Harnessing 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.
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, enough to power 50-100 Washington homes during the
pilot phase.
"We want to monitor the effects of this particular project, but
also understand the processes so we can apply the findings to other
potential tidal energy sites," Polagye said.
To do this, the UW team must assess a new technology that
operates in a little-explored environment.
"There's surprisingly little known about the oceanography of
these very fast waters," said collaborator Jim Thomson, a UW
assistant professor of civil and environmental engineering and an
oceanographer in the UW's Applied Physics Laboratory. "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."
The pilot site lies roughly 200 feet below the surface of
Admiralty Inlet, where the UW team has measured currents of up to 8
knots, or 9 miles per hour.
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 said. "It's similar to
when you're bicycling downhill and the air rushes past your
ears."
Chris Bassett, a UW doctoral student in mechanical engineering,
is testing approaches that would allow underwater microphones to
work in fast-moving water.
UW researchers used sound from a Washington state 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 UW 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.
The monitoring tripod holds instruments to track water quality,
ambient noise, currents, temperature and salinity, and to record
marine mammal calls and electronic tags on passing fish. This
observational data will help determine precisely where to put the
tidal turbines, and establish potential environmental effects once
they are in the water.
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.
The Admiralty Inlet characterization is being conducted by the
Northwest National Marine Renewable Energy Center, in which the UW
leads research on tidal energy. Polagye and Thomson lead research
on characterizing the physical attributes, such as currents and
sound propagation. UW fisheries scientists recently received
funding to test instruments for monitoring fish at the site, UW
mechanical engineers are using computer models to see how pressure
changes caused by tidal turbines could affect sediments and fish,
and UW oceanographers are calculating when turbines would begin to
affect the Sound's tides and currents.
The Washington state deployment is among three U.S. tidal energy
pilot projects now in the works (the others are in Maine and
Alaska). An array of smaller turbines was operated during a pilot
project in New York City's East River.
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