FIELD OF THE INVENTION

The present invention relates to an electrolyser system according to the preamble of the independent claim and a method of operating such system. In particular, it relates to use of an electrolyser system to support stability of a power grid.

BACKGROUND OF THE INVENTION

In large electric utility grids, an increasing portion of the power is produced by inverter-based systems. Such systems do not inherently contribute to the grid inertia in the same way as synchronous generators powered by fossil fuel inherently contribute, and this increases the risk of voltage- and frequency fluctuations. Maintaining a stable grid frequency and voltage on an electric grid based on primarily renewable sources such as photovoltage, wind power, water power, and battery technology will require active functions and control strategies to ensure that the grid frequency and voltage is maintained.

As the grid transitions from predominantly fossil fuel sources to a grid with predominantly renewable fuel sources, there will be periods with very high percentage of the power produced by renewable and with a very small number of fossil plants connected to the grid. Such periods pose a special challenge to the grid operators and may require that conventional fossil plants stay connected, not for generating energy but mainly for grid stabilization reasons. Some mitigations have already been developed for renewable energy sources, addressing this issue, like wind turbine frequency response and wind turbine based inertial response. These functions improve the grid stability, but due to the mechanical aspect of the functions, deploying these with very fast response times can have serious impact on the wind turbine, so there is a cost or a lifetime implication for the operators. Frequency response to low frequency requires some level of curtailment, and inertial response on turbines introduce an issue of a recovery delay after the initial energy response, reducing the value of the frequency stability contribution from wind turbines to some degree.

Periods when the renewable penetration is the highest are also periods when the energy prices tend to be low, so for energy storage systems, this would be the ideal time to charge or store energy.

From a grid-stability perspective, the frequency deviation from the nominal grid frequency represents an imbalance between the power delivered into the grid and the power being extracted from the grid. Any over-frequency, which is a frequency above the design frequency, is a result of more energy flowing into the grid than is actively being consumed, and any under-frequency is a result of more energy being extracted from the grid than what is flowing into the grid at that point in time. A typical response to under-frequency on a fossil grid is managed by the inherent inertia provided by synchronous generators, and on the larger time scale, additional power is provided by ramping up spinning reserve capacity.

In order to facilitate the transition from a fossil economy to a renewable economy, electrolysers, such as an alkaline electrolyser system, can be used to convert electrical energy to hydrogen when the energy prices are low. Energy storage by production of hydrogen for later use in a power plant is disclosed in European patent application EP2318678 Al. A hydrogen production system using power from wind farms is disclosed in international patent application W02010/048706A1, including power balancing controllers for weak electrical grids. By intelligent control of the electrolyser, it can also contribute to the frequency stability on the larger grid at the same time without mechanical risk or damage.

The prior art discusses adjustment of the electrical consumption by electrolysers relatively to the availability of electricity at low costs, as well as adjustment of the consumption in order to contribute to stabilization of the grid, for example including the possibility to ramp the consumption up or down relatively to a predetermined set point. For example, W02006/072576, W02014/037190, and W02013/004526 disclose methods where the load to the net is adjusted by extending or reducing the number of electrolysers in a system. Chinese patent application CN112165108A discloses a power grid auxiliary peak regulation system including electrolysers for hydrogen production as well as lithium batteries. Japanese patent application JP2021136709 A2 discloses energy storage of solar power by batteries and hydrogen production.

US2016/369416 and US2016/377342 disclose reversible fuel cell system that can switch between electrolyser function with a corresponding production og hydrogen gas and fuel cell function for production of electrical power, which can be used to stabilise the grid. A similar relatively slow acting reversible system for grid stabilization is disclosed in US2016/372775 and AU2021100419a4

Such switch is useful for slow variations in the grid but cannot be used for stabilization of the net at short time scale, where spikes or drops in the net occur within time frames of a second or less.

Additionally, the prior art discusses feeding current back into the grid for stabilizing reasons by using fuel cells that consume the earlier produced hydrogen. However, these measures for grid stabilization are relatively slow and include some time lag and hysteresis when it comes to electrical variations in the grid.

DESCRIPTION / SUMMARY OF THE INVENTION

It is therefore an objective of the invention to provide an improvement in the art. In particular, it is an objective to provide an electrolyser system that can be used for quick grid power stabilization within a fraction of a second. This objective and further advantages are achieved with an electrolyser system and a method of its operation as described below and in the claims.

In short, the electrolyser system is supporting stability of the power grid by three modes. In a first mode, the consumption is regulated in the direction of stabilizing the grid. In a second mode, an electrical capacitor effect of the electrolyser is used with quick discharge temporarily in reverse for counteracting short-time deviations in the power grid of frequency or voltage or both. In a third mode, the electrolyser shifts to a short-term fuel cell mode consuming the gases at the electrodes. For example, all three modes are triggered, one after the other.

The electrolyser imports energy from the grid to split water into hydrogen and oxygen, which then can be used for other purposes, for example as means for energy storage and later conversion back to electrical energy by fuel cells. During operation, the functionally connected inverter can be configured to support the grid voltage. In addition, the invention is a method of controlling the electrolyser such that the electrolyser can reverse its functionality to contribute to grid stability when needed. Accordingly, the device is used not only to convert energy to gas but due to its energy storage capability can also actively contribute to grid frequency and voltage stability.

Advantageously, and as exemplified in the following, the electrolyser is an alkaline electrolyser. During a conventional mode of operation, the alkaline electrolyser is controlled such that it is activated for gas production at a pre-set level when power from the grid is available and when the operator wishes to produce gas, and the electrolyser is disconnected again when gas production is not possible or desirable, for example when it is not profitable.

Typically, alkaline electrolyser, adjusts the power consumption according to the availability of power in the grid, potentially taking into regard the profitability as well. For example, if the electrolyser is connected to a photovoltaic (PV) system, it will be operated to consume high power when the sun is shining, and shut its productivity down at night.

As it appears more from the following, an electrolyser is provided that comprises a stack of electrolyser modules for producing hydrogen gas from water, each module comprising a pair of electrodes sandwiching a membrane therein between. Further, an inverter system is electrically connected to the stack of modules and electrical connected to an electrical power grid. For the control of the inverter system and the electrolyser, a control system that is functionally connected to the inverter system. Grid support, as described in the following, is generally relevant. The alkaline electro- lyser has the possibility of reacting on grid behavior in three different modes. In particular, the electrolyser system is configured for electrically supporting the power grid by three different support modes during power deviations from a predetermined operation state of the grid for counteracting the deviations.

In a first support mode A, the electrolyser system is configured for varying import of electrical energy from the grid in response to the deviations. In this first mode, the alkaline electrolyser can support instability in the grid by reducing or increasing the power consumption according to the conditions of the grid. For example, in the morning, when private consumers are using large amounts of electrical power, the power consumption by the electrolyser system is reduced. The consumption can then be adjusted to full power, when sufficient power is available and when the grid is functioning stable, and especially when the power is available at low costs.

This adjustment can be done by the control system through automatic monitoring of the actual grid frequency and voltage and by adjustment of the power, accordingly. Alternatively, or additionally, the control system is interfaced to the grid operator and receives information and/or even commands through the interface. As a further optional measure, consumption pricing is taken into regard by the controller, which in this case is receiving actual pricing levels and/or pricing forecasts in order to plan and regulate the consumption based on multiple parameters, potentially using artificial intelligence in order for the controller to learn grid behavior and potentially forecast consumption profiles as well as delivery profiles. For example, the controller takes into account weather forecasts when the electrolyser is used in a grid with a substantial portion of the power delivered by PV or wind turbines.

In principle, the electrolyser can be operated in a standard mode at a fraction of its maximum capacity, for example half capacity, and then ramped up or down as a stabilizing action for the grid. However, this implies operating the electrolyser at less than maximum capacity most of the time, which is not an optimum way of using an electrolyser. Therefore, different modes of grid stabilization by the electrolyser have been added. For electrical grid support, a second mode B is included, which is a fast-acting mode in which the electrolyser functions as a capacitor. Due to the electrodes of the modules being charged and having a voltage across the membrane in between the electrodes, each modules function as capacitors, and the stack of electrolyser modules can function as a series of serially connected capacitors. In this second mode, the modules are switching from an electrically charged operational state to a discharge state, in which the electrical power from the discharge is exported through the inverter into the grid for stabilizing unwanted short term variations of the power in the grid.

When the electrolyser system is large, the capacitance of the entire stack is substantial and can have a total capacitance up to several milli Farad, which makes it suitable as a substantially-sized quick-acting capacitor for short time-scale grid stabilization, especially when used for small grids, for example based on renewable sources, such as wind turbines and/or PV plants.

This ability of electrolyser systems to act as capacitors for storing electrical energy can advantageously be utilized to support the temporary energy reversal and contribute to grid frequency recovery. In this capacitor function of the electrolyser system, the grid stabilizing action can be performed at time scales from milliseconds and potentially up to a few seconds.

In practice, in case of faults or incidents in the grid, the electrolyser will use its inverter and the capacitive effect of the alkaline electrolyser stack to immediately support the grid to recover by returning bursts of electrical power into the grid. In a millisecond time frame, the alkaline electrolyser can go from passive consumer of power to a grid-supporting reverse action, contributing to maintain the grid in normal operation. Especially in weaker grids, such as micro grids dependent on wind and sunlight, this is critical in order to avoid a total black out. Especially, if the alkaline electrolyser is a large consumer with a major load in a weak grid, possibly representing several percent of the total grid consumption, it is very critical that this load can be able to react actively to support the grid to recover and not just cut out in case of grid faults. Although, the functionality of quick return effect by the electrolyser into the grid is most pronounced in weak and small grids, it may also be useful in stronger and larger grids. In particular, if the electrical return effects of several electrolyser systems are combined, even if having different locations, this functionality can be used to support the grid in maintaining the grid frequency and keep the grid stable.

It should be pointed out that, in stronger grids, electrolysers, such as alkaline electro- lysers, can also be installed with the direct purpose of stabilizing the grid, with the option of manufacturing hydrogen when stabilization is not required. In other words, the electrolyser can have a stabilizing functionality as the primary function and only be used for hydrogen manufacturing as a secondary functionality. This could then replace other reactive equipment, that traditionally will be used for the purpose, so that, instead of having a fully passive grid support component, the alkaline electrolyser will be used for manufacturing hydrogen when power is cheap and available, but standing by mainly for its stabilizing purpose.

When a grid goes in brown-out where parts of the grid are disconnected, i.e. due to temporary short circuits, the traditional power sources in the remaining grid will all try to maintain the voltage and frequency, and typically there will be a need of both active and reactive power to avoid a total black out, while the grid couples out the fault. Such incidents can last for several seconds until the fault is cleared, and the remaining grid can continue operation. Typical reaction from large consumers of power will be to cut out the load, which will also be the typical reaction from an electrolyser.

For such events, the electrolyser comprises a third mode for grid support, which is explained in the following. In this third support mode C, the electrolyser system is configured for switching instantly from a hydrogen production mode into a fuel cell mode, wherein gas at the two opposite electrodes of the electrolyser module from the immediately preceding hydrogen production is converted back into water inside the module.

During normal operation of the electrolyser, gas resides on the surface of the electrodes and between the electrodes. This residual oxygen and hydrogen gas can be used for conversion back into water with a reversal of electrical energy flow. This fuel cell mode of the electrolyser, without providing a separate fuel cell but merely using the reverse function across the already existing electrolyser electrodes and membrane, is then used for feeding energy back to the grid as long as there is gas available near the electrodes for the fuel cell function. Thus, the gas is already located at the electrodes and does not have to be transported to the electrodes from storage tanks. Although, the amount of energy originating from this relatively small amount of gas is correspondingly small, its capture and export to the grid is sufficient for a stabilizing action in the range of a second and in certain cases up to 10 seconds, further extending the duration and /or magnitude of the energy exported in response to a grid frequency dip.

In practical embodiments, the electrolyser system is configured for electrically supporting the power grid by the three different support modes one after the other with the first mode A reducing the power import to zero, then reversing power back into the grid within milliseconds in support mode B, then continuing reverse flow of electricity into the grid by fuel cell action in mode C, and then, after recovery of the grid, returning to consumption for gas production.

Accordingly, when combining mode B and mode C of recovery action, the electrolyser may as a first step react instantly to variations in the grid by feeding power back into the grid through the inverter in the time frame of milliseconds by using the capacitive effect. As a second step, if necessary for further stabilizing the grid, the alkaline electrolyser is set to consume the gas close to the electrodes in a fuel cell mode, and the correspondingly produced power is then fed reverse into the grid through the inverter to support the grid through a low voltage incident.

In practice, the electrolyser system is triggering a recovery sequence for power support of the grid. In this sequence, the electrolyser system is shifting from mode A to mode B, including reducing import of electrical energy from the grid to zero in the first support mode A, and then switching to the second support mode B with a capacitor function of the modules, in which the modules are switching from an electrically charged operational state to a discharged state, and exporting the discharge electrical power through the inverter into the grid for stabilizing unwanted short term variations of the power in the grid. If the fast recovery action by the second mode is sufficient to return the grid to normal operation, the third mode C need not be activated, irrespective of the fact that the system is capable of doing so.

Therefore, after performing the recovery sequence, the system checking whether the grid has recovered and in the affirmative, it is returning to power consumption and production of hydrogen gas.

However, if the grid has still not recovered, and the check reveals that further recovery action is necessary after mode B, the system is extending the recovery sequence by shifting from mode B to mode C and operating the electrolyser modules as fuel cells that are consuming gas at the two opposite electrodes of the electrolyser module and feeding the electrical power produced in this fuel cell mode through the inverter into the grid until the gas at the electrodes is consumed.

The recovery sequence may be based on measurements that the electrolyser system does on the grid. Alternatively, or in addition, the control system of the electrolyser system comprises a data interface for receiving external data for receiving digital trigger data from an external data provider, for example the operation system of the grid or from a central controller that is in data-communication with other electrolyser systems. The trigger data advantageously comprise information about at the actual state of the grid. However, it may also or alternatively comprise information about expected future states of the grid. These data can then be used for starting a recovery action for the grid automatically on the basis of the trigger data.

For the triggering, various parameters can be used by the electrolyser system. For example, it may be programmed to trigger a recovery mode for power support of the in dependence of measures parameters, the parameters including frequency of the grid and/or voltage of the grid. The measures parameters can be provided to the controller by measuring the conditions in the grid at the electrolyser system, or the measurement data are received from an external source through the data interface.

Opposite a wind turbine, where grid support reaction may result in heavy mechanical load, the chemistry in the recovery action will have no mechanical impact to the alka- line electrolyser, as the whole process is a purely electrical behavior, initially, and then a chemical behavior.

In weak grids, for example minor grids based on renewable energy plants, the capability to ride through instabilities is very important in order to maintain a stable grid operation. By utilizing the electrolyser actively for returning power to the grid in cases of wrong grid behavior, instead of considering it as a passive consumer, the overall grid complexity is reduced as well as the need of additional components for grid stability. Even in strong and potentially larger grids, the electrolyser can also support the grid, especially if multiple electrolyser plants are uses for a coordinated action through a correspondingly programmed main control system, even if the electrolyser plants located apart, as long as they are connected to the same grid.

Selecting a full controllable inverter technology instead of a traditional thyristor-based inverter makes it possible to completely control the energy flow from being a consumer, importing energy for its main purpose, to a power supporter by also allowing export of power.

This ability to both import and export of energy enables the system to respond to both fast and slow frequency events or frequency dips on the grid side and, instead of merely adjusting the gas production, the system as described herein has the additional advantage of temporarily extracting energy from the electrolyser in different modes with corresponding different time constants and feed this energy back to the grid in order to compensate for a drop in frequency.

Rates of change of power for import and export are suitably provided as programmable response curves in terms of at least one of time, time delay, ramp rates, duration, frequency impact, proportionality, magnitude and response profiles.

The fast response time and the ability to change power direction can also be used in association with Black Start and Block Loading where incrementally larger and larger loads are connected to the grid being brought online. When each new load is connected, it will have an impact on the grid frequency, and the electrolyser ability to ramp power fast without excessive mechanical loads will offer superior ramping capability and grid stability support compared to a fossil fuel generator or a renewable plant.

In the following, a dimensional example is given for purpose of illustration without limiting the general character of the invention. For example, the following parameters are valid.

For example, the direct current (DC) voltage from module to a subsequent module is 1.4 V. As an example, the electrode area is in the range of square meters. As the number of modules in a stack can range from hundreds to thousands of modules, the resulting voltage is in the kV range. Such systems are capable to substantially supporting micro grids in the range of tens of MW.

The above numbers show that the electrolyser system with its different assisting recovery modes for the grid is a substantial support factor for micro grids.

If several of such systems are used in combination, even if remotely spaces, even larger grids can be supported.

SHORT DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail with reference to the drawing, where FIG. 1 is a simplified system diagram;

FIG. 2 illustrates reactive power control as a first mode of operation;

FIG. 3 illustrates second and third modes of operation;

FIG. 4 is an illustration of frequency dependent power import or power export;

FIG. 5 illustrates a response to a grid frequency drop during a period with max power import;

FIG. 6 illustrates voltage droop control.

DETAILED DESCRIPTION / PREFERRED EMBODIMENT

In Fig. 1. an alkaline electrolyser system 1 is illustrated that comprises one or more stacks, here shown with two stacks 2 of electrolyser modules 3. Each of the modules 3 comprise two electrodes 4 on opposite sides of a membrane 5. The modules 3 in a stack 2 are electrically connected to each other in series, and the two stacks 2, and potentially additional stacks, are connected in parallel to an inverter system 6, which in turn is connected to the electrical power grid 7 by a grid connection 8. The inverter system 6 and the operation of the electrolysers in the system 1 is controlled by a control system 9 having a digital data interface 10 for remote data exchange.

FIG. 2 illustrates a first mode of operation of the electrolyser with time along the X- axis and power import relatively to a set point along the Y-axis. In this first mode, of operation, the electrolyser is set to work in predetermined conditions, for example maximum hydrogen production as long as the grid works in optimum or at least acceptable stable conditions. However, in case that the capacity of the grid decreases, the consumption/import of power is reduced, until the grid is working again appropriately, at which time, the consumption is ramped up again.

FIG. 3 illustrates some principles of a second mode B and a third mode C of operation by the alkaline electrolyser in order to support grid stability. The X-axis represents time t, and the Y-axis arbitrary normalised units related to grid power and power imported or exported by the electrolyser system. The upper curve, which is stippled, illustrates a grid power behaviour, and the lower curve, which is solid, the import and export of power by the electrolyser system. The diagram of FIG. 3 illustrates three different regimes, A, B, and C. The regime termed A illustrate normal operation, which is usually case and may last from hours to months and where also the electrolyser is running in normal operation for production of hydrogen gas. In this regime, the electrolyser may consume power from the grid up to a maximum value for maximum hydrogen production or to an otherwise set maximum for power to be imported from the grid. The maximum value is arbitrarily set to 1, and since it is an import of energy from the grid, the value given in the illustration for the electrolyser curve in the regime A is minus one. For illustrative purposes in relation to the curve, however, the scale or values are not important, as the curve solely reflects the principle.

In the second regime, B, the grid power exhibits some short drops, for example drops in the voltage. These drops are short, lasting a minor fraction of a second, such as few- or tens of milliseconds. In order to counteract these short drops in power, the electro- lyser system with its inverter is programmed to react quickly to not only reduce consumption but even export power into the grid by using its natural fast-reacting capacitive effect. This export of energy is illustrated by the solid curve in the positive regime of the vertical axis.

As mentioned above, the electrodes of the electrolyser modules are charged with a voltage across the membrane so that modules functions as a capacitor, and the stack of electrolyser modules can function as a series of serially connected capacitors. Accordingly, this ability of electrolyser systems to act as capacitors for storing electrical energy can advantageously be utilized to support the temporary power reversal into the grid and contribute to grid recovery.

The capacitive effect by the electrolyser can be of an intensity that substantially reduces the power drop in the grid and possibly even eliminates the power drop in the grid. This would be the case if the electrolyser is of a substantial size relatively to the power grid, for example a microgrid. Especially, several electrolyser systems, maybe even at various locations, may be connected through the data interface for cooperation in order to counteract drops in the grid by combined efforts.

In the regime C of FIG. 3, the grid has a brown out in the order of a second. In this case, the capacitive export effect of mode B would be quick to counteract the initial drop but not long lasting enough for stabilizing the net for a length of second. Therefore, the electrolyser system is changing into a third mode of operation C, in which it functions as a fuel cell using the gas available in the cell.

As discussed above, during normal operation, gas resides on the surface of the electrodes and between the electrodes, which can be used in a fuel cell mode for conversion into water. The produced electricity from the conversion of the residual gas is then used for feeding energy back to the grid as long as there is gas available in the fuel cell function. For a grid stabilizing action in the order of a second or some seconds, this third mode is useful. Notice that no separate fuel cell is provided, and the gas used for the fuel cell effect is only the gas at the electrodes and not gas supplied from a gas storage facility, as the latter would not be acting fast enough. The control algorithm for performing the frequency response is provided in the control system 9, which can be combined with the inverter system 6 or be provided as a separate control unit in electronic connection with the inverter system 6.

Trigger levels for when to feed electricity back to the grid and in what form and which mode is, as an option, defined by local parameter settings at the location of the elec- trolyser. In this case, the control system would take into account the electricity state of the grid, for example as measured or as received through the data interface. Alternatively, trigger data and levels are received through the data interface by remote signals transmitted to the controller from a remote location, for example from a power plant operator, or from a master controller that controls more than one electrolyser system with respect to grid support.

In order to use the electrolyser system in an optimum way for grid support, the control system, advantageously, has multiple types of pre-programmed or commanded responses in terms of response times, response magnitude, response durations and/or response profiles.

Various combinations of trigger functions may involve not just specific levels but also take into account time of week or day as well as grid or commercial aspects, such as electricity pricing.

Additionally, the control system may use artificial intelligence in order to optimize responses to unwanted grid power variations, where the program uses experience of the variations to learn providing optimum responses and reverse power for grid stability.

For example, the grid is stabilized in dependence of the frequency, and the control system is programmed to support frequency stability in the grid by injecting short term energy back to the grid during frequency drops.

As illustrated by the droop curve in in FIG. 4, electrical power PEXPORT is exported back into the net, or electrical power PIMPORT is imported from the grid, depending on the frequency in the grid deviating from a reference frequency fREFERENCE. The criteria for decisions as to whether the operation is in a mode for power import or power export can be based on linear relationships with a corresponding predetermined parameter, such as grid frequency, but need not be so. Any predetermined function that is commercially or technically beneficial in relation to the power exchange can be used as an option. Additionally, the correction function can be enabled or disabled as needed based on a commercial considerations or agreements with the grid provide or based on a technical grid state.

As it appears from this example, the system can be configured for operating at a power set point with a frequency droop curve applied for adjusting the resulting power output in response to the grid frequency, measured or provided from external equipment. The droop can be applied to power references in the entire power range of the electrolyser both power export and power import. The power direction will be restored automatically when the right combination of criteria is present.

Fig. 5 illustrates a response to a grid frequency drop during a period with max power import. Triggered by a certain frequency change threshold foip for the frequency drop, the import of energy is stopped, and power is exported to support the grid. Immediately after the frequency threshold has been passed, the consumption is decreased to zero according to the first mode A of function where power is only imported when the grid is able to deliver power under stable conditions. This is illustrated by the power curve in FIG. 5 rising from the negative max import level of power, PIMPORT (max), to zero.

The first portion of exported power, illustrates by the first linear curve portion into the positive region is due to the capacitance effect in the second mode B. After exhaustion of the capacitance effect, the electrolyser system enters the fuel cell effect in the third mode C. This third mode C has only a short duration, namely until the gas at the electrodes is used up, so that the power exports is soon exhausted and returns to zero. If the grid has recovered at this stage, the electrolyser system can start importing power again, which is shown to the right in the curve, decreasing to the max import power PIMPORT (max). An action as a response to a frequency drop in the grid being to below a setpoint frequency, i.e. an under-frequency event, can be triggered due to a measurement of the frequency or triggered by an under-frequency event command to the control system 9 through the data interface 10 from a remote location, for example a remote control system or remote control station of a power plant.

In such event, the power import may be ramped to a new set point according to an assigned ramp rate or response profile. The power export is maintained as per the assigned profile in terms of magnitude and duration until the profile has been executed or the stored energy has been exhausted. When the grid frequency has recovered sufficiently, the electrolyser will resume gas production following a ramp rate for the power import.

FIG. 6 illustrates a voltage droop curve, where the voltage of the grid relatively to a reference voltage VREF determines whether power is exported or imported.

The alkaline electrolyser is able to support the grid voltage and frequency as soon as it is in operation. The grid assistance of the electrolyser increases the value of the design from an end consumer perspective because the device combines functionality that today may be provided by multiple individual devices. For example, it is possible to build or upgrade a wind power plant with an electrolyser of this type and save substation power correction system or capacitor banks.

The alkaline electrolyser can directly receive voltage or reactive power references from a plant controller to meet the combined reactive power or voltage requirements and at the same time be used to produce gas.

In summary, the electrolyser system has dual function as hydrogen production facility and as stabilizing factor for a power grid. In the stabilizing function, it operates according to three modes. In a first of the three stabilizing modes, the consumption is regulated in the direction of stabilizing the grid. In a second mode, an electrical capacitor effect of the electrolyser is used with quick discharge temporarily in reverse for counteracting short-time power deviations in the power grid. In a third mode, the electrolyser shifts to a short-term fuel cell mode, consuming the gases at the electrodes. Such an electrolyser system is advantageously used as an energy storage plant as part of a grid recovery system, in addition to producing hydrogen gas.