Comparison of multiline anchors for offshore wind turbines with spar and with semisubmersible

Abstract

Offshore wind energy has become a promising source of renewable energy in recent years with many installed farms around the world successfully producing energy. As preliminary wind resource studies reveal, in the US much of the potential could be tapped in deeper water where floating solutions become favorable. The efficiency of floating offshore platforms is being studied and demonstrated in pilot projects such as Hywind in Scotland. In order to reduce the substructure cost in offshore wind projects, which is usually 25-30%, a novel shared anchor concept has been studied with spar supported turbines. Simulations are carried out with National Renewable Energy Laboratory’s (NREL) OC3 Hywind floating system and 5MW wind turbine. A similar study has been carried out with semisubmersible platforms earlier. Comparing the statistics of the net anchor forces from both the types of platforms reveals decreased anchor forces in case of spar due to large force cancellation and decreased response to wave action. Given the shared anchor concept in-principle reduces the material cost with reduced number of anchors than the conventional anchor types; further reduction in anchor forces in case of spar supported platform would be more cost-beneficial with more material savings.