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GEOTHERM ENERGY

THE U.S. could supply the world’s current energy needs for the next 30,000 years. Were we to tap only the most accessible of it, the energy obtained would be thousands of times the current annual U.S. usage.

We already have the means of exploiting it. What’s more, the best of this technology is environmentally friendly.

And it’s all beneath our feet—as part of the geophysics of Earth.

Reports on geothermal energy come from researchers at MIT (http://goo.gl/eoH6g) as well as an article in Science, 24 May 2013, published by the American Association for the Advancement of Science.

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Not that there’s anything particularly new about exploiting the Earth’s heat for electricity. According to Science, the first commercial geothermal power plant was built in Larderello, Italy, 60 miles southwest of Florence, in 1913. It’s in a volcanically active area, where granite at 500 deg F lies close to the surface. Water, brought to a boil over the granite, is transformed into steam that drives power turbines.

Calpine

The Sonoma Calpine 3 is one of 22 plants at The Geysers geothermal facility in California.

The U.S. leads the world in geothermal generation of electricity. California’s facility at The Geysers, 90 miles north of San Francisco, is the world’s largest and has been in operation since 1960. It produces 850 megawatts of electricity, sufficient to supply the needs of 850,000 households. Laderello, also one of the world’s largest, produces 594 MWe.

Future development of the Salton Sea geothermal field, about 160 miles southeast of Los Angeles, has a resource estimate exceeding 2000 MWe.

Despite this promise, geothermal energy is only a tiny portion, 0.4 percent, of U.S. electricity sourcing. This is less than wind (3.5 percent) and biomass (1.4 percent), but ahead of solar (0.1 percent); these figures from the U.S. Energy Information Administration.

It’s expensive technology to develop and maintain, though costs have decreased by 25 percent over the past two decades. Among the countries seriously committed to geothermal electricity are Iceland (30 percent of its sourcing), the Philippines (27 percent) and, curiously, El Salvador (25 percent).

Both Larderello and The Geysers are vapor-dominated, exploiting temperatures approaching 600 deg F. Liquid-dominated facilities known as flash plants (because their super-hot liquids “flash” into steam when brought to the surface) can function efficiently at only 400 deg F.

binary

A binary geothermal facility functions with two closed loops. Image from Geothermal Education Office.

Older plants exploit the super-heat—and accept the potential corrosion—directly in their turbines. A modern binary facility routes it through heat-exchangers; an organic liquid circulating through a second loop drives the turbines. Since the two have their own closed loops, there’s no CO2 nor more harmful things exposed to the environment.

Your

Your author tests an Icelandic geothermal supply being routed to Reykjavik homes. The insulated pipe was only moderately warm to the touch.

Iceland and 75 other countries have highly efficient direct exploitation of geothermal heat, not just in producing electricity. Water that’s only relatively hot (100-300 deg F) has supplied Reykjavik, Iceland, since the 1930s (and Boise, Idaho, since 1892). Today, 90 percent of Reykjavik homes are heated by geothermal water. As another benefit, sidewalks are deiced by underground pipes.

Heat-pump technology, efficient in moderate climates, exploits the coolest and shallowest geothermal energy. Forty-three countries currently have such installations, with applications increasing.

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An overview of geothermal options. Data from Science, 24 May 2013.

Deeper exploitation yields higher temperatures. Few geothermal applications have exceeded depths of a mile, though this isn’t precluded by technology. These days, advanced oil and gas recovery reaches down as far as six miles.

U.S.

The U.S., especially in the Rockies and west, is rich in geothermal resources. Image from U.S. Department of Energy.

Science notes that capturing even two percent of the thermal energy at depths of two to six miles could provide 2000 times the annual energy needs of the U.S.

The hot term is EGS, Enhanced Geothermal Systems, a geothermal analog of oil and gas hydraulic fracturing. The latter fracking is not without controversy. However, EGS uses no toxic chemicals and generally takes place at lower depths with less environmental impact.

Pilot EGS facilities exist in the Rhine Graben at Soultz-sous-Forêt, France, producing 1.5 MWe and two in Germany, Landau (3.0 MWe) and Insheim (4.5 MWe).

A promising EGS project lies in a remote part of South Australia, where granite at 450 deg F lies only 2.5 miles down—beneath a vast area of 770 sq. miles. ds

© Dennis Simanaitis, SimanaitisSays.com, 2013

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This entry was posted on June 22, 2013 by in Sci-Tech and tagged , , .
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