On the Use of Wire-wound Pressure Vessels for a Hydro-Pneumatic Energy Storage Concept Integrated in Floating Wind Turbines

Coupling energy storage to floating wind turbines will facilitate the integration of large floating wind farms into electricity grids. This paper deals with a hydro-pneumatic energy storage concept integrated in a floating offshore wind turbine in order to stabilize the intermittent power output from the turbine. The energy storage concept includes two pressure vessel bundles, one installed on the seabed and the other integrated in the floating spar supporting the turbine itself. The present study investigates the potential reductions in steel requirements for the storage system by introducing high strength wire winding around the cylindrical pressure vessels. The study is based on a storage system integrated in a spar supporting a 6 MW FOWT. A new mathematical approach for sizing the pressure vessels, determining the concrete requirements for ballasting the spar-type floater and anchoring the pressure vessels on the seabed is presented. A parametric analysis is then presented to examine the impact of the yield strength and diameter of the wound wire on the steel and concrete requirements for the energy storage system. It is shown that while circumferential wire winding brings about considerable reduction in the overall steel mass, the concrete requirements increase. Yet the increase in concrete required is not significant and, given that concrete cost is much lower than that of steel, it is expected that the net impact of wire winding would still result in reduced cost for the storage system.