Spar concrete monolithic design for offshore wind turbines

Significant research efforts are now being directed at floating offshore wind turbines. The main challenge posed by floating wind turbines is the high construction and installation costs of the substructure, which make it too expensive for commercial exploitation in the current energy market. With the aim of achieving a cost-effective floating platform for offshore wind turbines, a new concept of a monolithic floating spar buoy is hereby presented. The monolithic concrete structure includes both the tower and the floater, built as a continuous single piece. This new concept offers a significant cost reduction during the construction phase and also while in operation, because the platform becomes almost free of maintenance during its lifetime. The main dimensions and the hydrostatic and hydrodynamic properties are presented, including a basic structural assessment of the platform to ensure its structural integrity. The construction and installation processes are presented, taking into account the special requirements of the monolithic design. Finally, a cost comparison between a steel and an equivalent concrete platform design has been performed, showing a material cost reduction larger than 60% in the case of the concrete design.