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Wide range of wave and tidal technologies in playMichael Burnham, Greenwire reporterDevelopers of underwater tidal energy devices must thank the wind power industry for decades of equipment research and development. In fact, the device created by Verdant Power LLC and being tested in New York's East River looks very much like an underwater wind turbine. But because water is much denser than air, however, tides don't need to move as fast as winds to generate power. While wind turbines need gusts of 25 to 30 miles per hour to yield maximum power, in-stream turbines need currents of 3 to 3.5 mph, says George Hagerman of Virginia Tech University's Advanced Research Institute. While Verdant boasts of having the world's first grid-connected tidal turbine, United Kingdom-based Marine Current Turbines Ltd. has been testing a 300 kW prototype in the Bristol Channel since 2003. The company's 1 megawatt-rated Seagen features twin rotors that pitch 180 degrees to accommodate reversing flow. Another U.K. company, Lunar Energy Ltd., is taking a very different approach to capturing tidal power with its patented Rotech Tidal Turbine. The device features a cone-shaped duct that accelerates tidal flows that pass through an internal turbine. The company is planning to install a 1 MW-rated turbine next year at the European Marine Energy Centre off Scotland. There are also several devices for capturing energy from ocean waves. Ocean Power Delivery Ltd., also of Great Britain, has developed the Pelamis, a snake-like device that undulates on waves. Like Lunar Energy, OPD is testing its technology at the European Marine Energy Centre and says its future "wave farm" projects would feature an arrangement of "attenuators" linked to shore by a seafloor cable. A typical 30 MW wave farm would occupy a square kilometer of water surface, the company says. New Jersey-based Ocean Power Technologies Inc. is testing prototypes of its PowerBuoy off Atlantic City, N.J., and Oahu, Hawaii. The device, called a "point absorber," is tethered to the seafloor and bobs with the waves. Energetech Australia Pty. Ltd. is testing its "oscillating water column terminator," just south of Sydney. The crab-shaped device uses two large arms to funnel waves in a bid to maximize their height and density, the company says. As waves crash into the center of the parabolic arms, the water column moves up a central chamber and forces pressurized air at a variable-pitch turbine inside. |
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