H2SEA studies monopile-based structures for hydrogen offshore wind turbines

Dutch engineering company H2SEA, in cooperation with the Delft University of Technology (TU Delft), has performed an assessment of monopile-based support structures for hydrogen-producing offshore wind turbines.

Image courtesy H2SEA

H2SEA says that one of the main questions was if decentral hydrogen production on a monopile-based support structure of an offshore wind turbine would be structurally feasible.

The goal was also to define the differences in support structure geometry and assess the changes in the design methodology of an offshore wind turbine support structure, including a decentralised hydrogen production platform.

The assessment was based on a 15 MW reference turbine in a water depth of 45 metres in the F3 sector of the North Sea.

To obtain platform mass, dimensions, and rotational inertia, H2SEA and TU Delft selected and listed all required systems, and made an optimised platform layout and mass estimation. For the design of the platform support beams, gravitational loads and extreme wind gust loads were taken into account. The selection of the support structure concept was performed using a multi-criteria analysis, H2SEA says.

Furthermore, an analytical fully dynamical model was constructed in Maple for fatigue assessment. The structure was simulated by the equations of motions, including airy wave force, rotor damping, topside and platform mass and rotational inertia, embedded length and homogeneous soil stiffness. The Maple model was used to simulate the dynamic behaviour of both structures, determine the first and second natural frequency, and present displacements and overturning moments in these two mode shapes.

Finally, a fatigue damage calculation including 500 combinations of wave height and period was performed, for a 25-year lifetime.

The Dutch engineering company has already been involved in hydrogen projects, including the H₂opZee demonstration project, for which Neptune Energy and RWE awarded a contract to H2SEA back in 2022 for a feasibility study for the hydrogen platform concept design and engineering.

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For the H₂opZee project, H2SEA’s sibling company Enersea was awarded the pipeline concept design work and Siemens Gamesa the concept work for wind turbine systems.

At the beginning of last year, H2SEA announced that the company had developed solutions for system stability in off-grid offshore wind turbine hydrogen production. Three potential solutions were developed by H2SEA and have been analysed in an Electro Magnetic Transient (EMT) study together with high voltage engineering specialist Enersynt.

The preferred solution showed the feasibility of using conventional wind turbines in a system with grid-forming converters and energy storage.

In October last year, H2SEA said it had put together a strategy, together with the consulting firm Guidehouse, for pipeline system operators NGT (NoordGasTransport) and NOGAT (Northern Offshore Gas Transport). The strategy was focused on repurposing existing offshore pipeline infrastructure for hydrogen transport to shore.