Electrolysis plant, method for operating an electrolysis plant, and combination comprising an electrolysis plant and a wind turbine

Abstract

The invention relates to an electrolysis plant comprising at least one electrolysis module (3A, 3B), wherein an electrolysis module (3A, 3B) has a plurality of series-connected electrolysis cells (5). Provision is made for a DC-capable switching device (6) that is connected electrically in parallel and that has an activatable power resistor (7) such that, in the closed state, a current path through the power resistor (7) is able to be activated so as to bypass electrolysis cells (5) and to be able to drain excess power through the power resistor (7). The invention furthermore relates to a method for operating such an electrolysis plant (1) for breaking down water into hydrogen and oxygen, and to a combination (100) comprising an electrolysis plant (1) that is connected directly to a wind turbine (31).

Description

[0001] Description

[0002] Electrolysis plant, method for operating an electrolysis plant and plant combination comprising an electrolysis plant and a wind turbine

[0003] The invention relates to an electrolysis plant comprising at least one electrolysis module. The invention further relates to a method for operating an electrolysis plant for splitting water into hydrogen and oxygen, and to a plant combination comprising an electrolysis plant and a wind turbine connected to the electrolysis plant.

[0004] An electrolysis plant is a device that uses electrical current to transform substances (electrolysis). Due to the variety of different electrochemical electrolysis processes, there are also a variety of electrolysis plants, such as an electrolysis plant for water electrolysis.

[0005] Nowadays, hydrogen is produced from water using, for example, proton exchange membrane (PEM) electrolysis or alkaline electrolysis. The electrolysis plants use electrical energy to produce hydrogen and oxygen from the water supplied. This process takes place in an electrolysis stack made up of several electrolysis cells. Several electrolysis cells are connected in series to form an electrolysis module, or module for short. Several modules are then connected in series to form an electrolysis stack. Water is introduced as the reactant into the electrolysis stack, which is subjected to direct voltage (DC voltage). After the water flows through the electrolysis cells, two fluid streams emerge as electrolysis products, consisting of water and gas bubbles (O2 and H2 respectively).

[0006] Current considerations are to use surplus energy from renewable energy sources during periods of abundant sun and wind, i.e., when solar or wind power generation exceeds average levels, to generate valuable resources. One such resource could be hydrogen, which is produced by water electrolysis plants. Hydrogen can, for example, be used to produce so-called renewable energy gas—also known as EE gas. EE gas is a combustible gas that is obtained from renewable sources using electrical energy.

[0007] Hydrogen represents a particularly environmentally friendly and sustainable energy source. It has the unique potential to realize energy systems, transport, and large parts of the chemical industry without CO2 emissions. For this to succeed, however, the hydrogen cannot come from fossil sources, but must be produced using renewable energies. At least a growing share of the electricity generated from renewable sources is now fed into the public power grid. Thus, a corresponding share of green hydrogen can be produced, depending on the electricity mix, if an electrolysis plant is operated with electricity from the public grid.

[0008] In electrolysis on an industrial scale, the direct current is mainly provided via mains-commutated rectifiers.

[0009] EP 3 556 905 A1 discloses such a circuit arrangement for supplying direct current to a plurality of electrolyzers arranged in parallel. The circuit arrangement comprises a rectifier which converts an input-side alternating voltage into a first output-side direct voltage. Each electrolyzer is connected in parallel to the output of the rectifier via a rectifier, in particular a step-down converter, which converts the first direct voltage into a second direct voltage, such that the second direct voltage drops across the electrolyzer. Each of the rectifiers, in particular the step-down converter, is designed to be controllable or adjustable in order to adapt the level of its second direct voltage, its output voltage.By using controllable and / or adjustable step-down converters for each of the electrolyzers, the current flow through each electrolyzer can be adjusted as required, even when the electrolyzers are connected in parallel.

[0010] One source of renewable energy comes from the increasing use of wind power. Large electrical outputs can be achieved, particularly with offshore wind turbines. The challenge, however, is that the distance to the consumers is great. The energy should therefore be transported to the consumer with as little loss as possible. Hydrogen is an ideal transport medium and energy carrier. It can be transported in gaseous form, for example, through pipelines. A positive side effect is that a hydrogen-carrying pipeline can also serve as an energy storage device, since the internal pressure can be varied within certain limits.

[0011] Based on these considerations, it is of particular economic interest to produce hydrogen directly at the energy generation site, i.e., autonomously and independently of the public grid. To this end, it is proposed to install the electrolysis plants on offshore platforms in the maritime sector, directly adjacent to or in the immediate vicinity of offshore wind turbines, and to supply them with electricity using the generated power.

[0012] Similar concepts have also been proposed for the mainland, using electricity from onshore wind turbines or photovoltaic systems, at least in part, for hydrogen production by directly connecting and feeding it into an electrolysis plant. In all of these applications, the electrolysis plant is part of an island grid. The electrolysis power is therefore not drawn from the public grid, but rather supplied directly by a wind turbine or a PV system and fed into an electrolyzer in the electrolysis plant.In contrast to the grid-controlled operation described above, the direct connection in particular brings with it particular challenges and problems with regard to the electrical connection and interconnection of the electrolysis plant with the respective renewable energy generation plant, be it a wind turbine or a photovoltaic plant, in particular to ensure safe and, above all, trouble-free operation of the electrolysis plant in a direct plant network with the renewable energy generation plant.

[0013] There is therefore a great need for technical solutions and precautions for scheduled or unscheduled operating situations at an electrolysis plant, where, for example, a change in load must be responded to within a short period of time. This need can arise as a result of changes in generation capacity when connected to a renewable energy generation plant with regard to the line provided, which is naturally subject to fluctuations. However, sudden changes in the availability of the power consumption from an electrolysis plant can also occur, for example in the event of the failure of one or more electrolysis modules or an electrolysis stack with several modules connected in series.

[0014] The invention is therefore based on the object of specifying an electrolysis system by means of which, in particular, electricity from a renewable source can be fed directly into the electrolysis system, while ensuring high operational flexibility and simultaneous system reliability. Further objects include specifying a corresponding method for operating an electrolysis system and specifying a system network comprising an electrolysis system and a renewable energy system.

[0015] The first-mentioned object is achieved according to the invention by an electrolysis system comprising at least one electrolysis module, wherein an electrolysis module has a plurality of electrolysis cells connected in series, and comprising an electrically parallel-connected DC-capable switching device which has a switchable power resistor, so that in the closed state a current path can be activated through the power resistor, so that a bridging of electrolysis cells is effected and excess power can be dissipated through the power resistor.

[0016] The invention is based on the knowledge that in electrolysis systems the electrolysis cells of an electrolysis module are very sensitive to exposure to inadmissibly high current densities. Overloading can lead to a breakdown of the electrolysis cells and failure, and also to locally induced short circuits due to thermal overload as a result of the locally high current densities within the electrolysis cell and its components. In the worst case scenario, this can lead to the loss of an entire electrolysis module, which is generally composed of a large number of axially stacked electrolysis cells that are electrically contacted in a series circuit. Due to this series connection, an inadmissible current flow affects a large number of electrolysis cells and electrolysis modules equally.Therefore, precautions must be taken to ensure the operational and plant safety of an electrolysis plant to prevent overloading and breakdown. This can happen, for example, if an unforeseen, sudden - temporary or permanent - failure of electrolysis cells or an electrolysis module means that the input power or rated power is no longer available during normal operation of the electrolysis plant. Without protective measures, a sudden loss or instantaneous reduction in input power would endanger the entire plant and expose the electrolysis cells to overload, provided the direct current supplied to the electrolysis plant remains constant. This particularly affects the electrolysis modules that are still in parallel operation.In this case, the current density would increase until the converters have adjusted accordingly, since the excess power previously used for the now-deactivated electrolysis must be dissipated. With the invention, the excess power can be dissipated as needed on both the generator side and the load side through the power resistor, which is very advantageous for protecting the system.

[0017] By means of the DC-capable switching device electrically connected in parallel to the electrolysis cells or the electrolysis module, the invention creates a safety-related solution directly on the electrolysis plant itself. This can advantageously reduce the reaction time for the required switching on of the power resistor by activating the current path. A further advantage of this self-sufficient solution is that the protective function does not initially have to influence the external source, which continues to supply the rated current. This means that, at least for a certain time, control intervention via the power control of the power source is initially not necessary. This means that the control system can be designed more simply at this point, since the converters connected in parallel do not have to be preventively regulated down at the same time as the regulation of one converter.This is particularly advantageous when directly connected to a slow-moving power generator, such as a wind turbine. With wind turbines, tracking, in particular the necessary reduction and adjustment of the feed-in power to the input power, is only possible comparatively slowly, i.e. the power control on the generator side can only follow a new, reduced setpoint very slowly. On the other hand, bridging of individual or multiple electrolysis cells or, if necessary, an entire electrolysis module can be effected and brought about instantly. In this situation, the electrolysis plant can continue to operate and, for example, produce hydrogen, with the surplus energy being safely dissipated via the power resistor of the switching device. In island grid operation, this also prevents a voltage increase on the external power source side.This risk would arise if the power could not be consumed or taken up anywhere else.

[0018] Furthermore, the invention creates a particularly reliable protective circuit in the event of an overload, for example in the event of a failure of one or more electrolysis modules, in order to reliably ensure overload protection for the electrolysis cells and the electrolysis modules. Depending on the overload situation, the excess current then available cannot be distributed among the electrolysis cells or electrolysis modules that are still in operation. If one or more electrolysis cells or an electrolysis module fail or are switched off, the fed-in power can no longer be taken up by the electrolysis system without causing damage. If these components or electrical subsystems of an electrolysis system are switched off, the excess energy must be absorbed. This is what the power resistor, which can also be referred to as a braking resistor, is used for.When the current path is activated, the power resistor absorbs all the electrical energy and converts it into ohmic heat. This thermal energy can be further used as useful heat, if required, by coupling it to a heat reservoir or a heat exchanger, for example. An electromechanical high-performance variable resistor for power applications is preferably used as a power resistor. Its resistance elements are generally made of thick resistance wire, which is suitable for carrying the rated current over a longer period and for bridging the electrolysis cells, provided its ohmic resistance is minimal. However, a power resistor is also possible which only has to accept and dissipate the full electrolysis current for a few seconds. This time should be sufficient to be able to adjust the external power source for the power supplied to the electrolysis.

[0019] This problem is particularly pronounced when an electrolysis plant is directly connected to a DC power source, such as that provided by a photovoltaic system or a wind turbine. The electrolysis plant is therefore particularly advantageously set up for direct connection and direct feed-in of direct current from a renewable energy plant. This provides a very advantageous protective measure for scheduled or unscheduled operating situations of the electrolysis plant, where, for example, a changed load must be responded to quickly. This requirement can arise as a result of changes in generating capacity when connected to a renewable energy generating plant with regard to the line provided, which is subject to natural fluctuations in generation.However, particularly sudden changes in the availability of power consumption from an electrolysis plant can be advantageously counteracted, such as an unforeseen failure of one or more electrolysis cells, one or more electrolysis modules, or an electrolysis stack with several electrolysis modules connected in series. This also allows generation peaks from the generating capacity, e.g., a renewable energy plant, to be at least partially absorbed.

[0020] Furthermore, when the electrolysis system is directly connected to a wind turbine to supply 100% green electricity, any adverse feedback or reaction to the wind turbine, particularly its generator, is prevented by the switching device with the power resistor during a bypass. The systemic inertia on the generator side is thus decoupled. The electrolysis system is thus designed to allow tracking and adjustment on the generator side—for example, when directly connected to a wind turbine—via power control in accordance with the inherent control times.

[0021] In a particularly preferred embodiment, the electrolysis plant comprises at least two electrolysis modules connected in series, each having a plurality of electrolysis cells connected in series. The plant concept with the protective circuit provided by the integrated DC-capable switching device can therefore be expanded module by module. In this way, a plurality of electrolysis modules can advantageously be combined to form one electrolysis plant, it being possible to use the switchable power resistor as needed and in particular on a module by module basis. This makes high-performance electrolysis plants possible on an industrial scale. These are specially designed and prepared for temporary overloads on the generator side. A particularly high level of operating flexibility is achieved while maintaining plant reliability.

[0022] Preferably, the parallel-connected switching device, when closed, bypasses an electrolysis module. In a typically modular design of an electrolysis stack or electrolyzer comprising several series-connected electrolysis modules, it is highly advantageous if the switching device is configured to bypass a respective electrolysis module. Thus, if necessary, individual modules can be adapted and bridged, and a respective current path via the power resistor can be activated.

[0023] In this case, a bridging of several electrolysis modules is preferably effected in an electrolysis system by the switching device in the closed state. The electrolysis system is therefore advantageously set up so that a plurality of respective current paths can be activated for bridging a plurality of respective electrolysis modules. The power resistor or the respective power resistors in a bridging current path are dimensioned according to the power loss to be expected in the current path in the event of a failure or shutdown. For example, in an electrolysis stack or an electrolyzer comprising five electrolysis modules connected in series, the failure of an electrolysis module leads to a 20% lower power consumption on the electrolysis side. Accordingly, when bridging modules, the power resistor must be designed for the nominal power of an electrolysis module or, in the case of only temporary loading, well below the nominal power.The power resistor is designed so that it can be overloaded for a short time and is therefore particularly suitable for systems with short peak currents. In an electrolyzer, the individual electrolysis cells are typically stacked in an axial direction to form an electrolysis module comprising a large number of individual electrolysis cells and installed to form the module or electrolysis module. An electrolyzer as a functional unit of an electrolysis system usually has a plurality of electrolysis modules which together form a so-called electrolysis stack or simply "stack". For example, 50 electrolysis cells can be stacked axially to form a module and in turn 5 modules can be stacked in the axial direction to form a stack, so that such an electrolysis stack can therefore comprise, for example, 250 cells in an overall axial assembly.An electrolysis plant can have several electrolysis stacks or electrolyzers connected in parallel.

[0024] In a particularly preferred embodiment of the electrolysis system, the switching device comprises a mechanically closable switching element. The switching element is designed, in particular, as an electrically or electromagnetically controllable switch or contactor.

[0025] It is also possible for a switching device to provide a combination of a plurality of switching elements, in particular a combination of two switching elements, wherein the switching elements are preferably designed for staggered switching over time.

[0026] In the combination, a first switching element connects the current path via the power resistor. A second switching element disconnects the main supply line for the provision of electrolysis current for the electrolysis system. The resistance value of the power resistor is dimensioned such that it approximately corresponds to the resistance in the electrolysis path that it switches off. This advantageously prevents a short circuit, and the current would otherwise not commutate into the parallel path with the power resistor or be evenly split at a maximum of approximately 50:50.

[0027] This can be achieved in an advantageous and cost-effective manner using only one switching element—similar to a changeover switch—with two current-carrying switching states, which energizes the electrolysis unit in one position and, in the second position, applies current to the power resistor during a bypass. This changeover switch solution is preferred when, for example, a faulty electrolysis module is to be switched off and, if possible, no switching operations should take place on the parallel units.

[0028] Alternatively, it would be possible to work with just one switching element, as described above. This would then preferably be designed and activated in such a way that, for example, the faulty electrolysis unit to be bypassed is shut down, and these load resistors in the remaining parallel units are then switched on for a certain period of time to absorb or absorb the current peak on the generator side.

[0029] It is advantageous to design the switching element as a contactor or switching contactor. This is an electrically or electromagnetically operated switch for high electrical outputs and is similar to a relay. The contactor has two switching positions and normally switches monostable without special precautions. An electromechanical design is particularly advantageous for switching on the required high outputs in a very short time via the power resistor. In this case, a magnetic coil is provided in the switching element. If a control current flows through the magnetic coil of the electromechanical contactor, the magnetic field draws the mechanical contacts into the active state. When there is no current, a spring restores the idle state and all contacts return to their original position.The connections for control current for the solenoid coil as well as the contacts for auxiliary circuits (if present) and currents to be switched are insulated from one another in the contactor: There is no conductive connection between the control and switching contacts. A contactor is essentially a relay with a much higher switching capacity. Typical loads start at around 500 watts up to several hundred kilowatts or several thousand kilowatts. By connecting several switching elements or contactors in parallel, correspondingly higher power levels can be switched through, which can be flexibly adapted to the power to be dissipated via the power resistor depending on the application. It is also possible to provide several power resistors with the appropriate power consumption that are connected in parallel.

[0030] In a particularly preferred embodiment of the electrolysis plant, the switching device has a thyristor as a switching element, so that when the thyristor is triggered, the current path through the power resistor can be activated.

[0031] A thyristor is particularly advantageous as a switching element for high power levels. The thyristor is a semiconductor component made up of four or more semiconductor layers with varying doping. Thyristors are switchable components, which means they are non-conductive in their initial state and can be switched on by a small current at the gate electrode. Once switched on, the thyristor remains conductive even without gate current. It is switched off when the current falls below a minimum, the so-called holding current. By current injection into the third layer (control at the gate), the thyristor can be triggered, i.e. switched to conduction. This closes the current path through the power resistor, i.e. activated. This requires a positive voltage between the anode and cathode and a minimum current through the middle depletion layer.The thyristor is extinguished, i.e. put into the blocking state, either when the holding current falls below the limit (which generally occurs when the voltage in the load circuit is switched off or reversed, or when the current in the load circuit passes through zero (e.g. in a rectifier), or when the polarity is reversed into the blocking direction. The speed of this process is limited by the so-called recovery time, which is necessary for the thyristor to regain its full control and blocking capability after the conduction phase has ended.

[0032] It is also possible for the switching device to contain a thyristor and an electromagnetically controlled switch as switching elements. Combinations are possible depending on the design of the electrolysis system, the application, and the specific load situation in the current path to be switched.

[0033] Alternatively, in the switching device, the switching element is preferably designed as a semiconductor component which has an insulated-gate bipolar transistor (IGBT), so that when the gate of the IGBT is opened, the current path through the power resistor can be activated.

[0034] An IGBT is a component often used in power electronics because it combines the advantages of a bipolar transistor such as good conduction behavior, high blocking voltage, robustness and the advantages of a field-effect transistor with almost power-free control. The striking advantages of IGBTs are their high voltage and current limits with operating voltages of up to 6500 V and currents of up to 3600 A at an output of up to 100 MW. This makes the IGBT ideal for use in the rectifier 15 for the operating range of the electrolyzer 3. Depending on the application, the use of an so-called IGCT, i.e. an integrated gate-commutated thyristor, is also conceivable. This has reduced wiring complexity, an increase in the maximum pulse frequencies for control and better switching times when connected in series, which is advantageous. IGCTs are used in high-power power converters.A single module typically switches a few kiloamperes at a typical blocking voltage of 4500 V.

[0035] In a preferred embodiment, the power resistor is adjustable or controllable. In this case, it is designed as an adjustable high-load resistor, for example with a high rated current of 10 to 30 amperes, in particular 15.0 - 20.0 amperes, and a rated power of 1.5 to 10.0 kilowatts, typically 2.0 kilowatts. In order to achieve higher power levels and higher rated currents when bridging, parallel connections of several power resistors to form an overall power resistor in the respective current path are flexibly provided if required. Depending on the electrolysis technology, the current to be dissipated in practice will typically be a few kiloamperes in an electrolysis system, i.e. around a factor of 100 higher than possibly specified or available for a single power resistor. This therefore also includes arrangements and circuits comprising a number of power resistors.If required and depending on the application, the power resistor can also be designed as a water bath or have a water bath. The current is then simply discharged through the water bath as needed.

[0036] Further preferably, the power resistor is designed for an overload, so that the power resistor can be operated with a current supply of up to 5 seconds, in particular up to 10 seconds, with a decaying current and excess power can be dissipated.

[0037] Since the load resistor regulates the current when the braking resistors are bypassed, they should by definition be designed for a continuous current, the rated current. However, the load resistor can also be overloaded for a short time and is therefore particularly suitable for systems with short peak currents, as is particularly advantageous in electrolysis systems. According to the load curve, for example, for a braking energy of 2 kW to be dissipated, which lasts for a maximum of 4 seconds, a power resistor with a maximum continuous load of between 800 and 1000 watts can be used. This is around 200% to 250% of the nominal value of the rated current or rated power. It is therefore advantageous to use an overload-capable power resistor with the highest possible limit voltage of up to 5000 volts and a high rated current.

[0038] The overload capacity of the power resistor is preferably 200% to 300%, in particular approximately 250%, with a decaying current of up to 5 seconds. This is a particularly interesting operating range in which on the power source side, particularly in the case of a wind turbine, a corresponding power regulation can be carried out on the feed-in side within the same time of approximately 5 seconds and any necessary tracking or reduction of the direct current power that can be supplied to the electrolysis system to a reduced value is carried out. This very advantageously achieves an adaptation which, when the electrolysis system is directly connected to a wind turbine, enables a high level of operational reliability.

[0039] In a particularly preferred embodiment of the electrolysis system, a further current path is provided in the switching device parallel to the current path through the switchable power resistor, which further current path has a further switching element and a diode in the forward direction and / or a low-ohmic resistor in series with the further switching element, wherein the further current path in a closed state has a lower electrical resistance than the electrolysis cells, so that when electrolysis cells are bridged, a polarity and a protective voltage for the electrolysis cells are maintained.

[0040] The additional current path, which can be switched on in parallel to the current path as needed, very advantageously detects an additional protection requirement and implements it in the switching device. This protective circuit in the additional current path is particularly advantageous and flexible for operating situations with electrolysis cells or multiple electrolysis modules in partial load operation. In the event of insufficient availability and feed-in of electrolysis power from an external power source, in particular electrolysis current, the establishment of an additional current path for the targeted and at the same time safe bridging of individual or multiple electrolysis cells for safe partial load operation is provided, thus advantageously extending the operating window of the electrolysis system.By means of this designed switching device, the electrolysis system is equipped to withstand the risk of overload in the event of electrolysis cells failing or shutting down, as well as in the event of an underload situation, for example due to reduced generation, or in the event that selected electrolysis cells or an electrolysis module are temporarily shut down, e.g., for planned maintenance purposes. This type of bridging essentially short-circuits these components. The energizable electrolysis cells or electrolysis modules can essentially be operated at nominal load, which is more efficient than running all electrolysis cells or electrolysis modules at partial load.

[0041] In this case, a protective circuit is proposed in the further current path which ensures a protective voltage as a bias with corresponding polarity of the bridged electrolysis cells or optionally of an entire electrolysis module in the electrolysis system. This protective circuit leads to a considerable improvement in operational reliability in partial load operation, since the protective bias across the diode and / or across the low-ohm resistor very effectively counteracts the risk of damaging fuel cell operation in the bridged electrolysis modules. Without this protective measure, the remaining product gases, hydrogen and oxygen, in the cathode compartment or anode compartment of the bridged electrolysis module would trigger a very detrimental fuel cell process due to the electrochemical potentials, which must be avoided. This risk is specifically countered with this advantageous further development of the electrolysis system.Furthermore, by avoiding undesired fuel cell operation—the reverse of electrolysis operation—the service life of the components involved in an electrolysis cell is significantly increased. This also enables service life-optimized operation.

[0042] In a preferred embodiment, the electrolysis system has a plurality of electrolysis cells connected in series, so that an electrolysis model is formed, so that when the further current path is activated by closing the further switching element, a bridging of the electrolysis module is effected, wherein a polarity and a protective voltage for the electrolysis module are maintained.

[0043] This allows for bridging of an entire electrolysis module via the current path and the switchable power resistor in the event of an overload situation, or alternatively, the additional current path can be activated by closing the additional switching element, thus achieving improved and particularly economical partial-load operation with effective protection of the short-circuited electrolysis module. When the additional current path is activated for partial-load operation, the current path with the power resistor is not energized; instead, this current path is bypassed.

[0044] For this purpose, the resistance of the further current path is preferably selected such that the resulting current distribution leads to the electrolysis module being sufficiently energized in the relevant current range in order to prevent undesired fuel cell operation.

[0045] In a particularly preferred embodiment, the electrolysis system has a connection unit with an input for connection to an external direct current source and an output which is connected to an electrolysis module, wherein the connection unit has a transformer to which an inverter is connected on the primary side and a rectifier is connected on the secondary side, so that a direct current can be supplied to the electrolysis modules.

[0046] With this advantageous development of the electrolysis system by means of the connection unit, an AC intermediate circuit is provided which ensures galvanic decoupling between an external DC source and the electrolysis system. In the AC intermediate circuit, the inverter converts the DC voltage from the external DC source into an AC voltage, which is coupled to the transformer on the primary side. A rectifier is connected on the secondary side of the transformer and converts the voltage back into a DC voltage, specifically at a desired and predetermined voltage or current level for the electrolysis. The connection unit is therefore particularly advantageously designed as an AC intermediate circuit and conceived for the provision of DC current from an external DC source to supply the electrolysis system with electrolysis current. This is achieved by direct coupling or.Direct connection of the input to an external DC power source. A wind turbine or a photovoltaic system can be advantageously connected to the electrolysis system as an external DC power source. These systems can be designed to operate independently of the grid in so-called island operation, advantageous for both offshore and onshore applications.

[0047] The external DC power source can be connected directly via the input of the connection unit, thus providing a DC power supply to the electrolysis system. Thanks to the galvanic isolation and decoupling via the AC intermediate circuit, the connection unit also reliably prevents damaging stray currents and thus also earth fault currents and unwanted voltage losses in the electrolysis system. At the same time, a simple and reliable direct connection of the electrolysis system to a renewable energy generation system, in particular to a wind turbine, is achievable, thus promoting off-grid operation.

[0048] In a preferred embodiment, the rectifier can be adjustable and / or designed as a three-phase rectifier, in particular as a B6 bridge rectifier.

[0049] The controllability of the rectifier(s), which are advantageously designed as three-phase rectifiers or as B6 bridge rectifiers, makes it possible to adjust the total current generated by the rectifier(s) and thus, for example, to control the operation of an electrolyzer or several electrolyzers connected to the connection unit.

[0050] It is preferably provided that the alternating current frequency in the connection unit can be set to a predetermined value. By designing the circuit arrangement as an AC intermediate circuit, this does not have to be connected to a public grid, and one is therefore largely free to choose the alternating current frequency in the transformer. A high-frequency transformer is advantageously provided here so that deviations from the usual frequencies in public grids can be made if necessary. For example, the connection unit can be designed for an alternating current frequency in a transformer designed as a high-frequency transformer of 500 Hz to 50 kHz, in particular of 10 kHz to 30 kHz. However, a corresponding design and application of the transformer for operation at grid frequency are still possible.

[0051] In a preferred embodiment of the electrolysis plant, the connection unit is designed for an alternating current frequency that is higher than the usual grid frequencies of 50 Hz to 60 Hz in public grids. It is advisable to use high frequencies here because this reduces the size and weight of the transformer and also the amount of material used. This aspect is particularly advantageous when the electrolysis plant is connected directly to a wind turbine. Due to the more compact design and lower weight at high operating frequencies, the transformer can be accommodated, for example, in the nacelle of the wind turbine or in the base of the wind turbine tower. The entire circuit arrangement can also be arranged there. This means that the electrolysis plant can be located in the immediate vicinity of the wind turbine, for example, allowing short cable routes for the connection.

[0052] In a particularly preferred embodiment, the circuit arrangement is designed for an alternating current frequency of 500 Hz to 50 kHz, in particular from 10 kHz to 30 kHz. This frequency relates to the frequency of the inverter and the rectifier, which are connected to the transformer. In order to exploit the space and cost advantages, a high-frequency intermediate-circuit transformer is provided as the transformer.

[0053] The transformer preferably has a transformation ratio of less than 10, in particular between 1.5 and 7.5. This can be flexibly adapted to the requirements of the electrolyzer or the desired voltage level for the electrolysis process, so that larger transformation ratios are also possible depending on the application.

[0054] The ratio of the number of turns, or the primary and secondary voltages, is also referred to as the transformation ratio. By selecting the appropriate transformation ratio, i.e., the number of turns, the transformer can both step up and step down alternating voltages. This advantageously allows for adaptation with regard to electrolysis.

[0055] A voltage swing of more than 10 is also possible, depending on the application and design of the electrolysis plant and especially the transformer used. Known electrolysis plants are typically operated with a maximum of 1500 V DC, which still corresponds to a low voltage range. However, more than 15 kV DC can be provided and available for connection to a power generation plant. Therefore, an upper limit for the voltage swing of up to 70 can preferably be selected. The available connection voltage can then be up to around 70 kV - for example if the electrolysis plant were to be operated at just 1000 V DC. Currently available wind turbines, for example, can produce output voltages of 66 kV AC.

[0056] A further aspect of the invention relates to a method for operating an electrolysis plant with high operational flexibility and simultaneous plant safety.

[0057] The associated object is achieved according to the invention by a method for operating an electrolysis system for decomposing water into hydrogen and oxygen, in which an electrolysis system according to the invention is provided, in which an electrolysis current is supplied to at least two electrolysis modules in a standard operation, hydrogen and oxygen being generated in the electrolysis module, in which in the event of a failure of one of the electrolysis modules a bridging operation is initiated, the current path being activated by the power resistor so that the failed electrolysis module is bridged, and in which the excess power is absorbed by the power resistor.

[0058] The method immediately activates a protective procedure on the electrolysis plant side, particularly in the event of an unforeseen failure or emergency shutdown of one or more electrolysis modules, or of part of an electrolysis stack or an electrolyzer comprising one or more electrolysis modules, or even of the entire electrolysis plant. Depending on the reduction in power consumption, the failed electrolysis module or several failed electrolysis modules are taken out of operation or de-energized by instantly bridging them. This protects the entire electrolysis plant from overload. An external power control on the generator side, for example on the part of a power generator that is sluggish for mechanical reasons, cannot usually regulate the power output quickly enough, i.e. reduce it, to adapt it to and track the reduced power consumption of the electrolysis plant.An example of this is a wind turbine that, in the event of a 20% power loss in the electrolyzer, requires a few seconds to adjust the rotor blades' pitch accordingly. Depending on the previous operating point, the excess power generated during this time cannot be distributed among the electrolysis modules that are still running, in order to prevent excessively high current densities from being generated there.

[0059] In the bridging operation, the excess energy is therefore advantageously dissipated in the method of the invention by activating the current path through the power resistor in the electrolysis plant, in particular until the power generation plant has adjusted to the new situation, if necessary.

[0060] Preferably, in the method, the supplied electrical power is adapted to the reduced input power of the electrolysis system, whereby the electrolysis current is reduced and a time-decaying current intensity is brought about via the power resistor.

[0061] The electrical power supplied is preferably fed in by a wind turbine to which the electrolysis plant is connected, whereby in bridging operation the angle of attack of the rotor blades is adapted to the power input of the electrolysis plant.

[0062] More preferably, the supplied electrolysis current is adapted to the reduced power input of the electrolysis system within a maximum of 10 seconds, in particular within a maximum of 5 seconds. In the case of a wind turbine, typically up to 5 seconds is particularly advantageous for adapting and completing the power adjustment of the output power to the power input of the electrolysis system. At the same time, during this time, a decaying high current intensity can be passed through the overload-capable power resistor, so that in bridging operation, an advantageous adaptation of the output power to the power input is achieved and, at the same time, effective overload protection of the electrolysis system is provided.

[0063] A further aspect of the invention relates to a plant network comprising an electrolysis plant which has a high degree of operational flexibility while at the same time ensuring operational reliability of the plant network.

[0064] The associated object is achieved according to the invention by a system combination comprising an electrolysis system and a wind energy plant, wherein an output is provided for providing direct current, wherein the output is connected to an input of the electrolysis system.

[0065] In this case, the system combination according to the invention is to be understood functionally in such a way that the alternating voltage originally generated by the wind turbine at the generator is in any case rectified, i.e. is rectified in a rectifier for use and connection to an electrolysis system. Depending on the technical design of the system combination, the output of the rectifier for providing direct current can be arranged spatially within the electrolysis system, for example in a container of the electrolysis system or a container or housing of an electrolyzer. The wind turbine itself then preferably only outputs an AC voltage, which is accordingly rectified for electrolysis purposes. The output for providing direct current can be formed by the wind turbine itself, which has a rectifier or to which a rectifier is assigned.The rectifier can also be assigned to the electrolysis system.

[0066] This makes it possible to operate the plant in an island grid independent of the public grid and to use electricity exclusively from one wind turbine for electrolysis, so that 100% green hydrogen can be produced.

[0067] In this case, the wind turbine preferably further comprises a rectifier which is connected on the DC side to the input of the electrolysis plant or is electrically connected to the input. The rectifier converts the original alternating current from a generator of the wind turbine into direct current and at the same time advantageously provides the desired input DC voltage level for connection to the electrolysis plant. In an alternative embodiment, the electrolysis plant can also comprise the rectifier, so that alternating current from the wind turbine is fed in. The rectification in the application of an advantageous direct connection of a wind turbine to an electrolysis plant is to be understood functionally.

[0068] In an alternative embodiment, it is preferably also possible for the renewable energy system in the system network to be a photovoltaic system. A PV system already provides direct current during operation. However, it can then preferably be provided that the photovoltaic system in the system network has a DC / DC converter or DC / DC converter, the output of which is connected to the input of the electrolysis system. Particularly preferably, the renewable energy system in the system network is a wind turbine.

[0069] Advantages and advantageous embodiments of the electrolysis plant of the invention are to be regarded as advantages and advantageous embodiments of the method for operating an electrolysis plant and advantages and advantageous embodiments of the plant network and vice versa.

[0070] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the single figures can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0071] Examples of the invention are explained in more detail with reference to the accompanying drawings. These show schematically and in a highly simplified manner:

[0072] FIG 1 shows a system network with an electrolysis system comprising several electrolyzers and with a wind turbine;

[0073] FIG 2 shows a section of an electrolysis plant with an electrolyzer and several direct current switching devices.

[0074] The same reference symbols have the same meaning in the figures.

[0075] FIG 1 shows a system network 100 according to the invention. The system network 100 comprises an electrolysis system 1 and a wind turbine 31 connected to the electrolysis system 1 as a renewable energy system (RE system) and source of green electricity. The electrolysis system 1 has three electrolyzers 35A, 35B, 35C connected in parallel and a connection unit 19 which is electrically connected to the electrolyzers 35A, 35B, 35C. The connection unit 19 serves to supply the electrolyzers 35A, 35B, 35C with electrolysis current. The connection unit 19 is connected to the electrolyzers 35A, 35B, 35C via a respective output 23. Furthermore, the connection unit 19 has an input 21, via which a direct current can be supplied to the electrolysis system 1, in particular to the electrolyzers 35A, 35B, 35C. The direct current is supplied from a direct current source via the connection unit 19.For this purpose, the connection unit 19 has an inverter 27, a transformer 25 and a rectifier 29. A respective rectifier 29 is connected to the electrolyzers 35A, 35B, 35C, so that a respective rectifier 29 supplies one of the electrolyzers 35A, 35B, 35C with a direct current for the electrolysis. The connection unit 19 thus provides an AC intermediate circuit in the electrolysis system 1, by means of which the input 21 is galvanically decoupled from the output 23. The inverter 27 is connected to the transformer 25 on the primary side. The rectifier 23 is connected to the transformer 25 on the secondary side. The electrolyzer 35A, 35B, 35C is supplied with a direct current, the electrolysis current, via the rectifier 23 of the connection unit 19.The electrolyzers 35A, 35B, 35C can be designed as a PEM electrolyzer, as an AEM electrolyzer (AEM: anion-exchange-membrane) or as an alkaline electrolyzer.

[0076] To supply direct current for the electrolysis process, the electrolysis plant 1 is connected directly to the wind turbine 31. The connection is made directly via the input 21 of the connection unit 19, which is designed to receive and transmit direct current to the inverter 27. The wind turbine 31 first generates alternating current in a generator of the wind turbine 31. In order to be able to transmit direct current to the electrolysis plant 1, a rectifier 33 is provided, so that the connection is made via this rectifier 33, the rectifier 33 advantageously being an electrical power component of the wind turbine 33. In the exemplary embodiment shown, each of the electrolyzers 35A, 35B, 35C comprises a plurality of electrolysis modules 3A, 3B, which are each connected in series.For example, one or more electrolysis modules 3A, 3B can be connected in series to form a respective electrolyzer 35A, 35B, 35C. Each of the electrolysis modules 3A, 3B has a plurality, in particular a multiplicity, of electrolysis cells 5, which are stacked in an axial direction and are both electrically contacted and fluidically connected to one another, so that reactant water can be supplied and the product gas streams can be discharged for further use. For example, fifty electrolysis cells 5 can be installed to form one electrolysis module 3A, 3B, so that two hundred and fifty or more electrolysis cells 5 are installed in one electrolyzer 35A, 35B, 35C. An electrolyzer 35A, 35B, 35C configured in this way, comprising a plurality of electrolysis modules 3A, 3B, is also referred to as an electrolysis stack, which can be regarded as a functional unit in an electrolysis plant 1.In the design of an electrolyzer 35A as an alkaline electrolyzer, it is possible that only one electrolysis module 3A is provided due to the high performance of alkaline electrolyzers.

[0077] The electrolysis module 3A comprises a DC-capable switching device 6 which is electrically connected in parallel. The switching device 6 has a switchable power resistor 7. As a result, when the switching device 6 is closed, a current path through the power resistor 7 can be activated, whereby a number of electrolysis cells 5 of the electrolysis module 3A are bridged and excess power can be dissipated through the power resistor. In the present case, the electrolysis module 3A can be bridged and accordingly all electrolysis cells 5 of the electrolysis module 3A. It is also possible for all electrolysis modules 3A, 3B in an electrolyzer 35A, 35B, 35C to be provided with the switching device 6, or for the switching device 6 to be designed such that individual or multiple electrolysis cells 5 can be bridged.Combinations are also possible, so that bridging current paths can be closed individually and design-specifically for an electrolysis system 1 at the level of the electrolysis cell 5, the electrolysis modules 3A, 3B, or at the level of one of the electrolyzers 35A, 35B, 35C. Various configurations for the switching device 6 are possible.

[0078] In the electrolyzer 35A, for example, the switching device 6 has a mechanically closable switching element 9A, which is designed as an electromagnetically controllable switch with a short switching time in the range of only a few milliseconds, in particular between 2 ms and 10 ms, for example 4 ms. In the electrolyzer 35A, the electrolysis module 3A can be completely bridged when the switching element 9A is closed. In the electrolyzer 35B connected in parallel to the electrolyzer 35A, the switching device 6 has a thyristor 11 as the switching element 9B. The thyristor 11 is designed as a power component for high switching currents and has short switching times of only a few milliseconds, in particular of approximately 3 ms, so that the electrolysis module 3B can be bridged in a short time when the thyristor 11 is triggered.In the electrolyzer 35C, a circuit is selected in which the switching device 6 bridges all of the electrolysis modules 3A, 3B and thus the entire electrolyzer 35C. In this case, the two supply lines at the positive pole and the negative pole can be bridged via the switching device 6 directly at the output 23 of the rectifier 29, i.e., can be closed to form a short circuit if necessary. For illustrative purposes only, FIG. 1 shows, by way of example, both an embodiment of the switching element 9B with a thyristor 11 and a power resistor 7 and also as a switching element 9A with an electromagnetically controllable switch or contactor. Both embodiments are possible individually or in combination in the switching device 6.In this case, it can preferably be provided that - not shown in detail in FIG. 1 - depending on the bridging situation for a desired complete bridging, the switching contact is designed such that a first electrical contact goes to the electrolyzer 35C and a second electrical contact goes to the power resistor 7. Thus, a complete bridging of the electrolyzer 35C can be achieved.

[0079] The power resistor 7 is designed for overload, and its resistance value is adjustable or regulated, allowing adaptation to the respective application situation. The overload design is such that the power resistor 7 can be operated with a current supply of up to five seconds, and in particular up to 10 seconds, with a decaying load current. This even allows short-term operation above the rated current, and a very high power can be dissipated via the power resistor 7 during bridging.

[0080] During operation of the system combination 100, green electricity is generated in the wind turbine 31. The alternating current generated in the generator is converted into direct current in the rectifier 33. As a result, the wind turbine 31 provides a direct current source, so that a direct current is fed directly into the input 21 of the electrolysis system 1 via the output of the rectifier 33 and is initially passed on to the connection unit 19. In the connection unit 19, the circuits are galvanically isolated by the transformer 25, so that possible stray currents and earth faults in the system combination 100 that could damage the electrolysis cells 5 are effectively suppressed or even avoided. First, a conversion to an alternating voltage takes place for the connection on the primary side of the transformer 25.The transformer 25 transforms this alternating voltage so that a desired voltage level is achieved on the secondary side according to the set transformation ratio. The rectifier 29 provides an interference-free or hum-free electrolysis direct voltage at output 23. This voltage is used to operate the electrolyzers 35A, 35B, 35C in the electrolysis plant 1 in a stable manner, with the reactant water being split into hydrogen and oxygen. Ground loops are effectively avoided by the galvanic decoupling. The advantageous direct DC connection of the electrolysis plant 1 to the wind turbine 31 also enables grid-independent island operation and decentralized generation of green electricity onshore or offshore, depending on the application. The proportion of green hydrogen generated is 100%.

[0081] In principle, a DC connection of the electrolysis system 1 to a photovoltaic system or to another renewable energy system, for example a so-called CSP system (Concentrated Solar Power) or to an energy storage device charged with renewable energies in the system network 100 is also possible. For operation in a system network 100 with a direct connection to a wind turbine 31, the electrolysis system 1 is, however, advantageously configured and can be operated safely and flexibly, particularly due to the DC-capable switching device 6. During operation of the electrolysis system 1, reactant water is fed to the electrolysis cells 5 via the electrolysis modules 3A, 3B and decomposed into hydrogen and oxygen.

[0082] FIG. 2 shows a section of an electrolysis system 1 with an electrolyzer 35 having four electrolysis modules 3A, 3B, 3C, 3D and three direct-current-capable switching devices 6. Compared to the switching device 6 shown in FIG. 2, the switching device 6 is further developed for flexible operation of the electrolysis system 1, in particular for partial-load operation of an electrolyzer 35 of the electrolysis system 1.

[0083] Each of the electrolysis modules 3A, 3B, 3C, 3D comprises a plurality of axially stacked electrolysis cells 5. The electrolysis cells 5 are arranged between two pressure plates 37. The pressure plates 37 press the electrolysis cells 5, which in particular comprise a proton exchange membrane, intimately and firmly together, so that electrical contact is made between adjacent electrolysis cells 5 and a fluid-tight cell stack is created. The pressure plates 37, which are arranged at the axial end - i.e. at the edge - of the electrolyzer 35, are electrically connected to a direct current source via an electrical connection 39. Three switching devices 6 are arranged in parallel with the electrolysis modules 3B, 3C and 3D of the electrolyzer 35. The switching devices 6 are arranged electrically parallel to the electrolysis modules 5.In this example, a respective electrolysis module 3B, 3C, 3D can be electrically bridged by corresponding switching devices 6. Each switching device 6 is electrically connected to the pressure plates 37 that delimit the corresponding electrolysis module 3B, 3C, 3D.

[0084] In this exemplary embodiment, in the switching state shown, electrolysis, in particular the decomposition of water into hydrogen and oxygen, takes place in all electrolysis modules 3A, 3B, 3C, 3D of the electrolyzer 35, since all switching devices 6 are open. Electrolysis is carried out using a direct current. The switching devices 6 are each designed as direct current-capable switching devices 6, so that various current paths are available for bridging.

[0085] In comparison to the exemplary embodiment in FIG. 1, in the electrolysis system 1 in FIG. 2, a further current path is set up in the switching device 6 parallel to the current path through the switchable power resistor 7. This further current path has a further switching element 13 and a diode 15 in the forward direction and / or a low-ohmic resistor 17 in series with the further switching element 13. In a closed state, the further current path has a lower electrical resistance than the electrolysis cells 5, so that when electrolysis cells 5 are bridged, a polarity and a protective voltage for the electrolysis cells 5 are maintained. Various circuit implementations and combinations for the further current path are possible.For example, the electrolysis module 3B and 3C can be bridged via a respective additional current path, wherein the current path can only be closed in the forward direction via the corresponding diode 13 via the additional switching element 13. The electrolysis module 3D can be bridged via a low-ohm resistor 17 when the additional switching element 13 is closed, whereby the corresponding additional current path is closed. The diode 15 is connected in the forward direction in series with another switching element 13. Advantageously, the polarity and a protective voltage for the electrolysis cells 5 or the electrolysis modules 3B, 3C, 3D are maintained when the additional current path is closed. It is also possible to provide a combination of diode 13 and low-ohm resistor 17 in an additional current path, a possibly advantageous circuit variant which is not specifically shown in FIG 2.

[0086] The electrolysis system 1 has a large number of electrolysis cells 5 connected in series, so that electrolysis modules 3A, 3B, 3C, 3D are formed. When the further current path is activated by closing the further switching element 13, the corresponding electrolysis module 3B, 3C, 3D is bypassed, wherein a polarity and a protective voltage for the bypassed electrolysis module 3B, 3C, 3D are maintained. This is particularly advantageous for partial load operation of the electrolysis system 1, which is improved as a result. Thus, depending on requirements, individual or multiple electrolysis cells 5, one or more electrolysis modules 35 can be short-circuited by means of the further current path provided by the switching device 6 and thus produce no hydrogen, i.e. can be taken out of operation. This should only be done if damaging fuel cell operation - e.g.by using a pole rectifier, which advantageously supplies each cell individually. Thus, in conjunction with the current path provided in parallel in the switching device 6 through the power resistor 7, both overload operation, for example in the case of a high wind power feed-in, and partial load operation of the electrolysis system 1 are possible with great operational flexibility and operational reliability. Any necessary emergency shutdown of electrolysis modules or planned shutdown, e.g. for service purposes, with temporary shutdown can also be carried out safely using the bridging operation.

[0087] The electrolysis plant 1 is operated at full load in the switching state of the switching device 6 shown in FIG 2. If the electrical power in the grid decreases, in particular due to little wind and little sun, at least one switching device 6 can be closed. The electrolysis modules 3B, 3C and 3D can therefore be switched off in a modular manner or bridged via the further current path. In the example in FIG 2, the electrolysis module 3A is always operated when the electrolysis plant 1 is in operation. However, a bridging current path can also be provided by a switching device 6 connected to the electrolysis module 3A. If individual electrolysis modules 3B, 3C, 3D are switched off or bridged during operation depending on the available electrical feed-in power, the electrolysis module 3A can continue to operate at full load with a constant power density.Advantageously, none of the electrolysis modules 3A, 3B, 3C, 3D or the electrolysis cells 5 is operated at partial load. It is particularly advantageous to bridge the electrolysis modules 3B, 3C, 3D one after the other. In particular, module 3B can be bridged first for a predetermined period of time. Subsequently, electrolysis module 3C or electrolysis module 3D can be bridged for a corresponding period of time. In this way, the electrolysis modules 3B, 3C, 3D are operated and loaded evenly. Bridging via the further current path prevents the electrolysis cells 5 from aging quickly. Furthermore, it is ensured that the product gas quality, in particular of the hydrogen, remains constantly high.At the same time, during operation, the supplied electrical power can also be flexibly adapted to a reduced power consumption of the electrolysis system 1, whereby the electrolysis current is reduced and a temporally decaying current intensity is brought about via the power resistor 7 by selectively closing a current path via the power resistor 7. The further, parallel current path via the low-ohmic resistor 17 then remains open.

[0088] 2, the electrolyzer 35 has four electrolysis modules 3A, 3B, 3C, 3D. This is a simplified representation. It is also within the meaning of the invention for a larger number of electrolysis modules to be connected in series. It is also possible to arrange further staggered connections of the switching device 6 in order, on the one hand, to provide a sufficient number of switching devices 6 and, on the other hand, to prevent an excessive number of switching devices 6 and thus complexity. It is also very advantageous to integrate the electrolyzer 35 into a complex electrolysis system 1 with several corresponding electrolyzers 35A, 35B, 35C, as already explained in more detail in FIG 1. For this purpose, the electrical connection 39 in FIG 2 is connected to the output 23 of the rectifier 29 of the electrolysis system shown in FIG 1, so that the electrolyzer 35 is supplied with direct current.

[0089] 1, integration into an entire system network 100 comprising an electrolysis system 1 and a wind turbine 31 connected directly to the electrolysis system 1 is also very advantageously possible. For this purpose, the wind turbine 31 has an output for providing direct current, the output being connected to an input 21 of the electrolysis system 1. In the system network 100, the wind turbine 31 has a rectifier 33 which is connected on the direct current side to the input 21 of the electrolysis system 1. Alternatively, it is also possible for the required rectification of an alternating current originally generated in the generator by the wind turbine 31 to take place near the electrolysis system itself. This makes it possible for the rectifier 33 to be placed on the electrolysis system 1 or in the immediate vicinity thereof.Therefore, the rectifier 33 with the output for direct current for electrolysis can also be a component of the electrolysis system 1 itself or can be functionally considered as such in the structural design of the system network 100.

[0090] Although the invention has been illustrated and described in detail by means of preferred embodiments, the invention is not limited by the disclosed examples. Variations may be derived by those skilled in the art without departing from the scope of the invention as defined by the following claims.

Claims

Patent claims 1. Electrolysis system (1) comprising an electrolysis module (3A, 3B) , wherein the electrolysis module (3A, 3B) has a plurality of electrolysis cells (5) connected in series, and comprising an electrically parallel-connected DC-capable switching device (6) which has a switchable power resistor (7) such that in the closed state a current path through the power resistor (7) can be activated, so that bridging of electrolysis cells (5) is effected and excess power can be dissipated through the power resistor (7).

2. Electrolysis system (1) according to claim 1 comprising at least two electrolysis modules (3A, 3B) connected in series, each comprising a plurality of electrolysis cells (5) connected in series.

3. Electrolysis system (1) according to claim 2, in which a bridging of an electrolysis module (3A) is effected by the parallel connected switching device (6) in the closed state.

4. Electrolysis system (1) according to claim 2 or 3, in which the switching device (6) in the closed state causes a bridging of several electrolysis modules (3A, 3B).

5. Electrolysis system (1) according to one of the preceding claims, wherein the switching device (6) has a mechanically lockable switching element (9A), which is designed in particular as an electrically or electromagnetically controllable switch or contactor.

6. Electrolysis system (1) according to one of the preceding claims, wherein the switching device (6) has a thyristor (11) as a switching element (9B), such that when the thyristor (11) is triggered, the current path through the power resistor (7) can be activated.

7. Electrolysis system (1) according to one of the preceding claims, in which, in switching device (6), the switching element (9) is designed as a semiconductor component which has an insulated-gate bipolar transistor (IGBT) such that when the gate is opened, the current path through the power resistor (7) can be activated.

8. Electrolysis system (1) according to one of the preceding claims, wherein the power resistance (7) is adjustable or controllable.

9. Electrolysis system (1) according to one of the preceding claims, wherein the power resistor (7) is designed for an overload, so that the power resistor (7) can be operated with a current of up to 5 seconds, in particular up to 10 seconds, with a decaying current and excess power can be dissipated.

10. Electrolysis system (1) according to one of the preceding claims, wherein in the switching device (6) a further current path is provided in parallel to the current path through the switchable power resistor (7), which has a further switching element (13) as well as a diode (15) in the forward direction and / or a low-resistance resistor (17) in series with the further switching element (13) and which in a closed state has a lower electrical resistance than the electrolysis cells (5) so that when bridging electrolysis cells (5) a polarity and a protective voltage for the electrolysis cells (5) is maintained.

11. Electrolysis system (1) according to claim 10, comprising a plurality of electrolysis cells (5) connected in series, such that an electrolysis module (3A) is formed, such that when the further current path is activated by closing the further switching element (13), a bridging of the electrolysis module (3A) is effected, wherein a polarity and a The protective voltage for the electrolysis module (5) is maintained.

12. Electrolysis system (1) according to one of the preceding claims, comprising a connection unit (19) with an input (21) for connection to an external DC power source and with an output (23) which is connected to the electrolysis module (3A), wherein the connection unit (19) has a transformer (25) to which an inverter (27) is connected on the primary side and a rectifier (29) is connected on the secondary side, so that a DC current can be supplied to the electrolysis modules (3A, 3B).

13. Method for operating an electrolysis plant (1) for splitting water into hydrogen and oxygen, wherein an electrolysis plant (1) according to one of the preceding claims is provided, wherein in normal operation at least two electrolysis modules (3A, 3B) are supplied with an electrolysis current, wherein hydrogen and oxygen are produced in the electrolysis module (3A, 3B), wherein in the event of a failure of one of the electrolysis modules (3A, 3B) a bridging operation is initiated, wherein a current path through the power resistor (7) is activated so that the failed electrolysis module (3A, 3B) is bypassed, and wherein the excess power is absorbed by the power resistor (7).

14. Method according to claim 13, wherein the supplied electrical power is adapted to the reduced input power of the electrolysis system (1), the electrolysis current being reduced and a time-decreasing current intensity being effected via the power resistor (7).

15. Method according to claim 14, wherein the supplied electrical power is fed in from a wind turbine (31) to which the electrolysis plant (1) is connected, wherein in bridging operation the pitch angle of the rotor blades ter is adapted to the input power of the electrolysis system (1).

16. Method according to claim 13 or 14, wherein the supplied electrolysis current is adjusted to the reduced input power of the electrolysis system (1) within a maximum of 10 seconds, in particular within a maximum of 5 seconds.

17. Plant system (100) comprising an electrolysis plant (1) according to any one of claims 1 to 12, and a wind energy plant (31) , wherein an output is provided for supplying direct current, the output being connected to an input (21) of the electrolysis plant (1).

18. System assembly (100) according to claim 17, wherein the wind turbine has a rectifier (33) which is connected to the input (21) on the direct current side.

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