THE EARTH’S OCEANS, TUGGED BY THE moon and sun, ebb and flow over more than 70 percent of the planet. After fits and starts, researchers have developed a number of technologies to effectively harness some of that kinetic energy. Now a handful of entrepreneurs are trying to create a commercial market.

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Underwater Windmills
The most advanced demonstration operates at the bottom of New York City’s East River, which is actually a tidal channel. In 2006 Verdant Power planted six windmill-like turbines on the riverbed, underneath 30 feet of water, away from boat traffic. Each turbine, 16 feet in diameter, churns at up to 32 revolutions per minute to transform strong tidal forces into electricity. Despite initial setbacks—the river’s potent flow damaged some of the rotors and snapped some of the original fiberglass and steel blades—the company has kept two of the turbines operating, enough to attract $8.5 million in government funds for further development and testing.

To generate energy cost-effectively, Verdant’s turbines require tides that move at least six feet per second, and the East River is more than obliging. “Plus, New York is an expensive place to buy power,” says company president Trey Taylor, “so it would be easier here to prove that this could help.”

The East River site has the potential to support as many as 300 turbines. By 2010 Verdant hopes to have 30 in place, with a combined capacity of one megawatt of energy (enough to support approximately 800 households). Taylor would like to eventually complete two fields of underwater turbines that provide up to 10 megawatts. Other opportunities abound around New York State, he adds. One estimate predicts as much as 1,000 megawatts of potential. The company is looking at sites in China and India, too. Next year Verdant also plans to test a new type of turbine in the St. Lawrence River, near Cornwall, Ontario, that will be heavily weighted on the seabed rather than moored, making removal easier when repairs are needed.

Other tidal companies have begun to follow Verdant’s lead. U.K.-based Lunar Energy is working with Korea Midland Power Company to create a giant, 300-turbine field in the Wando Hoenggan Water Way off the South Korean coast. The installation is expected to provide 300 megawatts of power by December 2015. And researchers at Florida Atlantic University are developing designs that tap into the strong Gulf Stream off Florida’s shores. In September the U.S. Department of Energy indicated it would provide $1.2 million over five years to advance the commercial viability, cost-competitiveness and market acceptance of new technologies that harness oceans and rivers.

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The Water Snake
Tides, of course, manifest themselves as waves at the ocean’s surface, with help from winds. Pelamis Wave Power in Edinburgh, Scotland, is looking to ride this rolling source of energy.

Pelamis has built huge, floating tubes, each 427 feet long and 13 feet in diameter, weighing around 750 tons. Each tube has a number of cylindrical sections that are connected by massive hinges. As the links rise up and down on the passing waves, they tug on the hinges between them, but hydraulic rams resist by pumping high-pressure fluid through motors that turn electrical generators to produce electricity. “Our machine works by reacting against itself,” says Max Carcas, business development director at Pelamis. The power is fed down a line to an undersea cable that runs to the shore.

The tubes function best above water that is 165 to 230 feet deep, roughly half the wavelength of open-ocean waves, which tend to be 330 to 460 feet from peak to peak. Waves lose energy once the water depth is less than half a wavelength, Carcas says. The distance off the coastline to find such conditions varies but is typically 1.2 to 9.3 miles.

Pelamis, along with its business partners, has placed three of the water snakes about three miles off Portugal’s northern coast. This first phase will provide up to 2.25 megawatts of capacity and cost $13 million. The company plans 25 more “wave energy converters” starting next year, which would increase the output to 21 megawatts, enough to serve more than 15,000 Portuguese households, the company’s leaders estimate.

Although many renewable energy sources suffer from peaks and troughs in productivity, “we consider wave energy to be more predictable than wind,” says Phil Metcalf, Pelamis’s CEO. “You look at the ocean 1,000 miles out, you’ll get a good idea of what to expect over the next 24 to 48 hours. We think it’s actually going to be easier to dispatch to the grid.”

How much it would cost consumers to buy ocean energy is unclear. Verdant’s Taylor says his company is at least two years away from being able to quote rates to potential customers. That said, a rough estimate for the underwater turbines is $3,600 per kilowatt of capacity—somewhat higher than today’s fossil fuel or hydroelectric plants. Mass-production efficiencies could lower costs.

A smoother permitting process would help greatly. Securing the necessary permits from the New York State Department of Environmental Conservation and the U.S. Army Corps of Engineers for the East River demonstration took Verdant four years. And one third of the $9 million Verdant has spent on the project went to studies to gauge the potential impact of the turbines on vessel navigation, aquatic life and fish migration.