Geothermal could power millions of U.S. homes, Study says.

Geothermal power, a renewable energy source that has been largely ignored in the United States, could supply a significant share of the country's future energy needs, according to a recent Massachusetts Institute of Technology (MIT) study. The study notes that by investing some $1 billion over 15 years--less than the cost of building a single clean-coal power plant--geothermal energy could power an estimated 25 million U.S. homes by 2050.

"Heat mining can be economical in the short term," said Jefferson Tester, a professor of chemical engineering at MIT and the head of the 18-member panel that prepared the report. The 400-page assessment, sponsored by the U.S. Department of Energy, is considered the broadest review of geothermal energy in 30 years. It is based on a global analysis of existing geothermal systems, an assessment of U.S. geothermal resources, and continuing improvements in the technologies of deep drilling and reservoir stimulation.

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Most commercial geothermal production in the United States today occurs in isolated reaches of the West, where higher-grade heat sources lie closer to the surface. But the report notes that subsurface "hot rocks" (areas of the Earth's hard rock crust that store thermal energy) are present across the nation, offering the potential for more widespread use of the renewable resource. By drilling wells into hot rock regions and connecting them to water, geothermal developers would be able to generate large amounts of steam that could be used to power electric generators on the surface.

Because geothermal power is derived from underground heat and steam, the environmental impacts of its development are much lower than those from conventional coal-fired and nuclear power plants, the report notes. Geothermal also offers an uninterrupted power supply, unlike renewable energy sources like solar and wind that are affected by weather and time of day. The downsides of geothermal, according to the study, include large water requirements and higher seismic risk because the best places to access the hot rocks are near fault lines.

The report's authors believe that large geothermal stores could provide a viable alternative to U.S. fossil fuel use. "Geothermal energy could play an important role in our national energy picture as a non-carbon-based energy source," said panel member M. Nafi Toksoz, a professor of geophysics at MIT. Among the recommendations outlined in the study are more detailed and site-specific assessments of the U.S. geothermal resource and making a multiyear federal commitment to demonstrate the concept at a commercial scale.

Eye on Earth is produced in collaboration with the Blue Moon Fund (www.bluemoonfund.org).

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