FR2982876A1 - SYSTEM FOR CONVERTING SOLAR ENERGY IN ELECTRIC AND CHEMICAL ENERGY AND METHOD FOR OPERATING SUCH A SYSTEM - Google Patents

Abstract

An energy conversion system (100) comprising: - a power conversion plant (110), including a solar power conversion plant; and an electrolysis device (120) for steam including a water-steaming element (9) and an electrolyser (10) for the steam, the electrolysis device using energy converted by the power plant (110).

Description

The present invention relates to an energy conversion system comprising a power conversion plant. The invention also relates to a method of operating such an energy conversion system. The invention also relates to a system for storing and restoring energy to be coupled energetically to a power conversion plant. Thermodynamic solar power plants convert solar energy into electrical energy injected into an electricity grid, such as the commercial electricity grid. Tower type thermodynamic solar power plants are of different types depending on the heat transfer fluid they use and the type of thermodynamic cycle used to produce electricity via a turbine. One of the drawbacks of thermodynamic solar power plants and more particularly tower plants is that, because they use direct solar energy (direct radiation), the passage of a cloud strongly impacts their operation, which is why they are installed in regions with strong sunshine, typically deserts. However, it can happen that a cloud passes, or that it needs to run a few hours after sunset to meet the needs of the electricity network or even all night in some cases. In addition, the development of thermodynamic solar power plants is caused by the search for an increase in the electrical conversion efficiency and therefore, mainly, that of the temperature of the fluid entering the turbine of the turbo generator group. Finally, their connection to networks increases the search for regulation of the production and thus the search for possibility of storage of energy variable in time.

The main techniques currently used to overcome the intermittency of solar energy in this type of solar power plant are: - the use of heat storage in sensitive or latent form. Storage in latent form can be carried out using different types of materials (molten salts, oils, solids, metals, ....); - the use of a supplementary energy of fossil origin (in particular the gas in solar-gas hybrid power plants); - The storage of electrical energy in batteries, with restitution by electric heating upstream of the turbine. These solutions have limits which can be prohibitive according to the case of load and exploitation of the solar power station, but also according to the electrical conversion performance aimed at the turbo generator group. The use of a supplementary energy of fossil origin does not make it possible to have a completely decarbonated electrical production and especially requires a supply of natural gas (for example) which can be difficult in isolated site. On the other hand, it makes it possible to operate with high input temperature turbines and thus a high conversion efficiency. The storage in electric batteries presents various problems: storage limit (volume and cost of batteries), generic problem of power-energy coupling of this type of storage which forces to under or over-size the installation (flexibility limited to the load and discharge), battery life (especially if charges and discharges are incomplete) and environmental issues related to their management. It also has the disadvantage of storing energy in secondary form, that is to say electrical. The use of heat storage poses general problems specific to this storage mode and specific problems related to the storage material used.

The general problems with these storage modes are: - The energy storage limit. As for batteries, this type of storage is bulky and has a limit related to the size of the tank; in case of surplus thermal energy, it does not allow additional storage; - The low flexibility at the frequency and the level of storage charges and discharges, in particular for storage on sensible heat (the storage temperature is a function of its "filling" level); - The difficulty (cost) of arranging the tanks remote from the turbine. The transmission of heat over long distances is energy consuming or expensive, especially at high temperatures; - The temperature limit of restitution. Current materials do not allow storage temperatures above 750 ° C, which implies that the temperature of the fluid entering the turbine is less than 750 ° C (rather 700 ° C) during the restitution phases, which affects strongly the conversion efficiency of the turbo generator group; - The impossibility of adapting the quality of the storage (return temperature) to the amount of energy to be stored, that is to say the lack of flexibility in the load and discharge of thermal storage. A thermal reservoir can only be used at the restitution temperature if it is "full of energy" and can only be used when it is "full" (case of storage on sensible heat). Partial samples or partial fillings affect the quality (temperature) of the restitution of the energy; - the decrease in storage efficiency with time and storage temperature.

Other specific problems relate to safety, to the environment, for example in the case of use of oils or molten salts. It therefore seems interesting on high-temperature thermodynamic solar power plants: 1- to overcome the thermal storage return temperature limit which strongly penalizes the efficiency of electrical conversion; 2- to eliminate any use of supplementary energy of fossil origin; 3- to dissociate power and energy in the storage, 4- to increase the possibilities of storage of energy, 5- to increase the flexibility or to adapt the load of the storage to the availability and a fortiori to the destocking request . 6- to store the energy at a distance (out of the solar zone). 7- to possibly be able to use the energy stored in another application, in particular in an application external to the plant site. US Pat. No. 4,095,118 discloses a system for converting solar energy into electrical energy. Part of this energy is used to produce hydrogen by electrolysis. This hydrogen is then used during periods of low sunlight. The system uses a very special type of solar power plant that uses a fluid that can be ionized. It describes a storage of electrical energy by traditional electrolysis of liquid water. Document EP 1 982 954 A1 discloses a solar tower plant coupled with a system for producing hydrogen by thermochemical cycle and a thermal energy storage by molten salts. The object of the invention is to provide an energy conversion system making it possible to overcome the problems mentioned above and to improve the systems known from the prior art. In particular, the invention provides a system for returning a thermal input at the desired time to maintain the operation of the plant at its rated speed. The desired moment may be, for example, the passage of a cloud of a duration of a few minutes which abruptly drops the direct radiation of the sun and therefore the thermal energy that can be converted. This device is used for high temperature turbines either in addition to a "conventional" thermal energy storage or alone. This maintenance of the nominal operation during the passage of a cloud or during a period of low radiations makes it possible to avoid a sharp reduction in the efficiency of the turbine, or even its sudden stop (risk of damage due to thermal cycles) and guarantees a stable electricity production profile during the passage of the cloud. According to the invention, an energy conversion system comprises: an energy conversion plant, in particular a solar energy conversion plant; and a steam electrolysis device including a water-vapor-water transformation element and a steam-water electrolyzer, the electrolysis device using energy converted by the power plant; .

The system may include a dihydrogen storage element and / or a oxygen storage element. The system may include a combustion chamber for the combustion of dihydrogen. The system may include a thermal energy storage device. The electrolyser can be arranged to operate in an allothermal mode. The plant may be of the type operating with heated air, in particular air heated at high temperature, in particular of the tower type operating with air heated at high temperature. According to the invention, the method of operation of an energy conversion system defined above comprises the following steps: use of the energy converted by the plant to dissociate water into dihydrogen and oxygen; storage of dihydrogen and / or dioxygen, - combustion of dihydrogen, optionally in oxygen, to produce electrical energy. The stage of utilization of the energy converted by the plant may include: - the use of heat supplied by the plant to convert water into water vapor, and - the use of heat and electricity provided by the plant to dissociate water vapor. The step of using heat provided by the plant to convert water into water vapor may include the use of heat from a fluid exiting a turbine of the plant. The step of using heat provided by the plant to dissociate the water vapor can comprise the use of the heat of at least a fraction of a fluid after heating in the plant, in particular at a receiver solar power plant. The step of using the energy converted by the plant may include using energy to operate the electrolysis device in an allothermal mode.

According to the invention, the energy storage and return system intended to be coupled energetically to an energy conversion plant, in particular to a solar energy conversion plant, comprises: an energy storage device thermal; A steam electrolysis device including a water-vapor-water converting element and a steam-water electrolyzer; a hydrogen storage device; and 5 - a hydrogen combustion chamber; the storage device and the electrolysis device being intended to use energy converted by the power plant. The appended drawing represents, by way of example, an embodiment of an energy conversion system according to the invention. Figure 1 is a diagram of an embodiment of an energy conversion system according to the invention. An embodiment of a power conversion system 100 is described below with reference to FIG. 1. The system converts solar energy into electrical energy that is injected into an electrical network 13 (not shown in FIG. not part of the system). The system also converts solar energy into chemical energy that can be stored and subsequently converted into electrical energy. Thus, it is possible to convert chemical energy into electrical energy when solar energy is no longer available or when the power of solar radiation is not sufficient to allow the system to convert energy with desired yield. The system 100 mainly comprises a solar power conversion unit 110 for electrical energy and an electrolysis device 120 for steam.

The central unit 110 for converting solar energy into electrical energy mainly comprises the following members: a solar ray receiver 3 for heating a fluid (such as air) at high temperature, for example at about 900 to 1000 ° C .; this receiver is for example installed at the top of a tower 20. a set of heliostats 1 to deflect sunlight to direct them to the receiver 3; a turbine group 6 - compressor 2; the compressor for compressing the fluid before heating at the receiver, the turbine for converting the energy of the heated fluid and under pressure into mechanical energy by expansion of the fluid in the turbine. The compressor and the turbine are linked mechanically for example by means of a shaft 7; a generator 8 mechanically coupled to the turbine 6 and for converting the mechanical energy of the turbine not used by the compressor into electrical energy.

The plant can be of any type. Preferably, the plant is of the tower type operating with a gas cycle using air under pressure at about 1000 ° C in addition to a thermal storage at lower temperature. Solar thermodynamic tower plants operating with air heated at high temperature have many advantages: high efficiency due to the high temperatures used, fluid used (air) free and abundant, no use of oil, no salts melted, no cooling required of the fluid at the turbine outlet. Receivers allow the air to be efficiently heated to that temperature. Storage of a substantial amount of thermal energy at a temperature of 1000 ° C or more is difficult to achieve or even impossible in the current state of the art. On the other hand, a substantial amount of thermal energy can be stored at a temperature of about 750 ° C.

The electrolysis device includes an element 9 for converting water into water vapor and an electrolyzer 10 for steam. In order to dissociate (in 2982 876 9 dihydrogen and dioxygen by electrolysis) the water vapor, the electrolysis device uses solar energy converted by the plant into an energy of another type, in particular electrical energy. and thermal energy. The electrolyser is for example of the high temperature type. The electrolyser 5 operates in allothermal mode, that is to say using to dissociate the water molecules (steam) of electrical energy and thermal energy. The high temperature steam electrolyser (EVHT) is used to electrolyze water vapor at high temperatures (800-1000 ° C). The advantage of such an electrolyzer is that it makes it possible to use a large part of the energy necessary for the dissociation of water in the form of primary energy (thermal energy) and thus to limit the secondary energy withdrawal. (electrical energy) necessary. On the other hand, an excellent electrochemical conversion efficiency is obtained. Thus, the high temperature steam electrolyser (EVHT) lends itself well to coupling with the 15 solar power plants operating at high temperature and high efficiency of electrical conversion and the increase in its operating temperature increases all the energy efficiency of conversion of solar energy into chemical energy. The electrolyser is supplied with electricity by a fraction of the electrical energy generated by the alternator, which is itself powered by the turbine operating by means of the fluid heated by solar energy. The fraction of electrical energy used to supply the electrolyser is between 0 and 100% depending on the size of the system and the needs of the electrical network at any time. The fraction taken off may be greater if the need for injection into the electricity grid is limited. The electrical energy produced that is not consumed by the electrolyser is transferred to the electrical network. The fluid cooled (150 to 500 ° C) at the turbine outlet is conveyed to the element 9 for converting water into water vapor, such as a heat exchanger. A set of piping, valves, expansion valves, safety elements, etc. is used for this routing but not shown. The transformation element 9 makes it possible to heat and vaporise the water necessary for the high temperature electrolyser. The cold air is then released into the atmosphere. The steam from the transformation element 9 is then conveyed to the electrolyser. A set of piping, valves, expansion valves, safety elements, etc. is used for this routing but not shown. A fraction of the hot fluid leaving the solar receiver (800 to 1200 ° C) is also conveyed to the electrolyzer so as to maintain the temperature of the electrolyzer at about 900-1000 ° C. A set of piping, valves, expansion valves, safety elements, etc. is used for this routing but not shown. The dihydrogen on the one hand and the dioxygen on the other hand, generated by dissociation of the water inside the electrolyser are stored in a storage device. The networks for conducting and storing hydrogen and oxygen are preferably kept independent in order to avoid recombination in water. The storage device consists of one or more tanks of structure and volume suitable for storing dihydrogen and / or dioxygen. These reservoirs make it possible to store the gases under a relative pressure of approximately 10 to 700 bar. The storage of the hydrogen can alternatively or complementarily be carried out in other forms. Hydrogen can be stored at low temperature in liquid form. In this case, a hydrogen liquefaction system is set up between the exit of the dihydrogen from the electrolyzer and the inlet of the dihydrogen storage element. Such a liquefaction system includes boosters, heat exchangers, a cold utility and a set of components necessary for the liquefaction of hydrogen (valves, safety elements, etc.). Alternatively or additionally, the hydrogen can be stored at low relative pressure (10 to 60 bar) in the form of metal hydrides where it is adsorbed during storage phases and desorbed during use phases. Alternatively or additionally, hydrogen can be stored in the form of liquid hydrocarbons (methanol, formic acid, etc.) for longer storage periods (more compact storage). Storage in the form of liquid hydrocarbons involves the use of additional chemical transformation steps.

With regard to the electrolyser, at a vapor temperature of 1000 ° C., the necessary electrical energy is 2.2 kWh per Nm 3 of dihydrogen produced. The thermal energy or additional heat necessary for the dissociation of the water vapor is 0.9kWh per Nm3 of hydrogen produced. To this must be added the heat necessary for the vaporization (steam generation) of the water. It is equal to 0.5 kWh per Nm3 of hydrogen produced. In absolute terms, therefore, 39% of the dissociation energy can be supplied in the form of primary energy (heat energy obtained by heating by means of solar radiation). The amount of energy provided to vaporize the water can be provided by the fluid leaving the turbine. Indeed, this heat would simply be rejected otherwise. The amount of energy to maintain the electrolyser temperature at 900-1000 ° C. (corresponding to the allo-thermal energy) is 0.5 kWh per Nm3 of hydrogen produced.

Most of the time, a fraction of the heat and a fraction of the electricity produced by the plant are derived to maintain the temperature of the electrolyser in allothermal operation and to supply the electricity necessary for the electrolysis operation. . The electricity and the heat necessary for the operation of the electrolyser is a respective fraction of the corresponding energies taken downstream and upstream of the turbine. This fraction of energy dedicated to the production of hydrogen can vary according to the need for hydrogen necessary to overcome the intermittency of solar radiation and the need for electricity to supply the grid.

When thermal energy is needed to heat the output fluid of the receiver (in the absence of thermal storage or in case of empty storage) or at the output of the thermal storage device (if the thermal storage is operational) to compensate a drop in solar radiation, dihydrogen and dioxygen are transported to the combustion chamber, where they recombine very exothermically. This combustion chamber 282 can be either integrated with the turbine (internal combustion) or be positioned upstream of the turbine (external combustion). In the first case, the combustion (2H2 + 02 -> 2H20) is carried out in the fluid (air) taking advantage of the additional flow rate, the energy efficiency of destocking is then maximum. In the second case (illustrated in FIG. 1), an intermediate heat exchanger makes it possible to transfer the heat of combustion to the fluid without introducing water vapor. The thermal energy generated by the combustion of the hydrogen makes it possible to maintain the temperature of the fluid at the nominal operating temperature of the turbine. The combustion of hydrogen makes it possible to compensate for the decrease in available solar energy during a time t which depends on (1) the quantity of dihydrogen stored and (2) the fluid temperature before the combustion chamber (presence or no operational thermal storage). This duration t is determined at the time of sizing the system. The system 100 further comprises a chemical energy storage device 11, 12 (dihydrogen and dioxygen obtained by electrolysis) and a combustion chamber of the dihydrogen, optionally with the oxygen to heat the fluid if necessary. The storage device preferably comprises a dihydrogen storage element 11 and / or a dioxygen storage element 12. The combustion chamber can be in the turbine, the combustion being carried out in the turbine. The storage may or may not be distant from the solar tower, the transport of gas over long distances does not pose any energy problem. Dihydrogen and oxygen can be stored under pressure (typically from 10 to 50 bar relative). Advantageously, the system 100 also comprises a device 4 for storing thermal energy at a temperature of between 300 and 750 ° C. Thermal storage is carried out by sensible or latent heat. It can be sized to maintain the fluid temperature at 750 ° C for a defined time that may be greater than that imposed by the amount of available hydrogen. The sizing of the thermal storage is done according to the electricity production needs and the space available at the installation site of the system. In the case of the presence of a thermal storage device, the conversion system comprises a system 130 for storing and restoring energy energy-coupled to the energy conversion unit 110, this storage and retrieval system. of energy comprising: - the device 4 for storing thermal energy; the steam electrolysis device 120 including the element 9 for transforming the water into water vapor and the electrolyser 10 for the steam; the device 11 for storing hydrogen; and - the combustion chamber 5 of hydrogen. The storage device and the electrolysis device use energy (heat, electricity) converted by the central unit 110. Preferably, they use only this energy. Using the known conversion efficiencies of the various elements of the system, it is calculated that if the electric production is wholly drifted to the electrolyser for a time t1, the dihydrogen produced makes it possible to operate the plant autonomously for a period of time. t2 = 0.6 x t1. The use of a thermal storage at 750 ° C of sufficient size makes it possible to increase this restitution time. The dihydrogen makes it possible to complete the supply of energy for a definite duration representative of the duration of passage of a cloud; the heating of the fluid goes from 750 to 1000 ° C allowing normal operation of the turbine without any transient on the turbine and therefore without any variation in performance or decrease in the service life of the latter. As previously seen, hydrogen storage can be of any type and any volume. It is dimensioned to meet the need considered at the time of sizing the installation, depending on the duration and frequency of periods of low sun 5 during which the installation must operate. The sizing of the thermal storage and the electrolyser are carried out so as to compensate for a certain type of sunshine reduction. For example, the system can be sized to overcome 10-minute cloud passes (see the numerical example below) but also for longer periods of time. To overcome the longer intermittences, it is necessary to take a larger fraction of the thermal and electrical energy produced and thus limit the injection of electricity on the network. The example below gives dimensioning values of the device 15 providing only energy storage with the objective of mitigating the passage of a 10-minute cloud each day for a solar installation operating 8 hours per day. Considering 100% allothermal operation, a numerical example is set out below: Assumptions - Gas Turbine Power: 2MWe - Alternator Impeller Efficiency: 50% 25 - Power Solar receiver thermal: 4 MWt -% of Power derived to the electrolyser on a running time of 8 hours at nominal power: 2.5% (or sampling for 12 minutes of nominal power) Calculated values: 30 - Electrical energy consumed by the electrolyser: 0.4 MWh (= 0.025x2x8) - Thermal energy consumed by the electrolyser and the steam generator: 0.27MWh (at 1000 ° C about 40% of the dissociation energy of water can be brought in by the heat , as described above) - mass of dihydrogen produced to be stored: 16.3 kg. See above: 2.2 kWh electric plus 1.39 kWh thermal gives 1 Nm3 of dihydrogen is 0.09 kg so 400 kWh electric plus 270 kWh thermal gives 182 Nm3 of hydrogen) - Mass of oxygen to store: 130 kg (0.5 mole of oxygen generated by the electrolyser for 1 mole of hydrogen) - Storage efficiency: 60% (yield = stored energy / energy required to produce the hydrogen) Either: Stored energy: m (H2) x PCS = 16.3 x 39.41 = 642 kWh Energy required for production: Thermal energy + Electrical energy / turbine efficiency = 270 + 800 = 1070 Either efficiency = 60%) - Cloud transit time without additional thermal storage: 9 minutes (16.3 kg H2 gives 642 kWh or 4MWt during 9 minutes) - Compensated cloud transit time if only half of the energy is supplied by the hydrogen: about 18 minutes This example shows that by taking only 2.5% of the electrical energy produced by the turbine and a minimum of action of thermal energy at the solar receiver output, we can overcome the passage of an eighteen-minute cloud by combining the energy supply of hydrogen and that of a conventional thermal storage while maintaining a functioning and a optimal turbine efficiency. A cloud run lasting 18 minutes each day is an assumption that can be representative of the locations where these conversion systems are likely to be installed. One can imagine k days without decrease of solar radiation, the cumulative duration of compensation by the thermal energy is worth then k x 18 minutes. An embodiment of a method of operating an energy conversion system is described below. In a first mode of operation of the system, energy converted by the plant is used to dissociate water into dihydrogen and oxygen and the dihydrogen and oxygen is stored. Preferably, only the energy supplied by the plant is used, in particular the energy converted by the plant. The use of the energy converted by the plant includes for example the following actions: - The heat supplied by the plant is used to transform water into water vapor at the level of the transformation element 9. water vapor. To do this, one can for example use the thermal energy of the fluid leaving the turbine of the plant. Heat and electricity supplied by the plant are used to dissociate the steam at the level of the electrolyser 10 for converting water into water vapor. To do this, one can for example use at least a fraction of a fluid after heating thereof in the plant, especially at the solar receiver 3 of the plant. Preferably, the electrolysis device, in particular the electrolyser, is operated in an allothermal mode.

Complementarily, in this first mode of operation, it is possible to store thermal energy at the level of the thermal energy storage device. In this case, a fraction of the fluid is used after compression in the compressor 2 and heating, for example at the receiver 3, to heat the thermal energy storage device.

This first mode of operation is implemented when the network does not require all the electrical power supplied by the conversion system. This first mode of operation is in particular implemented when the primary source of energy is abundant, especially in the case of a solar power plant when it is completely exposed to solar radiation. Several types of storage can take place. They can allow a daily or seasonal energy storage. In a second operating mode of the system, chemical energy is used which has previously been stored to heat the fluid upstream of the turbine or in the turbine 6. To do this, it is realized in the combustion chamber 5, a combustion of the previously stored hydrogen. Preferably, oxygen is used as oxidant. The stored chemical energy is therefore used to produce electrical energy. This heating is carried out in addition to the heating of the fluid produced elsewhere in the central unit, for example at the level of the receiver 3. Additionally, in this second mode of operation, thermal energy stored at the level of the storage device can be used. thermal energy to heat the fluid. In this case, the fluid or a fraction thereof recovers heat up to a temperature of for example 750 ° C at the thermal energy storage device after compression in the compressor 2 and heating for example until at about 300 ° C, for example at the receiver 3.

This second mode of operation is implemented when the network requires more than can provide the plant taking into account only the primary energy source, such as solar radiation in the case of the solar power station. This second mode of operation is in particular implemented during a passage of a cloud or during a period of low radiation, so as to continue to heat the fluid to be expanded in the turbine. The product of the combustion of dihydrogen in oxygen is only water which is recovered by simple condensation either at the turbine outlet or at the outlet of the combustion chamber. Thus, in this second mode of operation, the stored chemical energy (and optionally the stored thermal energy) is used to increase the temperature of the fluid before expansion in the turbine or during expansion in the turbine. The increase in temperature by chemical energy makes it possible, for example, to heat the fluid from 750 ° C. to 1000 ° C. Thus, the turbine can continue to operate under nominal conditions without significant decrease in efficiency, nor premature deterioration due to degraded mode operation. The main advantages of this invention are those of: - to overcome the temperature limitation of thermal storage restitution and to be able to operate with a turbine inlet temperature well above 800 ° C and this without adding fuel of fossil origin ; - store and destock at partial load without affecting the storage or turbining efficiency; - store large amounts of energy and this possibly at a great distance from the plant; - limit the amount of secondary energy removed in the energy storage phase by consuming part of the solar primary energy; - allow long-term safe storage without loss of storage efficiency; - allow destocking if necessary to other sites or other uses (truck, pipeline ...).

The following variants of the conversion system can be envisaged: The temperature of the thermal storage can be any, it is just below the operating temperature of the turbine. Once the hydrogen stock is emptied, the turbine can operate in degraded mode at 750 ° C only with the energy from the thermal storage device. The thermal storage can be of different types: # Sensitive heat (molten salts, oil, solid, metal ...), # Latent heat (Materials with phase change). The fraction of electrical energy used for hydrogen production may vary depending on hydrogen and electricity requirements. Any form of chemical storage can be considered. Any type of solar power plant can be considered. The system can implement a combined cycle of turbining fluid and steam.

The principle of combining thermal storage and chemical storage generated in-situ from surplus energy can be extended to biomass thermal boilers and incinerators which are also intended to supply a network whose need is fluctuating and / or whose the primary energy supply fluctuates. The invention makes it possible to ensure continuous operation at the nominal efficiency of the turbine producing electricity in a so-called "tower" thermodynamic solar power plant, particularly when a cloud passes in front of the sun in order to avoid a sharp decrease in power generation and turbine efficiency, or even complete shutdown of electricity production until it has passed. This continuous operation is carried out by a device performing during periods of decline in illumination (clouds, ..) storage of a portion of the thermal energy received and a portion of the electrical energy manufactured by a vector Hydrogen type chemical or hydrogen compound synthesized via a steam electrolyser operating in allo-thermal regime and hybridized by the thermal and electrical way to the solar power station. Thus, in the conversion system, the electrolysis device is hybridized or coupled to the thermodynamic solar power station which supplies it with thermal energy and electrical energy. Similarly, in the conversion system, a thermal energy storage device can be hybridized or coupled to the thermodynamic solar power station to allow storage at a temperature below the operating temperature of the thermodynamic cycle and can constitute a passive reserve security or extra. The sizing of the various components of the system is optimized so that its operation covers a range of ratios "time of passage of clouds on sunshine time" compatible with the nominal operation of the solar power plant by integrating the specificities of the weather where is installed the system. Stored chemical energy is used during periods of lower sunlight (including the passage of a cloud) to supplement or replace the use of stored thermal energy which is a source whose temperature is limited and less than the nominal operating temperature of the turbine.

The notation "Nm3" means one cubic meter under normal conditions of temperature and pressure.

Claims (12)

REVENDICATIONS1. An energy conversion system (100) comprising: a power conversion plant (110), including a solar power conversion plant; and an electrolysis device (120) for steam including a water-vaporizing element (9) and an electrolyzer (10) for the water vapor, the electrolysis device using energy converted by the central (110). 2. System according to the preceding claim, characterized in that it comprises a member (11) for storing dihydrogen and / or a member (12) for storing oxygen. 3. System according to one of the preceding claims, characterized in that it comprises a combustion chamber (5) for the combustion of hydrogen. 4. System according to one of the preceding claims, characterized in that it comprises a device (4) for storing thermal energy. 5. System according to one of the preceding claims, characterized in that the electrolyser (10) is arranged to operate in an allothermal mode. 6. System according to one of the preceding claims, characterized in that the central unit (110) is of the type operating with heated air, in particular air heated at high temperature, in particular of the tower type operating with the air heated at high temperature. 7. A method of operation of a system (100) for converting energy according to one of the preceding claims, comprising the following steps: - use of the energy converted by the plant to dissociate water into dihydrogen and into oxygen, - storage of dihydrogen and / or dioxygen, - combustion of dihydrogen, possibly in oxygen, to produce electrical energy. Process according to the preceding claim, characterized in that the step of using the energy converted by the plant comprises: the use of heat supplied by the plant to transform water into water vapor, and the use of heat and electricity provided by the plant to dissociate the water vapor. Process according to claim 8, characterized in that the step of using heat supplied by the plant to transform water into water vapor comprises the use of the heat of a fluid leaving a turbine of water. the power plant. A method according to claim 8 or 9, characterized in that the step of utilizing heat supplied by the plant to dissociate the steam comprises using heat of at least a fraction of a fluid after heating in the plant, especially at a solar receiver (3) of the plant. Method according to one of claims 7 to 10, characterized in that the step of using the energy converted by the plant comprises the use of energy to operate the electrolysis device in an allothermal mode. 10 8. 15 9. 20 10. 25 11. 30 12. A system (130) for storing and restoring energy to be coupled energetically to an energy conversion plant (110), in particular to a solar energy conversion plant, comprising: - a device (4) thermal energy storage; - an electrolysis device (120) of water vapor including a member (9) for converting water into water vapor and an electrolyzer (10) of water vapor; a device (11) for storing hydrogen; and - a chamber (5) for burning dihydrogen; the storage device and the electrolysis device being intended to use energy converted by the central unit (110).