Geothermal Heat Mining Energy

Geothermal Heat Mining Energy

    
 
 January 2007  - 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) 
The professor of chemical engineering at the Massachusetts 
Institute of Technology, MIT, headed the 18 member 
international panel that prepared the study. 
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) 
To develop geothermal as a major electricity supplier for the 
nation, the panel recommends more detailed and site-specific 
assessments of the U.S. geothermal resource and a three to 
five year federal commitment to demonstrate the EGS concept in 
the field at commercial scale. 
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) 
This would almost double installed U.S. geothermal power 
capacity to over 5,000 megawatts, according to GEA, producing 
electric power roughly equivalent to all U.S. wind facilities 
operating in 2005. 
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.