Integration of a direct drive contra-rotating generator with point absorber wave energy converters

Wave energy converters (WECs) produce reciprocal motion which requires a complex power transfer and take‐off system to generate the rotary motion necessary to drive an electrical generator. These systems are often expensive and unreliable, and can introduce considerable power losses reducing the efficiency of the device. This study investigates the application of a direct drive contra-rotating generator (DD-CRG), originally designed for the tidal energy industry, to a generic point absorber wave energy converter. The contra-rotation of the generator facilitates lower torque and higher speed inputs compared to a
conventional direct drive generator, reducing the size, weight and cost of the power take-off system. It was found that the existing generator design was technically and physically compatible with the point absorber device. Furthermore the wave energy application enabled optimisation of the generator design to increase the generator speed and further reduce the applied torque. This led to a significant reduction in the levelised cost of energy of at least 20% compared to using a conventional hydraulic drivetrain in the same device. Adoption of the DD-CRG within the wave sector would bring additional benefits due to its tailored design for the marine environment, and further cost reductions could be realised through the increase in manufacturing volume.