The Mocean wave energy converter (WEC) is a hinged raft device. The dynamic response of the raft’s two bodies to wave forcing leads to a flexing motion about the hinge, which drives a power take-off mechanism that converts the kinetic energy into electricity.
The innovation of the Mocean WEC is in the design of the shapes of the bodies, which dramatically improves its dynamics and thus power absorption. The configurations are based around varying the ratio and position of the water-plane area to the submerged volume, where the water-plane area affects the hydrostatic restoring force and the volume affects the mass and added mass. By changing these values one can induce coupling between the modes of motion and so tune the resonant response to improve performance in wavelengths that are significantly longer than the overall length of the machine.
The component bodies are designed to be hydrodynamically quite dissimilar. Consequently, although the power take-off is solely in flex around the hinge, there is extensive cross-coupling with other degrees of freedom, and when excited by wave action the device responds not only in flex but substantially in heave and also pitch and surge. This results in greater cancellation of the incoming wave and a broader bandwidth response than a standard hinged raft.
This project has completed stage 3, and final public reporting is due to be published shortly.
The project has completed the detailed design, build, and testing of a ½ scale sea-going prototype Mocean WEC, named Blue X. The WEC comprises forward and aft hulls, patented wave channels, a PTO nacelle and power control subsystems in the forward hull. It was fabricated and assembled in Fife, then had its submergence and trim adjusted in the water by the addition of ballast, before being transported by road and ferry to Kirkwall in Orkney.
The test programme was performed at the EMEC nursery site in Scapa Flow, and focussed on the performance of the WEC. The sea state was measured with a wave buoy while the WEC response and its output power were continuously measured. Several testing campaigns of deployment, test and recovery were carried out, with maintenance and inspection between each. In addition to the power performance of the WEC, the test programme assessed the behaviour and practicalities of the mooring system and the electrical connection.
The long-term vision for the Mocean technology is to further develop the present concept of a 100kW WEC suitable for the commercial powering of subsea oil and gas infrastructure, as well as islands and small communities. With the technical and commercial experience and credibility gained from this first stage, we will commence the more ambitious development of a 1MW WEC suitable for deployment in grid-connected wave farms.