Det Norske Veritas, the international Marine and Offshore Certification and Classification agency (DNV)) has completed 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. DNV have issued a Statement of Conformity to certify that the performance of the world’s largest and most powerful tidal turbine, the 1.2MW SeaGen, which has been operating in Northern Ireland’s Strangford Lough since 2008 has been correctly evaluated according to the principles in the “Edinburgh Protocol” (using the MCT method statement which is based on the protocol for tidal turbine testing developed by the University of Edinburgh for the UK government DECC)
Marine Current Turbines, developer of the SeaGen turbine, as the leader in this field, has been pioneering testing procedures on the basis of protocols developed by Edinburgh University and by EMEC (the European Marine Energy Centre). 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 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) and the best result was a peak efficiency of 52% and 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. So 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 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.
The diagram below shows SeaGen’s power curve made up from data collected as part of this validation programme which was subjected to scrutiny by DNV. It can be seen that there is a slight variation in performance between the ebb and the flood tides. The ebb tide performance may be slightly enhanced by the streamlined cross-arm which carries the power trains, as this is upstream of the rotors on that tide.
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 very pleasing confirmation of the accuracy of the team’s design assumptions for a system which originally involved much uncertainty through being a “world’s first” “.
Notes to Editors:
1. Marine Current Turbines Ltd (www.marineturbines.com) is based in Bristol, England. The company was established in 2000 and its principal corporate shareholders include BankInvest, Carbon Trust Investments, EDF Energy, ESB International, Guernsey Electricity, High Tide and Siemens Energy.
2. In September 2009, MCT was ranked the world’s top tidal energy company in The Guardian/Clean Tech Global 100 Survey and in June 2009 won Renewable Energy Developer of the Year in the UK Renewable Energy Association Annual Awards.
3. MCT’s 1.2MW SeaGen was deployed in Northern Ireland’s Strangford Lough in April 2008; it has the capacity to generate power for the equivalent of about 1500 homes. It works in principle much like an “underwater windmill” with the rotors driven by the power of the tidal currents rather than the wind. The SeaGen turbine is subject to a rigorous monitoring programme imposed under its licensing conditions to ensure it does not threaten the marine life of Strangford Lough where it is located.
4. SeaGen is accredited by OFGEM as a UK power station and so is a recipient of Renewable Obligation Certificates (ROCs).
5. Since February 2008, MCT has partnered RWE npower renewables on plans to develop a 10MW tidal farm in waters off Anglesey, north Wales and is working with Minas Bay Pulp & Paper to deploy a single SeaGen system in Canada’s Bay of Fundy.
6. In March 2010, MCT secured approval for a lease from The Crown Estate to deploy its SeaGen tidal current technology off Brough Ness, on the southern most tip of the Orkney Islands (South Ronaldsay) and north east of John O’Groats. The company plans to have its first phase of SeaGen tidal turbines deployed there during 2017 with the whole scheme operational by 2020.
For further information:
Marine Current Turbines (www.marineturbines.com)
Martin Wright/Peter Fraenkel,
Tel: 0117 979 1888
Paul Taylor (Taylor Keogh Communications)
Tel: 020 3170 8465 / 07966 782611