This is an excerpt from EERE Network News, a weekly electronic newsletter.
Idaho's First Geothermal Power Plant is Now Online
U.S. Geothermal Inc. achieved commercial operation last week at its new geothermal power plant in Raft River, Idaho, making it the first commercial geothermal power plant in the state. Ormat Nevada built the power plant, which began producing power during a test phase in late October 2007. After some mechanical tweaks, the plant was restarted on November 22, 2007, and has continued to produce power since then. As a result, Idaho Power Company declared that commercial power operations began on January 3. So far, the plant output is around 9 megawatts, but the company expects the plant to achieve an average annual net power output of 13 megawatts. The company currently has a contract to sell Idaho Power Company up to 10 megawatts of geothermal power, but is in the process of trying to renegotiate that contract for the full output of the geothermal power plant. See the U.S. Geothermal press releases on the completion of construction (PDF 39 KB) and the start of commercial operations (PDF 37 KB). Download Adobe Reader.
The Raft River project employs binary cycle technology, in which the geothermal fluid is pumped through a heat exchanger to vaporize isopentane, an organic compound that vaporizes at lower temperatures than water. The isopentane vapor drives a turbine, which spins a generator to produce power. The vapor that exhausts from the turbine is then condensed and returned to the geothermal heat exchanger, forming a closed loop. The completion of the Raft River project also closes a loop in a historic sense, as the binary cycle technology was first tested at the Raft River site from 1980 to 1982 as part of a DOE demonstration project. See the U.S. Geothermal Web page on the Raft River project.
Coincidentally, a new report from the Geothermal Energy Association (GEA) claims that binary cycle technology revolutionized the geothermal power industry by allowing power production from medium-temperature geothermal resources. The report examines a number of other new and under-used technologies that could lead to similar drastic changes in the geothermal industry, while noting a number of incremental technology improvements that could benefit the industry in the near term. The report, "The State of Geothermal Technology - Part II: Surface Technology," also provides an excellent overview of the issues and technologies relating to geothermal power production, and provides a short overview of geothermal direct use technologies and geothermal heat pumps. See the GEA press release (PDF 77 KB) and the full report (PDF 5.76 MB).