Friday, July 27, 2007

Technology for geothermal plant developed in Idaho

Renewable electricity plant to come on line in October

Express Staff Writer

Diagram courtesy U.S. Geothermal Inc. This diagram shows how hot water is pumped from the earth to heat a second fluid to produce electricity. The water is pumped back into the earth where it is reheated and used again, making geothermal a renewable energy.

One of the technologies used to extract water heated deep within the earth—and then converting it into geothermal power—was developed just about 100 miles south of the Wood River Valley.

Different technologies developed at different times have been used to extract geothermal energy from the earth and the one being used at the Raft River geothermal plant was developed there. Raft River, located 40 miles southwest of Burley, Idaho, is expected to fire up and begin producing electricity in October.

The plant was built and will be run by Boise-based U.S. Geothermal, Inc. The geothermal potential at Raft River was explored by the U.S. Department of Energy from the mid-1970s until early 1980s when the DOE drilled seven test wells, said Doug Glaspey, chief operating officer for U.S. Geothermal.

U.S. Geothermal is using those seven DOE wells plus two more that it drilled, said Glaspey. Each well is 5,000 to 6,000 feet deep and costs $3 million to $3.5 million.

The DOE spent $40 million on "geothermal studies and production infrastructure" at Raft River, said the U.S. Geothermal Web site. A 1985 Bonneville Power Administration study ranked Raft River first in high temperature ranking of geothermal sites in the Pacific Northwest, the Web site said.

The wells were drilled under the aegis of the Idaho National Laboratory "and (the INL) demonstrated geothermal potential there," said INL spokesman John Walsh. "It's certainly one of the early ones (sites) that DOE explored in this region."

The technology used at Raft River is called "binary." A binary geothermal power plant is simply a system where hot water extracted from the earth heats a secondary fluid that has a lower boiling point. Vapor from the secondary fluid created in a heat exchanger and turns a turbine that produces electricity.

The two liquids are kept separate and after the hot water has cooled it is re-injected into the earth and is re-heated. That's the beauty of this "renewable" energy, said Glaspey. "We only take 50 percent of that heat ... and we keep from depleting the reservoir and get the renewable aspect."

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