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Hot Rocks, Cool Technology

From the May/June 2007 Issue

Greener than wind or solar, geothermal energy gets little attention—even though, as Nick Schulz writes, it could provide 2,000 times our current power needs.

A promising, but largely unrecognized, source of clean, renewable energy is right beneath your feet. It’s geothermal energy, which comes from the super-hot rocks just under the Earth’s crust. The United States is the global leader in geothermal, which provides about the same amount of power as the combined output of wind and solar energy, says MIT geophysicist M. Nafi Toksöz. That’s not much, but it could be a great deal more. Right now, geothermal gets little atten­tion—from environmentalists, traditional energy companies, or governments.

This lack of attention is all the more surprising since geothermal is a greener source of power than either solar or wind. But if several intrepid scientists and engineers are right, advanced-technology geo­thermal will get the respect it now lacks.

The idea is simple—tapping underground heat to generate electricity. The Earth’s core emits enor­mous amounts of heat, which, when combined with water—either naturally in hydrothermal reservoirs, or artificially—creates the steam needed to turn a turbine and produce electricity.

The idea isn’t new. Geothermal electricity was first generated in 1904 in Larderello, Italy, in a part of Tuscany called Valle del Diavolo—Valley of the Devil, known for boiling liquids that rise to the surface. Italian engineers slapped an electricity gen­erator on top of their Hades, and the first geothermal installation was born. Today, Iceland generates 15 to 20 percent of its electricity this way.

The problem for large-scale development of geothermal energy is that the planet’s underground heat is not evenly distributed. In the U.S., for exam­ple, hot rocks are closer to the surface in Western states such as California, Utah, and Nevada than elsewhere. The largest and best-known U.S. geother­mal installation is located at The Geysers, just north of San Francisco. Run by the Calpine Corporation, this field generates more electricity than any other in the world: 850 megawatts—enough to provide power for a million households.

In the 1970s, scientists affiliated with the Los Alamos National Laboratory wondered if they could tap heat located far deeper underground. If so, they figured, geothermal energy could be harnessed just about anywhere. They established the technological foundation for what they called Hot Dry Rock heat extraction and patented the idea in 1974.

The Earth's core emits enormous amounts of heat, which, when combined with water, creates the steam needed to turn a turbine and produce electricity.

Under this process (also known as Enhanced Geothermal Systems or “EGS”), wells are drilled into burning subterranean rock, which can be miles below the surface. Water is pumped down at high pressure, creating a reservoir amid the cracks and fissures in the rock. The water is returned to the surface, where hydrothermal energy is extracted to create electricity. The water is then recirculated. According to a paper from Los Alamos scientists, “In this closed-loop process, nothing is released to the environment except heat, and no long-term wastes accumulate.” Unlike with fossil fuels, no CO2 or other greenhouse gases are produced.

And the ecological advantages geothermal enjoys over other alternatives are considerable. It doesn’t compete with food crops like biomass does, and it can provide base-load electricity without the need for coal, nuclear, or natural gas as backups, unlike wind and solar. Also, a geothermal operation has a far smaller footprint than windmills and solar panels. Geothermal is as green as it gets.

So what’s the potential for harnessing much more of the Earth’s natural heat to meet our electricity needs? To find out, the U.S. Department of Energy and MIT convened a panel in 2005 to investigate the viability of large-scale geothermal energy use. The report was issued on January 22.

“Using reasonable assumptions regarding how heat would be mined from stimulated EGS res­ervoirs,” the authors say, the extractable portion would exceed “about 2,000 times the annual con­sumption of primary energy in the United States in 2005.” And heat mining may be economical, even in the short term.

The tools for making geothermal energy extract­able were developed by the oil and gas industry. Brian Anderson, a professor at West Virginia University who worked on the study, notes that advances in drill-bit technology, materials science, and the frac­turing of rocks—which have made it possible to go after fossil fuels in deep and inhospitable environ­ments—can also be used for deep-heat mining.

None of the oil, gas, or coal companies, however, is yet taking geothermal seriously. Anderson says that one reason the big energy firms are reluctant is that they “lack the expertise needed to connect geothermal installations to the electricity grid.” Another is that, for all its potential, geothermal will likely take decades to replace even one-tenth of the electricity generated by coal or natural gas.

So for now, geothermal is largely the province of government-backed efforts and specialist firms such as Nevada-based Ormat Technologies, Inc., a publicly traded company with a market cap of $1.3 billion that operates a total of 370 megawatts of gen­erating capacity globally, about two-thirds of which is in the U.S. (A single nuclear plant typically has a capacity of about 1,500 megawatts.)

Meanwhile, major government-sponsored efforts are underway in Soultz-sous-Forêts, France, and in Australia’s Cooper Basin. The MIT paper argues that projects like these are promising enough to war­rant U.S. government funds in “support of EGS as a long-term ‘public good,’ similar to early federal investments in large hydropower dam projects and nuclear power reactors.”

There’s a good argument that governments should steer clear of subsidizing any form of energy. Federal involvement, even in energy research and develop­ment, has been fitful and haphazard—and probably counterproductive. Remember synfuels? The flavors of the month now include biomass and hydrogen, both with strong political constituencies—but for how long? In the end, like every other energy source, geothermal should have to prove itself in the mar­ketplace. Even without government help, it may eventually do just that.

Nick Schulz is the editor of

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