Bad News for Geothermal Power

This article suggests that there is a problem with extracting energy from deep below the surface of the small blue planet. I guess it can’t really be a surprise, but I think it was a question of scale. It’s an application of Boyle’s Law that pressure and heat are equivalents. So as you increase pressure, you produce heat, as you release pressure, you reduce heat. So, as a geothermal plant withdraws heat from deep below the earth, the pressure at the source is reduced. If the pressure falls enough, it is logical to expect that the surrounding strata will shift. We call that an earthquake. Are these always going to be small, low damage earthquakes? Could the pressure reduction and triggered earthquakes trigger a larger earthquake? Who knows.

clipped from www.nytimes.com

German Geothermal Project Leads to Second Thoughts After the Earth Rumbles
LANDAU IN DER PFALZ, Germany — Government officials here are reviewing the safety of a geothermal energy project that scientists say set off an earthquake in mid-August, shaking buildings and frightening many residents of this small city.The geothermal plant, built by Geox, a German energy company, extracts heat by drilling deep into the earth. Advocates of the method say that it could greatly reduce the world’s dependence on fossil fuels by providing a vast supply of renewable energy.

Seismologists at the geological survey said that the larger Aug. 15 quake was also caused by the project. The epicenter was roughly 500 yards from a drill site at the plant and at about the same depth — 1.5 miles — as a steam bed that the plant was extracting heat from. “We are sure it’s from the geothermal plant,” said Harald Ehses, chairman of the geological survey.