Mocean Wave Energy Converter

Overview

The Mocean WEC is a hinged raft with seven degrees of freedom. Wave forcing and the bodies’ dynamic responses leads to flex about the hinge which drives a power take-off mechanism, converting the kinetic energy into electricity.

The innovation of the Mocean WEC is in the design of the shapes of the bodies, which dramatically improves the 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.

Changing these values can induce coupling between the modes and tune the resonant response to improve performance in wavelengths that are significantly longer than the overall length of the machine.

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. Changing these values can induce coupling between the modes and tune the resonant response to improve performance in wavelengths that are significantly longer than the overall length of the machine

During the course of the project, Mocean developed the concept for a 100kW WEC, and also designed, built and deployed an approximately a ½ scale sea-going prototype, called the BlueX.

The device geometry has two slender tubular hulls either side of the hinge, with the key innovation being two sloping, deeply-submerged plates at the fore and aft ends of the WEC, which are 3 times the width and depth of the tubular hulls. Overall, the forward section is twice the length of the aft. The combination of the asymmetrical sections and the submerged plates delivers performance that is 3 times greater than the classic hinged raft.

The main activities reported on are:

• Further development of the numerical optimisation suite.
• Design, build and wave-tank test scale models.
• Create the detailed engineering design of a full-scale WEC.
• Specification of the PTO components: the magnetic gear and generators, the power electronics and the high-level control.
• Clarify the marine operations that will be required to deploy, retrieve and maintain the WEC.
• Carry out a reliability study that will identify the main failure modes and repair & maintenance strategies.
• Evaluate the capital cost and LCOE of the WEC incorporating uncertainty.
• Create a Front-End Engineering Design of a large-scale prototype suitable for building in a Stage 3 project.

Within Stage 3 of this project, the team completed detailed design, build, and testing of the BlueX. 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 WEC concept and apply it to 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.