Assessing the lifetime O&M costs of co-located floating offshore wind and wave farms: a case study in Viana do Castelo, Portugal

Over recent decades, offshore wind has seen a rapid growth in capacity, number of turbines, turbine size, and required area — a trend that is expected to continue to accelerate. Although less mature and still above grid-parity costs, wave energy remains a promising source of clean renewable energy. Due to its complementarity with offshore wind, co-locating offshore wind and wave energy systems into an offshore hybrid farm may not only reduce generation variability but also take advantage of shared offshore transmission systems, vessels, port infrastructure, and marine area, leveraging the vast and underutilised space between offshore wind turbines. A critical aspect to consider in the development of offshore hybrid farms is the operation and maintenance (O&M) of these assets. In this study, the O&M requirements and costs of wave-floating wind farms are assessed, considering a case study at the Portuguese test-site offshore of Viana do Castelo. Preventive and corrective maintenance plans, as well as port and vessel requirements were identified based on experience and discussions with developers. A weather window assessment based on 30-years of hindcast data was carried out to assess the impacts of weather on vessel chartering strategy and total operation costs. A sensitivity analysis to major sources of uncertainty shows the impacts of changes in the distance to port, reliability assumptions (e.g. failure rates), distribution of failure events, on total O&M costs. Results suggest that co-locating wave and floating wind farms can lead to reductions in total O&M costs due to sharing  vessels and electrical assets.