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Tidal flow to power New York City

August 13, 2004 By Helen Pearson This article courtesy of Nature News.

Green energy firm plans turbines in the East River.

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Come September, the fishy inhabitants of New York's East River will acquire some sleek new neighbours.

Verdant Power, an energy company based in Arlington, Virginia, plans to plunge six electricity turbines into the East River. If the $4.5-million project is successful, the generators will form the first farm of tide-powered turbines in the world.

The plan is to attach the machines, which look like small wind turbines, to concrete piles hammered into the bedrock nine metres below the river's surface. As the tide surges in and out, the heads pivot to face the current and the blades spin.

The project is a modest one in electricity terms: the suite of turbines will generate just 200 kilowatts of power at their peak, enough to power perhaps 200 houses. Initially, the energy will be used to run some lights and machinery in a local supermarket and parking garage, avoiding the expense of transmission cables.

But if everything goes according to plan, company president Trey Taylor says he hopes to grow the field to 200-300 turbines stretched along the river. The UN headquarters in Manhattan is among those who have expressed interest in tapping into the environmentally friendly energy that would be produced by the project, he says.

Taylor's company chose New York as a test bed because the city chews up power so voraciously, and because state initiatives are encouraging a switch to renewable energy. But he hopes that the turbines might one day find a use across the United States and in developing countries. "The potential is very big," Taylor says.

Winds and tides

Efforts to harness tidal power have been relatively few and far between, particularly when compared with wind, solar or geothermal power. But moves to cut greenhouse gas emissions from conventional power stations are driving renewed interest in the technology around the world.

The biggest tidal project that has been installed is a huge barrage across the river in La Rance, France, which has a capacity of 240 megawatts. Such barrages work like hydroelectric dams, holding back a head of water to power generators. But they are expensive and can damage river wildlife.

The New York project signals a trend towards cheaper, free-standing turbines that can be dropped into oceans or estuaries. The first experimental tidal mills were installed last year: a 300-kilowatt turbine was sited off the north Devon coast in Britain and another of the same capacity was placed near Hammerfest, Norway. The two European companies behind them are planning to expand these individual mills into turbine fields.

Taylor believes he has an advantage over his competitors, because the design of his turbine blades means that they keep spinning even at slower water speeds. His team tested a smaller prototype of the turbine, suspended from a platform, in January 2003.

But Peter Fraenkel, technical director at Marine Current Turbines, the company that built the Devon turbine, is not convinced that Verdant will be the first to get a set of turbines up and running. "I'll be interested to see what they can do," he says, "but I'm slightly sceptical of how quickly they can do it."

Fraenkel believes that the team will hit snags when installing the machines. He also questions whether the small machines can generate power at a competitive cost. His company, in contrast, is developing huge one-megawatt turbines to bring down overheads. He hopes to have a field of them in the water by 2007.

Other power companies will be watching the New York project to see whether tidal power is an area to invest in, according to Mike Bahleda, who coordinates research on renewable energy at the Electric Power Research Institute in Palo Alto, California. "Tidal power never going to replace fossil or nuclear power, it'll supplement them," he says.

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