System and method for storing high temperature heat

Abstract

The invention relates to an energy storage system comprising a tank (1) and a heating assembly located inside same. The tank (1) has an inlet (2), an outlet (3), a length (L) and a cross-section (A). The tank (1) is filled with a porous material (4), comprising a number of particles (5) of a solid material, wherein the particles have an equivalent diameter, the solid material has a density value (ρs), specific heat (Cs) and a coefficient of thermal conductivity (ks), and the porous material (4) has a porosity value (ε). The heating assembly comprises at least one heating device (6) inserted inside the tank (1), wherein the heating device (6) extends across the entire cross-section (A) of the tank (1) and has a thickness (d), measured in the direction of the length (L) of the tank (1) and being at least 50 times smaller than the length (L) of the tank (1). The heating device (6) has a lattice structure with interwoven ribs (7), between which there are gaps larger than the thickness of the ribs (7). The midpoint of the heating assembly is located at a distance between 70% and 80% of the length (L) of the tank (1) from the inlet (2) of the tank (1).

Description

[0001] DESCRIPTION

[0002] HIGH TEMPERATURE HEAT STORAGE SYSTEM AND METHOD

[0003] FIELD OF INVENTION

[0004] The present invention belongs to the technical field of high-temperature heat storage systems and methods, of which there is a porous bed reservoir and a fluid passing through it.

[0005] BACKGROUND OF THE INVENTION

[0006] The intermittent nature of renewable energy generation has spurred many researchers to find controllable solutions that guarantee a continuous supply during periods of high energy demand. In response to this need, energy storage systems have gained significant popularity in recent years due to their flexibility in integrating with solar and wind power plants.

[0007] Traditionally powered by fossil fuels or electric heaters, one of the most important sectors for decarbonization is the high-temperature heat industry. Since these activities require large amounts of energy to operate, energy storage systems have become an essential tool for ensuring their flexibility and continuity. Typically, energy is stored when it is inexpensive (or readily available) and retrieved when its price is less competitive (or when needed). A widespread solution is the use of thermal energy storage (TES) systems combined with heat generation systems, preferably using renewable energy sources such as concentrated solar power (CSP) plants.However, often the thermal power supplied is not sufficient, and an additional temperature rise is required to meet the demand conditions.

[0008] The present invention provides a versatile and optimized solution for this type of energy storage system, ensuring that the working fluid passing through the system leaves the tank at the desired temperature. BRIEF DESCRIPTION OF THE INVENTION

[0009] The present invention provides an improvement to known energy storage solutions, by means of an energy storage system according to claim 1 and an energy storage method according to claim 14.

[0010] In a first inventive aspect, the invention relates to an energy storage system comprising a longitudinal tank with a straight axis and constant cross-section comprising an inlet and an outlet, wherein the tank has a length, a diameter and a cross-section, wherein the tank is filled with a porous material, wherein the porous material comprises a series of particles of a solid material, wherein the particles have an equivalent diameter, wherein the solid material has a density value, specific heat and a thermal conductivity coefficient, wherein the porous material has a porosity value;A heating assembly comprising at least one heating device inserted within the tank, wherein the heating device extends across the entire cross-section of the tank and has a thickness, measured along the length of the tank, at least 50 times smaller than the length of the tank, wherein the heating device has a lattice structure with interlaced ribs, between which there are gaps with a surface area greater than the thickness of the ribs; wherein the midpoint of the heating assembly is located at a distance from the inlet of the tank between 70% and 80% of the length of the tank.

[0011] A tank is a container that extends longitudinally with a straight axis and a constant cross-section. This section can be polygonal or curvilinear, so any type of prism or right cylinder would fall within the definition, particularly polygonal prisms or cylinders with a circular, oval, or any other closed curve as their cross-section.

[0012] This heating assembly is designed to allow the flow of a working fluid from the tank inlet to the outlet. In this way, thanks to the heat input within the heating assembly, the working fluid will experience a temperature increase. The position and thickness of the heating assembly optimize the energy exchange between it and the working fluid, maximizing the temperature increase for a given amount of heat input.

[0013] In preferred embodiments, the solid material is alumina, magnesium, or graphite. These materials, along with some others, allow for use at high temperatures and enable good heat transfer with the working fluid.

[0014] In preferred embodiments, the thickness of the heating assembly is at least 100 times smaller, in particular 200 or 500 times smaller, than the length of the tank.

[0015] The length of the tank is an important dimension, as it determines the distance along which heat exchange occurs between the porous medium and the working fluid. The thickness of the heating assembly is measured in the same direction as the length of the tank (i.e., longitudinally). When the thickness of the heating assembly, as in these cases, is much less than the length of the tank, better control of the temperature exchange is possible.

[0016] In preferred embodiments, the equivalent diameter of the solid material particles is between 1 / 1,500 and 1 / 750 of the tank length. In preferred embodiments, the equivalent diameter of the solid material particles is at least 1 mm.

[0017] The equivalent diameter of a particle is defined as the diameter of a sphere that has the same volume as the particle. In this way, the size of particles with irregular and different shapes can be compared and characterized.

[0018] When the particles have a size as defined in these embodiments, the heat transfer between the porous medium and the working fluid is optimized.

[0019] In preferred embodiments, the solid material has a specific heat between 750 and 1,000 J / kg-K at a temperature of 298 K. In preferred embodiments, the solid material has a density between 2,500 and 5,000 kg / m³. 3at a temperature of 298 K. In preferred embodiments, the solid material has a thermal conductivity between 35 and 115 W / nrK at a temperature of 298 K. These ranges optimize the behavior of the porous material composed of the solid material particles of the reservoir. In this way, the heat exchange between the porous medium and the working fluid is optimized.

[0020] In preferred embodiments, the energy storage system comprises at least two heating devices, where the separation between a pair of adjacent heating devices is equal to the separation between another different pair of adjacent heating devices.

[0021] Sometimes it's convenient to distribute the energy exchange across more than one heating device, for power reasons or other strategic purposes. In this case, the optimal distribution is for all heating devices to be evenly spaced within the heating unit area.

[0022] In preferred embodiments, the rib structure of a heating device is not aligned with the rib arrangement of the adjacent heating device, viewed in the direction of the tank length.

[0023] The storage system is configured so that a working fluid travels through it longitudinally. In this way, the working fluid "sees" the rib structure of each heating element in this direction. To achieve better heat transfer, it is advantageous for the alignment of each structure to be different from the working fluid's perspective. Therefore, when there are multiple heating elements, the next element can be rotated relative to the previous one, or it can have a structure transformed by displacement or any other modification that results in the working fluid's "view" in the longitudinal direction not being identical.

[0024] In preferred embodiments, the number of heating devices is a multiple of three; each heating device has external connection sockets and at least one internal connection socket; a first group of heating devices comprises one-third of the total number of heating devices, a second group of heating devices comprises one-third of the total number of heating devices, a third group of heating devices comprises one-third of the total number of heating devices, each external connection socket of a heating device in the first group of heating devices is connected to a first phase of a three-phase network, each external connection socket of a heating device in the second group of heating devices is connected to a second phase of a three-phase network,and each external connection socket of a heating device of the third group of heating devices is connected to a third phase of a three-phase network, each internal connection socket of a heating device of the first group of heating devices is connected to one of the external connection sockets of a heating device of the second group of heating devices, each internal connection socket of a heating device of the second group of heating devices is connected to one of the external connection sockets of a heating device of the third group of heating devices, and each internal connection socket of a heating device of the third group of heating devices is connected to one of the external connection sockets of a heating device of the first group of heating devices.

[0025] When greater heat dissipation power is required, the group of heating devices can be connected to the three-phase system. In this case, the number of heaters is divided into three groups, and the electrical connections are established either in a delta or a wye configuration (with or without a neutral wire). This increases the heat output that the device can provide.

[0026] In preferred embodiments, the heating elements are made of SiC or MoSh. These materials are suitable for withstanding high temperatures and provide a good balance between durability and performance.

[0027] In preferred embodiments, the heating device ribs form a honeycomb structure, where the ribs define hexagons interlocked with each other.

[0028] This structure allows for good heat exchange and predictable behavior.

[0029] In a second inventive aspect, the invention provides a method of energy storage comprising the following steps: defining a working fluid, wherein the working fluid has a density and a specific heat; providing an energy storage system according to the first inventive aspect; defining the value of four of the following six magnitudes: desired temperature rise, working fluid flow rate, required heat output, porosity of the porous medium, length of the reservoir, cross-sectional area of ​​the reservoir; obtaining the remaining two magnitudes by means of the following two relationships: exert a pressure difference between the tank outlet and the tank inlet, which causes the working fluid to flow from the inlet to the outlet of the tank with the defined or calculated working fluid flow rate; satisfy a heat power Q in at least one heating device, with the defined or calculated heat power value.

[0030] This method allows the design and use of a heating device according to the invention, optimized for specific operating conditions.

[0031] The device has several degrees of freedom in its implementation: porosity of the porous medium, length of the tank, and cross-sectional area of ​​the tank. Furthermore, the specific operating conditions can determine the desired temperature rise, mass flow rate of the working fluid, or the required heat output.

[0032] There are two equations that define the optimization of the process, so it is possible to leave two of these six parameters free: four of them are defined and the remaining two are calculated with the given equations.

[0033] For example, the desired temperature rise, the mass flow rate of the working fluid, the heat input demand, and the length of the tank can be defined, and the porosity of the porous medium and the cross-sectional area of ​​the tank can then be calculated. Once the six parameters are characterized, the device can be designed and adjusted and operated under optimal conditions. In particular embodiments, the product of the solid's density and its specific heat (volumetric specific heat) is between 10 4 and 10 6 times greater than the product of the density of the working fluid and the specific heat of the working fluid.

[0034] When this relationship is verified, the device's performance is optimized.

[0035] All terms and embodiments described anywhere herein are equally applicable to all aspects of the invention. It should be noted that, as used in the description and claims, the singular forms "a," "an," and "the" include their plurals unless the context clearly indicates otherwise. Similarly, the term "comprises" or "comprising," as used herein, also describes "consists of" or "consisting of" in accordance with generally accepted patent practice. Furthermore, any of the parametric ranges and / or single values ​​of temperature (T), pressure (P), etc., described in the examples may be used, in different embodiments of the invention, either individually or in combination.

[0036] DESCRIPTION OF THE FIGURES

[0037] The following is a brief description of each of the figures used to complement the description of the invention that follows, for illustrative and non-limiting purposes:

[0038] Figure 1 shows a cross-sectional view of an energy storage system according to the invention.

[0039] Figure 2 represents a cross-sectional view A - A elevation of said device, at the height of the heating devices.

[0040] Figures 3a and 3b show a first heating device and a second heating device, rotated relative to each other, within an energy storage system according to the invention.

[0041] Figure 4 shows a possible three-phase delta connection diagram between the three heating devices. Figure 5 shows another possible three-phase wye connection diagram with neutral between the three heating devices.

[0042] Figures 6 and 7 show examples of the operation of devices that are not in accordance with the invention, since they are data obtained with a device in which the heating device has a thickness 10 times smaller than the length of the tank.

[0043] Figure 8 shows an example of the operation of a device according to the invention, since these are data obtained with a device in which the heating device has a thickness 50 times smaller than the length of the tank and a heating assembly located at a distance from the inlet equal to 75% of the length of the tank.

[0044] Figure 9 shows an example of the operation of a device that is not in accordance with the invention, since the data was obtained with a device in which the heating device has a thickness 100 times smaller than the length of the tank, but the heating assembly is located at a distance from the inlet equal to 90% of the length of the tank.

[0045] Figure 10 shows an example of the operation of a device according to the invention, since these are data obtained with a device in which the heating device has a thickness 100 times smaller than the length of the tank and a heating assembly located at a distance from the inlet equal to 75% of the length of the tank.

[0046] Numerical references for the figures

[0047] In order to aid a better understanding of the technical characteristics of the invention, the aforementioned figures are accompanied by a series of numerical references where, for illustrative and non-limiting purposes, the following is represented:

[0048] DETAILED DESCRIPTION OF THE INVENTION

[0049] The detailed description of the present invention that follows refers to the accompanying drawings, which illustrate specific embodiments in which the present invention can be implemented. These embodiments are described in sufficient detail to enable those skilled in the art to implement the present invention. It should be understood that various embodiments of the present invention are different from one another, but are not necessarily mutually exclusive. Accordingly, the detailed description that follows is not intended to be taken in a restrictive sense, and the scope of the present invention, if properly described, is limited only by the appended claims, in addition to all scopes equivalent to those claimed by the appended claims. In the drawings, the reference numbers refer to the same or similar functions in various respects.

[0050] The preferred embodiments of the present invention will now be described in more detail with reference to the accompanying drawings.

[0051] Figure 1 shows a cross-sectional view of an energy storage system according to the invention. This system comprises a tank (1) with an inlet (2) and an outlet (3). The tank (1) is in this case a cylindrical tank and has a length (L) and a cross-sectional area (A).

[0052] This tank (1) is filled with a porous material (4), which occupies the entire interior of the tank. The porous material (4) comprises a series of alumina particles (5). The equivalent diameter of the alumina particles (5) is between 1 / 1,500 and 1 / 750 times the length (L) of the tank (1) and, in any case, is at least 1 mm.

[0053] Furthermore, the system comprises a heating assembly consisting of three heating elements (6) installed within the tank (1). Each heating element (6) is made of silicon carbide and is shaped like a disc with a honeycomb structure, occupying the entire cross-section of the tank (1). Silicon carbide can operate at high temperatures and allows for the dissipation of a high amount of heat. In fact, each heating element (6) is designed to produce a maximum Joule heating power dissipation in the range of 100 to 200 kW / m³. 2 .

[0054] The heating devices (6) are equally spaced, so that two adjacent heating devices (6, 6') are located from each other at a distance of 0.005 times the length (L) of the tank (1) and the midpoint of the second heating assembly (the one located in the middle) is located at a distance from the inlet (2) of the tank (1) of 75% of the length (L) of the tank (1).

[0055] The design and materials that make up the energy storage system are chosen based on its application and the working fluid to be used, as will be explained later.

[0056] Figure 2 represents a cross-sectional view (A - A) of said device, at the height of the heating devices (6).

[0057] The honeycomb structure consists of ribs (7) that form interlocking hexagonal elementary structures, creating the aforementioned honeycomb structure. The elementary structures are hollow, allowing fluid to flow through the heating devices (6). The ribs (7) of each heating device (6) have a porosity similar to that of the porous material (4). The rib structure (7) of one heating device (6) is not aligned with the rib arrangement (7) of the adjacent heating device (6') when viewed along the length (L) of the reservoir (1).

[0058] This is shown in Figures 3a and 3b, which depict a first heating device (6) and a second heating device (6'), located downstream of the first heating device (6). As can be seen in these figures, in both heating devices (6, 6') the rib structure (7) is of a honeycomb type, with a set of interlocking hexagons. In the second heating device (6'), this structure is rotated with respect to the structure of the first heating device (6), promoting a more homogeneous heat exchange.

[0059] Figure 4 shows a possible electrical connection scheme of the delta type between the three heating devices (6).

[0060] In this particular example, an electrical connection to a three-phase supply network is used.

[0061] As can be seen in the image, there are three heating devices in this case. Each heating device is connected between two phases of the three-phase power system. The external connection terminals (11) of the first heating device are connected to phase R, the external connection terminals (12) of the second heating device to phase S, and the external connection terminals (13) of the third heating device to phase T. The internal connection terminal (14) of the first heating device is connected to the external connection terminals (12) of the second heating device (phase S), the internal connection terminal (15) of the second heating device is connected to the external connection terminals (13) of the third heating device (phase T), and the internal connection terminal (16) of the third heating device is connected to the external connection terminals (11) of the first heating device (phase R).

[0062] Figure 5 shows another possible electrical connection scheme between the three heating devices (6).

[0063] In this particular example, a three-phase star-type electrical connection is used to a three-phase supply network, but its connection is compatible with a single-phase distribution network. In this case, there are also three heating devices (6), but this example can be extrapolated to the case of having a number of heating devices (6) that is not a multiple of three. Each heating device (6) has external connection terminals (11, 12, 13) and internal terminals (14, 15, 16). In this case, all the external connection terminals (11, 12, 13) of each heating device (6) are connected to one of the phases being distributed, while all the internal terminals (14, 15, 16) of the heating devices (6) are connected to the neutral conductor.If it were connected to a balanced three-phase network, and the number of heating devices (6) connected to each of the three phases were the same, all the internal connection sockets (14, 15, 16) could be electrically linked together, it would not be necessary to connect the neutral conductor since they would form an artificial neutral point.

[0064] When using an energy storage device according to the invention, the following steps are followed.

[0065] First, a working fluid is chosen, where the working fluid has a density (ρ) and a specific heat (C p This working fluid can be, for example, air or CO2.

[0066] Once the working fluid has been chosen, the energy storage device must be designed. This involves defining the value of four of the following six quantities: desired temperature difference (AT), mass flow rate of the working fluid (G), required heat output (Q), porosity of the porous medium (E), length of the tank (L), and cross-sectional area of ​​the tank (A).

[0067] Three of these parameters correspond to the design of the tank itself: porosity of the porous medium (E), length of the tank (L), cross-sectional area of ​​the tank (A), while three other parameters correspond to its operation: desired temperature jump (AT), mass flow rate of the working fluid (G), heat power demanded (Q).

[0068] Furthermore, because a particular working fluid has been chosen, this working fluid has a specific heat (C p), and because a particular porous material was chosen, this material has a thermal conductivity coefficient (k s ).

[0069] In the particular case at hand, the following tank parameters are defined:

[0070] • Porosity of the porous medium (E), to be calculated • Length of the deposit (L) equal to 6 m

[0071] • tank cross-sectional area (A), to be calculated

[0072] Regarding the solid material that will make up the porous medium:

[0073] • k s = 31 W / (mK)

[0074] Regarding the working fluid (air):

[0075] • C p = 1000 J / (kg-K)

[0076] Regarding the operating parameters:

[0077] • Heat demand (Q) equal to 1 kW / m 3

[0078] • Temperature jump (AT) equal to 500 K, since the desired operating temperature is between 500 and 1000 K

[0079] • Mass flow rate of the working fluid through the tank (G) equal to 0.040 kg / s

[0080] Once these parameters have been chosen, the porosity and cross-section of the deposit are calculated using the relationships indicated above:

[0081] 2 Q - L 2 , = 0.81

[0082] £ = 1 — 25 / c s • AT

[0083] AT

[0084] A — G ■ Cp • - = 3.33 m 2

[0085] Q - L

[0086] Once all the calculated values ​​are obtained and the device is customized with these porosity and cross-section values, a pressure difference will be exerted between the tank outlet and the tank inlet, which causes the working fluid to flow from the inlet to the outlet of the tank with the defined working fluid mass flow rate, while applying a heat power (Q) to the set of heating devices, with the defined heat power value.

[0087] In any case, the product of the density of the solid (p s ) by the specific heat of the solid (C s ) is between 10 4 and 10 6 times greater than the product between the density of the working fluid (p) and the specific heat of the working fluid (C p ).

[0088] Figures 6 and 7 show examples of the operation of devices that are not in accordance with the invention, since they are data obtained with a device in which the heating device has a thickness (d) 10 times smaller than the length of the tank; i.e., outside the range of 50 times smaller than the length of the tank, required in the present invention.

[0089] Under these conditions, the variable (0), representing the fluid temperature difference from the initial temperature (adjusted to the ideal temperature difference (AT), is shown versus the distance (q), which is the dimensionless longitudinal parameter representing the length of the tank. In other words, the desired outcome at the tank outlet (i.e., for q = 1) is a temperature of 0 = 1 (i.e., a temperature equal to the planned outlet temperature). This relationship is shown for three different values ​​of dimensionless time, which is the time parameter representing the time it takes the fluid to travel through the tank under steady-state conditions.

[0090] Under these circumstances, Figures 6 and 7 show that the temperature does not reach the ideal final temperature (0 does not equal 1 for q = 1). In Figure 6, the heating assembly is centered at the midpoint of the tank (at q = 0.5), and in Figure 7, the heating assembly is centered at 75% of the tank's length (at q = 0.75). In neither case is the desired temperature reached.

[0091] Figure 8 shows an example of the operation of a device according to the invention, since these are data obtained with a device in which the heating device has a thickness (d) 50 times smaller than the length of the tank and a heating assembly located at a distance from the inlet equal to 75% of the length of the tank.

[0092] Under these conditions, the same variables 0 and q are shown, at the same three different values ​​of dimensionless time.

[0093] Under these circumstances, it is observed how the temperature reaches the ideal final temperature (0 = 1 for q = 1 ).

[0094] Figure 9 shows an example of the operation of a device that does not conform to the invention, as the data was obtained with a device in which the heating element has a thickness (d) 100 times smaller than the length of the tank (which would conform to the invention), but the heating element is located at a distance from the inlet equal to 90% of the tank length (outside the range required by the present invention). Under these conditions, the same variables 0 and q are shown at the same three different dimensionless time values.

[0095] Under these circumstances, it is observed how the temperature does not reach the ideal final temperature (0 does not become equal to 1 for q = 1).

[0096] Finally, Figure 10 shows an example of the operation of a device according to the invention, since these are data obtained with a device in which the heating device has a thickness (d) 100 times smaller than the length of the tank and a heating assembly located at a distance from the inlet equal to 75% of the length of the tank.

[0097] Under these conditions, the same variables 0 and q are shown, at the same three different values ​​of dimensionless time.

[0098] Under these circumstances, it is observed how the temperature reaches the ideal final temperature (0 = 1 for q = 1 ) even before reaching steady state.

Claims

CLAIMS 1. An energy storage system comprising a longitudinal tank (1) with a straight axis and constant cross-section, comprising an inlet (2) and an outlet (3), wherein the tank (1) has a length (L), a diameter and a cross-section (A), wherein the tank (1) is filled with a porous material (4), wherein the porous material (4) comprises a series of particles (5) of a solid material, wherein the particles have an equivalent diameter, wherein the solid material has a density value (p s ), specific heat (C s ) and a thermal conduction coefficient (k s), where the porous material (4) has a porosity value (E); a heating assembly comprising at least one heating device (6) introduced into the tank (1), where the heating device (6) extends over the entire cross-section (A) of the tank (1) and has a thickness (d), measured in the direction of the length of the tank (1), at least 50 times smaller than the length (L) of the tank (1), where the heating device (6) has a reticular structure with interlaced ribs (7), between which there are gaps with a surface area greater than the thickness of the ribs (7); where the midpoint of the heating assembly is located at a distance from the inlet (2) of the tank (1) between 70% and 80% of the length (L) of the tank (1). 2.- Energy storage system according to claim 1, wherein the solid material is alumina, magnesium or graphite. 3.- Energy storage system according to any of the preceding claims, wherein the thickness (d) of the heating assembly is at least 100 times smaller, in particular 200 or 500 times smaller, than the length (L) of the tank (1 ). 4.- Energy storage system according to any of the preceding claims, wherein the equivalent diameter of the particles (5) of the solid material is between 1 / 1,500 and 1 / 750 times the length (L) of the tank (1). 5.- Energy storage system according to any of the preceding claims 1 to 3, wherein the equivalent diameter of the particles (5) of the solid material is at least 1 mm.

6. Energy storage system according to any of the preceding claims, wherein the solid material has a specific heat (C s ) between 750 and 1,000 J / kg-K at a temperature of 298 K. 7.- Energy storage system according to any of the preceding claims, wherein the solid material has a density (p s ) between 2,500 and 5,000 kg / m 3 at a temperature of 298 K. 8.- Energy storage system according to any of the preceding claims, wherein the solid material has a thermal conductivity between 35 and 115 W / nrK at a temperature of 298 K.

9. Energy storage system according to any of the preceding claims, comprising at least two heating devices (6, 6'), wherein the separation between a pair of adjacent heating devices (6, 6') is equal to the separation between another different pair of adjacent heating devices (6, 6'). 10.- Energy storage system according to claim 9, wherein the rib structure (7) of a heating device (6) is not aligned with the rib arrangement (7) of the adjacent heating device (6'), viewed in the direction of the length (L) of the tank (1).

11. Energy storage system according to any of claims 9 or 10, wherein the number of heating devices (6) is a multiple of three, each heating device has external connection sockets (11, 12, 13) and at least one internal connection socket (14, 15, 16); a first group of heating devices comprises one-third of the total number of heating devices (6), a second group of heating devices comprises one-third of the total number of heating devices (6), a third group of heating devices comprises one-third of the total number of heating devices (6), each external connection socket (11) of a heating device (6) of the first group of heating devices is connected to a first phase of a three-phase network R, each external connection socket (12) of a heating device (6) of the second group of heating devices is connected to a second phase of three-phase network S, and each external connection socket (13) of a heating device (6) of the third group of heating devices is connected to a third phase of three-phase network T, each internal connection socket (14) of a heating device (6) of the first group of heating devices is connected to one of the external connection sockets (12) of a heating device (6) of the second group of heating devices, each internal connection socket (15) of a heating device (6) of the second group of heating devices is connected to one of the external connection sockets (13) of a heating device (6) of the third group of heating devices,and each internal connection socket (16) of a heating device (6) of the third group of heating devices is connected to one of the external connection sockets (11) of a heating device (6) of the first group of heating devices. 12.- Energy storage system according to any of the preceding claims, wherein the heating devices (6) are made of SiC or MoSh. 13.- Energy storage system according to any of the preceding claims, wherein the ribs (7) of the heating device (6) form a honeycomb structure, wherein the ribs (7) define hexagons intertwined with each other. 14.- Energy storage method comprising the following steps: defining a working fluid, where the working fluid has a density (p) and a specific heat (C) p) provide an energy storage system according to any of the preceding claims; define the value of four of the following six magnitudes: desired temperature rise (AT), mass flow rate of the working fluid (G), required heat output (Q), porosity of the porous medium (E), length of the tank (L), cross-sectional area of ​​the tank (A); obtain the two remaining magnitudes by means of the following two relationships: exert a pressure difference between the outlet (3) of the tank (1) and the inlet (2) of the tank (1), which causes the working fluid to flow from the inlet (2) to the outlet (3) of the tank (1) with the mass flow rate value of the working fluid defined or calculated; satisfy a heat power (Q) in at least one heating device (6), with the heat power value (Q) defined or calculated. 15.- Energy storage method according to claim 14, wherein it is verified that the product of the density of the solid (p s ) by the specific heat of the solid (C s ) is between 10 4 and 10 6 times greater than the product between the density of the working fluid (p) and the specific heat of the working fluid (C p ).

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