Offshore availability for wind turbines with a hydraulic drive train

Hydraulic drive trains for wind turbines are under development by a number of different companies; at least one hydraulic drive train is in the final stages of development by a leading wind turbine manufacturer. Hydraulic drive trains have a number of advantages such as redundancy, modularity, compactness and track record in other industries. Currently there are few or no installed wind turbines with hydraulic drive trains onshore or offshore. As no data exists on reliability or failure rates for wind turbines with hydraulic drive trains, this paper estimates failure rates, repair time and availability for said turbines. The paper contains an availability comparison with other drive train types, in which the hydraulic drive train performs best. However, this superior performance should be validated because of the number of assumptions that have been made in this availability estimation.