Study Says Tapping of Granite Could Unleash Energy Source -

The United States could generate as much electricity by 2050 as that flowing today from all of the country’s nuclear power plants by developing technologies that tap heat locked in deep layers of granite, according to a new study commissioned by the Energy Department.
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There are already dozens of power plants worldwide that have long exploited hot spots of geothermal energy to drive steam turbines, but they are restricted to a few areas.
The new report, published online yesterday, focuses on a process that it said could affordably harvest heat locked in deep layers of granite that exist almost everywhere on earth. The technique, called enhanced geothermal, involves drilling several holes — some two to three miles deep — into granite that has been held at chicken-roasting temperatures, around 400 degrees or more, by insulating layers of rock above.
In the right geological conditions, pressurized water can be used to widen natural mazelike arrays of cracks in the granite, creating a vast, porous subterranean reservoir.
In a typical setup, water pumped down into the reservoir through one hole absorbs heat from the rock and flows up another hole to a power plant, giving up its heat to generate steam and electricity before it is recirculated in the rock below.
There are successful plants harvesting heat from deep hot rock in Australia, Europe and Japan, the report noted, adding that studies of the technology largely stopped in the United States after a brief burst of research during the oil crises of the 1970s.
The report’s 18 authors, from academia, government and industry, said that a public investment of less than $1 billion spread over 15 years would probably be enough to overcome technical hurdles and do initial large-scale deployment of the technology.
The generating capacity by 2050 could be 100 billion watts, about 10 percent of the country’s current generating capacity.
David Keith, an expert on energy technologies at the University of Calgary who was not involved with the study, said there were significant, but surmountable, hurdles to doing such operations at large scale.
Among them, Professor Keith said, are cutting the costs of drilling deep holes and increasing the efficiency of systems that can generate electricity from relatively low-temperature source of heat like deep rock.
“There’s no question there’s a lot of heat down there,” he said. “It’s about the cost of access, and about the value of low-grade heat.”
Jefferson W. Tester, the lead author of the study and a chemical engineer at the Massachusetts Institute of Technology, said there were many new justifications for aggressively pursuing this kind of energy option.
“Back then, we weren’t worried about carbon dioxide and climate, we weren’t running short of natural gas, and now energy is a national security issue in the long run,” Dr. Tester said. “While there’s no guarantee it’s going to work, this is not an unreasonable investment and it’s a good bet on the future.”
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