Assessing the impact of waves and platform dynamics on floating wind turbine energy production

Abstract. Waves have the potential to increase the power output of a floating wind turbine forcing the rotor to move against wind. Starting from this observation, we use four multi-physics models of increasing complexity to investigate the role of waves and platform movements in the energy conversion process of four floating wind turbines of 5–15 MW in the Mediterranean Sea. The current technology of spar and semi-submersible floating wind turbines is not suitable to exploit the energy of waves because their design philosophy aims to minimize motions and structural loads, whereas large along-wind rotor movements are needed to increase the power output. Instead, in a realistic met-ocean environment, the power curve of the floating wind turbines we analyzed is lower than with a fixed foundation, with AEP reductions of 1.5–2.5 %. The lower energy production is mainly ascribed to the platform static tilt, which reduces the rotor area projection on the vertical plane, and to floating-specific features of the turbine controller, that are thought to mitigate structural loading sacrificing performance.