  Policy makers are formulating offshore energy infrastructure plans, including
wind turbines, electrolyzers, and HVDC transmission lines. An effective market
design is crucial to guide cost-efficient investments and dispatch decisions.
This paper jointly studies the impact of offshore market design choices on the
investment in offshore electrolyzers and HVDC transmission capacity. We present
a bilevel model that incorporates investments in offshore energy
infrastructure, day-ahead market dispatch, and potential redispatch actions
near real-time to ensure transmission constraints are respected. Our findings
demonstrate that full nodal pricing, i.e., nodal pricing both onshore and
offshore, outperforms the onshore zonal combined with offshore nodal pricing or
offshore zonal layouts. While combining onshore zonal with offshore nodal
pricing can be considered as a second-best option, it generally diminishes the
profitability of offshore wind farms. However, if investment costs of offshore
electrolyzers are relatively low, they can serve as catalysts to increase the
revenues of the offshore wind farms. This study contributes to the
understanding of market designs for highly interconnected offshore power
systems, offering insights into the impact of congestion pricing methodologies
on investment decisions. Besides, it is useful towards understanding the
interaction of offshore loads like electrolyzers with financial support
mechanisms for offshore wind farms.
