Electrolysis system

Abstract

The invention relates to an electrolysis system (10) comprising an electrolysis plant (1, 1A, 1B) and a power supply source (3) with a direct voltage output (7) and comprising a central supply line (5), wherein the central supply line (5) is connected to the direct voltage output (7) of the power supply source (3) such that a direct current can be fed to the central supply line (5), wherein a central DC high-performance strand designed for the direct voltage is provided, to which high-performance strand the electrolysis plant (1) is connected via the central supply line (5), wherein at least the power supply source (3) and the DC high-performance strand are designed as a network (17) insulated from ground. The invention also relates to the use of an insulated DC network (17) in an electrolysis system (1).

Description

[0001] Description

[0002] Electrolysis system

[0003] The invention relates to an electrolysis system comprising at least one electrolysis unit and a power supply source with a direct voltage output and a central supply line. The invention further relates to a use.

[0004] During electrolysis, redox reactions associated with material transformations can be forced by applying an electric current through suitable cell elements. A device for this purpose is called an electrolyzer and can be used to produce important basic materials in the chemical industry. The anode and cathode half-spaces are often separated by diaphragms (or membranes) which enable electrical conductivity (ion and / or proton exchange) but prevent material exchange. If liquid electrolytes are used in electrolyzers which are changed or consumed by the material transformation, these can be continuously renewed during the process by means of appropriate supply and discharge lines. The material transformation rates for given cell elements are generally subject to strict limits due to current density limitations.For large-scale use, the active cell element area must therefore be increased in order to increase the material conversion rates. This can be achieved by enlarging the cell elements or by operating a number of smaller cell elements at the same time. A technically sensible and frequently used method is to arrange many (identical) cell elements in a stack. The electrical connection of the cell elements in a stack is a series circuit, i.e. the anode of a cell element N is electrically connected to the cathode of cell element N+1 and the cathode of cell element N is electrically connected to the anode of cell element N1. The series connection also multiplies the low cell element voltage from a few volts to, for example, several hundred volts.

[0005] The hydraulic connection of the cell elements in a stack to supply fresh electrolyte, on the other hand, represents a parallel connection. The hydraulic connection of the cell elements in a stack creates additional and undesirable electrically conductive connections between all cell elements. When the stack of cell elements is operated, i.e. when an electrical voltage is applied or an electrical current is impressed from the first to the last cell element, an electrical working current flows through all cell elements. However, undesirable so-called stray electrical currents also flow on the various parallel current paths. These stray electrical currents lead to local current density increases close to the supply and discharge lines of the electrolyte, particularly in the first and last cell element in a stack. This can lead to premature aging and destruction of the membranes and to the failure of the entire stack.

[0006] DE 10 2020 206 341 A1 describes a method for corrosion protection of an electrolysis stack comprising multiple cell stacks or modules, as well as a corresponding electrolysis stack. The method is particularly suitable for reliable corrosion protection of a CO2 electrolysis system during standstill operation or for transport purposes of the electrolysis stack.

[0007] There is considerable commercial interest and development effort in the electrolytic production of hydrogen as a product of the electrochemical decomposition of water as a starting material on an industrial scale. Today, hydrogen is produced from water using processes such as proton exchange membrane (PEM) electrolysis, anion exchange membrane (AEM), or alkaline electrolysis. Electrolysis plants use electrical energy to produce hydrogen and oxygen from the supplied water. However, electrolysis plants based on alkaline electrolysis are also widely used.

[0008] 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 is above average, to generate valuable materials. One such valuable material could be hydrogen, which is produced by appropriate water electrolysis plants. Hydrogen can, for example, be used to produce so-called renewable energy gas (REG). REG is a combustible gas obtained from renewable sources using electrical energy.

[0009] One source of renewable energy is emerging from the increasing use of wind power. Large electrical outputs can be achieved, particularly with offshore wind turbines. However, the challenge is that large distances to consumers must be overcome. The energy must 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.

[0010] For these reasons, it is of particular economic interest to produce hydrogen directly at the point of energy generation, i.e. self-sufficiently 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 next to offshore wind turbines or in their immediate vicinity and to supply electricity directly with the generated wind power from a wind turbine and to operate the electrolysis system in a so-called island grid, which is independent of the public grid. Similar concepts have also been proposed for the mainland, whereby the electricity from onshore wind turbines or photovoltaic systems can be used at least in part for hydrogen production by directly connecting it to and feeding it into an electrolysis plant. In all of these self-sufficient applications, the electrolysis plant is part of a so-called island grid.In this electrolysis system, the electrolysis power is therefore not usually drawn from the public grid, but rather is supplied directly from a wind turbine or a PV system and fed into an electrolyzer in the electrolysis system via a supply line. The electrical energy generated by a wind turbine or a PV system can also be temporarily stored, for example, in a battery.

[0011] In contrast to the above-mentioned grid-controlled operation, island grid operation brings with it particular challenges and problems for the electrolysis system 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.

[0012] A particular problem to be taken into account here is that in an electrolysis system forming an integrated and self-sufficient island grid, the hydrogen electrolysis cells in the electrolysis plants connected to it generate corresponding stray electrical currents against earth, originating from the modules. These stray currents flow through the process water pipes and cause undesirable corrosion damage, even with sufficient insulation. Metal ions are released into the process water, which lead to irreversible damage or accelerated aging, particularly in the (PEM) membranes. In applications with both PEM electrolysis and alkaline electrolysis systems, these stray currents also reduce efficiency. The corrosion effects caused by stray currents must therefore be reduced as much as possible.

[0013] A reduction in stray electrical currents can be achieved, for example, by increasing the electrical resistance of the supply and discharge lines of the electrolytes. The previous solution involves lengthening the supply and discharge lines, which results in an increase in resistance while keeping the cross-sectional areas the same. However, the disadvantage of extending the lines is that they increase flow resistance and increase the material requirements for production, resulting in additional costs for installation. This is particularly problematic in remote locations where electrolysis plants are to be operated in an isolated grid, which is necessary or desired, i.e. in situations where connecting the electrolysis plant to the public grid would not be technically or economically possible, or would only be possible with considerable effort.

[0014] There is therefore an increased need to identify cost-effective ways of remedying the corrosion problem in order to improve the operating times of an electrolysis system when designed as an island network.

[0015] It is therefore the object of the invention to provide an electrolysis system which is designed for grid-independent operation, in particular in conjunction with a wind turbine or a solar system, and which has a low tendency to corrosion due to stray currents.

[0016] The object of the invention is achieved according to the invention by an electrolysis system comprising an electrolysis plant and a power supply source with a direct voltage output and comprising a central supply line, wherein the central supply line is connected to the direct voltage output of the power supply source, so that a direct current can be fed into the central supply line, wherein a central DC high-power strand designed for the direct voltage is provided, to which the electrolysis plant is connected via the central supply line, wherein the power supply source and the DC high-power strand are designed as components of a network insulated from earth.

[0017] The invention is based on the realization that in an electrolysis system connected to and supplied by the public AC grid, galvanic isolation is achieved with a transformer. The high-current electrolysis circuit can therefore be operated as an isolated grid or grounded at a point on the modules. The current is reduced simply by the fact that the electrolysis system's process technology does not provide a good electrical return conductor for the stray current, or that no ground loop is formed.

[0018] However, if electrolysis is to be operated in an isolated grid, for example, as an electrolysis system encompassing an offshore wind turbine, or onshore in remote areas, or as a solar power system, there is no AC grid available or nearby with which to operate a transformer for galvanic isolation. In these electrolysis plant installation situations, it would be uneconomical to specifically construct an AC intermediate circuit for a transformer. This would result in high additional production and operating costs. Therefore, this design and integration with the public power grid would be disadvantageous for the operation of an electrolysis system in an isolated grid.

[0019] In order to reduce the corrosion problem as efficiently and, above all, reliably as possible for an island grid, i.e., for grid-independent operation of an electrolysis system, in addition to the connection and transmission problems, the invention proposes the connection or integration of the electrolysis system to a specially set up central DC grid, which is designed to be unearthed. The central DC high-power line and all operating components connected to it form a so-called IT grid (IT: isole terre). The operating components forming the IT grid of the electrolysis system, such as the power generator or generator of the power supply source, the central supply line, and the electrolysis system, are all designed to be unearthed. The power supply source supplying the operating voltage is thus insulated from earth, i.e.Therefore, they are generally open or have a symmetrical and high-resistance earthing of the electrolysis system. During normal operation, there is therefore no low-resistance connection between the active parts of the IT network and earth or the protective conductor. The central DC high-power train is part of the overall IT network, whereby the IT network also includes the connected operating components of the electrolysis system, such as the power supply with the DC voltage output and the electrolysis system.

[0020] The concept of the invention is therefore about designing and operating the entire supply line, including the provided DC high-power line and the electrolysis system, as an IT network starting from the generator in order to avoid corrosive stray currents in the electrolysis system. Compared to grid-controlled operation, an AC intermediate circuit for galvanic decoupling can advantageously be dispensed with. The proposed electrolysis system thus realizes an isolated DC high-power line in an electrolysis system, enabling island grid operation when the electrolysis system is connected to a renewable energy system (RE system), such as a wind turbine or a photovoltaic system, to the central DC supply line. By eliminating the galvanic decoupling in the central high-power line, the solution is significantly more compact, lighter, and less expensive.In this case, the high-performance strand is located with all conductors at an electrically undefined potential against earth.

[0021] The DC grid formed by the isolated high-power train of the electrolysis system provides the specified high voltage and direct current power on the central supply line and acts as a transmission and distribution network for the direct current. The required transmission power is brought from the power source to the electrolysis plant via the central and ungrounded DC grid, thus making the electrolysis direct current available. The high voltage of the DC grid can be flexibly selected and adjusted to the required DC voltage connection value. At the same time, by avoiding or reducing stray electrical currents, particularly through the process technology of the electrolysis plant, the effects of corrosion are reduced, thus reducing maintenance and service costs. The electrolysis system of the invention further promotes an increase in operating time.

[0022] In a particularly preferred embodiment of the electrolysis system, this has an insulation monitor so that a minimum insulation resistance of the insulated network with respect to earth can be monitored and an insulation fault can be detected.

[0023] The insulation resistance is preferably high-impedance, so a high-impedance grounding system is designed to a specified minimum insulation resistance that must not be exceeded during operation. For this purpose, an insulation monitor is provided, which serves as a protective element and can monitor or display the insulation resistance, allowing alarm signals to be generated and appropriate measures to be taken.

[0024] The use of the isolated DC network makes the use of an insulation monitor as a protective element very advantageous.

[0025] In the event of a simple earth fault, the electrolysis system can continue to operate, especially the electrolyzers of the electrolysis plant, as there is no immediate hazard, which increases availability.

[0026] The insulation monitor monitors the insulation condition of the IT network, for example, local low-voltage networks without a functionally grounded neutral point. It signals when the insulation resistance falls below a minimum value. Previously, this was done by simply measuring the current or voltage against ground (symmetry deviation). Today, however, reliable detection of symmetrical insulation faults is also required, which also requires a test current. In the event of a fault, if the insulation fault current is exceeded, either a warning can be issued or the affected network outgoing circuit can be shut down.

[0027] In an advantageous embodiment, the insulation monitor is designed to be single-fault tolerant, meaning that a simple fault (single-pole earth fault) does not lead to a failure of the power supply or the corresponding outgoing circuit in the electrolysis system. This effectively protects the power supply or its outgoing circuits in the isolated IT DC voltage network.

[0028] A first ground fault is harmless in the IT network because the currents caused solely by the line capacitances and insulation resistances of the electrolysis system and its equipment are small. If the electrolysis system or the IT network it forms is small, the leakage currents in the event of a fault are so small that they are also harmless.

[0029] The insulation monitor advantageously detects earth faults, asymmetries, and insufficient insulation resistance in the IT network. It measures the symmetry of the voltages between both network poles and earth. If the leakage currents of the two network poles are equal, the symmetry is maintained. During operation, a high-voltage direct current with a specified high voltage significantly above the usual mains voltage is supplied to the terminals of the central supply line. This allows the electrolyzers of the electrolysis plant connected to the central DC bus line in the IT network to be individually supplied centrally via a direct current network.

[0030] Preferably, the power supply source therefore comprises a boost converter with a DC voltage output, by means of which a predetermined high voltage can be provided for the central supply line in the IT network.

[0031] A boost converter, also known as a step-up regulator or boost converter, is a type of DC-DC converter in electronics. The output voltage is always greater than the input voltage. This allows the DC voltage level at the DC output to be flexibly adjusted to the specified high voltage on the central DC supply line. The use of a boost converter can be particularly advantageous when connected to a PV generator as the power source, where the PV DC voltage is increased so that the specified high voltage for feeding into the central supply line is provided at the DC output.

[0032] Preferably, the boost converter is designed as a controllable boost converter with a DC voltage output, via which a predetermined high voltage can be provided on the central supply line in the IT network with an output voltage above 1.5 kV, in particular above 10 kV.

[0033] Particularly preferably, the controllable boost converter is designed such that a DC voltage can be provided at a high-voltage level of 10 kV to 110 kV, preferably 30 kV to 60 kV. In a preferred embodiment of the electrolysis system, the power supply source comprises a wind turbine as the power generator, to which a rectifier with a DC voltage output is connected. The DC voltage output is designed for the high voltage in the central DC high-power train.

[0034] In this way, a connection or a direct current connection and supply of the electrolysis plant from a wind turbine or photovoltaic system is achieved in the electrolysis system via the central DC supply line designed as an IT grid, whereby reliable island grid operation is particularly advantageously achieved. If the electrolysis system is operated in an island grid, there is no connection to the public power grid. Thus, the grid frequency of the public power grid of 50 Hz to 60 Hz is irrelevant for the design and operation of the electrical components in the DC-operated IT grid. In particular, costs for components and conversion losses, such as transformers, or for the necessary conversion, transmission, or re-rectification are eliminated.This could result in a more favorable cost position in the future, while simultaneously providing flexibility in operation or, for example, in the design and selection of connection components in the DC grid. Grid-frequency-independent operation is achieved with the central supply line designed as a DC bus, which is part of the isolated DC high-power train. Depending on the design of the DC high-power train as an IT grid, the DC output of the rectifier can already provide the high voltage directly. However, it is also possible to connect a controllable boost converter downstream of the rectifier, whose DC output supplies a predetermined high voltage to the DC high-power train.

[0035] The isolated DC grid therefore makes it possible to overcome greater distances and cable routes between the power generators and the electrolysis plants in a cost-effective manner, if necessary, without having to carry out further AC conversion for step-up and step-down transformation, which can only be achieved using several expensive transformers. However, smaller distances and compact electrolysis systems are more advantageous in an IT grid with regard to ensuring better symmetry of the grid poles and lower voltages due to the shorter spatial distances between the protective earthing of the housings of the equipment, such as the tower of the wind turbine and the process technology unit of the electrolysis plant. In particular, all conductive components which are not part of the operating circuit are earthed either individually or together, or the components are earthed if necessary.connected together with the protective earthing of the system If the network is small in size, the leakage currents in the event of a fault are so small that they are not dangerous, which is why a smaller spatial extent and compact installation of the DC high-power line is generally preferable.

[0036] Preferably, in the electrolysis system, an electrolysis plant is arranged at the base of the tower of a wind turbine and, as operating equipment in the IT network, is connected directly to the central direct current supply line. In particular in the case of remote onshore wind turbines, it is advantageous to connect an electrolysis plant in the vicinity of the wind turbine to the central insulated DC bus line of the insulated DC high-power string. If DC / DC converters are then preferably used, the supply line is designed and loaded with a high direct voltage, so that the use of materials, in particular copper and aluminum, is reduced and manufacturing costs are correspondingly lower.

[0037] Preferably, in the electrolysis system, the electrolysis plant comprises a number of electrolysis modules connected in series so that a module row is formed.

[0038] In an advantageous design, each of the electrolysis modules can be a physical and functional unit in which a large number of electrolysis cells are stacked. Thanks to the modular concept of the electrolysis system, a row of modules can be easily expanded into an electrolysis stack comprising several modules, for example, 5 to 10 modules per row.

[0039] Preferably, a switchable, electrically conductive earth connection with a predetermined earth resistance is provided in a module row, by means of which stray currents can be controlled.

[0040] This provides a protective earthing connection on the housing, which is attached to the housing of a module, for example, on the last module in a module row facing away from the electrical connection to the central insulated DC supply line. The protective earthing can also be implemented as a grounded structure on the housing of the power supply source, for example on the tower of a wind turbine. This also optionally enables two-point protective earthing in the electrolysis system, which offers advantages in conjunction with the insulation monitor. In addition, the switchable, electrically conductive earth connection makes it easy to discharge the isolated network, in particular the high-power DC string, for example for maintenance purposes.

[0041] This prevents residual stray currents and ground loops. The protective ground wire is preferably located on the last module in a row, with a defined resistance for the ground connection being adjustable. This is beneficial for controlling and minimizing damaging stray currents that occur in the process technology unit. However, the respective tap of the protective ground wire on a module in a row can be flexibly adjusted depending on the DC voltage and its polarity at the DC voltage output.

[0042] If, for example, the DC output of a rectifier used produces a DC voltage of +250 V and -250 V on both poles, it is advantageous to ground the device via the protective earth wire in the middle of the electrolysis series, where the voltage is almost 0 V anyway.

[0043] However, if the DC voltage output of a rectifier used, for example, outputs a DC voltage of +500 V and 0 V on both poles, then earthing via the protective earth wire is preferably carried out at the last module, since the voltage to earth there is then almost 0 V.

[0044] This additionally addresses a persistent stray current problem resulting from the hydraulic interconnection of the cell elements in a stack to supply fresh electrolyte, in combination with the IT network design of all equipment. The hydraulic interconnection of the cell elements in a stack creates additional and undesirable electrically conductive connections and stray currents between all cell elements, which lead to corrosion.

[0045] In a particularly preferred embodiment of the electrolysis system, it has at least two electrolysis systems which are connected in parallel with each other with respect to the central supply line, wherein one electrolysis system is connected to the central supply line via a respective connecting line.

[0046] The isolated DC network is therefore easily expandable, with additional electrolysis systems being able to be connected to and supplied with power from the central DC supply line. Depending on the required transmission power of the high-power DC train, it is also possible for two or more central supply lines to be present in the electrolysis system, to which each electrolysis system with its respective row of modules is connected. All rows of modules are then optionally earthed, in particular with a common protective earth. An electrolysis system has at least one row of modules; for example, two rows of modules can be connected in parallel in an electrolysis system. However, it is also possible for an electrolysis system to have just one row of modules, with numerous electrolysis modules electrically connected in series.

[0047] In the electrolysis system, the electrolysis plants are preferably connected in parallel with each other with respect to the central supply line, with each electrolysis plant being connected to the central supply line via a respective connecting line.

[0048] This leverages the advantages of the DC bus principle with its central and isolated direct current supply line, which allows for and also provides for an independent connection line for each electrolysis plant. In the electrolysis system, the central DC supply network can be flexibly expanded as needed and can be expanded to include additional electrolysis plants, possibly by adjusting the feed-in power of the power sources feeding into the isolated DC network with regard to the required power consumption for the operation of the electrolyzers.

[0049] In a preferred embodiment of the electrolysis system, the power supply source comprises a photovoltaic system as a power generator, the DC voltage output of which is designed for high voltage, wherein the DC voltage output is connected to the central supply line.

[0050] This allows the DC voltage level at the DC output to be flexibly adjusted to the specified high voltage on the central DC supply line. If necessary, boost converters, known as boost regulators, can be connected downstream of the PV generator to adjust the specified DC voltage level at the DC output. This is necessary if the DC output of the photovoltaic system itself does not provide a sufficiently high DC voltage level to feed into the central supply line.

[0051] With this design, an advantageous connection and supply of the electrolysis system with electricity generated from a photovoltaic system is achieved in the electrolysis system via the central and isolated DC grid on the supply line. This enables island grid operation based on photovoltaics, whereby corrosion effects caused by stray currents in the IT system are avoided or reduced. In a similar way and in line with the advantages of the connection of the electrolysis system to a wind turbine described above, operation in an island grid is independent of the public grid frequency, which allows particularly great design flexibility and self-sufficient application options away from the public power grid. The grid frequency of the public power grid of 50 Hz to 60 Hz is therefore irrelevant for the design and operation of the electrical components within the DC grid.In this case, a boost converter (DC / DC converter) may be required to increase the voltage of the PV generator as needed, ensuring the precise feed-in of direct current at the specified high voltage into the central supply line. A boost converter can also be used, if necessary, in a wind turbine as a power source downstream of the rectifier, in order to set a higher voltage level on the central supply line than that supplied by the rectifier at the DC voltage output.

[0052] Preferably, in the electrolysis system, the power supply source comprises a hydropower plant with a generator as the power generator, wherein a rectifier with a DC voltage output is connected to the generator. In this embodiment too, all operating components from the generator of the hydropower plant to the electrolysis plant are not earthed, i.e. they are designed as unearthed components of the IT network. In particular, the generator of the hydropower plant is not earthed. This makes it possible and advantageous for a hydropower plant to use a generator which outputs a higher frequency than the grid frequency directly at the generator output. The generator of the hydropower plant can therefore advantageously be designed to the frequency of the AC voltage input of the rectifier.Conversely, the rectifier can also be flexibly adapted and selected to the respective output frequency of the hydropower plant's generator. This reduced complexity and number of components can result in additional cost advantages when connected to a hydropower plant, whereby island grid operation of the electrolysis system is also achieved here. The number of poles and the rotation speed determine the output speed and thus the alternating current frequency of the generator. Generators for hydropower plants in particular are therefore available for a higher frequency alternating current output, so that a corresponding rectifier with an input designed for a higher frequency is used in the electrolysis system. This makes off-grid operation, i.e. without the need to take the grid frequency of the public grid into account, very advantageous.Frequency-adjusted coupling, such as using expensive and large transformers, is therefore unnecessary or even eliminated in the central DC grid. To save on cable runs, the electrolysis plant is located in the immediate vicinity of the generator and the DC output of the hydropower plant's rectifier and integrated into the IT grid via the high-power DC line. This means that the equipment is ungrounded and operated in isolation.

[0053] A further particularly preferred aspect of the invention relates to the use of an isolated DC network in the described electrolysis system, in which an electrolysis plant is connected to a central supply line for direct current, so that a central DC high-power train designed for direct voltage and insulated from earth is provided, wherein electrolysis direct current is fed into the electrolysis plant.

[0054] Therefore, the use is such that starting from the generator of the power supply source, the entire DC high-performance train up to the electrolysis plant with the electrolyzers including the modules and the process technology is operated in one and the same IT network.

[0055] When used, an output voltage above 1.5 kV, in particular above 10 kV, is preferably provided on the central supply line at the DC voltage output.

[0056] When used on the central supply line, a high voltage of 10 kV to 110 kV, preferably 30 kV to 60 kV, is particularly preferably provided at the DC voltage output.

[0057] Advantages and advantageous embodiments of the electrolysis system of the invention are to be regarded as advantages and advantageous embodiments of the corresponding use and vice versa.

[0058] Further advantages, features and details of the invention emerge from the following description of preferred embodiments and from the drawings. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the individual 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.

[0059] Embodiments of the invention are explained in more detail with reference to a drawing. These show schematically and in a highly simplified manner: FIG. 1 shows an electrolysis system designed for stand-alone grid operation, comprising an electrolysis plant and a wind turbine;

[0060] FIG 2 an electrolysis system designed for island grid operation with several rows of modules.

[0061] The same reference symbols have the same meaning in the figures.

[0062] FIG 1 shows an electrolysis system 10 according to the invention. The electrolysis system 10 comprises an electrolysis plant 1 and a power supply source 3. The power supply source 3 has a wind turbine 9 as the power generator, which serves as a renewable energy plant (RE plant) and source of green electricity. In the electrolysis system 10, the power supply source 3 is connected to the electrolysis plant 1 via a central supply line 5. The electrolysis plant 1 functionally comprises, in a simplified representation, an electrolysis unit 21 with a multiplicity of electrolysis cells (not shown in detail in FIG 1) stacked in the axial direction and connected electrically in series, as well as a process technology unit 23. In the electrolysis unit 21, the actual conversion reaction takes place in the electrolysis cells, i.e. the electrochemical decomposition of water as the reactant into hydrogen and oxygen as the products.The process technology unit 23 is used for the hydraulic connection of the cell elements of a stack to supply them with fresh electrolyte, here with the reactant water.

[0063] In contrast to the electrical connection, the hydraulic connection is implemented in parallel. The hydraulic connection of the cell elements in a stack therefore creates additional and undesirable electrically conductive connections between all cell elements. When the stack of cell elements is operated—that is, when an electrical voltage is applied or an electrical current is impressed from the first to the last cell element—an electrical working current flows through all cell elements.

[0064] The electrolysis system 10 is supplied with electrolysis direct current directly via a central supply line 5, which is subjected to a high direct voltage, thus the central supply line 5 forms a central DC bus line, by means of which a direct current for the electrolysis process can be supplied directly in the electrolysis system 10 of the electrolysis plant 1.

[0065] On the power supply source 3 side, a rectifier 11 having a DC voltage output 7 is connected downstream of the wind turbine 9 on the output side of a generator. Thus, an alternating current generated by the generator of the wind turbine 9 can be converted into a direct current at a predetermined high voltage at the DC voltage output 7 and fed into the central supply line 5. This creates a central DC network designed for high voltage. To couple the power generated by the wind turbine 9 and fed into the rectifier 11, no additional active components, such as transformers, are required when connecting the wind turbine 19 to the central supply line 5, thus implementing a particularly simple supply topology for the electrolysis.

[0066] The connection topology illustrated in FIG 1 provides a central DC high-power string in the electrolysis system 10, which is designed as a component of a network 17 insulated from earth, a so-called IT network ("isole terre"). The entire DC high-power string is floating. All operating equipment, i.e. the power supply source 3, in this case the generator of the wind turbine 9, the rectifier 11, the central DC supply line 5, up to the electrolysis system 1 comprising the electrolysis unit 21 and the process technology unit 23, are insulated from earth by a high insulation resistance and are components of the IT network 17. During operation of the electrolysis system 10, it is operated electrically insulated from earth. A protective earth 19 is attached to the conductive housing parts that are not part of the operating equipment.Thus, the tower of the wind turbine 9 can be designed as an earthed structure with a protective earth 19. Likewise, a protective earth 19 is provided on the side of the electrolysis plant 1, which is attached to the housing of the process technology unit 23 and is routed to earth as a grounding cable.

[0067] Consequently, no electrically conductive ground connection is created anywhere in the electrolysis system 10—except, if necessary, locally within the electrolysis plant itself to control any residual stray currents that may still exist. This ground connection can be switched on or controlled as needed. The ungrounded supply topology prevents ground loops and significantly reduces stray current to ground throughout the entire plant.

[0068] To monitor the high insulation resistance of the electrolysis system 10 to ground, an insulation monitor 25A is provided in the isolated grid 17 and is located near the wind turbine 9. Another insulation monitor 25B is placed near the electrolysis system 1. This arrangement of the insulation monitors 25A, 25B creates two spatially spaced grid poles that serve as measuring points. The insulation monitors 25A, 25B thus detect possible ground faults, asymmetries, and insufficient insulation resistances of the isolated grid 17. The insulation monitors 25A, 25B measure the symmetry of the voltages of both grid poles to ground. If the leakage currents of the two grid poles are equal, the symmetry is maintained. In order to also detect symmetrical insulation faults, a test signal can be fed asymmetrically into the network via the insulation monitor 25A, 25B; in the simple case, a DC voltage and the reaction of the network 17 can be measured.Thus, a minimum insulation resistance of the isolated network 17 is monitored, an insulation fault is detectable, and a ground fault can be localized. Symmetrical and high-resistance grounding can be realized simultaneously via the two network poles of the paired insulation monitors 25A, 25B.

[0069] By eliminating the need for galvanic decoupling in the isolated network 17, specifically for supplying the central supply line 5 with direct current, a more compact, easier-to-implement, and very cost-effective supply topology is created, with high protection against stray currents and the associated adverse corrosion effects. In this case, the DC high-power line in the isolated network 17, with all conductors of the equipment, is at an electrically undefined potential against earth. For the operationally reliable design of the isolated network 17, the use of insulation monitors 25A, 25B is provided as a protective element. In the event of a simple earth fault, the electrolysis system 10 can continue to operate, as there is no immediate danger to the electrolysis system 1, which increases availability. The IT network 17 is fail-safe.

[0070] The DC voltage level at the DC voltage output 7 of the rectifier 11 can be flexibly adapted to the respective requirements in the electrolysis system 10, with a high output voltage being selected as the predefined high voltage, which is preferably greater than 1.5 kV. When designing and constructing the central and isolated DC network 17 through the central supply line 5, the nominal voltages of the grid levels commonly used in energy transmission can also be used, for example, or these values ​​can serve as a reference for the DC voltage level. Electrical energy is transmitted via high-voltage lines at various medium-voltage and high-voltage grid levels with the following common nominal voltages: medium voltage of 3 kV, 6 kV, 10 kV, 15 kV, 20 kV, 30 kV, and high voltage of 60 kV, 110 kV.The central supply line 5 acts very advantageously as a central DC bus line, which directly enables a high-voltage direct current supply to an electrolysis system 1. For a particularly compact, i.e. spatially limited, design and for correspondingly small line spacings in the isolated network 17, the electrolysis system 1 in the electrolysis system 10 can be arranged at the base of the tower of the wind turbine 9 and, as an operating device in the IT network 17, can be connected directly to the central supply line 5 for direct current.

[0071] In another highly simplified embodiment of an electrolysis system 10 according to the invention, FIG. 2 shows an alternative connection of the DC high-power train to a central supply line 5. A wind turbine 9, which has a generator with an AC output, is again shown as the power supply source 3 for providing direct current for the electrolysis. The alternating current is converted to direct current in the rectifier 11.

[0072] On the electrolysis system 10 side, a system concept similar in principle to that shown in FIG. 1 is used, and corresponding system components are provided, with all operating equipment being constructed and electrically connected in an isolated network 17 operable with direct current, comprising the DC high-power train. The electrical connection and supply of the electrolysis systems 1A, 1B is effected via respective connecting lines 15A, 15B. The connecting lines 15A, 15B form a pair of lines, the central DC bus line and the DC high-power train of the central supply line 5. To achieve this, an electrolysis system 1A is connected to a DC voltage output 7, and correspondingly another electrolysis system 1B is connected via the connecting line 15B, parallel to the connecting line 15A, to another DC voltage output 7 of the rectifier 11.The electrolysis systems 1A, 1B each have a module row 13 comprising a number of electrolysis modules electrically connected in series. Each of the modules in a module row 13 has a plurality of electrolysis cells electrically connected in series.

[0073] A switchable earth connection 19 is provided locally as a protective earth on the housing parts of the equipment of the electrolysis system 1A, 1B. The equipment itself is at a potential with respect to earth. The local earth connection of the housing parts is attached as a conductive connection to the last module of each module row 13. The conductive earth connection 19 has a predetermined low earth resistance, which allows for the control and diversion of stray currents and can be optimized. For this purpose, the conductive earth connection 19 can have an adjustable resistance. This additional measure prevents or further reduces corrosion caused by any stray currents that may still be present through the advantageous island grid operation.

[0074] Alternatively, depending on the voltage value and polarity at the two DC voltage outputs 7 of the rectifier 11, the conductive earth connection 19 is made for a module within the module row 13. This can be flexibly adapted to the respective DC voltage level at the DC voltage output 7 and the electrical design of the system concept of the electrolysis system 10. Depending on the topology, the earthing can therefore also be made right in the middle of a module row 13. In the event that the rectifier 11 outputs a symmetrical voltage at the DC voltage output 7, for example values ​​of + / - 250 V at the DC voltage output 7, this would be advantageous and should be provided accordingly. This earth connection 19 can also be designed as a fixed connection, i.e., it does not necessarily have to be switchable, but can also be simply a fixed earth connection 19.

[0075] If necessary, a step-down converter (not shown in detail in FIGS. 1 and 2) can be connected to a connecting line 15A, 15B to adjust the voltage level. The step-down converter's input voltage corresponds to the high-voltage DC in the central DC network and the output voltage is designed for the respective operating voltage of the electrolysis system 1A, 1B. This enables an adapted operation of the electrolysis system 10 and sets up an individual DC voltage supply for each electrolysis system 1A, 1B. The use of, if necessary, several high-current DC / DC converters connected in parallel and designed in a modular manner in a connecting line 15A, 15B is particularly advantageous.

[0076] This enables industrial application and integration into an electrolysis system 10. The buck converter (step-down converter) converts an input voltage into a lower output voltage. It is also called a step-down converter.

[0077] Any number and any dimensioned electrolysis systems 1A, 1B with individually adaptable module rows 13 can thus be advantageously connected to one or more such central DC branch lines in the isolated DC network 17 or the connecting lines 15A, 15B by means of controllable DC / DC converters, in particular so-called controllable step-down converters or buck converters, and operated in an island network designed as an isolated DC network 17.

[0078] The DC / DC converters individually reduce the DC voltage to the desired values ​​without any significant conversion losses. Thus, in the electrolysis system 10, both the electrolysis power of the electrolysis systems 1A, 1B can be regulated and switched on and off as needed. Partial load capability or partial load control is achieved by regulating the electrolysis current. By coordinating the power controllers, islanding capability in the isolated DC network is ensured and expanded, which offers significant cost advantages for remote onshore or offshore systems. To provide higher electrolysis currents, several DC / DC converters can be connected in parallel if required and used in a connecting line 15A, 15B. A controllable buck converter with output voltage regulation via pulse-width modulation in continuous operation can be used as a step-down converter, for example.In this way, continuous operation of the step-down converter is achieved and controllability of the electrolysis current supplied to the electrolysis systems 1A, 1B.

[0079] In the electrolysis system 10, it is also possible for the power source 3 to comprise a photovoltaic system with a plurality of PV modules (not shown in detail). The photovoltaic system could, for example, be designed as a large-scale, high-performance open-field system—preferably in sunny regions—so that PV outputs of 10 MW and more are available for electrolysis. Other types of power generation from renewable sources are also possible.

[0080] The central DC high-power line of the isolated grid 17 largely eliminates the need for transformers compared to an AC-based power supply. The material and installation space requirements due to the weight and size of the transformers required for an AC grid connection can be significantly reduced by designing and specifying a central high-voltage direct current supply network. This reduces material usage, especially with regard to iron and copper, which in turn requires less installation space.

[0081] The electrolysis system 10 of the invention provides a particularly advantageous and cost-effective electrical connection of, preferably onshore, wind turbines to electrolysis systems in an isolated DC grid 17, which is generally set up within a limited space. This reduces potential voltage differences across the grid poles a priori. The insulation monitors 25A, 25B also provide precautions for safe IT grid operation, particularly with regard to second-order faults, i.e., to detect symmetrical insulation faults in both grid poles. A possible first ground fault is harmless in the IT grid 17 because the currents caused solely by line capacitances and insulation resistances of the equipment in the electrolysis system 10 are small. If the grid 17 is small in size, the leakage currents in the event of a fault are so small that they are also harmless.

Claims

Patent claims 1. Electrolysis system (10) comprising an electrolysis plant (1, 1A, 1B) and a power supply source (3) with a DC voltage output (7) and a central supply line (5), wherein the central supply line (5) is connected to the DC voltage output (7) of the power supply source (3) so that a DC current can be fed into the central supply line (5), wherein a central DC high-power train designed for the DC voltage is provided, to which the electrolysis plant (1) is connected via the central supply line (5), wherein the power supply source (3) and the DC high-power train are designed as components of a network (17) insulated from earth.

2. Electrolysis system (10) according to claim 1, wherein an insulation monitor (25A, 25B) is provided so that a minimum insulation resistance of the insulated network (17) with respect to earth can be monitored and an insulation fault can be detected.

3. Electrolysis system (10) according to claim 1 or 2, wherein the Power supply source (3) as a power generator has a wind energy plant (9) to which a rectifier (11) with a DC voltage output (7) is connected, wherein the DC voltage output (7) is connected to the high voltage in the central DC high-power train is designed.

4. Electrolysis system (1) according to claim 3, with an electrolysis plant (1) which is arranged at the base of the tower of the wind turbine (9) and is connected there directly to the central supply line (5).

5. Electrolysis system (10) according to one of the preceding claims, wherein the electrolysis plant (1, 1A, 1B) comprises a number of electrolysis modules connected in series so that a module row (13) is formed.

6. Electrolysis system (10) according to claim 5, wherein a switchable electrically conductive earth connection (19) with a predetermined earth resistance is provided in a module row (13), by means of which a control of stray currents can be carried out.

7. Electrolysis system (10) according to claim 5, wherein a permanently installed electrically conductive earth connection (19) with a predetermined earth resistance is provided in a module row (13), by means of which a control of stray currents can be carried out.

8. Electrolysis system (10) according to one of the preceding claims, comprising at least two electrolysis plants (1A, 1B) which are connected in parallel with one another with respect to the central supply line (5), wherein an electrolysis plant (1A, 1B) is connected to the central supply line (5) via a respective connecting line (15A, 15B).

9. Electrolysis system (10) according to one of the preceding claims, wherein the power supply source (3) comprises a photovoltaic system as a power generator with a DC voltage output (7), wherein the DC voltage output (7) is designed for the high voltage, and wherein the DC voltage output (7) is connected to the central supply line (5).

10. Electrolysis system (10) according to one of the preceding claims, wherein the power supply source (3) comprises a hydroelectric power plant with a generator as the power generator, wherein a rectifier (11) with a DC voltage output (7) is connected to the generator.

11. Use of an isolated DC network (17) in an electrolysis system (1) according to one of the preceding claims, in which an electrolysis plant (1, 1A, 1B) is connected to a central supply line (5) for direct current, so that a DC voltage-designed and isolating lated central DC high-power train is provided, whereby electrolysis direct current is fed into an electrolysis plant (1, 1A, 1B).

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