Why isn't there more use of geothermal energy for power plants?
HOT ROCKS: Geothermal power is abundant, renewable and clean. So why isn't it employed more often? Image: Photograph by Julie Donnelly-Nolan, USGS
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Here's another use for fracking: expanding access to hot rocks deep beneath Earth?s surface for energy production. In April Ormat Technologies hooked up the first such project?known in the lingo as an enhanced geothermal system, or EGS?to the nation's electric grid near Reno, Nev.
"The big prize is EGS," enthuses Douglas Hollett, director of the Geothermal Technologies Office at the U.S. Department of Energy (DoE). "The key is learning how to do it in a reliable way, in a responsible way."
By some estimates, the U.S. could tap as much as 2,000 times the nation?s current annual energy use of roughly 100 exajoules (an exajoule equals a quintillion, or 1018 joules) via enhanced geothermal technologies. With respect to electricity, the DoE concludes at least 500 gigawatts of electric capacity could be harvested from such EGS systems. Even better, hot rocks underlie every part of the country and the rest of the world. Australia's first enhanced geothermal system, spicily named Habanero, began producing power in May, and Europe has brought three such power plants online.
The idea is simple: pump water or other fluids down to the hot rocks beneath the surface. Heat from the rocks turns the water to steam. The steam rises and turns a turbine that spins a magnet to make electricity.
The technology is proved. For years people have turned naturally produced steam from hot springs and the like into electricity. A geothermal power plant in Larderello, Italy, has churned out electricity this way in Tuscany for more than a century, and big power plants can be built this way. The Geysers in California can produce 850 megawatts of electricity alone. But that's because the geothermal resource is close to the surface and obvious, thanks to hot steam rising into the sky.
Although similar natural bounty has turned Iceland into a geothermal powerhouse, there are only so many such sites around. That's where fracking, the controversial practice of pumping fluid underground to shatter shale and release oil or gas, can help. Fracking ?enhances? geothermal by making cracks in hot rocks where none existed, allowing heat to be harvested from Earth?s interior practically anywhere, although this reduces the total power produced because of the need to pump water through the system.
As an added benefit, however: geothermal power can run constantly?the hot rocks don't cool very fast?which makes it renewable and predictable. "Geothermal is homegrown, reliable and clean," says Rohit Khanna, program manager at the World Bank for its Energy Sector Management Assistance Program. That is a big part of the reason it is being pursued in developing countries such as Chile, Indonesia, Kenya and the Philippines.
In the case of the Philippines geothermal power now produces nearly 2,000 megawatts, or nearly 20 percent of the country's electricity, thanks to investments that were made in the 1990s. And Kenya, according to its ambassador to the U.S., Elkanah Odembo, would like to derive more than half its electricity from geothermal by 2030. The goal: a combination of geothermal and hydroelectric power that will make them entirely renewably powered. "The potential is there," Odembo promises. He says the Rift Valley contains an estimated 15 gigawatts of potential geothermal power. Nairobi has already become a boomtown for such development.
Source: http://rss.sciam.com/~r/sciam/basic-science/~3/up8cV0_hDjY/article.cfm
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