Investigation of a dynamically positioned floating offshore wind turbine concept

Abstract

The dynamically positioned wind turbine concept consists of a floating platform equipped with a wind turbine and propellers. In contrast to a conventional floating offshore wind turbine, it has no moorings. Instead, the propellers are used to keep the wind turbine stationary. It may also be equipped with an on-board energy storage system (e.g. batteries, hydrogen, etc.) to avoid grid-connection. This concept is well suited for deployment in the far-offshore, where grid-connection and installation operations are challenging. As the propellers which are used to control the position of the wind turbine require power supply, the aim of this study is to investigate whether and in what conditions there can be a positive net power production. To this end, we have developed a velocity and power prediction program (VPPP) to estimate the power consumed by the propellers and the power generated by the wind turbine, as a function of wind conditions, and design parameters (e.g. diameter of the wind turbine and characteristics of the propellers rotors). The VPPP is based on Newton’s first law of motion. The forces applied on the system are: the wind turbine thrust, the mean wave drift, and the propellers thrust. Inspired by an existing floating offshore wind concept, an example design has been developed. The diameter of the wind turbine’s rotor is 78 m. Its rated power is 2 MW. The wind turbine is mounted on a 40 m square barge. The diameter of the propellers’ rotor is 6 m. Using the VPPP, the power performance of this example design has been investigated as function of wind conditions. The maximum generated power is 0.89 MW. It is obtained for a true wind speed of 13.4 m/s. If deployed in the Northern Atlantic Ocean, this design could achieve a capacity factor of 15%, which is low in comparison to the 70% capacity factor which would be achieved by a moored floating offshore wind turbine if deployed at the same location.