DNV confirm’s Seagen’s performance
SeaGen has met its design goals, with the peak efficiency for both rotors on both tides averaging 48%.
Norway based Det Norske Veritas (DNV) has certified that the performance of the world’s largest tidal turbine, the 1.2MW SeaGen, has been correctly evaluated according to the Edinburgh Protocol.
The protocol for tidal turbine testing was developed by the University of Edinburgh for the UK Government’s Department of Energy & Climate Change, and also the European Marine Energy Centre’s own testing protocol.
DNV undertook a detailed review of the measurement programme used by Marine Current Turbines (MCT) for determining the performance of the company’s SeaGen tidal energy turbine, which has been operating in Northern Ireland’s Strangford Lough since 2008. DNV has verified that the measured results have been correctly obtained and interpreted.
Testing a large machine installed in the aggressive conditions of a tide race is a technically challenging process and large volumes of data are needed to be recorded and analysed. Some key results that came from this programme indicate that SeaGen has met its design goals with the peak efficiency for both rotors on both tides averaging 48% (Cp = 0.48) The best result was a peak efficiency of 52% and the worst peak was 45%. This compares favourably with the recorded efficiency claims of leading wind turbine manufacturers which function analagously, albeit using a fluid that is 800 times less dense. The absolute theoretical maximum efficiency for a perfect rotor would be 59.3%, a well known limit generally attributed to the German aerodynamicist Albert Betz. SeaGen has been found to achieve from 75% to 88% of the theoretical ideal.
The corresponding overall system efficiency, including all losses in the generator, gearbox and power electronics, was found to be in the range 40% to 45% That is the proportion of energy in the flow of water intercepted by SeaGen’s rotors that can get delivered as electrical energy into the grid. Because SeaGen is accredited by regulator OFGEM as a UK generator, the world’s first and only official tidal current power plant, and therefore sells electricity and earns ROCs (Renewable Obligation Certificates), the output to the grid is also independently metered and audited.
Peter Fraenkel, technical director of MCT said, ‘Our engineering team are delighted that SeaGen has been shown to deliver such good results, and DNV’s endorsement provides a valuable confirmation of the accuracy of the team’s design assumptions for a system which originally involved much uncertainty through being a world’s first.’
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