Waves And Tides

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The surging ocean offers a huge, but virtually untapped, energy resource. Companies are now gearing up to catch the wave

The tide has clearly turned for the dream of harnessing the incessant motion of the sea. "Ocean energy is about 20 years behind wind power," acknowledges Roger Bedard, ocean energy leader at the Electric Power Research Institute. "But it certainly isn't going to take 20 years to catch up."

Through the 1980s and 1990s, advocates of tidal and wave power could point to only two commercial successes: a 240-megawatt (MW) tidal plant in France and a 20-MW tidal station in Nova Scotia. Now China has jumped onboard with a 40-kilowatt (kW) facility in Daishan. Six 36-kW turbines are soon to start spinning in New York City's East River. This summer the first commercial wave farm will go online in Portugal. And investors and governments are hatching much grander schemes.

The grandest is in Britain, where analysts suggest ocean power could eventually supply one fifth of the country's electricity and fulfill its obligations under the Kyoto Protocol. The U.K. government in July ordered a feasibility study for a 16-kilometer dam across the Severn estuary, whose tides rank

▼ Tide farm planned by Marine Current Turbines would use an array of turbines spaced more closely than wind generators are. The rotors, each up to 20 meters in diameter, drop to sap energy from tidal currents but can surface for servicing.

Tidal and Wave Energy Projects

□ Northern Ireland: 1 MW in late 2006

□ Northern Portugal: 24 MW by 2007

□ Northern Devon, England: 10 MW

by 2010

no date announced

REALITY FACTOR

▼ Tide farm planned by Marine Current Turbines would use an array of turbines spaced more closely than wind generators are. The rotors, each up to 20 meters in diameter, drop to sap energy from tidal currents but can surface for servicing.

▲ Wave energy devices made by Ocean Power Delivery derive electrical power from the flexing motion at their joints as waves pass underneath. Because they dive into oncoming waves, the Pelamis machines can survive the high seas that accompany intense storms.

second largest in the world. The Severn barrage, as it is called, would cost $25 billion and produce 8.6 gigawatts when tides were flowing. Proponents claim it would operate for a century or more.

Environmental groups warn that the barrage would wreak havoc on the estuarine ecosystem. Better than a dam, argues Peter Fraenkel of Marine Current Turbines, would be arrays of the SeaGen turbines his company has developed. Such tide farms dotting the U.K. coast could generate almost as much electricity as the Severn dam but with less capital investment, power variation and environmental impact.

Fraenkel's claims will be put to a small test this year, when a tidal generator the company is installing in Strangford Lough begins contributing an average power of 540 kW to the grid in Northern Ireland. The machine works much like an underwater windmill, with two rotors sharing a single mast cemented into the seabed.

"The biggest advantage of tidal power is that it is completely predictable," Bedard says. "But on a global scale, it will never be very large." There are too few places where tides move fast enough.

Energetic waves are more capricious but also more ubiquitous. An analysis by Bedard's group found that if just 20 percent of the commercially viable offshore wave resources in the U.S. were harnessed with 50-percent-efficient wave farms, the energy produced would exceed all conventional hydroelectric generation in the country.

Four companies have recently completed sea trials of their wave conversion designs. One of them, Ocean Power Delivery, will soon begin reaping 2.25 MW off the coast of Portugal from three of its 120-meter-long Pelamis machines. If all goes well, it will order another 30 this year. Surf's up.

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Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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