Paradoxically, sea surface area for offshore wind farms is limited in some countries like Japan. While the distance from the shore to a wind farm is limited due to the cost of electric transmission, the near shore area has considerable traffic of ships and is restricted by complex rights of local fisheries. One approach to the problem is inviting the local fishermen to the management of the wind farm. It requires higher economic performance of the wind farm than the original fishing activity in the same sea surface area.

The proposed concept is the combination of a floating wind turbine and counter-rotating water current turbine. The water current turbine partially cancels the reaction torque of electric generator and provides additional energy production from water current. The rotating axis of the turbine is not fixed in the upright position to reduce the size of supporting structure. Regular maintenance work is only in low altitude on the float. These features lead to the reduction of O&M costs and higher utilization of sea surface area.

This paper describes the prototype sub-megawatt turbine under construction and its expected economic performance.

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