Driving Down Cost: A Case Study of Floating Substructure for A 10MW Wind Turbine

Power generation costs must be competitive for the offshore wind industry to survive and advance consistently. It is widely believed that adopting high-capacity wind turbines (10 MW or higher) is an effective approach to reduce levelized costs of energy. Industry trends indicate that use of high-capacity turbines is imminent, and the suitability of existing floating substructure concepts is being challenged. This paper assesses characteristics of a floating substructure for supporting high-capacity turbines. A 10 MW wind turbine application with the floating structure concept in 100m water depth is investigated and verified by using aero-hydro-servo-elastic dynamic simulations. Environmental loads considered are wind, wave and current, and simulations are performed in time domain to capture interactions and non-linear responses. Wind loading on the RNA is modeled using turbulent wind fields, with turbulence intensities representative of offshore environments, whereas wind loads on the platform are captured using reliable wind load coefficients. Effects of a 10MW turbine on the nacelle, tower, platform and moorings are highlighted, and correlations between the responses are discussed. The responses are quantified and compared using power spectral densities (to delineate low, wave and high frequency effects) and extreme statistics. Comparisons discussed in this paper underscore the importance of adaptability of platform features to maintain favorable responses of floating substructures for high-capacity turbine applications. A hull steel efficiency indicator is adopted for the quick and simple measure of substructure hull efficiency. Findings of this study offer one solution to drive down the cost dramatically and provide insights for future developments.