Buoy for linear wave energy converter

• A wave energy converter (WEC) of point absorber type has been developed and tests have been conducted outside Lysekil. The project started in 2002 and linear permanent magnet generators together with a subsea substation and buoys of various geometric shapes have been built and tested. The system is based on a low number of mechanical moving parts and the power conversion from ocean waves to electricity maintaining the quality of the national grid is handled electrically, due to the long life span of electric components. Reliability is highly prioritized in this design. To monitor the test site, measurements of electric output are done on the generators and substation. Also measurements of acceleration in heave mode are done on the buoy itself together with measurements of force between the buoy and the generator. The measurements are transmitted through the public cellular network. Also a internet based camera is set up at the site to monitor the buoys of the WECs visually. The monitoring systems, both visual and quantitative have proven to work successfully. In order for a WEC to produce electricity at competitive prices, the generator must not be larger than necessary in order to save economically on production, transport and installation. However, the WEC must be dimensioned to withstand harsh sea states. High added mass will in some cases create harsh inertia forces on the generator and large inertia forces on the buoy which might shorten the life time of the system considerably. The magnitude of the unwanted forces can be reduced by taking account for added mass when choosing a buoy geometry. A toroidal buoy is found to have less added mass than a vertical cylindrical buoy with similar excitation force.

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