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Geothermal Energy

November 9, 2011

I reviewed geothermal energy in a 2007 article (Geothermal Energy, January 26, 2007), so it's time for an update. Renewable energy has become all that more important since 2007; but, as the chart shows, non-hydroelectric renewables comprise less than 10% of the US energy output, and geothermal electrical energy in the US , which is about three gigawatts of installed capacity, is less than a tenth of this.

U.S. Energy Production by Energy Source, 2000–2009

U.S. Energy Production by Energy Source, 2000–2009, US Department of Energy, 2009 Renewable Energy Data Book, August 2010, page 8.[1]

The US has always been optimistic about the future of geothermal energy. A 2006 report, funded by the U.S. Department of Energy , concludes that geothermal electrical generation in the US can be increased to ten percent (100 gigawatts) by 2050.[2] Unlike other energy sources, such a large increase in capacity would be feasible, since geothermal energy harvesting is extremely simple. The usual technique is to pump water into fractured rock deep underground, where it is heated. The resulting steam or hot water is used to generate electricity at the surface, and the cooled water is cycled back underground to be heated again.

In just one year, 2009, US geothermal capacity increased by six percent when six new geothermal plants which came online to add about 175 megawatts capacity.[4] A 6% compound annual growth rate will give a ten-fold increase in forty years. The Geothermal Energy Association estimated that the total online geothermal capacity in the US was 3.15 gigawatts in August, 2009.[4] If the growth rate is constant, this will lead to about 32 gigawatts by 2050, so significant growth will be needed to attain the DOE goal of 100 gigawatts by 2050.

In September of this year, the DOE announced funding by its Office of Energy Efficiency and Renewable Energy of $38 million over three years in geothermal energy development.[5] This is part of an effort to have the US produce 80% of its electricity from clean energy sources by 2035.[5] The main goal of this program is to reduce the cost of geothermal electricity to make it competitive with other electrical generators.

Fortunately, for the scientific community, some major funding was given to universities and research laboratories . The funded institutions included Lawrence-Berkeley National Laboratory (Berkeley, California), $540,000; Stanford University (Stanford, California), $680,000; the Colorado School of Mines (Golden, Colorado), $1.73 million; the University of Hawaii (Honolulu, Hawaii), $980,000; the Idaho National Laboratory (Idaho Falls, Idaho), $1.0 million; Los Alamos National Laboratory (Los Alamos, New Mexico), $2.6 million; Sandia National Laboratories (Albuquerque, New Mexico), $740,000; the University of Nevada (Reno, Nevada), $380,000; Brookhaven National Laboratory (Upton, New York), $600,000; the National Energy Technology Laboratory (Albany, Oregon), $770,000; the National Energy Technology Laboratory (Pittsburgh, Pennsylvania), $1.0 million; Temple University (Philadelphia, Pennsylvania), $1.5 million; the University of Texas (Austin, Texas), $1.699 million; and the University of Utah (Salt Lake City, Utah), $1.99 million.[5]

As present problems with some hydraulic fracturing projects in the United States illustrate, there are always unintended consequences involved with almost everything we do. Disaster caused by underground drilling has captured the popular imagination. Crack in the World (1965, Andrew Marton, Director) was one of the first films to propose that too much tampering with the Earth's crust to access geothermal energy can have serious consequences.[3] Two episodes of Doctor Who , The Hungry Earth (May 22, 2010), and Inferno (June 20, 1970), have about the same plot.

The most important physical variable in geothermal energy production is the temperature gradient from the surface of the Earth to its interior. This gradient is a consequence of the temperature of the Earth's core , estimated to be about 6000°C. The gradient varies from place to place because of local geology, but it averages about 25°C per kilometer. Other important factors are the thermal conductivity of the Earth's crust (about 1.7 W/m/K), and the specific heat of rock (about 1260 J/kg/K).

In 2004, David Blackwell and Maria Richards of Southern Methodist University produced a detailed geothermal energy map of the US from data obtained peripherally in oil and gas drilling . This map was one of the resources used in the 2006 US Department of Energy geothermal energy report.[2]

Blackwell and Richards have just updated this map, with funding from Google , to include twice the number of data sites, bringing the total to 35,000 and improving the map contours (see figure). One result is that West Virginia is now identified as an Appalachian region with higher heat flow and temperature. The West Virginia geothermal energy potential is theoretical equivalent to its existing, mostly coal-fired , power.[6]

Heat flow map of the United States (SMU Geothermal Laboratory, 2011)

(Image via SMU Geothermal Laboratory. Used with permission.).

Th West Virginia finding is just one important consequence of this study. Most US geothermal energy production has been concentrated in the most visibly geothermal areas in the west, such as the Geysers Field north of San Francisco .[6] The study revealed that some places in the east are hotter than some areas in the west, so the eastern states can profit from geothermal energy, also. Such efforts will be aided by newer drilling methods and technologies that can extract energy from temperature reservoirs as cool as 100°C.[6]

Blackwell released a paper with details of the results of the research at the 2011 meeting of the Geothermal Resources Council .

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