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Electricity From the Sea - 18/08/2008
 
Turbines harness power of tidal flows
1. An underwater turbine that generates electricity from tidal streams was connected last month to the national grid. It’s the first time a commercial-scale underwater turbine has fed power into the network and represents the start of a new source of renewable energy for the UK. Its introduction has been attended by a little controversy.

2. Viewed as plentiful, predictable sources of “clean” energy, the tidal streams could be harnessed to yield at least five gigawatts of power around Britain, but there could be as much as 15GW. At the opening trial of the SeaGen turbine (launch seems an unapt word) in Strangford Lough, Northern Ireland, 150kW was generated. Output should be doubled by the end of the summer. When it is eventually running at full power SeaGen will have an output of 1.2MW, which is enough for about 1,000 homes.

3. SeaGen was designed and built by the Bristol-based company Marine Current Turbines (MCT), which also installed the test device at Strangford in May. Tidal streams and the generators harvest energy with the advance that the resource, unlike wind, is predictable. In Strangford Lough, the tide runs very fast and the site is sheltered from bad weather. The turbines are mounted on wing-like extensions either side of a steel tube 3m in diameter that can be raised for maintenance: it is an underwater windmill.

4. The secretary of state for business, John Hutton, said: "Marine power has the potential to play an important role in helping us meet our challenging targets for a massive increase in the amount of energy generated from renewables." The Department for Business, Enterprise and Regulatory Reform backed SeaGen with a £5.2m grant. The cost of installing the marine turbines is £3m for every megawatt they generate, which compares to £2.3m per megawatt for offshore wind. MCT plans to build a farm of turbines before 2011. Its next site will be off the coast of Anglesey, where the initial farm will be rated at 10.5MW, with a potential of 350MW.

5. We hail this advance in generating renewable energy, which could suit many island and estuarine communities with little environmental disturbance and loss in long-distance transmission. However, we note that powerful tides, although predictable, may entail rises and falls (of 10m or more) and variable flows during ebb and flood and spring and neap tides; they would probably need compensative back-up at times or balancing with other tidal sources not too distant but remote enough to rectify extremes of highs and lows.  
 
 

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