GeoThermal Stirling

Instead of using steam it would be just as efficient and a lot cheaper to use the well as a really long displacer cylinder in a beta Stirling.

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MIT study touts geothermal energy: Heating water is key
By Jay Fitzgerald Technology Section
Boston Herald 1/23/07
America needs to get more steamed up to meet its future energy needs, a
new Massachusetts Institute of Technology study says.
An 18-member panel led by MIT yesterday reported that tapping into natural heat under the Earth's rock crust could yield enough energy to generate a "substantial portion" of the nation's electric power at a relatively low economic cost.
The report, the first of its kind on geothermal energy in 30 years, urged the federal government to invest more in promising technology, which could meet about 10 percent of U.S. electricity needs by 2050.
The technology - in which water is pumped thousands of feet into the hot rock crust and extracted as steam - should be tested first in western states where underground hot rocks are closer to the surface, the report said.
But so-called "heat mining" is also feasible in eastern states, where naturally heated rock exists deeper down toward the Earth's core, the
report said.
"We've determined that heat mining can be economical in the short term, based on global analysis of existing geothermal systems," said panel head Jefferson W. Tester, a professor of chemical engineering at MIT.
Ronald DiPippo, professor emeritus at the University of Massachusetts at Dartmouth, said rocks 15,000 feet to 20,000 feet deep in this area should be sufficiently hot - at about 300 degrees Fahrenheit - to produce steam energy.
Granite rock crusts at those levels have naturally radioactive elements, such as uranium and thorium, that heat them up.
One well could be drilled into the deliberately "fractured" rock and water could be pumped in, he said. A second well would extract the steam to power electric plants, said DiPippo, a member of the panel that drew
up the nearly 400-page report.
So-called "hydrothermal" technology - in which heated water already
exists below the surface - is currentlybeing used in California, Nevada
and other western states to generate about 2,500 megawatts of power, he
said.
Inserting water into other promising sites is merely modifying existing
technology, he said.
"It can be done anywhere in the United States," he said.
Funded by the U.S. Department of Energy, the report said geothermal energy is cleaner and more plentiful than fossil fuels, which will become more expensive in future years as they become more scarce.
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Bret Cahill
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