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Underwater wings for tidal power

September 24, 2003

A NOVEL machine that generates electricity from marine tides will be put to the test off the Scottish coast next year. Called the Snail, it uses the flow of water over wings to anchor it to the seabed. This will allow it to operate at a greater range of sites than rival models, its designers say.

Tidal flows have the potential to supply large quantities of renewable energy. But the few large-scale generators currently in operation create environmental problems that have prevented the technique from becoming popular. They work by forcing the tidal flow of water in shallow estuaries through narrow channels containing a turbine, but this can disrupt the tidal ecosystem.

Turbines in deeper coastal waters are a different story: they can exploit a tidal flow without significantly changing it. The sea around Scotland alone could generate up to16 gigawatts of electrical power, an output equivalent to that of about seven nuclear power stations. Generating power in remote locations is much more challenging, however.

Just securing power turbines to the seafloor is a tricky business that limits where they can be used. One option is to drive pillars into the seafloor, but this is expensive and impossible in water more than50 metres deep. Another option is to make the structure heavy enough for its weight to hold it in place, but this makes it difficult to transport. Such a generator would have to weigh almost 200 tonnes.

The Snail, designed by engineers at The Robert Gordon University in Aberdeen, is smaller and lighter than its rivals, standing 15 metres high and weighing only 20 tonnes.A set of underwater wings or hydrofoils generates a downward force as the current passes over it. "This acts to secure the device onthe seafloor without substantial preparation of the seabed," says Ian Bryden, who runs the project. The team plans to test a prototype early next year in Eynhallow Sound in Orkney.
Author: Sasa Petejan

http://www.newscientist.com">New Scientist issue 27 September 2003

New Scientist