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Science and Technology

Tidal Power a Reality

In a novel use of clean energy, the world's most northerly town will soon be the first to get electricity from a sub-sea power station run on tidal currents tugged by the moon.

Gigantic forces in the oceans waves, currents, and tides have often proved too costly or awkward to harness, compared to wind or solar power, in global efforts to cut reliance on nuclear power or on fossil fuels blamed for global warming.

Starting in late November or early December, however, a tidal 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 Stroem.

Other unorthodox sub-sea experiments to generate power from tidal currents from Australia to Britain have not gotten to the stage of selling power. All the technologies mark a shift in traditional methods of exploiting the tide. Tides have previously been tapped for use in power plants in France, 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 sliced up.

"Of all the renewable energy technologies, ocean energy is probably the one in the earliest stages," said Mark Hammonds at the International Energy Agency (IEA) in Paris. "Many projects have proved to be too costly."

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.


The Norwegian sub-sea turbine will have a tiny capacity of 300 killowatts and is due to expand to 20 mills from 2004, giving enough power for perhaps 1,000 homes.

Hammerfest, with 11,000 inhabitants, calls itself the world's northernmost town. Johansen reckons the project there has cost 50 million Norwegian crowns (US$6.7 million) so far and will cost 100 million by completion in 2004.

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 sub-sea maintenance costs. Storms have wrecked many experimental ocean power stations.

"We need to harness all low-impact renewables we can develop. But offshore wind is more competitive and solar has more potential," said Greenpeace spokesman Truls Gulowsen.

The biggest tidal power plant in the world is a barrage across the La Rance river in northern France, in place since the 1960s. It has a 240-megawatt capacity, but Electricite de France has no plans to build new ones.

Canada's Bay of Fundy in Nova Scotia has the highest tides in the world, at about 39 feet. Nova Scotia Power's 20 megawatt plant at Annapolis Royal, built in 1984, is the only one in North America, but the company is now focusing more on wind. "There are ecological objections to building more tidal plants along the coast," said Margaret Murphy, spokeswoman for Nova Scotia Power.

All the plants are tiny. Western-style nuclear generators typically have a capacity of 500 to 1,000 megawatts and can be counted on for reliable power generation, unlike many renewable energy sources.


In Norway, Hammerfest Stroem reckons that building tidal turbines could become a business worth hundreds of millions of dollars. It notes many experts used to dismiss windmill parks, now widespread in countries like Denmark, as quixotic.

In Kvalsund, the water flows at about 8.2 feet per second apart from a pause at high and low tides. By contrast, windmills are useless in calm weather and have to be built to withstand hurricane force winds.

Solar power is a non-starter in winter in Hammerfest, where the sun sets for about two months in mid-winter. The town was the first in Europe to get street lighting almost 100 years ago.

But costs of the electricity are initially likely to be three times that of typical hydro-generated electricity in Norway. Tidal power will be added to the mix of electricity in the local grid and consumers will be obliged to swallow the cost.

The tidal turbines weigh about 200 tons including 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.

British-based Marine Current Turbines, which plans to test a similar tidal current system off Devon in southern England next year, says that maintenance could be a problem for Hammerfest. "When you have strong enough currents for tidal energy generation, there are few slack tides when divers can work," said Peter Fraenkel, the group's technical director.

Marine Current Turbines' design, which sticks above the water, allows the turbines to be winched up to the surface. "The size of this resource is not understood," he said. He said that a British study a decade ago estimated that the eight most promising sites off the British coast alone could generate one-fifth of Britain's electricity.

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