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Currents run deep

Tidal energy in Puget Sound could become a reality if studies already underway prove its economic viability and consequent negligible environmental impacts.

The Snohomish County Public Utility District received permits from the Federal Energy Regulatory Commission this spring to study seven sites in Puget Sound for tidal energy, including Deception Pass and Admiralty Inlet.

Representatives from the PUD, as well as a researcher from the University of Washington and an oceanographic consultant, visited Admiralty Inlet last Wednesday afternoon to retrieve two electronic devices that have been mounted on the bottom of Puget Sound for approximately 30 days.

The acoustic Doppler current profilers are a type of sonar that produce a record of water current velocities over a range of depths. Two have been placed in Admiralty Inlet below the surface 278 feet and 213 feet, respectively, and one at Deception Pass 131 feet underwater. The latter was retrieved later in the afternoon when currents were optimal.

Neil Neroutsos, Snohomish PUD spokesperson, said Wednesday near the Keystone Ferry dock that research work at the UW is helping ascertain the viability of the revolutionary technology. ADCP is one key component in the renewable energy research that is also providing researchers with a better understanding of Puget Sound.

“They’re doing a lot of study of the ecosystems here in Puget Sound,” Neroutsos said. “So, the studies we’re doing here today, acoustic Doppler current profiling, is useful for that beyond the tidal energy applications.”

Jeff Cox with the oceanographic consulting firm Evans-Hamilton said there are various types of turbines, each driven at different current speeds. He had been told by experts that the turbines generally begin rotating in currents of about one knot. Four knots should generate a peak output.

Cox said the ADCP is being used to collect measurements for the studies. His company first traveled a specific track line to determine where best to place the meters.

“That allows us to go across the inlet or along the inlet and get an understanding of the variation of the current,” Cox said. “So, we can first get an idea how this current varies across this channel and select sites to go back and put current meters on the bottom for 30 days that will sit there and give us a much better idea of how the current varies over time and especially the lunar cycle of a month.”

On Wednesday it was time to retrieve the meters and find out what they had to say. Mounted in cages on the seabed, the devices are released by firing signals down into the water. When they hit their mark, the buoy floats to the surface with a recovery rope used to safely pull the meter onboard.

“We can service it and redeploy it, or bring it home, whichever we need,” Cox said.

Operating in choppy waters made recovering the devices difficult. After several failed attempts, the vessel sent out the signal from one mile away, successfully triggering the release.

“I’m always happy when they come home,” Cox said after he watched the meter pulled safely onto the boat deck.

The data will now be passed on to the university, where Brian Polagye, a pre-doctoral research associate in the UW’s mechanical engineering department, is one of the specialists eagerly awaiting its arrival.

“What we’ve been doing is analyzing the first round of results from the acoustic Doppler profiling, specifically the results when we did over-the-side measurements,” Polagye said. “Admiralty Inlet’s a big place. We want to know where the currents are the highest, where it makes most sense to put tidal energy in the water.”

Starting out, the only information available on currents in the area came from historical data compiled by the National Oceanographic and Atmospheric Administration decades ago using much cruder methods. Polagye said the currents have thus far proven to be stronger than anticipated, especially near Admiralty Head. And the NOAA data has not been the most reliable.

“We actually found stronger currents where NOAA predicted weaker ones,” he said. “The stationary units have indicated a higher power density at the site.”

As exciting as the preliminary numbers are, the researcher was loath to draw any conclusions, as the measurements represent a single point in time and could be an anomaly.

Cox said Tuesday that the meters revealed a maximum current speed of 7.9 knots at Deception Pass with an average speed of 3.5 knots. At Admiralty Inlet the maximum speed was less, 5.8 knots with an average speed of 2 knots.

The seven sites combined could provide as much as 100 average-megawatts of energy, or enough power for about 60,000 homes. The projected megawatt production was a conservative estimate based on the NOAA data. New studies will undoubtedly modify the numbers.

“It’s looking very good,” Polagye said. “We will be able to make predictions as to the annual power density at the site.”

The research associate said Deception Pass has the distinction of offering the strongest currents. However, a site’s viability is based on the overall amount of energy potential, in addition to current strength.

“Deception Pass has by far the strongest currents in Puget Sound,” Polagye said. “But it is much smaller.”

The FERC permits do not authorize construction, nor has the PUD made any commitment to construct tidal facilities. Rather, the permits allow the utility to apply for construction permits in the future. The PUD will only consider moving forward on a tidal project once studies have confirmed both the technical and economic viability, and the utility district is convinced that the project can be executed in an environmentally responsible manner.

The series of studies is being funded in part by a $220,000 grant from the Bonneville Power Association.

All of the data will be crucial if the PUD moves into the pilot phase, which would happen at the end of the three-year studies.

Snohomish County is one of the fastest growing counties in the region, Neroutsos said.

“We’re adding about 10,000 new customer connections each year, every year,” he said. “That’s about the size of a town a little smaller than Edmonds every year. We want to meet as much of that growth as possible through renewable energy like we’re looking at today.”

The PUD is exploring other forms of energy besides tidal power. It is considering acquiring additional bio-mass and has already purchased a portion of a wind energy project in Eastern Washington that will start in 2008.

“We’re continuing to promote small-scale solar installations as well,” Neroutsos said.

For more information about the tidal energy studies or to submit ideas or input, contact project leader Craig Collar at 425-783-1825 or email him at cwcollar@snopud.com.

Further information about tidal energy can be found at www.sno

pud.com under “Energy Resources.”

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