Steam rising from a valley just north of San Francisco reminded early explorers of the gates of hell. Others saw the potential healing powers of the naturally heated water, and still others realized the steam could drive turbines to generate electricity.
It's been 50 years since power plants began running off the pools of steam that sit under California's Mayacamas Mountains. The pioneering plants in the area known as The Geysers highlighted the promise of geothermal energy, internal heat from the Earth with vastly greater energy potential than that of fossil fuels. But geothermal, virtually free of carbon emissions and more reliable than intermittent wind and solar energy, still provides only a small slice of the world's energy.
Now amid the rush to alternative energies, geothermal advocates sense a new chance to mine the heat rising from Earth's white-hot core. They plan to generate man-made steam by pumping water deep underground into hot, dry rocks in what's called enhanced or engineered geothermal systems. They also despair that governments and businesses aren't investing enough in the sophisticated technology needed to unlock the deep-seated energy.
"There's a window of opportunity where geothermal can play a part in our energy future, and we risk missing it," says David Blackwell, a geophysicist at Southern Methodist University.
(Related: Biothermal Energy Basics)
Blackwell contributed to a broad study released in 2007 that predicted geothermal could provide one tenth of U.S. power by 2050. But that progress depends on new technology that can move geothermal beyond naturally occurring steam deposits. These enhanced geothermal systems would use tricks learned from oil and gas drilling. They would fracture rock with high-powered streams of water, generating steam to power turbines running above ground.
"That's really the holy grail of geothermal: that you can go anywhere and extract the Earth's heat," Blackwell says.
It also remains experimental. For now, geothermal energy depends on hot water and steam deposits lying within two miles or so of the Earth's surface. "You still have to be in the right area to exploit geothermal," says Max Krangle, managing director of ABS Energy Research in London, England. That means population or industrial centers must be near steam reservoirs to benefit from them, a scenario that could limit geothermal's contribution to the world's energy needs, Krangle says.
Some countries astride strong volcanic activity have eagerly exploited their geothermal resources, which generates about 18 percent of the electricity in the Philippines, about 25 percent in Iceland, and 26 percent in El Salvador, according to the Geothermal Energy Association.
(Related: How Iceland Uses Geothermal Energy)
Still, ABS analysts predict that power generated from geothermal deposits will grow slowly through 2020. It will lag behind the gains of other energy sources and still make up just a small slice of the electric pie—about 0.2 percent of world production. Fossil fuels would fall a bit from about 67 percent of generating capacity to 61 percent, with gains in wind and solar making up most of the difference, ABS estimates.
Groups promoting geothermal, such as the Geothermal Resources Council, think the technology could grow more rapidly. They cite a coming spurt of new geothermal projects, with wells planned to exploit natural steam deposits in North America, Africa, and Indonesia, among other places. Kenya, for one, has committed itself to aggressive drilling in its stretch of the East African Rift Valley, a geologically active area thought to hold large geothermal reserves.
Kenya made its move after a recent drought that tested its dependence on hydropower, including a shutdown of its main hydro dam. By 2030, Kenya aims to have generating capacity of 5,000 megawatts of geothermal electricity, or more than twice the capacity of all of Kenya's current electrical plants. It's also almost twice the 2,800 megawatts of geothermal generation capacity that ABS says now exists in the United States, the current world leader. (Worldwide, geothermal produces about 10,000 megawatts of capacity that can meet the needs of about 60 million people, according to the Geothermal Energy Association).
Before exploring new drilling sites, Kenya is first expanding several geothermal plants it operates in the Rift Valley. The power stations sit inside the country's Hell's Gate National Park, also named for the natural steam releases seen by early European explorers in the 1800s.
Expanding Into New Territory
Utilities have commissioned a number of projects to expand plants above natural deposits in North America. They include plans at California's own hell's gate, later named The Geysers—a misnomer, as there are no geysers there—already the site of the world's largest geothermal plant.
But it's the man-made steam that would thrust geothermal into prominence, according to the 2007 study, which was funded by the U.S. Energy Department and led by the Massachusetts Institute of Technology. Several dry-rock projects are under way, including a system planned for Oregon by AltaRock, one of several companies with projects in the works to create underground steam. AltaRock's backers include the Energy Department and high-profile investors such as Google, which has been plowing money into alternative energy projects.
Enhanced geothermal applies rock-cracking technology that's already widely used in oil and gas drilling. One challenge is making it work amid the underground heat needed to generate steam, says Susan Petty, who helped found AltaRock after contributing to the 2007 report.
"We have technology that can do it today—this is not the Easter Bunny," she says. But the new approaches are expensive, making it difficult to compete financially with conventional electrical plants, notably those that burn coal or gas.
While cleaner than fossil fuels, man-made steam faces its own environmental concerns, primarily the threat of small, man-made earthquakes. In 2006, a quake shook Basel, Switzerland (map), amid drilling and underground rock-cracking for an enhanced geothermal system there. The quake forced that project to shut down, and its sponsor had to make millions of dollars in payments for damaged buildings.
Blackwell at SMU jokes that the damage likely included "a lot of cracks that were hundreds of years old." He says the threat of dangerous quakes is a "red herring" that has slowed investment, particularly federal money.
Petty at AltaRock says small quakes always accompany the rock fracturing in oil-and-gas drilling, but industry has learned how to monitor and control their severity. The Basel project targeted a particularly sensitive seismic area, and drilled in the middle of a city because of plans to divert steam for heating buildings, another use of geothermal energy.
"There were people who felt the Basel plan was high-risk," she says.
AltaRock suffered its own setback when it failed in an effort to redrill an existing well at The Geysers, where electricity production has fallen as steam has been depleted. But Petty says she continues to believe in enhanced geothermal systems, encouraged by recent tests of some of AltaRock's technology. "I have a lot of confidence we're going to be able to do this."