Offshore electrolysis system, and method for operating an offshore electrolysis system

Abstract

The invention relates to an offshore electrolysis system (100) comprising a wind turbine (1) having a tower (19), which is anchored to the seabed, and having an electrolysis plant (5), wherein the electrolysis plant (5) is connected to the wind turbine (1) by a supply line (11), and wherein the electrolysis plant (5) has an electrolyser (13) which is arranged in a container (9), wherein the container (9) is arranged below sea level (25). The invention also relates to a method for operating a corresponding offshore electrolysis system. In this method, water is broken down into hydrogen (H2) and oxygen by an electrolyser (13) of the electrolysis plant (5), which electrolyser is located below sea level (25), wherein the hydrogen (H2) produced is transported away via a product gas line (7).

Description

[0001] Description

[0002] Offshore electrolysis system and method for operating an offshore electrolysis system

[0003] The invention relates to an offshore electrolysis system and a method for operating an offshore electrolysis system.

[0004] An electrolysis plant is a device that uses electrical current to transform materials (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. Electrolysis plants are connected to power generation plants to supply direct current with electrolysis current, thus forming an electrolysis system. Typically, an electrolysis plant has several electrolyzers, so that with appropriate scaling, high electrolysis capacities for electrochemical material conversion can be achieved.

[0005] Hydrogen is now produced from water using methods such as proton exchange membrane (PEM) electrolysis or alkaline electrolysis. The electrolysis plants use electrical energy to produce hydrogen and oxygen from the supplied water. This process takes place in an electrolysis stack composed of several electrolysis cells. Water is introduced as the reactant into the electrolysis stack, which is under DC voltage. After passing through the electrolysis cells, two fluid streams emerge, 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., with above-average solar or wind power generation, to generate valuable materials. One such valuable material could be hydrogen, which is produced by water electrolysis plants. Hydrogen can, for example, be used to produce so-called renewable energy gas. A renewable energy 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 energy.

[0008] One source of renewable energy is wind power. Large electrical outputs can be achieved, particularly with offshore wind turbines located close to the coast. 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. 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. For this reason, it is of particular interest to produce the hydrogen directly at the site of energy generation, i.e. to position offshore electrolysis plants directly at offshore wind turbines or in their immediate vicinity.For example, offshore electrolysis systems are currently being discussed in which an electrolysis plant is set up directly on the platform of an offshore wind turbine. The wind turbine can be linked up with the electrolysis plant to form a largely self-sufficient, i.e. almost grid-independent, electrolysis system and can be specially equipped for offshore island operation. In the best case, these electrolysis systems can comprise a combination of a wind turbine and an electrolysis plant and can be built entirely without any auxiliary connection to a power grid and can be designed exclusively for island operation. This particularly applies to electrolysis systems set up far off the coast in order to avoid long connections to the public grid in the coastal region. The electrolysis plant with a number of electrolyzers is ideally located close to the renewable energy sources, i.e.of the wind turbine, in order to reduce or avoid both transformation and line losses. For this reason, offshore electrolysis systems with electrolysis plants are currently being developed with great intensity. These electrolysis plants are set up directly on a large supply platform with an offshore wind turbine. With this type of coupling, regardless of whether it is onshore or offshore, the plant can also be operated without a connection to the power grid. Without a grid connection, however, during calm periods, i.e. when there is no wind, no wind at all, or during planned maintenance work, neither power from the generator nor from the power grid is available.

[0009] If, on the other hand, renewable electricity is not available during very cold weather - for example because there is no wind or if the wind turbine has to be shut down for unforeseen maintenance - the heat energy to maintain the temperature in the electrolysis plant must be provided safely and reliably by another source. Otherwise, there is a risk of irreversible damage to the electrolysis cells due to frost and even total loss of the electrolyzers installed in the electrolysis plant. The water pipes between the containers or enclosures must also be kept at a minimum temperature to prevent them from freezing. This also requires energy, which has to be provided from other sources when there is no wind.The object of the present invention is therefore to provide an offshore electrolysis system that, compared to known concepts, enables reliable operation at reduced production costs, while at the same time being designed for operation that is as self-sufficient and low-maintenance as possible. A further object is to provide a method for operating an offshore electrolysis system.

[0010] The object directed to an offshore electrolysis system is achieved according to the invention by an offshore electrolysis system comprising a wind turbine with a tower anchored on the seabed and with an electrolysis system, wherein the electrolysis system is connected to the wind turbine by a supply line, and wherein the electrolysis system has an electrolyzer arranged in a container, wherein the container is arranged below sea level.

[0011] The invention is based on the knowledge that in future renewable energy sources such as wind and solar energy will be used primarily to reduce CO2 emissions. In addition to being used as an electrical energy source, renewable electricity should also be used as a raw material for producing basic chemicals or fuels such as hydrogen. The electrolysis plants with the electrolyzers are ideally located close to the renewable energy sources in order to reduce or avoid transformation and line losses. In conventional designs for offshore electrolysis systems, sufficient space and installation space must always be created or found, which may result in considerable additional costs due to the design of the wind turbine platform.

[0012] During initial planning for decentralized, direct coupling of electrolysis systems to offshore wind turbines, designs were proposed that were mounted directly on a platform as a supporting structure on the tower of the offshore wind turbine. The invention has now recognized that this type of platform-based construction and installation of an offshore electrolysis system causes additional static loads for the wind turbine during operation, as well as considerable costs for the assembly and installation of this necessary platform.

[0013] The invention proposes an underwater installation of the electrolyzer for an offshore electrolysis system. This eliminates the need for a complex construction of a large operating and supply platform on the wind turbine tower with the numerous system components mounted thereon. Only a small supply platform is required - if at all - for selected auxiliary systems, such as a system control system and power supply for the electrolysis system or a seawater treatment facility to provide reactant water for the underwater electrolysis. However, even these auxiliary systems can be installed below sea level in one or more containers, enabling a virtually self-sufficient subsea installation of the electrolysis system, connected to the wind turbine via a supply line.The electrolyser is housed and protected in a container.

[0014] The invention thus creates an alternative solution to a platform previously customary in the prior art for installing electrolysis systems on an offshore wind turbine, wherein the electrolyzers are preferably arranged in the container underwater near the wind turbine. This also advantageously results in reliable protection against freezing due to the arrangement of the electrolyzer at a frost-free depth below sea level. The risk of water-bearing components of the electrolysis system freezing, in particular the sensitive electrolysis cells of the electrolyzer, is thus intrinsically counteracted. In particular, no active temperature maintenance systems need to be provided in the event of a risk of frost. It is conceivable to install the electrolysis units either directly on the seabed or at any desired, but fixed, water depth.This design offers the advantage that the tower of the wind turbine is not subjected to any additional static load and the costs for the platform are eliminated. Furthermore, above a certain water depth, the risk of icing of the water-based media required for electrolysis and the potential resulting damage to the system is no longer present. This eliminates the need for complex heating systems, including their power supply, and thus also system costs. The same applies to the cooling systems required for electrolysis operation, which can be made significantly smaller and more cost-effective because temperatures are constantly lower in deeper water layers and the required size of cooling systems is generally inversely proportional to the available cooling temperature difference.

[0015] In a particularly preferred embodiment of the offshore electrolysis system, the container has an underwater-compatible encapsulation which is configured for use of the electrolyzer below sea level.

[0016] The underwater capsule is advantageously designed as a diving capsule or as a casing that is watertight and pressure-resistant. In one possible advantageous embodiment, the underwater encapsulation can be designed as a pressure-compensated housing filled with a liquid having an internal pressure that is balanced with the pressure of the medium surrounding the underwater casing, such as seawater. The electrolyzer is arranged within the encapsulation. Pressure equalization can be achieved by a pressure equalizer that can be attached to the underwater casing or be part of it. In other embodiments, the underwater housing can also be a pressure-resistant housing that maintains a pressure of typically less than 3 - 5 bar inside, for example between about 1.5 bar or about 2.5 bar. This is therefore still relatively close to atmospheric pressure conditions.The fluid for pressure equalization can be a chemically inert and, if possible, incompressible hydraulic fluid. It is also conceivable that the fluid used for pressure compensation could be seawater or demineralized water, e.g., appropriately treated reactant water for electrolysis.

[0017] A particular advantage of underwater installations is that underwater-operated pressure electrolyzers can be designed lighter and therefore more cost-effectively. The hydrostatic pressure prevailing in the water depths below sea level can be used particularly efficiently as a counterforce to the operating pressure of an electrolysis system with a pressure electrolyzer. This allows the vessel wall thicknesses and bracing devices typically required for an underwater pressure electrolyzer to be made significantly thinner, lighter, and thus more cost-effective.

[0018] The novel approach presented here advantageously integrates renewable energy generation, electrolysis, and storage at an offshore location with the unique aspect of underwater hydrogen generation and storage, thereby avoiding compression losses. The change in ambient water pressure affects the cell voltage of the electrolysis itself, leading to a future trade-off between compression requirements and electrolysis losses. The new concept has several advantages over current approaches. By conducting electrolysis underwater, the ambient pressure underwater is used to generate high-pressure hydrogen, significantly reducing the need for energy-intensive compression systems. This directly translates into reduced operating costs due to the energy savings.Underwater production, for example, enables the direct storage of hydrogen in high-pressure tanks, reducing the need for additional compression and further improving energy efficiency. The produced high-pressure hydrogen can be transported directly to land using specially adapted vessels or fed into an underwater pipeline, offering flexibility and potential cost savings compared to the conventional method of compressing and transporting hydrogen.

[0019] In a preferred embodiment of the offshore electrolysis system, the wind turbine has a generator which is accommodated within the nacelle of the wind turbine, wherein the supply line is led down within the tower and led out of the tower below sea level and connected to the electrolysis system.

[0020] In this way, it is possible to supply the electrolyzer with electrical current, with the supply line being laid and well protected within the tower. The rectification of the alternating current initially generated in the generator can be achieved by a suitable rectifier arrangement, which is preferably arranged within the nacelle and connected downstream of the generator. Control and regulation devices for the electrolysis plant can also be housed in the nacelle. The supply line itself can be set up for several purposes and, in addition to supplying the electrolysis plant with electricity, can also perform other supply tasks. For example, the supply line can integrate lines for measuring the status and / or controlling or regulating the electrolyzer, such as sensor lines and control lines.It is also conceivable for the supply line to comprise a fluid line, wherein the fluid is a hydraulic fluid, e.g., water or seawater, for pressure compensation of the encapsulation, or even treated reactant water, demineralized water, for operating the electrolyzer. In a further preferred embodiment of the offshore electrolysis system, the container is positioned at a depth below sea level and can be flooded with a liquid, so that a predetermined fluid pressure can be set in the container, which acts on the electrolyzer.

[0021] The fluid can be a hydraulic fluid, in particular water or seawater. The underwater-compatible encapsulation can thus also be designed as a submersible capsule and safely accommodate the electrolyzer and, if necessary, other components of the electrolysis system. This advantageously makes it possible to provide a submersible electrolysis system which, depending on the selected diving depth below sea level, can be operated at a predeterminable hydrostatic pressure level of the ambient water pressure. A displacement device for the fluid can be provided if required, which can be activated, for example, by an oxygen pressure tank.

[0022] In a preferred embodiment, depending on the design, an electrolyzer, a gas separator, a gas tank, the electrolyzer's control and process technology, as well as equipment for desalination and purification of the salt water into reactant water for electrolysis can be arranged within a pressure-compensated housing. This achieves a virtually self-sufficient underwater installation of an electrolysis plant in the offshore electrolysis system.

[0023] Due to the underwater installation of the electrolyzer, the offshore electrolysis system is particularly suitable for the integration and operation of a pressure electrolyzer in the container.

[0024] Therefore, in the offshore electrolysis system the electrolyzer is preferably designed as a pressure electrolyzer and prepared for operation at a working pressure of greater than 5 bar, in particular greater than 10 bar. Because the ambient pressure in the container can be adjusted hydrostatically due to the immersion depth below sea level, a counterpressure is provided so that the material usage and the wall thicknesses of a pressure electrolyzer can be made significantly lower than when used at atmospheric pressure as ambient pressure. The same applies to the dimensioning of the bracing devices for the axially stacked and pressure- and fluid-tight clamped cells. The ambient pressure thus reduces the material usage and the material stress on the fluid-carrying components of the pressure electrolyzer. At the same time, manufacturing costs are reduced.The choice of the operating pressure of the pressure electrolyzer can be adapted to the depth below sea level and vice versa.

[0025] In a preferred embodiment, the offshore electrolysis system can be designed such that the container is located directly on the seabed. For this purpose, the container with the electrolyzer can be placed on the seabed and, if necessary, additionally anchored.

[0026] In a particularly preferred embodiment of the offshore electrolysis system, the container is placed on a detachable support device at a height above the seabed.

[0027] This enables the container to be elevated at a working height. The support device can be firmly connected to the seabed via a foundation in the seabed and have a detachable fastening device opposite the container. This means that the container with the electrolyzer is accessible at its installation location for maintenance, inspection and servicing. On the other hand, the detachable elevation of the container means that the container can be replaced. For maintenance, inspection or repairs, the container can be salvaged and lifted above the sea surface using a hoist. It is also possible to flood the container with a gaseous medium, for example oxygen or hydrogen from a tank, which displaces the water. The container rises to the sea surface, similar to a submarine.This also eliminates the need for heavy lifting equipment and large cable winches on a service vessel. The gaseous medium is preferably product gas obtained from the electrolysis process, i.e., hydrogen or oxygen, which is stored in gas storage tanks for flooding.

[0028] In a preferred embodiment of the offshore electrolysis system, a coupling device is attached to the outer shell of the container, which is designed for the engagement of a lifting device.

[0029] This means that the container with the electrolyzer can be brought to the surface and placed on the deck of a service vessel for inspection or maintenance of the electrolyzer. It is advantageous for the offshore electrolysis system to be provided with several underwater containers that perform different specific tasks. For example, auxiliary systems, electrical supply equipment, treatment equipment for the reactant water, sensor equipment, and control and regulation equipment for the electrolyzer can be housed in a respective container for functional separation and to ensure appropriate container volume. Certain functional elements can also be housed together in one container.

[0030] Preferably, in the offshore electrolysis system, the electrolysis plant has a product gas line which is led out of the container, wherein hydrogen generated under a gas pressure can be transported as product gas by means of the product gas line.

[0031] The gas pressure of the product gas approximately corresponds to the water pressure at the installation site at the selected sea depth. However, the working pressure of the pressure electrolyzer can also be selected somewhat higher than the prevailing water pressure. This allows pressure electrolysis to be carried out, whereby the product gas, in particular hydrogen, can be generated at a pressure significantly higher than atmospheric pressure. This product gas pressure level enables transport via a product gas pipeline and further processing, for example, compression, with lower energy consumption.

[0032] In a particularly advantageous embodiment of the offshore electrolysis system, the electrolyzer is designed as a PEM electrolyzer.

[0033] The PEM electrolyzer uses demineralized water as the reactant, which is easily obtained in the maritime environment. The water can be extracted and provided by a container-based water treatment unit, which is located underwater near the electrolysis container or can be housed in the container with the electrolyzer. Therefore, the electrolyzer design as a PEM electrolyzer is particularly advantageous and practical. In principle, it is also possible for the water treatment unit to be installed within the wind turbine tower or on a small work platform on the tower.

[0034] The object directed to a method is achieved according to the invention by a method for operating an offshore electrolysis system described above, in which water is supplied to the electrolysis plant in an electrolyzer arranged below the sea level and is split into hydrogen and oxygen, the hydrogen (H2) produced being transported away via a product gas line.

[0035] Preferably, in the method, pressure electrolysis is carried out in the electrolyzer at a working pressure, wherein the working pressure is adapted to the hydrostatic pressure at the site of use below sea level. In this way, small differential pressures can be set between the working pressure in the electrolyzer and the water pressure on the housing, so that the material load on the housing construction is reduced. The wall thicknesses of the housing construction can therefore be reduced compared to conventional pressure electrolyzers when operated in an atmospheric environment. The differential pressure is adapted and set by selecting the working pressure of the electrolyzer and adjusting the water pressure via the immersion depth, typically to less than 1 bar, in particular less than 0.5 bar.

[0036] Embodiments, features, and / or advantages that relate to the offshore electrolysis system in this case also apply analogously to the operating method, and vice versa. Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. These show schematically and in a highly simplified manner:

[0037] FIG 1 an offshore electrolysis system with an electrolysis plant and with a wind turbine according to the state of the art;

[0038] FIG 2 is a schematic side view of an offshore electrolysis system with an electrolyzer arranged in a container;

[0039] FIG 3 a schematic side view of an offshore electrolysis system with a container support;

[0040] FIG 4 a schematic side view of the offshore electrolysis system in a maintenance situation.

[0041] The same reference numerals have the same meaning in the figures. FIG. 1 shows an offshore electrolysis system 100, as is known from the prior art. The offshore electrolysis system 100 comprises an electrolysis plant 5 and a wind turbine 1, which has a tower 19, as shown in the upper right part of FIG. 1. In the lower area of ​​the tower 19, a large-format platform 3 is attached to the tower above sea level 25 (see FIG. 2), which is specially designed and configured to accommodate various system components for the intended operation of the offshore electrolysis system 100. These necessary system components are shown in an enlarged illustration in the lower part of FIG. 1:

[0042] An electrolysis plant 5 is set up on platform 3 and is systemically connected to the wind turbine 1 to form the offshore electrolysis system 100. For this purpose, containers 9 are set up on platform 3, in which electrolysis elements (not shown in detail) such as individual electrolyzers are accommodated, so that particularly sensitive functional components of the electrolysis plant 5 are protected from the effects of the weather. Some of the containers 9 set up on platform 3 comprise control devices 27 or so-called "balance of plant" elements and accommodate them protectively. These are selected containers 9 that are usually reserved exclusively for the accommodation and operation of these control devices 27 and, if applicable, other auxiliary systems of the electrolysis plant 5. In contrast, the electrolyzers for the electrochemical material conversion are arranged in containers 9 provided specifically for this purpose.Other components or parts of the system accommodated in the containers 9 may also include storage tanks for the reactant water of the electrolyzers, or the like.

[0043] In this case, the wind turbine 1 preferably has no grid connection or grid coupling, but rather, in the self-sufficient offshore electrolysis system 100, supplies the absorbed wind energy directly to the described electrolysis system 5, which is designed to produce preferably green hydrogen from water electrolysis. Thus, the offshore electrolysis system 100 is designed for grid-independent island operation and equipped for self-sufficient use in regions farther from the coast. The wind turbine 1 is therefore an offshore wind turbine.

[0044] The strategy of providing the electrolysis plant 5 via a number of containers 9, preferably ISO containers, advantageously ensures a simple maintenance and repair process, and simultaneously protects the plant components from climatic and weather influences as well as from corrosion and damaging mechanical influences during operation. The electrolysis system 100 is particularly vulnerable in situations in which the wind turbine does not produce any power for the electrolysis in frost conditions, so that there is an acute risk of water-carrying systems of the electrolysis plant 5 freezing, particularly during a prolonged period of darkness with the associated risk of frost during standstill operation.

[0045] In addition to exposure to weather and the risk of freezing, the known offshore electrolysis systems 100 have the disadvantage that the platform construction, with a large, heavy platform 3 and the diverse system components arranged thereon, places considerable static loads on the wind turbine 1. This entails considerable costs for the construction and operation of the offshore electrolysis system 100 in the known design.

[0046] These disadvantages are counteracted by the invention with a novel system concept for an offshore electrolysis system 100, wherein particularly reliable operation is achieved with reduced production costs. FIG. 2 shows, by way of example, a schematic side view of an appropriately equipped offshore electrolysis system 100 with a container 9 arranged below sea level 25. The offshore electrolysis system 100 has a wind turbine 1 with a tower 19 anchored on the seabed 21. The anchoring is via a massive foundation 33 which is inserted into the seabed. The tower 19 carries a nacelle 17 with the turbine as a structural element and extends from an above-water area 29 into an underwater area 31 down to the seabed 21.Furthermore, an electrolysis plant 5 is provided, which comprises an electrolyzer 13, wherein the electrolysis plant 5 is connected to the wind turbine 1 via a supply line 11.

[0047] A generator (not shown in more detail) is arranged in the nacelle 17, so that electricity generated in the generator from the wind turbine 1 can be fed as electrolysis current to the electrolyzer 13 via the supply line 11. The supply line 11 is laid in the above-water area 29 within the tower 19 and is led out of the tower 19 at the base of the tower 19 into the underwater area 31 and into a container 9. The electrolyzer 13 is arranged in the container 9, which has an underwater-suitable encapsulation for accommodating the electrolyzer 13. The container 9 is arranged below sea level 25 at a depth h, in this case positioned on the seabed 21 and set up for electrolysis operation in the maritime area underwater.Here, an arrangement is implemented in which the container 9 can be flooded with a liquid, for example sea water or a hydraulic fluid from a storage tank, so that a predetermined fluid pressure p can be set in the container 9, which is present and acts on the housing parts of the electrolyzer 13. As a result, the electrolyzer 13 can be designed in a particularly advantageous manner as a pressure electrolyzer and operated at an operating pressure of, for example, greater than 5 bar. The underwater installation particularly advantageously produces hydrogen H2 as a product gas by electrochemical decomposition of water under a correspondingly high working pressure p. The pressurized hydrogen H2 is led out of the container 9 via a product gas line 7, transported away and fed for further use.It is possible that hydrogen H2 and / or oxygen is partially stored in a respective tank under water and kept at the electrolysis plant 5.

[0048] FIG 3 shows a possible variant or further development of the positioning and anchoring of the container 5 with the electrolyzer 13. This shows a schematic side view of an offshore electrolysis system 100, an elevation of the container 9. The elevation of the container 9 is effected by a detachable support device 23 which holds the container 9 in position at a height above the seabed 21. The support device 23 is anchored in the seabed via a foundation 33. The support device 23 spaced the container 9 with the underwater-suitable encapsulation 15 surrounding the electrolyzer 13 from the seabed 21, so that accessibility as required and all-encompassing washing of the container is achieved. This is advantageous for maintaining a uniform temperature of the surrounding walls of the container 9 and for heat management.Freezing is not to be feared at a depth h below sea level, so that special temperature maintenance concepts for the water-bearing components of the electrolyzer 13 are not necessary in the event of a prolonged period of darkness for the wind turbine in the cold winter months. In a special embodiment, the underwater-compatible encapsulation 15 can be designed as a pressure-compensated housing filled with a liquid having an internal pressure that is balanced with the pressure of the medium surrounding the underwater housing, such as seawater. The electrolyzer 13 is arranged within the encapsulation 15.

[0049] FIG 4 shows a schematic side view of the offshore electrolysis system 100 in a maintenance situation or in the event of a necessary revision or inspection of the electrolyzer 13. A coupling device 35 is attached to the outer shell of the container 9 and is designed for intimate engagement of a lifting gear 39. During the revision, a corresponding service vessel 37 is used which has a lifting gear 23 and lifts the container 9 with the electrolyzer 13 out of the seawater. The lifting gear 23 is designed for engagement with the coupling device 25. In this way, in a maintenance situation, a container 9 with an electrolyzer 13 requiring maintenance can be taken out and easily replaced with a fully functional electrolyzer 13 in another container 9. Due to the rapid interchangeability and the modular concept, maintenance-related production downtime of hydrogen H2 is reduced.

[0050] The major advantage of the solution presented here is that it eliminates the need for the complex and costly installation of a platform 3 for accommodating a decentralized electrolysis plant 5. Furthermore, the underwater installation offers significant savings potential in terms of plant construction costs and the necessary pressure-stable design of individual components, including the electrolysis plant's thermal management system. The constant underwater temperature eliminates the need for additional adiabatic air cooling, which would otherwise be required for electrolysis plants 5. This leads to further energy savings and simplifies the system by reducing it to a single heat exchanger circuit using cold water.Furthermore, this approach proposes the use of existing offshore structures, which could significantly reduce the capital investment required for the construction of offshore electrolysis and storage facilities. Eliminating the compression stage in pressure electrolysis will significantly reduce the system's maintenance requirements.

Claims

Patent claims 1. Offshore electrolysis system (100) comprising a wind turbine (1) with a tower (19) anchored on the seabed (21) and with an electrolysis system (5), wherein the electrolysis system (5) is connected to the wind turbine (1) by a supply line (11), and wherein the electrolysis system (5) has an electrolyzer (13) arranged in a container (9), wherein the container (9) is arranged below sea level (25).

2. Offshore electrolysis system (100) according to claim 1, wherein the container (9) has an underwater encapsulation (15) configured for use of the electrolyzer (13) below sea level (25).

3. Offshore electrolysis system (100) according to claim 1 or 2, wherein the wind turbine (1) has a generator which is accommodated within the nacelle (1) of the wind turbine (1), wherein the supply line (11) is led down within the tower (19) and is led out of the tower below sea level (25) and is connected to the electrolysis system (5).

4. Offshore electrolysis system (100) according to claim 1, 2 or 3, wherein the container (9) is positioned at a depth (h) below sea level (25) and can be flooded with a liquid, so that a predetermined fluid pressure (p) can be set in the container (9) which acts on the electrolyzer (13).

5. Offshore electrolysis system (100) according to one of the preceding claims, wherein the electrolyzer (13) is designed as a pressure electrolyzer and is designed for a working pressure of greater than 5 bar, in particular is operable at a working pressure of greater than 10 bar.

6. Offshore electrolysis system (100) according to one of the preceding claims, wherein the container (9) is arranged on the seabed (21).

7. Offshore electrolysis system (100) according to one of the preceding claims, wherein the container (9) is placed on a detachable support device (23) at a height above the seabed (21).

8. Offshore electrolysis system (100) according to one of the preceding claims, wherein a coupling device (35) is attached to the outer shell of the container (9), which is designed for the engagement of a lifting device (37).

9. Offshore electrolysis system (100) according to one of the preceding claims, wherein the electrolysis plant (5) has a product gas line (37) which is led out of the container (9), by means of which hydrogen (H2) generated under a gas pressure (p) can be transported as product gas.

10. Offshore electrolysis system (100) according to one of the preceding claims, wherein the electrolyzer (13) is designed as a PEM electrolyzer.

11. A method for operating an offshore electrolysis system (100) according to one of the preceding claims, wherein water is decomposed into hydrogen (H2) and oxygen by an electrolyzer (13) of the electrolysis plant (5) arranged below sea level (25), the hydrogen (H2) produced being transported away via a product gas line (7).

12. The method according to claim 11, wherein pressure electrolysis is carried out in the electrolyzer (13) at a working pressure (p), wherein the working pressure (p) is adapted to the hydrostatic pressure at the site of use at a depth (h) below sea level (25).

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