Towards offshore hydrogen production via floating wind turbines: a comparative study on main electrolyzer technologies in two Mediterranean case studies

This study evaluates the performance of different electrolyzer technologies in offshore wind-to-hydrogen systems, focusing on improving integration with fluctuating power from floating offshore wind turbines (FOWTs). Electrolyzers with wide operational ranges, such as proton exchange membrane (PEM) and anion exchange membrane (AEM), while less industrially ready than alkaline ones (ALK), may indeed offer advantages in adapting to variable wind power, reducing energy curtailment, and improving overall hydrogen production efficiency. To assess this integration, a comparison between the performance of PEM, AEM, and ALK electrolyzers under different wind conditions is presented, using four 15 MW FOWTs with specific power values ranging from 260 to 175 W/m2, deployed in a 1 GW reference floating wind farm at two Mediterranean sites. The deployment of hydrogen production stations in this area is indeed key for decarbonizing some hard-to-abate industries (e.g., shipyards, steelmaking, etc.) that are largely present close to Mediterranean ports. The analysis incorporates realistic electrolyzer polarization curves, calendar degradation, and thermal effects in 10-min time-dependent simulations to mimic the system behavior accurately. This leads to a novel approach that combines the assessment of turbine-specific power and electrolyzer operational behavior using high-resolution dynamic simulations, enabling a technology-consistent comparison of ALK, PEM, and AEM technologies under realistic offshore wind variability in the Mediterranean context. Results indicate that the optimal specific power for FOWTs is 262 and 175 W/m2, for the installation site in Sicily and Cyprus, respectively. These configurations contribute to reduce the levelized cost of hydrogen, with a benefit up to 1.5 €/kg in the Cypriot case with respect to the reference 15 MW turbine. The findings underscore the importance of selecting electrolyzers with high flexibility to enhance the stability of hydrogen production, particularly in regions with low and variable wind speeds. On the other hand, despite the higher energy curtailments, ALK's lower capital expenditures and degradation rates result in the most cost-effective solution in the simulated scenarios. This study provides valuable insights for optimizing offshore wind-to-hydrogen systems, demonstrating that a combination of electrolyzer technology and low-specific-power turbines can improve economic viability and facilitate large-scale hydrogen production also in sea basins with moderate wind speeds like the Mediterranean Sea.