University of Washington | 13 Dec 2010
Calculating tidal energy turbines' effects on sediments and fishHarnessing the power of ocean tides has long been imagined, but countries are only now putting it into practice. A demonstration project planned for Puget Sound will be 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.
University of Washington researchers are devising ways to site the tidal turbines and measure their environmental effects. Brian Polagye, UW research assistant professor of mechanical engineering, will present recent findings this week in an invited talk at the American Geophysical Union's annual meeting in San Francisco.
Polagye and colleagues are involved in environmental monitoring before and during a planned deployment of two 30-foot-wide turbines in Admiralty Inlet, the main entrance to Washington state's Puget Sound.
"There really isn't that much information, anywhere, about the environmental effects of tidal turbines," Polagye said.
Although European countries have more experience with tidal energy devices, they are not as far ahead on environmental monitoring, Polagye said. 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 said.
University of Washington | 13 Dec 2010
Testing the Waters with Tidal EnergyThe emerging tidal-energy industry is spawning another in its shadow: tidal-energy monitoring. Little is known about tidal turbines' environmental effects and environmentalists, regulators and turbine manufacturers all need more data to allow the industry to grow.
Engineers at the University of Washington have developed a set of numerical models, solved by computers, to study how changing water pressure and speed around turbines affects sediment accumulation and fish health. They will present their findings this week at the American Geophysical Union's meeting in San Francisco.
The current numerical models look at windmill-style turbines that operate in fast-moving tidal channels. The turbine blade design creates a low-pressure region on one side of the blade, similar to an airplane wing. A small fish swimming past the turbine will be pulled along with the current and so will avoid hitting the blade, but might experience a sudden change in pressure.
Teymour Javaherchi, a UW mechanical engineering doctoral student, says his model shows these pressure changes would occur in less than 0.2 seconds, which could be too fast for the fish to adapt.
If the pressure change happens too quickly the fish would be unable to control their buoyancy and, like an inexperienced scuba diver, would either sink to the bottom or float to the surface. During this time the fish would become disoriented and risk being caught by predators. In a worst-case scenario, severe pressure changes could cause internal hemorrhaging and death.
It's too early to say whether tidal turbines could harm fish in this way, Javaherchi said. The existing model uses the blade geometry from a wind turbine.
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Another set of numerical modeling looked at whether changes in speed of water flow could affect the settling of suspended particles in a tidal channel. Slower water speeds behind the turbine would allow more particles to sink to the bottom rather than being carried along by the current.
Javaherchi's modeling work suggests this is the case, especially for mid-sized particles of about a half-centimeter in diameter, about two-tenths of an inch. This would mean that a rocky bottom near a tidal turbine might become sandier, which could affect marine life.
The UW research differs from most renewable energy calculations that seek to maximize the amount of energy generated.
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Aliseda says engineers in the wind-turbine industry are already adapting the UW work to look at interactions between wind turbines and bats, since high-frequency pressure changes are now thought to be responsible for the mysterious deaths of bats caused by wind turbines.
Scientific American | 06 Dec 2010
For eons, powerful tides have raged through Puget Sound, ripping along at 11 feet per second at their peak, predictable as the phases of the moon.
Three years from now, a local utility hopes to begin converting a portion of that raw energy to electricity, part of a growing effort to harness the tides to power homes and businesses miles from the smell of salt air.
The Snohomish County Public Utility District's pilot project is small – two turbines with 500 kilowatts of total capacity and an average output of 50 kilowatts – hardly a panacea for all that ails the United States' energy portfolio. But tidal power is garnering increasing attention as a niche supplier of renewable alternative energy in Washington, Maine and Alaska. The tides, some say, have the potential to light five percent of the nation's homes – nearly nine gigawatts of generating power.
And with wind and solar increasingly seen as viable commercial energy alternatives in the United States, investors and public utilities also seem more willing to literally test tidal energy's waters.