Storage power station and method for operating a storage power station

Abstract

The invention relates to a storage power station for generating steam with defined steam parameters, wherein the steam which can be generated can be expanded in a steam turbine (2), and wherein a rotational energy resulting from the expansion of the steam can be used to drive a generator (3). The storage power station comprises two energy stores (4, 5) integrated in a water-steam cycle (1), wherein the first energy store (4) is designed as a thermal energy store and the second energy store (5) is designed as a chemical energy store. The chemical energy store (5) comprises an electrolyser (6) for breaking down water into hydrogen and oxygen, at least one first store (7) for storing the hydrogen and at least one second store (8) for storing the oxygen. Furthermore, the water-steam cycle (1) comprises a steam generator (9) for internal combustion of the hydrogen with the oxygen.

Description

[0001] The invention relates to a storage power plant according to the preamble of independent patent claim 1 and to methods for charging and discharging the energy storage devices of such a storage power plant according to the preambles of claims 4 and 5, respectively.

[0002] With the increasing use of renewable energies for electricity generation, the demand for suitable storage solutions and capacities is increasing sharply, as renewable energies, such as solar and wind energy, are not always available in the required quantities at the time of energy demand.

[0003] The use of thermal energy storage (often referred to as heat storage) is already state of the art in solar thermal power plants. The thermal energy storage is charged with solar energy primarily through a fluid-based process (e.g., thermal oil). This concept is generally transferable to storage power plants, although the thermal energy storage can also be charged using electrical energy or other fluid-based heat flows (e.g., waste heat from industrial processes). Waste heat refers to excess heat (e.g., from an industrial process) that would otherwise be released unused into the environment.

[0004] The maximum operating temperature of the thermal energy storage system varies depending on the type of energy flow during charging and the design of the thermal energy storage system. The stored energy is converted (back) into electricity using a generator-connected steam turbine in a water-steam cycle. The temperature of the thermal energy storage system thus influences the fluid temperature of the water-steam cycle. The use of the steam turbine requires minimum fluid parameters at the turbine inlet (minimum temperature depending on the pressure), below which operation is not possible due to excessive moisture during the expansion process. Operation above the minimum fluid parameters (temperature increase or combined temperature and pressure increase) is possible within certain limits (up to the maximum fluid parameters are reached) and can lead to increased cycle efficiency.

[0005] Document US 2010 / 154381 discloses a state-of-the-art storage power plant.

[0006] A general problem with thermal energy storage systems, however, is the loss of heat to the environment, which leads to a loss of stored energy. For this reason, thermal energy storage systems cannot currently be used for long-term storage. Chemical energy storage systems are more suitable for long-term storage than thermal energy storage systems; for example, excess electrical energy can be used to generate hydrogen through electrolysis. The hydrogen can be burned in a hydrogen-fired combined cycle power plant to reconvert it to electricity. However, chemical energy storage systems have the disadvantage of higher electricity generation costs. Consequently, upgrading thermal energy storage systems to long-term storage systems holds great economic potential.

[0007] The object of the present invention is to provide a storage power plant with improved storage technology. Furthermore, the object of the present invention is to provide methods for charging and discharging the energy storage devices of such a storage power plant.

[0008] The problem is solved with regard to the storage power plant by the features of patent claim 1, with regard to the method for charging the energy storage devices by the features of patent claim 4 and with regard to the method for discharging the energy storage devices by the features of patent claim 5.

[0009] Further advantages of the invention, which can be used individually or in combination with one another, are the subject of the dependent claims.

[0010] The storage power plant according to the invention comprises at least one water-steam cycle, wherein the water-steam cycle comprises at least one steam turbine with a generator operatively connected to the steam turbine, as well as two energy storage units. The energy storage units are arranged and designed such that they can transfer energy to the H2O flowing in the water-steam cycle to generate steam with defined steam parameters. H2O, hereinafter also referred to as the working medium of the water-steam cycle, generally stands for water in different states of aggregation (liquid, vapor). The steam that can be generated can be expanded in the steam turbine, wherein rotational energy generated during the expansion of the steam can be used to drive the generator.

[0011] The first energy storage device is designed as a thermal energy storage device and the second energy storage device as a chemical energy storage device. The chemical energy storage device can be charged using electrical energy and comprises an electrolyzer for splitting water from the water-steam cycle into hydrogen and oxygen, and a first storage device for storing the hydrogen and a second storage device for storing the oxygen. Furthermore, the water-steam cycle comprises a steam generator for the internal combustion of the hydrogen with the oxygen, wherein the steam generator has a connection via which H2O for steam conditioning can be supplied to the steam that can be generated in the steam generator. According to the invention, the water-steam cycle is designed as a closed circuit.

[0012] The steam generator used for internal combustion is referred to below as a clean steam generator (CSG). The CSG generates steam through pressurized internal combustion of hydrogen and oxygen. This initially generated steam is conditioned by the addition of H2O. This conditioned steam is referred to below as CSG steam. Chemical reactions may occur during conditioning.

[0013] The storage power plant according to the invention thus combines the advantages of thermal energy storage with those of chemical energy storage. Thermal energy storage gradually loses its stored energy over time through heat loss, but hydrogen and oxygen can be stored with low time-dependent losses, making these substances a suitable storage medium for long-term energy storage (chemical energy storage, power to H 2 & O 2 ). By combining the advantages of thermal and chemical energy storage, the storage power plant according to the invention can play a crucial role in power grids with a high proportion of volatile power sources (renewable energies). During standard use, the energy storage systems (thermal energy storage, chemical energy storage) are used as short- and medium-term storage. In this case, chemical energy storage offers several advantages in terms of operational flexibility, e.g.by CSG steam injection for the purpose of extending operating time or for control power (other advantageous operating regimes are possible). However, the main advantage of the storage power plant according to the invention lies in the rare occurrence of longer-term power underproduction in the grid (e.g. .Due to the low time-dependent losses of the chemical energy storage system, the stored energy can be reliably discharged even after long periods of downtime, meaning that the storage power plant also supplies a predictable minimum energy in this case. Therefore, in contrast to purely thermal storage power plants, the storage power plant according to the invention can also be used for long-term storage. However, the electricity generation costs in the storage power plant according to the invention are lower than in a storage power plant with purely chemical energy storage. By specifically adjusting the respective proportions of the two storage principles (thermal and chemical), an individually optimized storage power plant can be achieved.

[0014] By designing the water-steam cycle as a closed loop, the storage power plant is particularly suitable for operation in regions where water is a scarce resource. The water required for electrolysis is taken from the condensate of the water-steam cycle (the mass balance is closed due to the internal combustion of the hydrogen and oxygen produced in the CSG). This closed loop is a key difference from other systems, such as storage power plants based on a gas turbine fired with hydrogen from electrolysis. In these systems, the water is lost through the stack, resulting in significant water consumption.

[0015] One embodiment of the invention provides that the thermal energy storage device has a connection for supplying fluid-bound heat. This makes it possible to charge the thermal energy storage device additionally or alternatively (to electrical charging) using a fluid. This can, for example, be a thermal oil heated by a solar thermal power plant and / or waste heat from industrial processes. A possible temperature difference of the working fluid between the outlet of the thermal energy storage device and the target parameters at the inlet to the steam turbine is compensated by admixing CSG steam.

[0016] A further embodiment of the invention provides that the connection on the CSG is operatively connected to the condenser and / or the thermal energy storage device. Depending on where the connection(s) to the CSG branch off, water and / or steam can be sprayed into the CSG, thus adjusting the steam parameters of the CSG steam. Another possibility is to first feed the water discharged from the condenser to a preheater and then feed the heated water to the CSG. The preheater can be operated, for example, by means of intermediate steam extraction from the steam turbine.

[0017] The method according to the invention for charging the energy storage of a storage power plant according to one of the preceding claims is characterized by the following method steps: Heating the thermal energy storage device by means of electrical current and / or fluid-bound heat and / or decomposition of water into hydrogen and oxygen by applying electrical current to the electrolyzer and storing the hydrogen in the first storage device and the oxygen in the second storage device.

[0018] Energy storage systems are generally charged preferably at times when there is a surplus of electrical energy. Part of the electrical energy is used to heat the thermal energy storage system (power to heat). Alternatively (or additionally), the energy can be introduced into the thermal energy storage system via fluid-bound heat, for example by means of waste heat injection. Another part of the electrical energy is stored in the chemical energy storage system. For this purpose, water is split into hydrogen and oxygen using electrolysis and then stored in storage systems (e.g. pressure tanks). The respective proportion of electrical energy used to charge the respective energy storage system can vary, even during the charging process, whereby a customer-optimized solution with low electricity generation costs should be sought wherever possible.

[0019] The above-mentioned proportions of electrical energy used to charge the respective energy storage device can also be zero, independently of one another.

[0020] The water supplied to the electrolyzer is taken from the water-steam cycle. This creates a closed loop, allowing the process to operate without significant water consumption (only a small amount of water may be required to compensate for leaks), making the process particularly suitable for use in arid regions.

[0021] The water required for electrolysis is recovered from the condensate of the water-steam cycle (the mass balance is closed due to the internal combustion of the produced hydrogen and oxygen in the CSG). This closed cycle represents a significant difference from existing processes.

[0022] The method according to the invention for discharging the energy storage of a storage power plant according to one of claims 1 to 3 is characterized by the following method steps: Transferring heat energy from the thermal energy storage device to the working medium flowing in the water-steam circuit in order to bring about a temperature increase and / or a phase change (evaporation) of the working medium, and / or supplying hydrogen and oxygen from the respective storage device to the steam generator and burning the hydrogen with the oxygen in the steam generator, subsequent and / or simultaneous conditioning of the CSG steam generated in the steam generator by adding working medium which is taken from the water-steam circuit, whereby the working medium can be in liquid and / or vapor form, expanding the steam flowing in the water-steam circuit in the steam turbine, generating electrical power by means of the generator.

[0023] During the discharge process, thermal energy is transferred from the thermal energy storage unit to the working fluid in the water-steam cycle to cause a temperature increase and / or phase change (evaporation). Simultaneously, subsequently, or alternatively, hydrogen and oxygen from the respective storage unit (oxygen storage unit / hydrogen storage unit) are fed to the CSG and combusted in the CSG. To condition the steam generated during combustion, additional working fluid is injected into the CSG. The working fluid is primarily taken from the water-steam cycle and can be preheated by regenerative preheating or by the thermal energy storage unit.

[0024] Any possible temperature difference of the working fluid between the thermal energy storage outlet and the target parameters at the steam turbine inlet is compensated by admixing CSG steam. The operating mode (distribution of energy flows and temperature levels between the thermal energy storage and the chemical energy storage) and the location of the steam feed depend on the specific application.

[0025] Based on the present invention, thermal energy storage systems with temperatures below the target temperature at the steam turbine inlet can also be used for reconversion into electricity using conventional water-steam cycles. No additional energy sources are required, resulting in higher net electricity generation and self-sufficiency.

[0026] An embodiment of the method according to the invention for discharging the energy storage of a storage power plant is characterized in that at least a part of the working medium flowing in the water-steam cycle is removed before, inside, or at the outlet of the steam turbine and the removed working medium is made available as process steam and / or hot water, for example for district heating supply.

[0027] Hot water / intermediate steam extraction allows the storage power plant to operate even more flexibly. The hot water / steam can also be extracted directly from the thermal energy storage system.

[0028] Further advantages of the invention are explained below using exemplary embodiments. It shows: Fig. 1 : An embodiment of a storage power plant according to the invention; Fig. 2 : A first operating mode of the Fig. 1 shown storage power plant, in which the steam is provided to operate the steam turbine by discharging both energy storage units and conditioning the CSG steam by means of condensate, as well as a subsequent mixing of the CSG steam with the working medium, which is heated / evaporated by the thermal energy storage unit; Fig. 3 : A second operating mode of the Fig. 1 shown storage power plant, in which the steam for operating the steam turbine is provided by discharging the chemical energy storage and conditioning the CSG steam using condensate, as well as subsequent mixing of the CSG steam with condensate; Fig. 4 : A third operating mode of the Fig. 1 shown storage power plant, in which the provision of steam for operating the steam turbine is carried out by discharging both energy storage units and conditioning the CSG steam using the working medium from the thermal energy storage unit, as well as a subsequent mixing of the CSG steam with the working medium, which is heated / evaporated by the thermal energy storage unit; Fig. 5 : A fourth operating mode of the Fig. 1 shown storage power plant, in which the steam for operating the steam turbine is provided by discharging the chemical energy storage and conditioning the CSG steam using the working medium from the thermal energy storage; Fig. 6 : A fifth operating mode of the Fig. 1 shown storage power plant, in which the steam for operating the steam turbine is provided by discharging the chemical energy storage and conditioning the CSG steam using condensate.

[0029] The figures show only a schematic, simplified, and not to scale representation of the storage power plant. Identical or functionally identical components are provided with the same reference numerals throughout the figures.

[0030] Fig. 1 shows an embodiment of a storage power plant according to the invention. The storage power plant has a water-steam circuit 1 which is operated with H2O as the working medium. The working medium can be present locally and depending on the mode of operation in liquid form and / or as water vapor. The water-steam circuit 1 comprises a thermal energy storage unit 4 and a chemical energy storage unit 5. The two energy storage units 4, 5 are integrated into the water-steam circuit 1 with parallel fluid flow to one another. The thermal energy storage unit 4 can be charged using electrical energy 13 (power to heat) or alternatively (or additionally) using fluid-bound heat 11, for example by introducing waste heat.The chemical energy storage device 5 can be charged using electrical energy 13 and comprises an electrolyzer 6 for decomposing water from the water-steam circuit 1 into hydrogen and oxygen, as well as a first storage device 7 for storing the hydrogen and a second storage device 8 for storing the oxygen. Furthermore, the water-steam circuit 1 comprises a CSG 9 for the internal combustion of the hydrogen with the oxygen. The CSG has a connection 10 through which the working medium for steam conditioning can be supplied to the steam generated in the CSG.

[0031] When the energy storage devices 4, 5 are discharged, the energy storage devices 4, 5 release energy to the working medium of the water-steam cycle 1, thereby heating and / or evaporating the working medium. The resulting steam can then be expanded in the steam turbine 2. The steam turbine 2, in turn, drives a generator 3, which generates electrical power and can feed it into an electrical grid or forward it to an electrical consumer. The steam leaving the steam turbine 2 is condensed in a condenser 14, and the condensate is collected in a tank 12. From there, the condensate is pumped back to the energy storage devices 4, 5 by means of a pump 15, where it is heated or evaporated. The water-steam cycle 1 is thus a closed cycle in which no working medium is lost (except for possible leakage losses). This closed cycle is a significant difference from other systems, e.g.Storage power plants based on a gas turbine fired with hydrogen from electrolysis. There, the water is lost through the chimney, resulting in significant water consumption. For flexible operation of the storage power plant, the water-steam circuit 1 comprises a piping system equipped with multiple valves 16, allowing separate discharge of one or parallel discharge of both energy storage units 4, 5. Furthermore, a piping system designed in this way enables flexible admixture of working medium (condensate, heated and / or evaporated water from thermal energy storage) to the CSG 9 and thus appropriate conditioning of the CSG steam. For mixing the CSG steam with the condensate from the condenser or the working medium heated and / or evaporated by the thermal storage unit 4, the water-steam circuit 1 has a mixer 17.The mixer 17 is preferably designed as a control element so that the respective partial mass flows can be adjusted and the steam parameters of the steam supplied to the steam turbine 2 can be precisely adjusted. The water-steam circuit 1 further has at least one intermediate steam extraction point 18, through which process steam with defined steam parameters can be extracted and fed to a subsequent process. Furthermore, an extraction point from the heat storage unit is provided, through which hot water and / or steam can be provided, for example, for district heating. When water or steam is extracted, the extracted mass flow must be fed back into the water-steam circuit 1.

[0032] The charging of the two energy storage devices 4, 5 using electrical energy (the thermal storage device 4 can be charged additionally or alternatively using fluid-bound heat 11 as described above) generally and preferably takes place at times when there is an excess supply of electrical energy. Whether the thermal energy storage device 4, the chemical energy storage device 5, or both energy storage devices are charged using electrical energy first depends on the individual case and can vary, even during the charging process. The aim is to achieve a customer-optimized solution with low electricity generation costs. Typically, the priority is initially to charge the thermal energy storage device 4 used as a short-term storage device, and the chemical energy storage device 5 intended as a long-term storage device is only charged when sufficient electrical energy is available.To charge the chemical energy storage system, water is split into hydrogen and oxygen using electrolysis and then stored in storage tanks 7 and 8. The water is taken from tank 19, which is fed with condensate via tank 12. Tank 12 and / or 19 can also have a connection through which any potential leakage can be compensated.

[0033] The discharging of the energy storage and the reconversion of the stored energy can be carried out in different ways. The following describes different operating modes based on the Fig. 2 bis 6 The exemplary embodiments do not represent an exhaustive list of all possible operating modes; further operating modes are possible without departing from the scope of the present invention.

[0034] To increase the efficiency of reconversion to electricity, several measures can be taken that deviate from the illustrations. For example, the temperature of the working fluid used to condition the CSG steam can be increased through regenerative water preheating.

[0035] To make the functionality easier to understand, the following figures only show the lines that are necessary for the respective operating mode, but the figures generally refer to the Fig. 1 shown storage power plant.

[0036] Fig. 2 shows the storage power plant according to the invention in a first operating mode. In this operating mode, the steam for reconverting the stored energy into electricity is provided by discharging both energy storage units 4, 5 and conditioning the CSG steam using condensate, as well as subsequently mixing the CSG steam with the portion of the working fluid that is heated / evaporated by the thermal energy storage unit 4.

[0037] First, a portion of the working medium (condensate) is pumped from tank 12 to the thermal energy storage unit 4 using pump 15. In the thermal energy storage unit 4, the stored thermal energy is transferred to the working medium, heating the working medium and, depending on the temperature level of the thermal energy storage unit 4, evaporating and possibly superheating it. At the same time, the energy stored in the chemical energy storage unit 5 is converted into thermal energy in the CSG 9 through the internal combustion of the hydrogen taken from the first tank 7 with the oxygen taken from the second tank 8. By adding working medium, which is taken from tank 12 and fed to the CSG 9 via connection 10, the steam produced in the CSG 9 can be conditioned. The portion of the working medium coming from the thermal energy storage unit 4 and the portion of the working medium coming from the CSG 9 are then mixed in the mixer 17.The mixer 17 is operated in such a way that the working medium has steam parameters that allow expansion of the working medium in the steam turbine 2. The stored energy is subsequently converted back into electricity by the generator 3 driven by the steam turbine 2.

[0038] Fig. 3 shows the storage power plant according to the invention in a second operating mode. In this operating mode, the steam for reconverting the stored energy into electricity is provided by discharging the chemical energy storage unit 5 and conditioning the CSG steam using condensate from tank 12, which is fed to the CSG unit 9 via connection 10. The conditioned CSG steam is then additionally mixed in the mixer 17 with a portion of the working medium, which is also taken from tank 12, whereby the steam parameters can be adjusted so that they are optimized for expansion in the steam turbine 2. The reconversion of the stored energy is subsequently carried out by the generator 3 driven by the steam turbine 2. This operating mode is particularly suitable for periods of darkness in which the thermal energy storage unit 4, used as a short-term storage unit, is already completely discharged.

[0039] Fig. 4 shows the storage power plant according to the invention in a further operating mode. In this operating mode, the steam for reconverting the stored energy into electricity occurs by discharging both energy storage units 4, 5. The CSG steam is conditioned by a first partial mass flow of the working fluid, which is fed to the thermal energy storage unit 4 and heated or evaporated as it flows through the thermal energy storage unit 4. The supply to the CSG 9 occurs via the connection 10 arranged on the CSG 9. The second partial mass flow flowing through the thermal energy storage unit 4 is fed to the mixer 17 and mixes there with the CSG steam. The steam parameters of the steam supplied to the steam turbine 3 can be adjusted by adjusting the mixer 17 or the mixing ratio. The reconversion of the stored energy is subsequently carried out by the generator 3 driven by the steam turbine 2.This mode of operation is particularly suitable when the thermal energy of the thermal storage 4 is not sufficient to evaporate the working medium or to achieve the required steam parameters.

[0040] Fig. 5 shows the storage power plant according to the invention in a further operating mode. In this operating mode, the steam for reconverting the stored energy into electricity is provided by discharging the two energy storage units 4, 5. The entire partial mass flow of the working medium, which is fed to the thermal energy storage unit 4 and heated or evaporated there, is then introduced into the CSG 9 via connection 10 for conditioning the CSG steam. The total mass flow of the working medium is thus present in the CSG 9 and the steam leaving the CSG 9 can be fed directly to the steam turbine 3 without a mixer and reconverted into electricity via the generator 3. Such an operating mode is suitable, for example, when the thermal energy storage unit only has (still) a low heat capacity and therefore only small mass flows of the working medium can be heated / evaporated.

[0041] Fig. 6shows the storage power plant according to the invention in another operating mode. In this operating mode, the steam for reconversion of the stored energy is provided by discharging the chemical energy storage unit 5. . The CSG steam is conditioned by supplying condensate to the CSG 9 via connection 10. This condensate is taken from tank 12 or the downstream tank 20 belonging to the chemical energy storage system 5. This operating mode is preferably used during periods of low light, when the thermal energy storage system, which is primarily used for short-term storage, is already completely discharged. The chemical energy storage system 5 can then extend the operating time of the storage power plant.

[0042] In summary, it can be stated that the storage power plant according to the invention achieves low electricity generation costs and re-conversion costs by combining a thermal energy storage system and a chemical energy storage system.

[0043] Chemical energy storage is also suitable for long-term energy storage, which is beneficial, for example, in power grids with a high proportion of volatile power sources (renewable energies) for electricity production during periods of darkness.

[0044] Combining chemical and thermal energy storage expands the portfolio of applicable thermal energy storage systems, which can be an advantage for customers (an efficient and cost-optimized solution). For example, thermal energy storage systems with temperature levels below the required steam turbine inlet temperature can also be used. In this case, the temperature difference is compensated by admixing CSG steam.

[0045] In a storage power plant without steam extraction, the water-steam cycle can be designed as a closed system. Apart from compensating for system-related water losses (e.g. . No external water supply is necessary due to leaks. This makes the storage power system suitable for regions with water shortages.

[0046] The mode of operation, ie .The distribution of energy flows and temperature levels between the thermal storage and the chemical storage, as well as the location of the CSG steam feed-in, can vary depending on the application and operating mode of the storage power plant. This allows the levelized cost of electricity to be kept low and the degree of self-sufficiency to be increased. If a temperature difference of the working fluid occurs between the outlet of the thermal storage and the target parameters at the inlet to the steam turbine, this is compensated by adding CSG steam.

[0047] One or more intermediate steam extraction points can be provided on the steam turbine. These intermediate steam extraction points allow steam to be extracted along the expansion section with defined steam parameters. Additionally or alternatively, water and / or steam can be extracted from the thermal storage system. The extracted working fluid can be used, for example, as process steam or for district heating. If intermediate steam extraction and / or extraction from the thermal storage system occurs, the extracted mass flow must be returned to the water-steam cycle.

Claims

1. Storage power plant, comprising at least one water-steam cycle (1), wherein the water-steam cycle (1) comprises at least one steam turbine (2) with a generator (3) in operative connection with the steam turbine (2), and also two energy stores (4, 5), wherein the energy stores (4, 5) are arranged and formed in such a way that they can deliver energy to the working medium flowing in the water-steam cycle (1) to generate steam with defined steam parameters, wherein the steam that can be generated in the steam turbine (2) can be expanded, and wherein a rotational energy produced during the expansion of the steam can be used to drive the generator (3), wherein a first energy store (4) is formed as a thermal energy store and a second energy store (5) is formed as a chemical energy store, and wherein the chemical energy store (5) can be charged by means of electrical energy, and wherein the chemical energy store (5) comprises an electrolyser (6) for breaking down water from the water-steam cycle into hydrogen and oxygen, and comprises at least one first store (7) in each case for storing the hydrogen and at least one second store (8) in each case for storing the oxygen, characterized in that the chemical energy store (5) also comprises a steam generator (CSG) (9) for internal combustion of the hydrogen with the oxygen and the steam generator (9) has a connection (10) via which working medium for steam conditioning can be supplied to the steam (CSG steam) that can be generated in the steam generator, wherein the water-steam cycle (1) is formed as a closed cycle.

2. Storage power plant according to Claim 1, characterized in that the thermal store (4) has a connection (11) for supplying fluid-bound heat.

3. Storage power plant according to Claim 1 or 2, characterized in that the connection (10) at the steam generator is in operative connection with a condenser (12), which is downstream of the steam turbine (2), and / or the thermal energy store (4).

4. Method for charging the energy stores (4, 5) of a storage power plant according to one of the preceding claims, characterized by the following method steps: - heating the thermal energy store (4) by means of electrical current and / or fluid-bound heat and / or - breaking down water into hydrogen and oxygen by applying electrical current to the electrolyser (6) and storing the hydrogen in the first store (7) and the oxygen in the second store (8).

5. Method for discharging the energy stores (4, 5) of a storage power plant according to one of Claims 1 to 3, characterized by the following method steps: - transferring thermal energy from the thermal energy store (4) to the working medium flowing in the water-steam cycle (1) in order to bring about an increase in temperature and / or a phase change (evaporation) of the working medium, and / or - supplying hydrogen and oxygen from the respective store (7, 8) to the steam generator (9) and combusting the hydrogen with the oxygen in the steam generator (9), - subsequent and / or simultaneous conditioning of the (CSG) steam generated in the steam generator (9) by adding working medium which is removed from the water-steam cycle (1), - expanding the steam flowing in the water-steam cycle (1) in the steam turbine (2), - generating electrical current by means of the generator (3).

6. Method for discharging the energy stores (4, 5) of a storage power plant according to Claim 5, characterized in that at least part of the working medium flowing in the water-steam cycle (1) is removed upstream in the direction of flow, within or at the outlet of the steam turbine (2) and the working medium removed is made available as process steam and / or hot water, for example for the district heating supply.

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