E.ON and tidal stream technology

It is adventurous of E.ON to decide to invest in tidal stream generator farm. The announcement in the last few days confirmed that the company intended to put a tidal plant off the coast of Wales in a partnership with Lunar Energy.

The Severn barrage scheme (see Carbon Commentary Newsletter #3) is a ‘tidal range’ scheme. The electricity is generated by damming the river at high tide and then letting the water flow out through turbines as the tide falls. Tidal stream technology captures the energy of the tide as it flows through constricted channels. The UK has many potential sites for tidal stream power stations, but the best locations are off the north coast of Scotland and around Alderney in the Channel Islands.

Why then has E.ON chosen Wales? Perhaps the company doesn’t want to test the technology in the toughest conditions. An attempt to use similar underwater turbines in New York’s East River has been frustrated by the breaking off of the tips of the turbine blades in the fast flowing tides. The UK’s offshore conditions will be far tougher. Or it might be that E.ON knows that it would be expensive or impossible to connect the turbines to the distribution grid in the locations of highest energy potential (see the news story in this section on BT’s plans for wind turbines in Orkney and Shetland). Previous rumours have suggested that the eventual site chosen will either be off the coast of Pembrokeshire or off Anglesey.

The recent report into the Severn barrage noted that there at least 24 different technologies for capturing tidal stream energy in the UK. The device promoted by Lunar Energy sits on the sea floor, is about 20m long and has a turbine diameter of about 12m. The blades sit within a case which focuses the tidal flow. As a Venturi device, the speed of the water flow within the case is greater than the flow outside, adding to the amount of energy that can be captured.

Is wave power economic? It is probably too early to say. The UK has excellent tidal streams around the country, but even this advantage may not be enough. Lunar Energy optimistically quotes figures of around 2.5p to 5p per kilowatt hour, which would make the technology extremely attractive, but these figures appear only to be based on some guesses made in the US. The Carbon Trust’s recent report suggested figures at least three times as much for the first implementations of tidal stream power plants. On the other hand, informal figures from the New York project have suggested figures close to the Lunar Energy estimates.

E.ON has been working with Lunar Energy for some time. It had been thought that the generator would not commit until after sea trials of the first Lunar device in Scotland next year. Last week’s announcement suggests that E.ON’s confidence in the technology and Lunar Energy is high.