed on top. This upper frame portion is fastened to the side walls of the cassette frame, for example, by welding. This assembly can be carried out in an upright position so that the thermal storage rods face vertically.

[0053] Next, the heat storage cassette can be transported in a horizontal position, with the longitudinal direction of the heat storage rod in a horizontal plane. As a result of the above design, the heat storage rod remains held in place within the cassette frame.

[0054] The thermal storage module can be assembled at the installation site of the thermal storage unit. For this purpose, the module frame with a base plate is placed at the final destination. The thermal storage cassette is lifted by crane and placed on the base plate of the thermal storage module, and the lateral projections of the thermal storage cassette are engaged with the corresponding grooves in the module frame. This operation is performed for all thermal storage cassettes and electric heating devices.

[0055] The described method makes it possible to assemble a heat accumulator in which mechanical stress caused by thermal expansion is largely relieved. In this process, the rigid fastening of the heat accumulator rods, electric heating devices, and heat accumulator cassettes to the surrounding components is omitted, but the described retainers provide sufficient mechanical stability.

[0056] Operation of the heat storage unit A heat accumulator can convert supplied electrical energy into heat using an electric heating device (filling the heat accumulator). The heat transfer fluid flowing through the heat accumulator can be used, on the one hand, to distribute the heat generated by the heating device, and on the other hand, to remove (release) thermal energy from the heat accumulator. For release, the heated heat transfer fluid can be removed from the heat accumulator, or the heat transfer fluid can dissipate heat in at least one heat exchanger without leaving the heat accumulator. Thus, the heat exchanger can be placed inside or outside the casing of the heat accumulator, which tends to become hot during operation.

[0057] The heat storage unit can be filled at varying intervals. In particular, the electric heating device can be switched on or off depending on the surplus of electrical energy from the external power grid or connected generators (e.g., wind turbines or solar power plants). The heat storage unit can also release heat at varying intervals. It is also possible to perform filling and releasing simultaneously.

[0058] General characteristics To indicate similar measured dimensions, the term "substantially" can represent a deviation of up to 5%. This means that two lengths or areas that are substantially the same may differ by up to 5%.

[0059] The features of the present invention described as additional apparatus features are intended to also apply to modifications of the method according to the present invention. [Brief explanation of the drawing]

[0060] Further effects and features of the present invention will be described below with reference to the attached schematic diagram. [Figure 1] This figure shows an exemplary embodiment of a heat storage cassette for a heat storage device according to the present invention. [Figure 2] This diagram shows the cassette frame of a heat storage cassette. [Figure 3] This diagram shows the details of the heat storage cassette. [Figure 4]This figure shows an electric heating device of an exemplary embodiment of a heat storage device according to the present invention. [Figure 5] This figure shows the module frame of a heat storage module in an exemplary embodiment of the heat storage device according to the present invention. [Figure 6] Figure 5 shows the module frame together with the electric heating device. [Figure 7] This figure shows an upright heat storage module of an exemplary embodiment of the heat storage device according to the present invention. [Figure 8] This figure shows a horizontal heat storage module representing an exemplary embodiment of the heat storage device according to the present invention. [Figure 9] This figure shows an exemplary embodiment of the heat storage device according to the present invention. [Figure 10] Figure 9 is a cross-sectional perspective view of the heat storage container. [Figure 11] This figure shows a further exemplary embodiment of the heat storage device according to the present invention. [Figure 12] Figure 11 is a perspective view of the heat storage device. [Modes for carrying out the invention]

[0061] Various exemplary embodiments are described below with reference to the figures. As a general rule, similar components and components having similar functions are given the same reference numerals.

[0062] Figures 1-3: Heat storage cassette An exemplary embodiment of a thermal storage cassette according to the present invention will be described with reference to Figures 1 to 3. This thermal storage cassette is used to store thermal energy. The interaction between this thermal storage cassette and other components of the thermal storage unit will be described thereafter with reference to further figures.

[0063] Figure 1 shows a front view (left) and a perspective view (right) of the heat storage cassette 10. The heat storage cassette 10 includes a cassette frame 20 and a plurality of heat storage rods 30 held inside the cassette frame 20. Figure 2 shows two perspective views of the cassette frame 20 without the heat storage rods. Figure 3 is an enlarged view of a part or component of the heat storage cassette 10.

[0064] As shown in Figure 1, multiple heat storage rods 30 are held in a heat storage cassette 10. The length of these heat storage rods 30 can be, for example, 5 to 9 m, and the weight of the heat storage cassette can be in the range of 1000 to 7000 kg. The heat storage rods 30 are arranged in a single row and are held in place relative to the cassette frame 20 by a retainer 22. This holding is done without fixing or rigid fastening, allowing the heat storage rods 30 to expand freely along their longitudinal direction L. The components of the retainer 22 will be described in more detail in relation to Figure 2.

[0065] As shown in Figure 2, the cassette frame 20 has a frame portion 24 on its bottom or base side 21 and another frame portion 24 on the opposite end side. These two frame portions 24 are connected by a side wall 26, so that the cassette frame 20 is closed in cross-section. On the other hand, the front and rear sides are completely open, so that the heat transfer fluid can flow through the cassette frame 20.

[0066] Each of these two frame sections 24 has a receiving hole 24A intended for a heat storage rod. Thus, both ends of the heat storage rod 30 protrude into the corresponding receiving holes 24A. These receiving holes 24A define the extent of space for the heat storage rod in the plane perpendicular to the long axis L, and thus hold the heat storage rod. In this way, the frame section 24 with the receiving holes 24A forms part of the retainer 22.

[0067] The retainer 22 is also formed by guide rails 23 extending between the side walls 26 of the cassette frame 20. These guide rails 23 are provided with holes 23A, which, in terms of their arrangement, correspond to receiving holes 24A of one of the frame portions 24. In the assembled state, each heat storage rod 30 extends through one of the holes 23A.

[0068] The frame portion 24 defines the extent of the clearance F for the heat storage rod in the longitudinal direction L. The length or measured dimension of the clearance F should be understood here to include the additional space provided by the receiving hole 24A. The frame portion 24 ensures that the heat storage rod is securely fixed in the longitudinal direction L. By making the length of the clearance F slightly greater than the length of the heat storage rod, the thermal expansion of the heat storage rod can occur without generating pressure against the cassette frame 20.

[0069] Once assembled, the heat storage cassette 20 may be placed in different orientations, for example, for transport. Therefore, it is important to securely fix and hold the heat storage rod, that is, to restrict the space for the heat storage rod within the heat storage cassette 20 in all directions.

[0070] Since the heat storage rods are not rigidly fastened to any other components, these heat storage rods can expand thermally freely (particularly in their longitudinal direction) without the risk of generating associated material stress in relation to adjacent components. In particular, the heat storage rods are not rigidly fastened to the cassette frame 20, but are merely supported by the cassette frame 20 and held or supported in a certain position.

[0071] This relates to the design of the frame portion 24, which is most clearly shown in Figure 3. The upper part of Figure 3 shows the frame portion 24 semi-transparently to illustrate the protrusion of the heat storage rod 30 into the frame portion 24. The middle part of this figure is a perspective view of the frame portion 24. The lower part of this figure is a cross-sectional view, in which the heat storage rod 30 can be seen protruding into the frame portion 24.

[0072] This frame portion 24 is hollow and has a receiving hole 24A on one side. On the other hand, the opposite side, i.e., the outer wall of the frame portion 24, has no holes, or at least no holes large enough for the heat storage rod 30 to pass through.

[0073] The dimensions of the heat storage rod 30 and the cavity in the frame portion 24 are determined so that a gap L1 remains between the heat storage rod 30 and the inner surface 24B of the outer wall of the frame portion 24 at any operating temperature (i.e., any temperature within a predetermined design temperature range). This gap is also sized so that the heat storage rod 30 still protrudes into the receiving hole 24A even at the minimum operating temperature (i.e., a predetermined minimum design temperature). This ensures that the heat storage rod 30 is reliably supported by the receiving hole 24A of the frame portion 24 at any expected temperature. On the other hand, if the heat storage rod 30 does not protrude into the receiving hole 24A of the frame portion 24 at low temperatures in an upright system, the guide rail(s) become the sole protection against tilting, and in this case, even a displacement of a few degrees in the angle of a steel rod several meters long could potentially lead to the accumulation of high torque and destabilizing forces that are problematic.

[0074] The cassette frame 20 has outwardly protruding projections 25 on its two side walls 26. These projections 25 allow the cassette frame 20 to be held in place within the module, which will be explained in more detail later.

[0075] In addition, the upper / outer side of the upper frame portion 24 is provided with (at least) two protrusions or knobs 27, which can be used to lift the heat storage cassette 10 with a crane or other machine.

[0076] Figure 4: Electric heating device Figure 4 is a perspective view of an electric heating device 40 of an exemplary embodiment of the heat storage device according to the present invention.

[0077] The electric heating device 40 converts electrical energy into heat. For this purpose, the electric heating device 40 comprises a plurality of heating wires or, more generally, conductors 41, which generate heat through electrical resistance when an electric current flows through them. The conductors 41 are wound in a meandering or reciprocating manner over an area whose measured dimensions substantially correspond to the cross-sectional area of ​​the heat storage cassette. A cover, frame, or housing can surround the conductors 41 and provide electrical insulation and / or mechanical support for the conductors 41. The conductors 41 are also held by a plurality of retaining plates 43. Each retaining plate has a plurality of openings, for example, at least 20 openings through which the conductors 41 extend and are held.

[0078] The electric heating device 40 also has a support rod 42 that protrudes laterally. The conductor 41 extends only on one side of the support rod 42, and in the illustrated orientation, only below the support rod 42. The electric heating device 40 can be held in the heat storage module by the support rod 42, which will be described in detail later. An electrical supply conductor 44 is provided on the opposite side of the support rod 42 (above the support rod in the illustrated orientation) and is electrically connected to the conductor 41. This supply conductor 44 forms a cooling section to protect electronic equipment located at a distance from thermal damage. These electrical supply conductors 44 lead to a connection box 45, which contains electrical connections for connecting to electronic components located at a distance, particularly a PLC.

[0079] The arrangement of the electric heating device 40 and the heat storage cassette within the heat storage module will be explained with reference to the following diagram. Note that the number of heat storage cassettes in the heat storage module shown in the diagram is merely an example. The number of heat storage cassettes per heat storage module may be more or less than the example shown here.

[0080] Figures 5-7: Thermal storage module Figure 5 shows the module frame 51 of the heat storage module on the left. This module frame 51 is used to hold the electric heating device and the heat storage cassette. On the right side of Figure 5 is a cross-sectional perspective view of the module frame 51. Figure 6 shows the module frame 51 together with the electric heating device 40 housed within it. Figure 7 shows the heat storage module 50 comprising the module frame 51, the electric heating device 40 housed within the module frame 51, and the held heat storage cassette 10.

[0081] As shown in Figure 5, the module frame 51 includes a plurality of receiving grooves 52 for holding a heat storage cassette and two heating device receiving grooves 53 for holding an electric heating device. In this illustrated example, the receiving grooves 52 are located only on the upper frame portion of the module frame 51. However, it is also possible to provide additional lateral rails or side walls with grooves on the module frame 51 so as to extend along the entire length of the heat storage cassette or heating device (not shown).

[0082] The module frame 51 is connected to a base plate 54, for example, at its bottom, and is welded, for example. The measured dimensions of the base plate 54 substantially correspond to the measured dimensions of the cross-section of the module frame 51. Multiple module frames 51, each with a base plate 54, can be arranged close to and adjacent to one another. By providing a gap of, for example, at least 2 mm between adjacent module frames 51, it can be ensured that adjacent module frames 51 do not press against each other and exert (material) stress on each other, regardless of the thermal expansion of the module frames. This distance between modules allows the modules to be positioned apart from each other using fixtures. Certain components, in particular, components for actively controlling the flow profile (e.g., flow breakers, baffles, diffusers, nozzles, etc.) can also be introduced between modules.

[0083] Figure 6 shows a module frame 51 into which the electric heating device 40 is inserted. The heating device 40 is erected on a base plate 54, and the base plate 54 bears the weight of the heating device 40. However, the heating device 40 is not fixed to the base plate 54. The projection 46 of the heating device 40 protrudes into the receiving groove 53 for the heating device, thus eliminating the risk of the heating device 40 tipping over (see the detailed view on the left side of Figure 6). The electric heating device 40 is thus held on the module frame 51 without being rigidly fixed. This prevents mechanical stress that may be generated by thermal expansion of the components. Modules or components contained within modules (cassettes and heating elements) can also be installed symmetrically, resulting in the center of gravity of the module system always being in the center and additional stability against tipping being obtained. Alternatively, by providing an irregular number of heat storage cassettes 10 for each heat storage module 50, it is possible to arrange different numbers of heat storage cassettes 10 before and after the electric heating device 40 inside the heat storage module 50.

[0084] Figure 7 shows how the module frame 51 holds multiple heat storage cassettes 10 in addition to the electric heating device 40. The heat storage cassettes 10 are also erected on the base plate 54, and are held in place by lateral projections 25 (shown in Figure 1) of the heat storage cassettes 10 engaging with receiving grooves 52 to prevent them from tipping over. The fact that the heat storage cassettes 10 are not rigidly connected to the module frame 51, the base plate, or any other components prevents mechanical stress that may arise due to thermal expansion.

[0085] Since the weight of the heat storage cassette 10 and the heating device 40 is supported by the base plate rather than the module frame 51, the module frame can be designed more simply accordingly.

[0086] The flow direction 70 of the heat transfer fluid is indicated by an arrow in Figure 7. This flow direction 70 is perpendicular to the surface area of ​​the heat storage cassette 10 and the electric heating device 40, where this surface area extends, for example, along the long axis of the heat storage rods and in the direction in which the heat storage rods are aligned within the heat storage cassette 10. The heat transfer fluid flows through the heat storage module 50 and across the entire surface of the heat storage cassette 10.

[0087] During assembly and / or operation of the heat storage unit, the heat storage module 50 can be positioned upright, as shown in Figures 5 to 7. Other arrangements will be explained with reference to the following figures.

[0088] Figure 8: Horizontal thermal storage module Figure 8 shows a horizontally arranged heat storage module 60. This heat storage module can be designed as described with reference to the previous figure. In the horizontal arrangement, the long axis L of the heat storage rod extends horizontally. In this case, the heat storage module 60 is not erected on a base plate as described above (the base plate is not shown in Figure 8, or can be omitted on this side). The flow direction 70 remains perpendicular to the surface area of ​​the heat storage cassette 10.

[0089] In the horizontal arrangement shown here, each heat storage cassette 10 is erected on its longest side wall, so that the heat storage rods 30 held by the heat storage cassettes 10 lie overlapping each other. It is also possible to rotate them 90° to adopt a different horizontal arrangement, in which case the heat storage rods 30 of one heat storage cassette 10 lie in the same horizontal plane. In this case, the heat storage cassettes 10 are stacked vertically within the module frame 51.

[0090] Figures 9 and 10: Thermal storage unit with upright thermal storage module Figures 9 and 10 show an exemplary embodiment of a heat storage accumulator 100 according to the present invention. Figure 9 is a perspective view, while Figure 10 is a cross-sectional perspective view. The heat storage accumulator 100 comprises a plurality of heat storage modules 50, which are arranged upright on a base plate. The plurality of heat storage modules 50 are arranged in succession in rows, so that the heat transfer fluid flows sequentially through the heat storage modules 50 in a given row. In the illustrated example, three such rows are shown. The flow through these rows can be made parallel, resulting in the heat transfer fluid being divided between different rows, or these rows can be connected in series with corresponding baffle walls, resulting in the heat transfer fluid flowing continuously through these rows. The number of rows selected and the number of heat storage modules 50 per row can be varied and depend on the planned capacity of the heat storage accumulator 100. In addition to the heat storage modules 50 with electric heating devices 40 described so far, it is also possible to use heat storage modules 55 without electric heating devices 40. These heat storage modules 55 are placed at the beginning and end of each row of heat storage modules. This reduces the loss of thermal energy from the electric heating device 40 at the edge of the heat storage unit 100. The thermal stress to which the interfaces with other components of the heat storage system (e.g., inlet and outlet pipelines for circulating heat transfer fluid to the heat exchanger) are exposed can also be reduced, because the distance from the hottest component (heating element) in the heat storage system is increased. The heat storage module 55 can be designed in the same way as described with reference to the heat storage module 50, except that it lacks the electric heating device 40 and optionally does not have a groove for the electric heating device 40 on the module frame. The heat storage module 55 can be designed to be smaller than the heat storage module 50, and in particular, the number of heat storage cassettes 10 can be reduced. Here, the symmetrical relationship can be maintained.

[0091] When the electric heating device 40 is switched on during filling (heating), the heat transfer fluid alternately absorbs heat in one of the electric heating devices 40 and releases heat in the next heat storage cassette 10. When the heat storage device releases heat, the heat transfer fluid flows through the heat storage device, absorbs heat from the hot heat storage cassette 10 and heating element, and then releases heat to the internal or external consumer. The heating element can generally be switched on or off during release. When the heating element is switched off, its temperature may become similar to that of the heat storage rod 30, so heat is also transferred from the heating element to the heat transfer fluid during release.

[0092] The heat storage unit 100 may be equipped with an insulated outer wall, which defines the extent of the outer heat storage module relative to the outside. The outer wall may be provided with an inlet opening 71 for the heat transfer fluid and an outlet opening (not shown herein). The outlet opening can lead the heat transfer fluid to a heat exchanger or evaporator and then back to the inlet opening 71. Blowers, pumps or other conveying means may be provided for the heat transfer fluid, but these can be positioned in particular in the area from the outlet opening to the inlet opening 71 so as not to be exposed to the heat that is dominant in the heat storage module 50.

[0093] The heat storage module 50 is erected on a support block 75, but this support block 75 can be equipped with insulation and erected on a foundation. This foundation can be, for example, concrete, CMS fiber, mineral fiber, or ceramic.

[0094] Figures 11 and 12: Thermal storage systems with upright and horizontal thermal storage modules Figures 11 and 12 show further exemplary embodiments of the heat storage unit 100 according to the present invention. Figure 11 is a cross-sectional perspective view, and Figure 12 is a perspective view. In the previous exemplary embodiment, all heat storage modules were arranged upright, but here only some of the heat storage modules 50 are arranged upright, while the other heat storage modules 60 are arranged horizontally. Multiple horizontal heat storage modules 60 can be stacked one after another on top of other storage modules, so that the height of this stack is exactly equal to the height of the upright heat storage modules 50. When stacked, the heat storage modules 60 may be directly stacked on top of each other, or they may be supported by a frame (not shown here) so that the lower heat storage modules 60 do not have to bear the weight of the upper stacked heat storage modules 60.

[0095] The mixed arrangement of vertical heat storage modules 50 and horizontal heat storage modules 60 influences the flow of the heat transfer fluid, potentially ensuring a more uniform temperature distribution within the heat storage unit and increased heat output transfer due to increased turbulence in the heat transfer fluid.

[0096] The modifications described with reference to various figures can be combined with one another. The exemplary embodiments described are for illustrative purposes only, and these modifications are possible within the scope of the appended claims. [Explanation of Symbols]

[0097] 10 Heat Storage Cassettes 20 Cassette Frames 21 Cassette frame base 22 Retainer for holding the heat storage rod 30 23 Guide rail for holding the heat storage rod 30 23A Guide rail hole 24 Frame section 24A Receiving holes for heat storage rods on the frame section 24B Inner surface of the outer wall of frame section 24 25. Protrusions on the cassette frame / Edges of the cassette frame 26 Side walls of the cassette frame 27. Perforated projection for lifting the heat storage cassette. 30 Heat Storage Rods 40 Electric heating device 41 Conductors 42 Support rod 43 Retaining plate for conductor 41 44. Supply conductor for electric heating device 45 Control Box 46 Protrusions / edges of the heating device 40 50 (Upright Type) Thermal Storage Module 51 Module Frames 52 Receiving grooves in the module frame for holding the heat storage cassette 53 Receiving grooves in the module frame for holding the electric heater 54 Base plate of the heat storage module 55. Thermal storage module without electric heating device 60 Horizontal Thermal Storage Modules 70 Flow direction of heat transfer fluid 71 Inlet opening for heat transfer fluid 75 Support Block 100 Heat storage F: Empty space L Longitudinal direction of the heat storage rod L1 gap

Claims

1. A heat storage device for storing electrical energy as thermal energy, It includes at least one electric heating device (40) for converting electrical energy into thermal energy, A plurality of heat storage cassettes (10), each of which comprises a cassette frame (20) and a plurality of heat storage rods (30) held within the cassette frame (20), characterized by a plurality of heat storage cassettes (10), A heat storage device in which each heat storage cassette (10) is provided with a holder (22) for holding the heat storage rod (30) in a predetermined position, and at least one end (31) of each heat storage rod (30) is left unfixed so as to allow free thermal expansion of the heat storage rod (30) in the longitudinal direction (L) of the heat storage rod (30) inside the cassette frame (20).

2. When the heat storage cassette (10) is fully assembled, each cassette frame (20) is closed in such a way that the heat storage rod (30) cannot extend out of the cassette frame (20) in the longitudinal direction (L) of the held heat storage rod (30). To allow free thermal expansion of the heat storage rod (30) in its longitudinal direction (L), the open space (F) defined by one of the cassette frames (20) in the longitudinal direction (L) of the held heat storage rod (30) is greater than the length of the heat storage rod (30). The heat storage device according to claim 1, wherein if the cassette frame (20) has a receiving hole (24A) for the heat storage rod (30), the empty space (F) includes a space extending into the receiving hole (24A), and if the cassette frame (20) does not have a receiving hole (24A) for the heat storage rod (30), the empty space (F) extends between opposing portions of the cassette frame (20).

3. The heat storage device according to claim 2, wherein the gap (L1) between the empty space (F) and the length of the heat storage rod (30) is selected such that when the heat storage rod (30) is heated over the design temperature range of the heat storage device, the gap (L1) remains longer than the thermal expansion length of the heat storage rod (30) in the longitudinal direction (L).

4. The retainer (22) of one of the cassette frames (20) is provided with at least one guide rail (23), Each of the guide rails (23) extends perpendicular to the longitudinal direction (L) of the heat storage rod (30) and is provided with a plurality of holes (23A). The heat storage device according to any one of claims 1 to 3, wherein one of the heat storage rods (30) extends through each of the holes (23A).

5. Each of the cassette frames (20) has a base side and an end side facing the base side, The heat storage device according to any one of claims 1 to 4, wherein the cassette frame (20) has a frame portion (24) on the base side and / or the end side having a receiving hole (24A) or receiving recess for supporting the heat storage rod (30), and the frame portion (24) having the receiving hole (24A) or receiving recess forms part of the holder (22).

6. A heat storage device according to any one of claims 1 to 5, further comprising a plurality of heat storage modules (50, 60), each of which has a module frame (51), the module frame being configured to hold the plurality of heat storage cassettes (10) and at least one electric heating device (40) without fixing them in place.

7. The heat storage device according to claim 6, wherein each of the module frames (51) has a plurality of receiving grooves (52) on two opposing sides for each projection of one of the heat storage cassettes (10), so that all of the heat storage cassettes (10) are held in the two opposing receiving grooves (52).

8. The heat storage device according to claim 6 or 7, wherein the module frame (51) is provided on two opposing sides with at least one receiving groove (53) for each edge (46) of the electric heating device (40).

9. The heat storage accumulator according to any one of claims 6 to 8, wherein at least some of the heat storage modules (50) are arranged adjacent to each other with gaps that allow for thermal expansion so that the heat transfer fluid flowing through the heat storage modules flows sequentially through the heat storage modules, and the module frames (51) of the heat storage modules are not rigidly fixed to each other.

10. The heat storage cassette (10) is arranged upright such that the longitudinal direction (L) of the heat storage rod (30) is oriented vertically. The heat storage rod (30) is erected on the cassette frame base (21) so as to be able to expand freely in the vertical direction. The heat storage device according to any one of claims 1 to 9, wherein the retainer (22) provides protection against tilting of the heat storage rod (30).

11. The heat storage cassette (10) of one of the heat storage modules (50) is erected on the base plate (54) of the heat storage module (50), The base plate (54) bears the weight of the heat storage cassette (10), The heat storage device according to any one of claims 6 to 10, wherein the heat storage cassette (10) is prevented from tipping over by a receiving groove (52) on the side of the heat storage module (50) and an edge portion (25) of the heat storage cassette (10) that protrudes into the receiving groove (52).

12. At least one (60) of the heat storage modules is arranged horizontally such that the longitudinal direction (L) of the heat storage rod (30) is oriented horizontally. The heat storage device according to any one of claims 6 to 11, wherein the holder (22) supports the weight of the heat storage rods (30) and supports each heat storage rod (30) at least at two locations without fixing the heat storage rods (30) in the longitudinal direction (L).

13. A method for manufacturing a heat storage device for storing electrical energy as thermal energy, A step of providing at least one electric heating device (40) for converting electrical energy into thermal energy, A step in which multiple heat storage cassettes (10) are formed, Starting from a cassette frame (20) whose cross-section is closed on three sides and open on a fourth side, a holder (22) is provided on the cassette frame (20) for holding the heat storage rods (30) in place, a plurality of heat storage rods (30) are inserted into each of the cassette frames (20) through the open fourth side, and the heat storage rods (30) are held in place by the holder (22), and then each of the cassette frames (20) is closed on the fourth side, leaving at least one end of each heat storage rod (30) unfixed so as to allow free thermal expansion of the heat storage rods (30) in the longitudinal direction (L) of the heat storage rods (30) inside the cassette frame (20). The process, Methods that include...

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