Session: Hybrid System & Substation

Paper Number: 165410

165410 - Pre-Conceptual Design of a Floating Offshore Hydrogen Substation 

Abstract: 

Electricity produced by floating offshore wind farms can contribute to the development of renewable hydrogen production. As part of the collaborative project OPHARM2, a pre-conceptual study of a floating substation integrating hydrogen production from offshore wind energy has been conducted. The objectives of this study are to better understand the requirements of an offshore hydrogen substation, by specifying and sizing the topside and the floater. As a case study, the floating offshore hydrogen substation is considered off grid, located in the North Sea deep waters (Norway) and linked to a 960 MW offshore wind farm.

The first achievement of this study is the topside arrangement. The electrolysis workflow diagram is performed to size and specify the different components. Hydrogen is produced by Proton Exchange Membrane (PEM) electrolyser and exported via pipeline. The off-grid hypothesis leads to hydrogen storage on the substation and the presence of fuel cells and batteries. Seawater is pumped and desalted using multiple effect distillation (MED) process.

A comparative study of existing demonstrators or projects of offshore hydrogen production concept and HVDC/HVAC floating substation has been performed to obtain useful indicators on the structure, such as the topside density, that should be between 0.09 to 0.13 t/m3, and the structural topside weight, considered as 42% of the total equipment weight.

Finally, the topside dimensions are 100m x 80m x 16m and a mass of 25 068t for a total of electrolysis power of 760MW. The floater conceptual design was performed in two main stages: floater screening and hydrodynamic analyses.  Considering the environmental conditions, the study was oriented towards a semi-submersible floater rather than a tension leg platform (TLP) or a spar. Six columns are considered to ensure structural integrity considering the dimension and mass of the topside. The floater screening provided optimal geometry of pontoons and columns to meet standard design criteria. A mooring concept organised around 4 fairleads, one at each corner of the floater with three lines, was also defined using polyester and chain materials to achieve the required offset. The hydrodynamic analyses demonstrated the floater met all design criteria in terms of dynamic air gap, offset, rotation, acceleration at several points on the topside deck, and line tensions, showing an overall good behaviour under the extreme conditions tested: H_s ∈ [1.5;15.3]m, T_p ∈ [4.6;23.5]s.

Finally, the floating offshore hydrogen substation has been pre-designed, providing insight into its requirements. The high masses and dimensions led to challenges in terms of manufacturing and installation. The motions on the electrolyser units have been extracted from hydrodynamic simulations to serve as input to further experimental studies about the impact of motion and acceleration on electrolyser performance. The flowrate of brine water discharges from MED and from the cooling system was also estimated to study the impact on the environment of H2 production at sea through numerical simulations and experimental phase.

Presenting Author: Mélanie Roulet France Energies Marines

Presenting Author Biography: Mélanie Roulet is a mechanical engineer and has a PhD in instrumentation. She joined France Energies Marines in 2022 as a research project leader. She participated to two innovative projects regarding low carbon hydrogen production linked to offshore wind farm. Her work focuses on dimensioning and sizing systems.

Authors:

Mélanie Roulet France Energies Marines
Camil Matoug France Energies Marines
Laura Suarez INNOSEA
Caroline Valenchon INNOSEA
Florian Dupriez-Robin France Energies Marines
Caroline Mevel Ekium
Gweanëlle Benoit Ekium
Sylvanie Sieng Seaway7
Bertrand Auriac Seaway7
Marie Robert France Energies Marines
Lénaïg Mellaza France Energies Marines