Friday, December 07, 2007

Chemistry Helps Scientists Spot Geothermal Power Sources

Wired News

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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