For decades, energy companies have tapped steam from deep in the earth to make electricity. Now at least five American power producers are testing a simple idea that could dramatically expand the industry’s reach: Bring your own water. Instead of producing power only in places where steam flows naturally, these companies are drilling deeper to inject water into superhot, dry rocks to create the vapor needed to generate electricity. The technology “offers the opportunity of creating additional reserves,” says Mark Walters, a geologist at Calpine, the biggest U.S. geothermal power producer. “The heat is a resource in areas around existing plants, but right now we really can’t get at” it.
If successful, the technology could be used in hundreds of locations worldwide. In the U.S., such plants could supply 100 gigawatts of power by 2050, says Ernest L. Majer, an energy geophysicist at Lawrence Berkeley National Laboratory. That would boost geothermal’s share of the country’s power supply to 10 percent, from less than 1 percent today. “There’s a lot of hot rock out there,” Majer says.
The U.S. Energy Dept. has earmarked $182 million in grants for “enhanced geothermal systems,” or EGS, since 2009. In such projects, water is pumped into wells where rocks can be 750F. The water causes the stone to crack. It flows through those fissures and turns into steam that is piped back to the surface. The process is similar to the hydraulic fracturing done by the oil and gas industry, but it happens far deeper underground and uses only water, which is injected at a lower pressure than the solutions used in “fracking.”
In early October, Calpine planned to start piping water two miles into the ground near The Geysers, a Northern California area that’s home to the world’s largest cluster of geothermal power plants. The challenge is to create enough “fractures to heat up a sufficient volume of water,” says Calpine geologist Walters. The Energy Dept. provided $6.2 million in grants for Calpine’s $11 million project, the second EGS installation in the U.S. to reach the injection phase. A year ago, Ormat Technologies began injecting water at Desert Peak in western Nevada. Four other projects may be active by late next year, Majer says.
While a handful of small EGS plants are operating overseas, some have experienced setbacks ranging from blowouts to minor earthquakes caused by fracturing rocks deep underground. A project in Switzerland was shut down in 2006 after residents nearby started feeling tremors and fretted that the installation might destabilize surrounding areas. In 2009, Seattle-based AltaRock Energy suspended a project at The Geysers because of drilling problems. And it’s not yet certain that EGS projects can create enough steam to make them profitable, warns Ann Robertson-Tait of energy consultancy GeothermEx. While the technology has long-term potential, “there are few places where EGS can be considered commercial at present,” she says.
Proponents of EGS say it can breathe new life into geothermal installations that are running out of steam. Calpine generates roughly 725 megawatts of capacity at 15 traditional geothermal plants around The Geysers, some 100 miles northeast of San Francisco. Problem is, the steam output there today is about half its 1987 peak. By introducing more water, Calpine expects to add at least 5 Mw of capacity to an existing plant at The Geysers. The company may expand the use of EGS to other plants in the area if the test is successful.
Geothermal has many advantages over solar and wind: It’s typically far cheaper to operate and generates electricity 24 hours a day (though there’s no guarantee how much power can be produced until a costly well is drilled). EGS could give the industry a lift by opening up development in regions that lack underground steam pockets. AltaRock is working on an EGS test near the Newberry National Volcanic Monument in Oregon, where there’s plenty of heat but little steam, says William Osborn, who manages the project. “The same technologies will be applicable … across the U.S.,” he says, “where you have high temperatures at depths everywhere, but you don’t have open cracks.”