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Swell magnet stokes support for wave power

October 11, 2005 By Mark Peplow This article courtesy of Nature News.

Simple generator pulls green energy from the ocean.

A generator that produces electricity from the ocean's swell has been unveiled, and its inventors hope that its simple design will beat existing wave-power technologies on efficiency and cost.

Engineers have tried a range of different techniques to tap the power of the sea, but none has yet seen large-scale use. Most rely on channelling water over turbines, pushing air through pipes or harnessing the gentle rocking motion of a buoy. Although prototypes have shown promise, scaling up these devices has proven tricky.

Hugh-Peter Kelly, the founder of Trident Energy, a small British company based in Southend-on-Sea, thinks his system might crack previous problems and allow wave energy to come of age.

Wave power is a lot less fickle than wind.
Hugh-Peter Kelly
Trident Energy, Southend-on-Sea, UK
His invention uses the up and down motion of a floating buoy to move an electrical coil along a stack of magnets, which generates an alternating current in the coil.

"At a stroke you get rid of all the hydraulics that the rotary generators used by other wave power devices need," says Kelly. This should make the device relatively cheap and reliable, he says. And as the generator only moves up and down it takes up very little space, so a number of them could be crammed into a small area.

In July, Kelly tested a one-fifth scale model of the generator in a large wave tank at the New and Renewable Energy Centre in Blyth, Northumberland. Results show that each full-scale generator should supply up to 100 kilowatts of power.

Buoys are us

The generator would have to be attached to a platform in the sea, rather like a small oil rig. That means more construction, but it would use well-established techniques says Richard McMahon, an engineer from the University of Cambridge who helped Trident to refine its prototype.

Kelly calculates that a wave farm covering at most 1.5 square kilometres would generate about 100 megawatts of power: the equivalent of a small power station.

Trident's floats would be the only thing exposed to corrosive salty water, as all the electronics are kept high and dry on the rig. And even the floats could be drawn up out of harm's way during a storm by reversing the current through the generators and turning them into motors.

Powered up

The company is planning to spend about £4 million (US$7 million) on a quartet of full-size generators, which they hope to deploy at the European Marine Energy Centre in Orkney, off the north coast of Scotland, by the end of 2007.

The system works most efficiently when the waves are 0.5-5 metres high, and Kelly says that in an ideal location like Orkney the generators should be able to run about half of the time. That beats most wind-power generators, which can spend 75% of their time idling. "Wave power is a lot less fickle than wind," says Kelly.

But it may be many more years before the Trident system starts to put electricity into the national grid. "Power generation from waves is still in an early stage of evolution," admits McMahon, much as wind energy was some 20 years ago. Only time will tell, he says, which design will prove best over the coming years.


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