U. WASHINGTON-SEATTLE (US) — Two turbines, each 30 feet wide, are being deployed in Puget Sound to test the feasibility of feeding power from ocean tides into an electrical grid.
Brian Polagye, a research assistant professor of mechanical engineering at the University of Washington, recently described at the American Geophysical Union’s annual meeting in San Francisco the site and how the team will measure environmental effects.
The effort is the first tidal energy project on the west coast of the United States, and the first array of large-scale turbines to feed power from ocean tides into an electrical grid.
“There really isn’t that much information, anywhere, about the environmental effects of tidal turbines,” Polagye says. He believes the Pacific Northwest installation will have the most comprehensive environmental monitoring of any tidal project so far.
“The results of this pilot project will help decide if this is an industry that has potential for going forward at the commercial scale, or if it stops at the pilot stage,” Polagye adds.
The Snohomish County Public Utility District, just north of Seattle, received a $10 million grant from the Energy Department for the tidal project now in the final phase of obtaining permits. The turbines would generate an average of 100 kilowatts of electricity.
The pilot site lies roughly 200 feet below the surface of Admiralty Inlet, where researchers have measured currents of up to 8 knots, or 9 miles per hour.
“There’s surprisingly little known about the oceanography of these very fast waters,” says collaborator Jim Thomson, an assistant professor of civil and environmental engineering. “These kinds of tidal channels where water is going very fast only happen in a few areas, and have not been well studied. The currents are so fast that it’s hard to operate vehicles and maintain equipment. And it’s too deep for conventional scuba diving.”
One area of concern is how underwater noise generated by the turbines could affect marine mammals that use auditory cues to navigate and communicate with each other. Strong currents complicated the task of measuring how sound travels in the channel.
“When currents were more than about 2 knots the instruments are hearing considerable self-noise,” Polagye says. “It’s similar to when you’re bicycling downhill and the air rushes past your ears.”
Researchers used sound from a ferry to learn how turbine noise would spread from the project site. The data suggest that Admiralty Inlet tends to lessen sound. This reduces the effect on animals’ hearing, which is good, but it also means less noise for marine mammals to detect turbines and avoid them.
The team has been measuring currents continuously at the proposed site for almost two years, using a monitoring tripod the size of a small refrigerator. With added ballast for stability, the device weighs 850 pounds in water. Even so, it can barely stay put on the ocean floor.
So far, researchers say, the data support the notion that the Admiralty Inlet is well suited for a tidal energy installation from an engineering perspective. Once the turbines are in the water, likely in 2013, researchers will monitor environmental effects.
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