Tidal energy: Is it too costly?

A decision by Tacoma Power that tidal energy will be too expensive to develop in the near future will not affect the Snohomish County PUD’s study of that alternative energy source, according to the PUD.

Tacoma Power concluded that current tidal-power technology won’t stir up the energy needed to make it worthwhile to install turbines in the Tacoma Narrows, officials with the agency said after its decision was announced Thursday.

It could take eight to 10 years for technology to make the investment pay off, Tacoma Power officials said.

“For the technology that’s available right now, the tides are just not strong enough,” Tacoma Power spokeswoman Chris Gleason said.

The PUD is one year into its own three-year study of tidal power. The Snohomish County utility is investigating seven locations between the San Juan Islands and Bremerton — including Admiralty Inlet between Whidbey Island and Port Townsend — as possible locations for the underwater windmill-like turbines.

“Nothing is off the table at this point,” PUD spokesman Neil Neroutsos said.

In January, the PUD filed key documents with federal regulators to begin testing tidal turbines at Admiralty Inlet by the end of 2010. If those tests are successful, the utility could eventually put as many as 1,662 turbines in the water. The turbines could generate enough electricity for 70,000 homes.

Tacoma Power began studying the issue two years ago, engineer Scott Amsden said. Consultants for the agency measured currents in the Tacoma Narrows, near Point Evans on the east side of the Narrows just north of the Tacoma Narrows bridges. The currents were measured in May, June and July of 2007 because the water, driven by snowmelt, moves its fastest that time of year, Amsden said.

The data was combined with information from 44 different companies in varying stages of developing tidal-power technology to determine how much energy could be generated at what cost, Amsden said.

The study concluded it would cost $266 per megawatt hour to generate power with current tidal technology at the Narrows, he said. By contrast, wind power costs about $90 per megawatt hour and hydroelectric power about $40 per megawatt hour, Amsden said.

The power of the currents in the Narrows was a factor along with the technology, Amsden said.

“It’s a combination, although it’s more the equipment than it is the tides,” he said.

Currents in the Narrows average about 2 to 3 knots per hour and run as high as 7 to 8, depending on the time of year, Amsden said. During the study period, it was about 4 1/2 to 6 knots, he said. In Admiralty Inlet, the currents average about 6 knots, Neroutsos said.

Officials with both agencies said the depth at which the turbines are placed also makes a difference. The Tacoma study tested at a depth of about 65 to 130 feet, Amsden said. Admiralty Inlet is up to 250 feet deep, Neroutsos said.

“The deeper the water, the bigger the piece of equipment you can put in, and the bigger the equipment, the more energy is available,” Amsden said.

Each of the sites being studied by the PUD has its own characteristics, Neroutsos said.

As of now, the PUD is expecting tidal power to cost close to what Tacoma Power concluded, or slightly less — $170 to $230 per megawatt hour, Neroutsos said. The agency is anticipating that the cost will come down by the time any action is taken.

“These are initial estimates,” he said.

The PUD’s study of tidal power is farther along than any other in the nation, agency officials have said.

Herald reporter Lukas Velush contributed to this story.

Reporter Bill Sheets: 425-339-3439 or sheets@heraldnet.com.

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