FIELD OF THE INVENTION The present invention relates to the field of electric energy generating based on wind turbines, more specifically to the field of wind turbines dedicated for generation of electric power for powering an electrolyzer system for hydrogen generation. BACKGROUND OF THE INVENTION

Storing of energy generated by renewable energy sources, e.g. wind turbines, is a general problem. Generation of hydrogen by means of electrolysis, i.e. based on electrical power, is one solution. Stored hydrogen can be used e.g. for fuel cells, such as in hydrogen driven vehicles, or heating sectors, heavy transport industries and grid size storage.

However, even though generation of hydrogen based on electrical power from the grid provides a flexible solution to the problem of storing of energy, such solutions often provide a poor efficiency, since the route of electrical power from the source to a hydrogen electrolyzer facility is often complex and involves many electrical components such as cables, switches and voltage conversion components, each contributing to power loss. Even further, the complex electrical system involved in hydrogen production based on e.g. wind turbine power causes such hydrogen generation to be expensive.

SUMMARY OF THE INVENTION

Thus, according to the above description, it is an object of the present invention to provide an efficient and yet low cost solution for utilizing wind power for generation of hydrogen. In a first aspect, the invention provides an off-grid wind turbine system comprising

- a wind turbine comprising a tower, a nacelle, and a blade system arranged to drive an electric generator for generating an initial electric power output,

- an electrolyzer system comprising an electrolyzer arranged to generate hydrogen to a hydrogen output by an electrolysis process, wherein at least part of the electrolyzer is located adjacent to the wind turbine,

- an electric converter system arranged to convert the initial electric power output into a DC electric power output dedicated for powering the electrolyzer, and

- a hydrogen storage system comprising a hydrogen storage tank arranged to receive hydrogen from the hydrogen output in order to store hydrogen generated by the electrolyzer system.

The invention is based on the insight that hydrogen generation based on electric power from wind turbines is inefficient and expensive due to the expensive and electrically complex wind turbines required for generation of electric power to the grid. The wind turbine system according to the invention is advantageous, since it allows wind turbines with a rather simple electrical system compared to wind turbines for power production to the grid. A dedicated electrical converter solution between the electric generator in the wind turbine and the hydrogen electrolyzer can be designed for optimal efficient transformation of produced electrical power for hydrogen generation.

By dedicating electric components of the wind turbine to hydrogen generation, helps to provide a simple and efficient wind-to-hydrogen facility. Further, local hydrogen generation near the wind turbine reduces electric power loss in long distance cables.

By "off-grid" is understood a wind turbine which is not connected so as to allow generation of electric power to the electric grid according to a standard grid code and involving switchgear etc. However, still the wind turbine may be connected to the grid for receiving power to power auxiliary systems necessary for operation of the wind turbine, e.g. in cases where the wind turbine is unable to generate electric power for maintaining its basic operation. By "located adjacent to the wind turbine" is understood a location at a distance less than 100 m from the wind turbine tower, such as a location on the ground next to the wind turbine tower, e.g. in a housing separate from the wind turbine tower at a distance of less than 100 m from the wind turbine housing, or a housing built together with wind turbine tower. Further, a location in the ground below the wind turbine is also considered as adjacent to the wind turbine.

In the following, preferred features and embodiments will be described.

It is to be understood that the electric converter system may partly or entirely be located inside the wind turbine, i.e. inside the nacelle or inside the tower, or partly inside the wind turbine and partly adjacent to the wind turbine. Especially, the entire electric converter system may be located adjacent to the wind turbine, e.g. formed more or less integrated with the electrolyzer.

The electric converter system may be arranged to convert the initial electric power output from the electric generator into the DC electric power output dedicated for powering the electrolyzer in one single conversion step. Hereby, a simple and compact converter design can be used.

The initial electric power output from the electric generator may be an AC output, e.g. such as the electric generator being a Permanent Magnet (PM) synchronous generator type designed for generation of an electric AC output with one, two or three phases.

In some embodiments, the electric is a synchronous generator excited by an external exciter. Such generator can provide an electric output which allow a simplified converter system to be used.

In preferred embodiments, the electrolyzer is located in an enclosure separate from the wind turbine tower, e.g. at a distance of 0-100 m from the wind turbine tower, or at a distance of 0-20 m from the tower, or at a distance of 0-10 m from the tower, e.g. at a distance of 2-10 m from the tower. This allows easy maintenance service of the hydrogen electrolyzer system without entering the wind turbine tower. In some embodiments, at least part of the electric converter system is located inside the same enclosure, e.g. a container, as the electrolyzer. In some embodiments, the electric converter system is entirely integrated with the electrolyzer to form one unit. Thus, in such embodiments a compact design is provided. It may be preferred that the hydrogen storage tank is placed outside the enclosure housing the electrolyzer and possibly part of or the entire electric converter system.

The hydrogen storage tank may be located adjacent to the wind turbine, such as the hydrogen storage tank being located on the ground adjacent to the tower, or such as the hydrogen storage tank being located in the underground, e.g. below the wind turbine tower. Hydrogen outputs from a plurality of wind turbines may be connected via a pipe system to one common storage tank located adjacent to the wind turbines, or located remotely from at least some of the plurality of wind turbines.

In some embodiments, the wind turbine is located off-shore while the hydrogen storage tank is located on-shore. This allows a simple off-shore design, since no off-shore storage tank is required. Rather, hydrogen is transported in a pipe system from off-shore to on-shore, e.g. in one single pipe connected to hydrogen outputs from a plurality of wind turbines off-shore.

Especially, a hydrogen pipe system may be arranged to transport hydrogen from a location of the electrolyzer to another location of the storage tank, e.g. at another location adjacent to the wind turbine, or the storage tank may be located at a remote location of the wind turbine. Further, the electrolyzer and the storage tank may be arranged within one common housing, e.g. the electrolyzer and the storage tank may be partly or fully integrated to form one unit. Especially, all of the electrolyzer, the hydrogen tank and at least a part of the electric converter system may be located within one common housing placed on the ground adjacent to the wind turbine tower, or placed in the ground below the tower.

In the following, various concepts for dedicated electric conversion from the initial electric power generated by the electric generator to a suitable DC electric power output to be applied to the hydrogen electrolyzer. In Concept A, an AC to DC converter serves to convert the initial electric power output from the electric generator into the DC electric power output for powering the electrolyzer, and wherein at least the electrolyzer is arranged inside a housing located on the ground adjacent to the wind turbine. Concept A is advantageous e.g. due to the fact that a simple power architecture can be used, and further Concept A can be implemented by means of standard components that already exist. Especially, the AC to DC converter and at least part of the electrolyzer may be integrated so as to form one unit. Alternatively, the entire electric converter system including the AC to DC converter is located inside the nacelle or tower, while a Low Voltage or Medium Voltage DC power cable leads electric power from the wind turbine to the electrolyzer inside the housing on the ground.

In Concept B, a torque converter, e.g. a hydraulic torque converter, is mechanically connected between the blade system and the electric generator, wherein the electric generator is a synchronous generator excited by an external exciter, wherein the electrolyzer is located in an enclosure in the underground below the wind turbine tower or in an enclosure on the ground adjacent to the wind turbine. Concept B is advantageous, since the torque converter allows a simple converter system to be used, e.g. using passive diodes, thus providing a low cost and robust converter system. Most preferably, Concept B is used at Low Voltage levels. Further to Concept B, in Concept C, the electric converter system comprises a series connection of a transformer and an AC to DC converter, such as an AC to DC converter comprising passive diodes. Concept C is advantageous over Concept B in that it is suitable for Medium Voltage levels, thus increasing power rating and reduces cost and power loss in electric cables in the tower.

In Concept D, the electric converter system comprises an AC to DC converter arranged to convert the initial electric power output from the electric generator into an intermediate DC electric power output, and wherein a DC to DC converter serves to convert the intermediate DC electric power output into the DC electric power output for powering the electrolyzer. Concept D is advantageous in that it allows a high power rating, e.g. up to 15 MW, and use of a medium frequency transformer will help to reduce cost and weight of magnetic material, even further a high annual energy production can be expected due to the high efficiency topology. Especially, the DC electric power output for powering the electrolyzer is a Low Voltage or Medium Voltage DC level. It may be preferred that the electrolyzer is powered by the intermediate DC generated by the AC to DC converter, while the DC to DC converter up-converts the DC voltage level to a Medium Voltage DC level to be used for grid connection.

In Concept E, the electric generator is a synchronous generator excited by an external exciter, and wherein the electric converter system comprises a Dynamic Voltage Restoring circuit. Compared to Concept D, Concept E can provide a simplified DC to DC converter arrangement. Especially, the Dynamic Voltage Restoring circuit may be located inside the nacelle. Especially, the electrolyzer may be arranged in an enclosure adjacent to the wind turbine. Especially, the electric converter system is arranged to generate the DC electric power output for powering the electrolyzer at a Medium Voltage DC level or at a Low Voltage DC level.

In Concept F, the electric generator is a synchronous generator, and wherein the electric converter system comprises a modular converter with a plurality of converter modules, and wherein each of the plurality of converter modules is arranged to generate a DC electric power output for powering respective electrolyzer modules. Concept F is advantageous due to the modular converter and electrolyzer, thereby allowing an easy up-scaling and use of standard components for a variety of system ratings. Especially, the electric converter system is arranged to generate the DC electric power output for powering the electrolyzer at a Medium Voltage DC level or a Low Voltage DC level.

In Concept G, the electric generator is a synchronous generator, and wherein the electric converter comprises one transformer with a plurality of secondary windings each connected to a (thyristor like) rectifier, each being arranged to generate a DC electric power output for powering an electrolyzer module. Concept G is advantageous due to a very simple and robust power architecture.

A plurality of off-grid wind turbines according to the first aspect may be arranged so that hydrogen outputs from each of the plurality of wind turbines are connected to one common hydrogen storage system. In a second aspect, the invention provides a method for storing energy based on wind power, the method comprising

- generating an initial electric power output by means of an electric generator in a wind turbine comprising a tower, a nacelle, and a blade system arranged to drive the electric generator,

- converting the initial electric power output into a DC electric power output dedicated for powering a hydrogen electrolyzer,

- generating hydrogen by applying the DC electric power output to the hydrogen electrolyzer, wherein at least part of the hydrogen electrolyzer is located adjacent to the wind turbine, and

- storing the generated hydrogen in a hydrogen storage tank.

In one embodiment, the method comprises the step of providing the hydrogen electrolyzer adjacent to the wind turbine. More specifically, providing an electric cable connecting the electric power output, either the initial electric power output from the generator or the dedicated DC electric power output, to the electrolyzer at its location adjacent to the wind turbine.

It is to be understood that the same advantages and preferred embodiments and features apply for the second aspect, as described for the first aspect, and the aspects may be mixed in any way.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described in more detail with regard to the accompanying figures of which

FIG. 1 illustrates a wind turbine,

FIGs. 2a and 2b illustrate block diagrams of examples of location of the electric converter, the hydrogen electrolyzer and the hydrogen tank in relation to the wind turbine,

FIGs. 3a-3e illustrates various implementations of Concept A,

FIG. 4 illustrates Concept B,

FIGs. 5a-5c illustrates various implementations of Concept C,

FIGs. 6a-6d illustrates various implementations of Concept D, FIGs. 7a-7g illustrate various implementations of Concept E,

FIGs. 8a-8c illustrate various implementations of Concept F,

FIGs. 9a and 9b illustrate implementations of Concept G, and FIG. 10 illustrate steps of a method embodiment.

The figures illustrate specific ways of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a wind turbine system embodiment. The wind turbine has at least two, e.g. three rotor blades BL for driving an electric generator located inside the nacelle NC on top of a tower TW. Typically, a power converter system in a wind turbine can be placed in the nacelle NC or inside the tower TW. Wind turbines may generate an electric power of at least 1 MW, such as 2-10 MW, or more. The electric power converter system of the wind turbine may be configured to generate a dedicated DC power for powering a hydrogen electrolyzer at a DC voltage within the range +/-0.5 kVDC to +/-50 kVDC range. Especially, a DC voltage range of 2-10 kV may be preferred. In the present invention, the wind turbine provides a DC voltage for powering the electrolyzer which is placed adjacent to the wind turbine, i.e. outside the space provided by the nacelle NC and the tower TW, e.g. at a distance of 0-100 m from the tower TW.

FIGs. 2a and 2b illustrate block diagrams of two examples of location of components in relation to the off-grid wind turbine WT. An electric generator G driven by a blade system generates an initial electric power output ACV, typically an AC voltage. An electric converter CNV converts the initial electric power from the generator G into a dedicated DC voltage DCV for powering the hydrogen electrolyzer ELT which produces hydrogen H based on a water input W according to an electrolysis process.

Via a pipe, the produced hydrogen H is transferred for storage in a hydrogen tank HTK system for later tapping of stored hydrogen H_S, e.g. for powering hydrogen driven vehicles or other fuel cell driven applications. E.g. the storage tank HTK can be connected to provide hydrogen H_S via a pipe system to larger storage tanks, or hydrogen can be transported by vehicles for use at other locations. The hydrogen tank HTK is preferably located adjacent to the wind turbine tower WT, e.g. on the ground at a distance of 2-50 m away from the wind turbine tower. Alternatively, the hydrogen tank HTK may be placed remotely to the wind turbine, i.e. more than 50 m away from the wind turbine tower. Still further, the hydrogen tank HTK may be located in the ground, e.g. below the wind turbine tower.

FIG. 2a shows an embodiment where the converter CNV is located inside the wind turbine WT, while the electrolyzer ELT is located outside the wind turbine WT, adjacent to the wind turbine. The hydrogen storage tank HTK is also located outside the wind turbine WT, either remotely or adjacent to the wind turbine WT.

FIG. 2b shows an embodiment where the converter CNV and the hydrogen electrolyzer ELT are both located in a housing HS located adjacent to the wind turbine WT. E.g. the converter CNV or part of the converter CNV may be integrated with the electrolyzer ELT to form one unit. The hydrogen tank HTK is located adjacent to the wind turbine tower TW, e.g. adjacent to the housing HS with the electrolyzer ELT and converter CNV inside. The hydrogen tank HTK may alternatively be located inside the housing HS together with the converter CNV and the electrolyzer ELT.

In the following, various concepts for power architectures to provide the dedicated DC voltage for powering the hydrogen electrolyzer.

FIGs. 3a illustrates a block diagram of an embodiment of Concept A, where a permanent magnet type synchronous generator PMSG provides an initial AC output which is converter by an AC to DC converter into a DC voltage dedicated for powering the hydrogen electrolyzer ELT. Further, the DC voltage serves to power a compressor CMP for compressing the produced hydrogen, a pump PMP for pumping produced hydrogen, and finally auxiliary equipment AUX which includes e.g. all necessary equipment for normal operation of the wind turbine, e.g. computer system and vital electric motors for control of the blade system etc. Thus, in principle the wind turbine can operate without any connection to an electric grid, even though it may be preferred that the auxiliary equipment AUX can be power from the electric grid in cases where the wind turbine generator PMSG can not provide sufficient power, e.g. at shut down.

FIG. 3b shows a sketch of one configuration of Concept A, where the electrolyzer ELT is located below the wind turbine tower, in the underground, or in case of a floating off-shore wind turbine, inside the floating foundation. A pump PMP provides water to the electrolyzer ELT which produces hydrogen H stored in an underground storage tank HTK located adjacent to the electrolyzer ELT. A pipe serves to lead hydrogen H from the tank HTK away from the underground. E.g. from an off-shore position of the wind turbine to an on-shore location, or merely from the underground to an on ground location, e.g. for a larger hydrogen storage and/or distribution system. In FIG. 3b the electric converter system is understood to be located inside the wind turbine, e.g. the nacelle, and a DC power cable provides the necessary DC voltage for powering the electrolyzer in its underground location.

FIG. 3c shows an alternative layout for Concept A, where the electrolyzer ELT is located on the ground separate from the wind turbine, and wherein the hydrogen tank HTK is located on the ground, separate from the electrolyzer ELT. As in FIG. 3b, the electric converter system is understood to be located inside the wind turbine, e.g. the nacelle.

FIG. 3d shows location of components in an embodiment of Concept A. In the nacelle NC, the generator G is connected electrically to an AC to DC converter which generates a DC voltage at a Low Voltage level LVDC for driving the electrolyzer ELT which is located on the ground in a housing HS, adjacent to the tower TW. A compressor CMP is located inside the housing HS as well, to provide a sufficient hydrogen pressure for leading hydrogen via a pipe to the tank HTK located on the ground adjacent to the housing HS.

FIG. 3e shows a variant of the embodiment of FIG. 3d, differing with respect to the location of the AC to DC converter ACDC, since in FIG. 3e the AC to DC converter ACDC is located inside the housing HS along with the electrolyzer ELT, e.g. forming one unit together with the electrolyzer ELT. FIG. 4 illustrates Concept B, where a hydraulic torque converter HTC inserted between the blade system via a gearbox GB for driving the electric generator which is a synchronous generator SG excited by an external exciter EXC. The generator SG provides a controllable AC voltage which is converter by an AC to DC converter for powering the electrolyzer ELT, here as an example two separate branches of converter and electrolyzers are shown. The use of the torque HTC converter and the exciter system EXC allows use of a simple and efficient electric AC to DC converter system. The location of components in Concept B can be as described e.g. in FIGs. 3c, 3d and 3e for Concept A.

FIG. 5a illustrates an embodiment of Concept C, which is similar to Concept B except for the use of a transformer TR between the generator SG and the AC to DC converter. Especially, this can be combined with the use of an AC to DC converter with passive diodes. Concept C is suitable for Medium Voltage levels and can thus handle higher electric power levels compared to Concept B which is best suited for Low Voltage levels.

FIG. 5b illustrates an embodiment of Concept C, where a hydraulic torque converter HTC is inserted between the blade system and the electric generator G. The output of the generator G is applied to an AC to DC converter ACDC via a transformer TR. A Low Voltage level DC voltage LVDC is transferred to a housing HS adjacent to the wind turbine, wherein the housing HS houses a DC to DC converter DCDC, an electrolyzer ELT and a compressor CMP. Thus, in this embodiment, the converter system is located partly in the nacelle and partly in the housing HS along with the electrolyzer ELT. The DC to DC converter receives the intermediate DC voltage from the AC to DC converter and generates in response the DC voltage for powering the electrolyzer ELT. The compressor CMP serves to provide sufficient pressure for transporting the hydrogen produced by the electrolyzer ELT to the storage tank HTK.

FIG. 5c illustrates another embodiment of Concept C. The difference from FIG. 5b is, that the Medium Voltage level AC output MVAC from the generator G is provided to the housing HS which houses the entire converter system including transformer TR and AC to DC converter ACDC which serves to generate the DC voltage for powering the electrolyzer. FIG. 6a illustrates an embodiment of Concept D, which differs with respect to the AC to DC converter system, namely in that an intermediate AC to DC converter ACDC converts the AC voltage from the generator G into an intermediate DC voltage which is then converted into the dedicated DC voltage for powering the electrolyzer ELT by a DC to DC converter DCDC.

FIG. 6b shows an embodiment of Concept D, where the nacelle NC houses the generator G and the AC to DC converter ACDC, while a housing HS adjacent to the wind turbine houses the DC to DC converter DCDC and the electrolyzer. The hydrogen storage tank HTK is located separate from the housing HS and separate from the wind turbine.

FIG. 6c illustrates an example of implementation of Concept D, where the nacelle houses a part of the converter system while another part of the converter system, connected by a Medium Voltage DC cable for transferring an intermediate Medium Voltage level DC MVDC to a housing HS on the ground adjacent to the wind turbine. The housing houses conversion of the intermediate DC to the DC for powering the electrolyzer ELT. The housing HS further comprises a compressor CMP, as also described above. In the nacelle, a filter followed by an AC to DC converter, followed by a DC to AC converter which applies an AC voltage to a transformer which generates an AC voltage to an AC to DC converter followed by a filter. In the housing HS, a filter is followed by a DC to AC converter which applies an AC voltage to a transformer which generates an AC voltage to a final AC to DC converter for powering the electrolyzer ELT.

FIG. 6d illustrates yet another example of implementation of Concept D.

Compared to the implementation in FIG. 6c, the entire converter system is located outside the wind turbine. The Medium Voltage AC MVAC generated by the generator G is applied to a separate housing which houses the components located in the nacelle in the embodiment of FIG. 6c. This housing further houses a low voltage control panel LVC intended to control the converter stages, perform measurements and ensure operation of the system. Finally, the Medium Voltage DC generated by the first part of the converter system is then applied to a housing HS similar to the one described for FIG. 6c. FIG. 7a illustrates an embodiment of Concept E, where a synchronous generator SG excited by an external exciter generates an initial AC voltage. In Concept E, a Dynamic Voltage Restoring circuit DVR forms part of the converter system, as well as a low frequency transformer which provides an AC voltage output to an AC to DC converter ACDC followed by a DC to DC converter DCDC. This architecture involving a DVR allows generation of a Medium Voltage level DC voltage for powering the electrolyzer ELT. FIG. 7b illustrates a variant of Concept E, which is similar to the embodiment in FIG. 7a, except that the transformer is eliminated.

FIG. 7c illustrates another variant of Concept E, similar to the embodiment in FIG. 7a except that the AC to DC and DC to DC converters are eliminated and replaced by a silicon controlled rectifier SCR. Thus, the use of the DVR allows a rather simple conversion by means of a transformer and a rectifier in the form of an SCR.

FIG. 7d illustrate yet another variant of Concept E, namely similar to the embodiment of FIG. 7c, except that the transformer is eliminated, thereby providing a very simple architecture.

For concept E, it is understood that the electrolyzer may be located in a housing adjacent to the wind turbine. However, it may be preferred that both the converter system, or at least a part of if, and the electrolyzer are located adjacent to the wind turbine.

FIG. 7e illustrates an example of an implementation of Concept E. As in FIGs. 6c and 6d, a housing HS on the ground adjacent to the wind turbine houses the electrolyzer ELT and a part of the converter system, namely a filter followed by a DC to AC converter with an intermediate transformer to a final AC to DC converter for powering the electrolyzer ELT. In the nacelle, the generator G excited by an external exciter EXC is connected via the Dynamic Voltage Restoring circuit DVR, and a transformer to an AC to DC converter which generates the Medium Voltage DC MVDC which is applied to the converter part in the housing HS. FIG. 7f shows an embodiment differing from the one in FIG. 7e in that the initial converter parts, i.e. DVR, transformer and AC to DC converter, are here located in a separate housing adjacent to the wind turbine, wherein this housing further houses a low voltage control panel LVC for ensuring operation of the converter, measurement acquisition and safe operation. Thus, the Medium Voltage AC MVAC provided by the generator is provided to this housing. The second converter part and electrolyzer ELT are provided in the same housing HS as described for FIG.

7e.

FIG. 7g shows an embodiment differing from the one in FIG. 7e in that the transformer in the nacelle is eliminated, thus here the DVR is followed directly by an AC to DC converter generating a DC voltage to the final part of the converter located in the separate housing HS.

FIGs. 8a and 8b illustrate implementation examples of Concept F, where electric generator is a synchronous generator PMSG, e.g. a permanent magnet type synchronous generator, and wherein the electric converter system is a modular converter with a plurality of converter modules, and wherein each of the plurality of converter modules is arranged to generate a DC electric power output for powering respective electrolyzer modules. Such architecture allows low cost large scale manufacturing of rather small converter and electrolyzer modules, which can easily be combined to allow easy scaling to match a given electric voltage or power rating.

FIG. 8a illustrates one embodiment of Concept F, where the AC voltage generated by the generator PMSG is applied to a series connection of a plurality of converters in the form of half or full bridges HFB each generating a DC voltage for powering an electrolyzer module ELT.

FIG. 8b illustrates another embodiment of Concept F, where sets of a number of series connected modules C_ELT_C are connected to the output phases of the electric generator PMSG. Each module C_ELC_C, as illustrated to the left in the dashed box, is formed by a modular multilevel converter cell MMC_C and an electrolyzer cell ELT_C. It is to be understood that the converter and electrolyzer modules according to Concept F can be located adjacent to the wind turbine in a separate housing. However, some modules may be located inside the wind turbine, if preferred, while other modules are located adjacent to the wind turbine.

FIG. 8c shows an example of an implementation of Concept F. Here, a Medium Voltage AC MVAC is generated by the generator G and applied to a housing HS located on the ground adjacent to the wind turbine. The modular converter M_ACDC and electrolyzer M_ELT are located inside this housing HS together with a compressor CMP for compressing generated hydrogen for transport to the storage tank HTK located outside the housing HS. The housing HS further houses a low voltage control panel LVC for control purposes of the converter system.

FIG. 9a illustrates an embodiment of Concept G, where the electric generator PMSG is a synchronous generator, e.g. a permanent type synchronous generator, and wherein the electric converter comprises a plurality of secondary transformer windings each being arranged to generate a DC electric power output for powering an electrolyzer module. This provides a rather simple and robust architecture. In the illustration, all three phases of the generator PMSG are transformed by respective transformers and rectified to arrive at DC voltages for powering respective electrolyzer modules. The electrolyzer module may be located adjacent to the wind turbine in a separate housing.

FIG. 9b illustrates an implementation of Concept G, where a Medium Voltage AC MVAC is generated by the generator G and applied to a housing HS located on the ground adjacent to the wind turbine. The transformer and the modular converter M_ACDC and electrolyzer M_ELT are located inside this housing HS together with a compressor CMP for compressing generated hydrogen for transport to the storage tank HTK located outside the housing HS. The housing HS further houses a low voltage control panel LVC for control purposes of the converter system.

FIG. 10 illustrate steps of a method embodiment, namely steps of a method for storing energy based on wind power. In a first step, an initial electric power output is generated G_I_P by means of an electric generator in a wind turbine comprising a tower, a nacelle, and a blade system arranged to drive the electric generator. Next, converting C_DC the initial electric power output into a DC electric power output dedicated for powering a hydrogen electrolyzer. Next, providing a hydrogen electrolyzer inside a housing P_ELT_HS located adjacent to the wind turbine, e.g. on the ground at a distance of 0-20 m from the tower.

Next, generating G_H hydrogen by applying the DC electric power output to the hydrogen electrolyzer inside the housing. Finally, storing S_H the generated hydrogen in a hydrogen storage tank.

To sum up: the invention provides an off-grid wind turbine system comprising a wind turbine with an electric generator (G) for generating an initial electric power output (AC). An electrolyzer system with a hydrogen electrolyzer (ELT) located adjacent to the wind turbine, so as to generate hydrogen (H) by an electrolysis process. An electric converter system (CNV) serves to convert the initial electric power output (AC) into a DC electric power output (DC) dedicated for powering the electrolyzer (ELT). The produced hydrogen (H) is stored in a hydrogen storage tank (HTK), e.g. located adjacent to the wind turbine. Modules each comprising a converter and an electrolyzer may be stacked to provide the necessary capacity.

In some embodiment, a synchronous generator excited by an external exciter (EXC) is used, and in some embodiments a hydraulic torque converter (HTC) is used. In some embodiments an AC to DC converter system involving a transformer is used, while in other embodiments an intermediate DC to DC converter is used. By placing the electrolyzer (ELT) adjacent to the wind turbine, a dedicated and compact wind turbine system can be provided which allows a rather simple and low cost wind turbine especially suited for storing energy in the form of hydrogen based on wind.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is to be interpreted in the light of the accompanying claim set. In the context of the claims, the terms "including" or "includes" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.