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Chemistry Helps Scientists Spot Geothermal Power Sources


By Alexis Madrigal
Wired Science
November 30, 2007


Scientists have announced a new method for evaluating an area's geothermal
energy potential, and it doesn't require drilling, or that the site be nestled
among volcanoes. The discovery could help unlock some of geothermal's massive
potential to provide clean power for the world.

As reported in the journal Science, Mack Kennedy at Lawrence Berkeley National
Laboratory and Matthijs van Soest of Arizona State have created a new technique
for finding geothermal sources. By evaluating samples from surface wells for a
high ratio of Helium 3 (common in the mantle) to Helium 4 (common in the crust)
isotopes, the scientists can identify potential geothermal heat sources anywhere
they exist, not just in volcanic regions. That could open up resources in less
environmentally sensitive areas than, say, Yellowstone.

"We believe we have found a way to map and quantify zones of permeability deep
in the lower crust that result not from volcanic activity but from tectonic
activity, the movement of pieces of the Earth's crust," said Kennedy.

A few months ago at a conference I attended in Silicon Valley, leading greentech
VC John Doerr (of Al Gore fame) said that the lack of investment in tapping
geothermal energy sources bordered on criminal. Geothermal power has admirable
characteristics after all: it's clean, available in the US, and consistent,
which makes the power grid engineers happy.

But finding and tapping geothermal power has been difficult. Iceland generates
about 25% of its power from geothermal, but globally, geothermal is responsible
for less than 1% of energy generation.

The scientists' discovery could reduce the cost of finding geothermal
reservoirs. Exploration can account for up to one-third of the cost of a
geothermal power plant (although that scales down as the size of the plant
grows). This is important because the high up-front costs of building geothermal
plants has handicapped them in competing with fossil fuel plants. However, the
costs of fossil fuel plants are rising as companies are forced to clean up their
toxic and greenhouse gas emissions. That will make geothermal plants, along with
all cleaner energy technologies, more attractive options in the near-future.

Here's a very quick primer on geothermal power. You can think of a geothermal
reservoir as a capped geyser. Geothermal plants tap into would-be steam that is
kept liquid by the high pressure underground. The superheated liquid is trapped
in a geothermal reservoir between magma and some impermeable rock. Through
various methods (flash steam, binary cycle) that steam can be turned into power.

 

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