Contra-rotating marine current turbines: single point tethered floating system - stabilty and performance

The Energy Systems Research Unit within the Department of Mechanical Engineering at the University of Strathclyde has developed a novel contra-rotating tidal turbine (CoRMaT). A series of tank and sea tests have led to the development and deployment of a small stand-alone next generation tidal turbine. Novel aspects of this turbine include its single point compliant mooring system, direct drive open to sea permanent magnet generator, and two contra-rotating sets of rotor blades. The sea testing of the turbine off the west coast of Scotland in the Sound of Islay is described; the resulting stability of a single-point tethered device and power quality from the direct drive generator is reported and evaluated. It is noted that reasonably good moored turbine stability within a real tidal stream can be achieved with careful design; however even quite small instabilities have an effect on the output electrical power quality. Finally, the power take-off and delivery options for a 250kW production prototype are described and assessed.