Undercurrents The world's most northerly town will soon be the first to get electricity from an underwater power station run on tidal currents. Starting from December 2002, the current will start turning the blades of a windmill-like turbine standing on the seabed near Kvalsund at the Arctic tip of Norway. "We will be the first in the world to use tidal currents to generate electricity to be fed into the local grid,' said Harald Johansen, managing director of Hammerfest Strom, the company installing the turbine.

The tidal turbines weigh about 200 tonnes at the base and are well below the keels of passing ships. They turn to face the tide when the currents change direction. The turbines are designed to be maintenance free for three years, but divers can go down if needed. At present, the turbines will have a tiny capacity of 300 kilowatts, but it would be expanded starting from 2004, giving enough power for perhaps 1,000 homes. Johansen reckons the project has cost us $6.7 million so far and will cost twice as much by completion. Due to this, the initial cost of electricity is likely to be three times that of typical hydro-generated electricity in Norway. The tidal power will be added to the mix of electricity in the local grid, and consumers will be obliged to swallow the cost.
Waves of hope Tidal power exploits the gravitational pull of the moon, and to a lesser extent the sun, on the oceans as the Earth spins. The seas rise and fall in a cycle of 12 hours and 25 minutes and can cause sweeping currents along the seabed at the same time, like the ones seen off the north Norway coast.

High oil prices and pledges to curb emissions of greenhouse gases as part of the Kyoto pact to limit global warming, blamed on emissions from burning coal or oil, are helping make green technologies like tidal power more attractive despite their drawbacks. Other systems to tap the oceans range from giant snakelike tubes that generate power when rocked by waves, to machines that extract power from the contrast between warm surface waters and chill temperatures at ocean depths. But experts are uncertain about the potential, especially because of subsea maintenance costs.

Other unorthodox subsea experiments to generate power from tidal currents from Australia to Britain have not reached the stage of selling power. All the technologies mark a shift in traditional methods of exploiting the tides. Tides have previously been tapped for use in power plants in Canada and Russia by building barrages to trap water in artificial lagoons at high tide. When the tide goes out, gravity sucks the water through turbines to generate electricity.

But giant damming projects are out of fashion because they can damage the ecology of rivers and coastlines. Seabed turbines, by contrast, are silent and invisible, and fish can swim around them without getting hurt. "Of all the renewable energy technologies, ocean energy is probably the one in the earliest stages,' said Mark Hammonds at the International Energy Agency in Paris. "Many projects that were undertaken in the recent past proved to be extremely costly.'

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