Geothermal Heat Mining Promises Abundant, Cheap Energy

CAMBRIDGE, Massachusetts, January 22, 2007 (ENS) - Mining the heat that resides as stored energy in the Earth's hard rock crust beneath the United States could supply a substantial portion of the electricity the country will need in the future, probably at competitive prices and with minimal environmental impact, new research shows.

Sponsored by the U.S. Department of Energy, the study is the first in 30 years to take a new look at geothermal energy, a source that has been largely ignored.

"We've determined that heat mining can be economical in the short term, based on a global analysis of existing geothermal systems, an assessment of the total U.S. resource, and continuing improvements in deep-drilling and reservoir stimulation technology," said Jefferson Tester.

MIT Professor Jefferson Tester points to a geothermal map of the United States. (Photo by Donna Coveney courtesy MIT)

Although geothermal energy is produced commercially today and the United States is the world's biggest producer, existing U.S. plants have focused on the high-grade geothermal systems located in isolated regions of the west.

The new study, "The Future of Geothermal Energy," takes a fresh look at this resource and evaluates its potential for wider deployment.

The study shows that drilling several wells to reach hot rock and connecting them to a fractured rock region that has been stimulated to let water flow through it creates a heat-exchanger that can produce large amounts of hot water or steam to run electric generators at the surface.

Unlike conventional fossil-fuel power plants that burn coal, natural gas or oil, no fuel would be required for this enhanced geothermal system, EGS, technology.

And unlike wind and solar systems, a geothermal plant works night and day, offering a non-interruptible source of electric power.

The largest geothermal field in the world is The Geysers, near San Francisco, California. (Photo courtesy PG&E)

Panel member David Blackwell, professor of geophysics at Southern Methodist University in Texas, points out that geothermal resources are available nationwide, although the highest-grade sites are in western states, where hot rocks are closer to the surface, requiring less drilling and producing the energy at lower cost.

The environmental impacts of geothermal development are "markedly lower than conventional fossil-fuel and nuclear power plants," the panel concluded

"This environmental advantage is due to low emissions and the small overall footprint of the entire geothermal system, which results because energy capture and extraction is contained entirely underground, and the surface equipment needed for conversion to electricity is relatively compact," Tester said.

But meeting water requirements for geothermal plants may be an issue, particularly in arid regions, the panel notes, adding that the potential for seismic risk needs to be carefully monitored and managed.

Even in the most promising areas, drilling must reach depths of 5,000 feet or more in the west, and much deeper in the eastern United States for the EGS technology to perform.

Still, "the possibility of drilling into these rocks, fracturing them and pumping water in to produce steam has already been shown to be feasible," said panel member M. Nafi Toksoz, professor of geophysics at MIT.

Toksoz says the electricity produced annually by geothermal energy systems now in use in the United States at sites in California, Hawaii, Utah and Nevada is comparable to that produced by solar and wind power combined.

Some 58 new geothermal energy projects are already under development in the United States, according to a November 2006 survey by the Geothermal Energy Association, GEA, an industry trade group, which says federal and state incentives to promote geothermal energy are paying off.

“This represents the U.S. geothermal industry’s most dramatic wave of expansion since the 1980s,” said Karl Gawell, GEA’s executive director. "We are seeing a geothermal power renaissance in the U.S."

These projects, when developed, would provide up to 2,250 megawatts of electric power capacity, enough to serve the needs of 1.8 million households.

The Heber Geothermal Power Station operated by Imperial Power Services is located in Imperial County, California. The facility began commercial operation in July 1985. (Photo Wayne Gretz courtesy NREL)

Government funded research into geothermal energy was active in the 1970s and early 1980s, but as oil prices declined in the mid-1980s, enthusiasm for alternative energy sources waned, and funding for research on geothermal power was reduced.

"Now that energy concerns have resurfaced, an opportunity exists for the U.S. to pursue the EGS option aggressively to meet long-term national needs," Tester observed.

On December 20, President George W. Bush signed legislation to extend federal tax credits through 2008 for for renewable energy and energy efficiency projects including geothermal power. The measure provides a similar one-year tax credit extension for new properties that produce geothermal power.

In its report, the panel recommends that the shallow, extra-hot, high-grade deposits in the west should be explored and tested first. Other geothermal resources such as co-produced hot water associated with oil and gas production and geopressured resources could be pursued as short-term options.