Patent Description:
Power plants for generating electric power can be various and are typically connected to an electric grid, local or national, to which the plant provides electric energy.

The total amount of power provided by power plants to the electric grid have to ensure a balance between the electricity supply and the electricity demand in order to guarantee for example the stability of the grid and the continuity of grid operability. For instance, the activity of managing and balancing the flows of electric power through the national grid is known as energy dispatching and is typically managed by grid operators; in Italy the central grid operator is Terna.

Power plants that can adjust their power output according to the demand for electricity are called "dispatchable power plants". Depending on their start-up time and flexibility, dispatchable power plants make long and/or short term offers to grid operators to provide electricity over various time periods. For example, gas turbine or gas engine power plants have short start-up time so they can operate many hours a day or may operate only a few hours per year, being started up and stopped many times due to short starting transients.

On the contrary, power plants that do not have short starting transients are usually designed for continuous operation. An example of plants that may take several days to start up and shut down are nuclear plants or combined cycle plants (=CC); a combined cycle plant includes a gas turbine to produce electricity, a steam turbine to produce electricity, and a steam-producing heat exchanger which uses hot exhaust gas from the gas turbine to generate steam for the steam turbine; the gas turbine is fed by a gas fuel, often natural gas. For example, the gas turbine may produce <NUM>% of CC power output and the steam turbine may produce <NUM>% of CC power output.

In conventional combined cycle plants the electric power output of steam turbine can be lightly reduced, for example reaching a <NUM>% steam turbine power decrease by partialization of the steam turbine, or by regulating the steam produced by the steam-producing heat exchanger and fed to the steam turbine. Partialization of the steam turbine is carried out by closing one or more parts of the turbine inlet annulus, so that the steam passes only through one or more circular sectors; however partialization introduces additional dissipation, due to ventilation losses of blades which drags the steam, and asymmetry of the thrusts on the turbine wheel. The steam regulation is typically carried out by using "sliding pressure" control, i.e. reducing evaporation pressure in the heat exchanger, also called "heat recovery steam generator" (=HRSG); however, sliding pressure control fails in case of sudden change in energy demand, due to the long transient.

In case more significant reductions of the electric power output from the CC plants are desired, for example a <NUM>% reduction of combined cycle power output, the steam turbine is stopped (bypassed), wasting the hot exhaust heat from the gas turbine and resulting in a reduction of combined cycle efficiency. During stopping, the steam turbine is decoupled from HRSG for example by means of a steam bypass system, dumping the steam to the condenser, or by means of a HRSG bypass stack, discharging hot exhaust gas in atmosphere. These off-design conditions may occur during unbalance between energy production and energy demand of power grid, in particular when production exceeds demand, which typically occurs at night because manufacturing operations, in general, stop.

It is known, for example from <CIT>, to use energy, including excess energy from power plants, by producing hydrogen through electrolyzes and storing the hydrogen in large tanks for future use, for example vehicular fueling (including but not limited to: cars, trucks, trains, ships, aircrafts, etc.) - hydrogen vehicles are becoming very popular. However, storing large quantities of hydrogen for a long time causes safety problems for the possibilities of both explosions and/or leakages into the atmosphere. Therefore, in order to overcome these problems.

It would be desirable to increase the flexibility of a combined cycle power plant in terms of electric power provided to an electric grid. In particular, the increased flexibility should be obtained in a relatively easy and cheap way without adding safety problems to the power plant. More in particular, the desired solution should be relatively easily applicable also to already-installed and operating power plants.

According to an aspect, the subject-matter disclosed herein relates to a power plant for generating electric power to be provided to an electric grid; the power plant includes a gas turbine, a steam turbine and at least one electrolyzer that is designed to use electric power in order to generate hydrogen starting from water; the electrolyzer is arranged to be selectively coupled to the electric grid; the hydrogen is temporarily stored inside the power plant in a tank - as it will be apparent from the detailed description the capacity of the tank may be very small, theoretically null. When power plant energy production exceeds grid energy demand, the electrolyzer is connected to the electric grid so to usefully consume the electric power not desired by the grid operator and generate hydrogen that is used by the gas turbine engine as secondary fuel together with a primary fuel. As excess energy is consumed locally to the plant for a useful purpose, the gas turbine and/or the steam turbine may be maintained permanently at the same or approximately the same operating conditions, preferably exactly or approximately at optimal operating conditions.

Advantageously, coupling/decoupling of the electrolyzer to/from the electric grid is performed under the control of a control unit that may store and use predetermined rules and/or receive and use requests.

A more complete appreciation of the disclosed embodiments and of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:.

The subject matter herein disclosed relates to a power plant for generating electric power to be provided to an electric grid that is able to reduce the amount of electric power provided by the plant to the grid without reducing the overall cycle efficiency.

During periods of low energy demand, for example overnight, a grid operator may ask to a plant operator to reduce significantly the electric power received from its plant, for example by <NUM>-<NUM>%. Typically according to the prior-art, in order to reduce electric power output, the plant operator changes the operating conditions of the turbines of the plant but, in so doing, a relevant reduction of overall cycle efficiency arise.

In order to achieve reduction of the electric power provided by a plant to the grid and to avoid reduction of the efficiency of the plant, according the subject-matter disclosed herein the turbines are preferably maintained at their rated capacity, i.e. maximum electric power production (by both the gas turbine and the steam turbine), and one or more electric loads are connected to the grid so to locally consume the electric power not desired by the grid operator at a certain time. The electric loads have a useful purpose, namely generating hydrogen that is as a fuel, in particular a secondary fuel (the turbine of the power plant may burn both a primary fuel, e.g. natural gas, and a secondary fuel, i.e. hydrogen); a machine for generating hydrogen starting from water and electricity is known as "electrolyzer" or "electrolytic cell".

Reference now will be made in detail to embodiments of the disclosure illustrated in the drawings.

The embodiments are provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure.

With non-limiting reference to <FIG>, a power plant <NUM>, in particular a combined cycle power plant, is arranged to generate electric power to be provided to an electric grid <NUM>, the electric grid <NUM> being for example a national grid or a local grid (for example a microgrid or a nanogrid).

The power plant <NUM> includes a gas turbine <NUM>, in particular a compressor compressing inlet air A, a combustor receiving a gas fuel F, also referred in the following as "primary fuel" and being typically natural gas, and a gas hydrogen H, also referred in the following as "secondary fuel", burning the fuel or fuels with an oxidant A, being typically air-fuel, and an expander expanding burned gas, the compressor and the expander having a first rotary shaft. The oxidant A is sucked by the compressor through a suction inlet of the compressor and the expanded burned gas are discharged through an exhaust outlet of the expander. In general, the combustor may be premixed-type or diffusion type. The gas turbine is configured for selective burning, in particular so that, at some times its combustor burns only the primary fuel while at other times it burns both the primary fuel and the secondary fuel, i.e. hydrogen; only during very limited times (if any), it may burn only the secondary fuel, i.e. hydrogen.

A first electric power generator <NUM> (that is included in the power plant <NUM>) is coupled to a first rotary shaft of the gas turbine <NUM> and generates a first electric power output. As shown in <FIG>, the electric power output of the first electric power generator <NUM> is arranged to be coupled to the electric grid <NUM>, supplying electric power to the electric grid <NUM>.

According to this embodiment, an exhaust outlet of the gas turbine <NUM>, in particular of its expander, discharges a hot exhaust gas flow still having heat capacity that can be exploited by a heat exchanger <NUM> that is included in the power plant <NUM>.

The heat exchanger <NUM> is advantageously a heat recovery steam generator (HRSG) which is coupled to the exhaust outlet of the gas turbine <NUM> and it uses part of heat capacity of the exhausted gas to generate steam; therefore, the heat exchanger <NUM> may also be called "steam generator". Advantageously, the steam produced by HRSG is arranged to be fed to a steam turbine, in particular to a steam inlet of the steam turbine.

The power plant <NUM> additionally includes a steam turbine <NUM> having a second rotary shaft to which a second electric power generator <NUM> (that is included in the power plant <NUM>) is coupled; the second electric power generator <NUM> generates a second electric power output. As shown in <FIG>, the electric power output is arranged to be coupled to the electric grid <NUM>, supplying electric power to the electric grid <NUM>.

Furthermore, the power plant <NUM> includes at least a first electrolyzer <NUM> having a first electric power input arranged to be selectively coupled to the electric grid <NUM>. In other word, the first electrolyzer <NUM> can be coupled/decoupled to/from the electric grid <NUM> and receive an electric input from the electric grid <NUM>. As excess energy is consumed locally to the plant for a useful purpose, i.e. generating hydrogen by the at least one electrolyzer <NUM>, the gas turbine <NUM> and/or the steam turbine <NUM> may be maintained permanently at the same or approximately the same operating conditions (preferably exactly or approximately optimal operating conditions) which means generating the same or approximately the same electric power by generators <NUM> and/or <NUM>. It is to be noted that <FIG> shows direct connections between the power plant <NUM> and the grid <NUM>; however, the one or more generators of the plant and the one or more electrolyzers of the plant may be directed or indirectly connected to the grid; for example, there may be internal electrical lines for diverting electric energy of the generators directly from the grid to the electrolyzers.

Preferably, the power plant <NUM> has a first electric switch <NUM>, located between the first electric input of the first electrolyzer <NUM> and the electric grid <NUM>, and a control unit <NUM>, coupled to the first electric switch <NUM> and arranged to control switching of the first electric switch <NUM>, for example sending input to the first electric switch <NUM>. In particular, the electric switch <NUM> is arranged to connect the first electrolyzer <NUM> and the electric grid <NUM> when it is in closed status and disconnect the first electrolyzer <NUM> and the electric grid <NUM> when it is in open status.

Preferably, the control unit <NUM> is arranged to control switching of the first electric switch <NUM> according to at least one predetermined rule stored in the control unit <NUM>.

For example, the power plant operator may have entered into agreements with the grid operator in such a way as to pre-define periods in which the electric switch <NUM> is closed and periods in which the electric switch <NUM> is open, i.e. respectively periods in which the electrolyzer <NUM> is coupled with the electric grid <NUM> and receive an electric input from the electric grid <NUM> and periods in which the electrolyzer <NUM> is not coupled to the electric grid <NUM>.

Advantageously, the electrolyzer <NUM> is coupled with the electric grid <NUM> when the electric energy demand of the grid from the power plant <NUM> is reduced, in such a way that part of the electric power supplied by the power plant <NUM> to the electric grid <NUM> is immediately and locally consumed by the electrolyzer <NUM>. In this way, the power plant <NUM> can be advantageously operated always in nominal conditions even if, in such conditions, the agreements with grid operator would have established a reduced electric power supply to the electric grid <NUM>.

Alternatively or additionally, the control unit <NUM> is arranged to control switching of the first electric switch <NUM> according to at least one request received by the control unit <NUM>.

For example, the control unit <NUM> may receive from the grid operator or the plant operator an extemporaneous request of reducing electric power supply to the electric grid <NUM>, due for example to a sudden decrease in electric energy demand. In this case, the control unit <NUM> closes the electric switch <NUM> to couple the electrolyzer <NUM> with the electric grid <NUM> in such a way that the electrolyzer <NUM> immediately and locally consumes part of the electric power supplied by the power plant <NUM> to the electric grid <NUM>.

It is to be noted that, differently from what described above, the electric power input of the first electrolyzer <NUM> may be directly connected to the electric power generator <NUM>, <NUM> output without being connected to the power grid <NUM> first. In this configuration, the electric switch <NUM> is located between the electric power generator <NUM>, <NUM> output and the electric power input of the first electrolyzer <NUM>.

According to the embodiment shown in <FIG>, the power plant <NUM> further comprises a second electrolyzer <NUM> having a second electric power input selectively coupled to the electric grid <NUM>. In other word, the second electrolyzer <NUM> can be connected to the electric grid <NUM> and receive a second electric input from the electric grid <NUM>. In is to be noted that second electrolyzer <NUM> can be identical or different from first electrolyzer <NUM>.

Preferably, the power plant <NUM> has a second electric switch <NUM>, located between the first electric input of the second electrolyzer <NUM> and the electric grid <NUM> and a control unit <NUM> coupled to the second electric switch <NUM> and arranged to control switching of the second electric switch <NUM>, for example sending input to the second electric switch <NUM>. In particular, the electric switch <NUM> is arranged to connect the second electrolyzer <NUM> and the electric grid <NUM> when it is in closed status and disconnect the second electrolyzer <NUM> and the electric grid <NUM> when it is in open status.

Preferably, the control unit <NUM> is arranged to control switching of the second electric switch <NUM> according to at least one predetermined rule stored in the control unit <NUM>.

Alternatively or additionally, the control unit <NUM> is arranged to control switching of the second electric switch <NUM> according to at least one request received by the control unit <NUM>.

It is to be noted that the control unit <NUM> coupled to the first electric switch <NUM> and the control unit <NUM> coupled to the second electric switch <NUM> may be the same control unit. In other word, the control unit <NUM> is arranged to control both first electric switch <NUM> and second electric switch <NUM>; <FIG> shows switch <NUM> and switch <NUM> as assembled in a single switching arrangement <NUM>.

Advantageously, the control unit <NUM> can control the first electric switch <NUM> and the second electric switch <NUM> in different way and with different control logics, for example according to a predetermined rule stored in the control unit <NUM> or according to at least one request received by the control unit <NUM>. For example, the control unit <NUM> may close the first electric switch <NUM>, coupling the first electrolyzer <NUM> with the electric grid <NUM>, and may open the second electric switch <NUM> in such a way that the second electrolyzer <NUM> does not receive electric input from the electric grid <NUM>. In this way, the electric power immediately consumed from the electric grid <NUM> by the power plant <NUM>, in particular, by the electrolyzers <NUM> and420, can be modulated at least in four different manners:.

Advantageously, the power plant <NUM> may have additional electrolyzers with their respective electric switch that can be selectively coupled to the electric grid <NUM> by the control unit <NUM> to more finely modulate the electric power immediately and locally consumed by the power plant <NUM>.

It is to be noted that electrolysis performed by electrolyzers requires water as well as electric power, so the electrolyzers <NUM> and/or <NUM> are fluidly connected also to a water source that provides a water flow, in addition to the electric input provided by the electric grid <NUM>. The water flow source may be external to the power plant <NUM> and different depending on the plant configuration or the amount of water required.

The power plant <NUM> includes further a tank <NUM> for storing the hydrogen produced by the first electrolyzer <NUM> and by the second electrolyzer <NUM> (if present), and to be burned by the gas turbine <NUM> (when desired); hydrogen storage is preferably performed at ambient temperature (for example in the range between -<NUM> and +<NUM>); hydrogen storage is preferably performed at relatively low pressure, for example in the range between <NUM> bar and <NUM> bar; it is to be noted that pressure fluctuation in the tank <NUM> may be for example of <NUM>-<NUM> bar depending on the specific embodiment. In the light of the temporary storage and local use of hydrogen, the tank <NUM> may be very small; theoretically, its capacity could be null as the hydrogen might be used by the combustor as soon as it is produced by the electrolyzer(s). Typically, the tank is fluidly coupled only to the electrolyzer(s) for receiving hydrogen and only to the combustor of the turbine for transmitting hydrogen; such couplings may be through controlled valves.

A control unit, that advantageously may correspond to control unit <NUM> already mentioned, may be arranged to control the primary fuel flow and the secondary fuel flow to the a gas turbine <NUM> through e.g. one or more valves. Preferably, control of the fuel flow or flows is performed according one or more predetermined rule stored in the control unit. This control unit may be further arranged to check a hydrogen level in the tank <NUM> (that may correspond to the hydrogen pressure in the tank); based on the hydrogen level, the control unit my decide to issue alarms and/or to regulate appropriate the fuel flow or flows.

As already anticipated, the tank <NUM> has a limited capacity. Its capacity is sufficient, typically exactly sufficient, for assuring operation of the gas turbine <NUM> for a predetermined time at a predetermined ratio of the secondary fuel and the primary fuel. Advantageously, the predetermined time is in the range <NUM>-<NUM> minutes; it is to be noted that the predetermined period of time may be chosen so to guarantee smooth operation of the combustor even if fluctuations of the primary fuel flow and of the secondary fuel flow occur and considering the speed of the flow control valves. Advantageously, the predetermined ratio is in the range <NUM>-<NUM> % in weight. For example, in a 12MW power plant designed to burn CH<NUM> and H<NUM>, wherein <NUM>-minutes combustor operation is guaranteed by the hydrogen tank at a blending ratio of about <NUM>%, the tank may have a capacity of approximately <NUM><NUM> - the pressure in the tank may vary between e.g. <NUM> bar and e.g. <NUM> bar.

According to a second embodiment <NUM> of a power plant shown in <FIG> (that is conceptually similar to the plant of <FIG>), the power plant further comprises a heat exchanger <NUM> for heating a water flow W and producing a heated water flow to be fed at least to the first electrolyzer <NUM>. The heat exchanger <NUM> increases the efficiency of the electrolyzer and allows the use of medium-high temperature electrolyzer fed by the heated water flow produced by the heat exchanger <NUM>.

It is to be noted that the heated water flow W fed to the electrolyzer <NUM> can be water flow, steam flow or a mixed water-steam flow depending on the type of electrolyzer used, for example an alkaline electrolyzer, a proton exchange membrane (PEM) electrolyzer or solid oxide electrolyzer cell (SOEC).

With non-limiting reference to <FIG>, the heat exchanger <NUM> receives heat from the heat recovery steam generator <NUM> that is used to heat the water flow W fed to the electrolyzer <NUM>.

In particular, the heat received from the heat recovery steam generator <NUM> is in the form of hot water flow, in particular a steam flow, for example a steam flow picked up between the HRSG evaporator <NUM> and the HRSG superheater <NUM>. In particular, the power plant <NUM> has a valve <NUM>, downstream the evaporator <NUM>, adapted to deviate part of the steam flow of the steam turbine engine, for example <NUM>-<NUM>%, to the heat exchanger <NUM>. Once the picked-up flow has passed through the heat exchanger <NUM> and has released heat to the water flow W fed to the electrolyzer <NUM>, the picked-up flow is reintroduced to the steam cycle, typically in condensate condition. Advantageously, the picked-up flow is mixed with the outlet flow of the steam turbine <NUM>, before entering in the condenser <NUM>.

According to a third embodiment <NUM> of a power plant shown in <FIG> (that is conceptually similar to the plants of <FIG> and <FIG>), the heat exchanger <NUM> receives heat from the heat recovery steam generator <NUM>, that is used to heat the water flow W fed to the electrolyzer <NUM>.

Preferably, the heat from the heat recovery steam generator <NUM> is generated by exploiting the residual thermal capacity of exhausted gas EG before being released into the atmosphere. This is achieved by passing the water flow W to be fed to the electrolyzer <NUM> in an economizer <NUM> of the heat recovery steam generator <NUM>, just before releasing exhausted gas EG into the atmosphere. It is to be noted that, as shown in <FIG>, the heat exchanger <NUM> may receive heat both by exploiting the residual thermal capacity of exhausted gas EG and by deviating part of the steam flow of the steam turbine engine.

The electrolyzers <NUM> and <NUM>, receiving electric energy from the grid <NUM> and heated water flow, produce as output an oxygen flow O and a hydrogen flow H by electrolysis. It has to be noted that both oxygen flow O and hydrogen flow H may not be pure oxygen or pure hydrogen flows; in particular, the hydrogen flow H can be a mixture of hydrogen and water (in particular steam) flow and/or a mixture of hydrogen and oxygen flow.

Advantageously, the power plants <NUM> and <NUM> further comprise heat exchangers <NUM> and <NUM> and the hydrogen flow H produced at least by the electrolyzers <NUM> and <NUM> is cooled down by the heat exchangers <NUM> and <NUM>. Advantageously, the heat exchangers <NUM> and <NUM> work also as a preheater of the water flow W by using the heat removed from the hydrogen flow H to heat the water flow W. Advantageously, the heat exchangers <NUM> and <NUM> are pre-heaters of the water flow W fed to the heat exchangers <NUM> and <NUM>; in other word, the heat exchangers <NUM> and <NUM> are arranged to feed the heated water flow to the heat exchangers <NUM> and <NUM>. With non-limiting reference to <FIG>, the heat exchanger <NUM> is between the economizer <NUM> of the heat recovery steam generator <NUM> and the heat exchanger <NUM>.

Advantageously, the power plants <NUM> and <NUM> are arranged to feed the cooled hydrogen flow to the gas turbines <NUM> and <NUM>. In other word, the gas turbines <NUM> and <NUM> are arranged to receive hydrogen flow H produced by the electrolyzers <NUM> and <NUM> and use it as fuel, in particular as "secondary fuel". In particular, the hydrogen flow H is fed to mixers <NUM> and <NUM> wherein is mixed with a gaseous fuel F, i.e. the "primary fuel" that is typically natural gas, and then the hydrogen-fuel mixture is injected in the combustors <NUM> and <NUM> of the gas turbines <NUM> and <NUM>.

Advantageously, the amount of the hydrogen flow H fed to the mixers <NUM> and <NUM> can be regulated by regulating valves <NUM> and <NUM> and the amount of the gaseous fuel F fed to the mixers <NUM> and <NUM> can be regulated by regulating valves <NUM> and <NUM>, so that the gas turbines <NUM> and <NUM> can be fueled by a mixture which can have different amount of hydrogen and fuel, for example can be fueled with a mixture of <NUM>% fuel and <NUM>% hydrogen or can be fueled up to <NUM>% by the hydrogen flow H produced by the electrolyzers <NUM> and <NUM>.

The power plants <NUM> and <NUM> are premixed-flame combustion type. However, the technical teachings disclosed herein, in particular one or more of the technical features described with reference to <FIG> and <FIG>, may be applied also to power plants wherein diffusion-flame combustion occurs.

Advantageously, the power plants <NUM> and <NUM> comprise separators <NUM> and <NUM> to separate the hydrogen-water flow produced by the electrolyzers <NUM> and <NUM> to increase the purity level of hydrogen flow H received by the gas turbines <NUM> and <NUM>.

Advantageously, the power plants <NUM> and <NUM> comprise a deoxygenation stations <NUM> and <NUM> to separate the hydrogen-oxygen flow produced by the electrolyzers <NUM> and <NUM> to increase the purity level of hydrogen flow H received by the gas turbines <NUM> and <NUM>.

Advantageously, the power plants <NUM> and <NUM> comprise a station for removing water from hydrogen flow H, for example with a gravity separator of entrained liquid water from the electrolyzer or dehydration stations <NUM> and <NUM> to separate the water that may have remained even after the separators <NUM> and <NUM> to increase the purity level of hydrogen flow H received by gas turbines <NUM> and <NUM>.

Advantageously, the power plants <NUM> and <NUM> comprise also a tank <NUM> and <NUM> for storing hydrogen produced by the electrolyzers <NUM> and <NUM> (or further electrolyzers as shown e.g. in <FIG>). In particular, these tanks are positioned upstream of the combustor <NUM> and <NUM> and downstream of the electrolyzers <NUM> and <NUM> and possibly one or more of the components <NUM>, <NUM>, <NUM>, <NUM> shown in <FIG> and <NUM>, <NUM>, <NUM>, <NUM> shown in <FIG> are fluidly coupled in-between. It is to be noted that none of these components is a compressor, i.e. a machine arranged to increase the pressure of the hydrogen generated by the electrolyzer or electrolyzers.

In general, the coupling components are such that the pressure in the tank(s) is smaller (typically, only few bars smaller) than the pressure at the outlet of the electrolyzer(s); in other words, the coupling components introduce a (small) pressure drop.

Claim 1:
A power plant (<NUM>, <NUM>, <NUM>) configured to generate electric power to be provided to an electric grid (<NUM>), the power plant comprising:
- a gas turbine (<NUM>, <NUM>, <NUM>) having a first rotary shaft and configured to burn a primary fuel and a secondary fuel, wherein the gas turbine has an exhaust outlet,
- a first electric power generator (<NUM>, <NUM>, <NUM>) coupled to the first rotary shaft, wherein the first electric power generator has a first electric power output,
- a steam turbine (<NUM>, <NUM>, <NUM>) having a second rotary shaft, wherein the steam turbine has a steam inlet,
- a second electric power generator (<NUM>, <NUM>, <NUM>) coupled to the second rotary shaft, wherein the second electric power generator has a second electric power output,
- a steam generator (<NUM>, <NUM>, <NUM>) coupled to said exhaust outlet and arranged to feed steam to the steam inlet,
- a first electrolyzer (<NUM>, <NUM>, <NUM>) having a first electric power input, and
- a tank (<NUM>, <NUM>, <NUM>) for storing hydrogen to be produced at least by the first electrolyzer (<NUM>, <NUM>, <NUM>) and to be burned by the gas turbine (<NUM>, <NUM>, <NUM>);
wherein the first electric power output of the first electric power generator (<NUM>, <NUM>, <NUM>) is arranged to be coupled to the electric grid (<NUM>); wherein the second electric power output of the second electric power generator (<NUM>, <NUM>, <NUM>) is arranged to be coupled to the electric grid (<NUM>); wherein the first electric power input of the first electrolyzer (<NUM>, <NUM>, <NUM>) is arranged to be selectively coupled to the electric grid (<NUM>); characterized in that the tank (<NUM>, <NUM>, <NUM>) is fluidly coupled to the gas turbine (<NUM>, <NUM>, <NUM>) for selectively burning also hydrogen as a secondary fuel.