California’s Underground Hot Rocks Probed for Energy of 100 Nuclear Plants
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 may 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 and create the vapor needed to generate power.
The technology “offers the opportunity of creating additional reserves,” said Mark Walters, a senior geologist at Calpine Corp. (CPN), 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. The Houston-based company is expected to begin testing this process today.
There are hundreds of sites worldwide where the technology may be used to generate electricity. In the U.S., such plants could supply 100 gigawatts of power by 2050, said Ernest L. Majer, an energy geophysicist at Lawrence Berkeley National Laboratory. That’s the equivalent of 100 nuclear reactors and would boost geothermal’s share of the country’s power supply to 10 percent, from less than 1 percent now.
“There’s a lot of hot rock out there,” Majer said. “That would replace our nuclear power plants.”
The U.S. Energy Department has earmarked $182 million in grants for enhanced geothermal systems, or EGS, since 2009. In such projects, water is piped into wells that extend down to hot rocks -- in the Calpine test, the rocks are about 750 degrees Fahrenheit (400 degrees Celsius).
This causes the stone to crack, creating tiny fissures. Once the site goes into operation, water flows through these fissures and is heated into steam that’s piped back to the surface to produce electricity.
The process is similar to the hydraulic fracturing done by the oil and gas industry, though different in scale. With “fracking,” water, sand and chemicals are injected horizontally at extremely high pressure to create cracks in underground rocks so petroleum and natural gas can be extracted.
EGS systems have smaller goals. “We are trying to create a cloud of small fractures,” Walters said. “We’re talking millimeter fractures.”
Calpine is planning to begin injecting water today two miles (3.2 kilometers) into the ground near The Geysers, a region about 100 miles northeast of San Francisco 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,” said Walters.
The Energy Department provided $6.2 million in grants for Calpine’s $11 million project, the second EGS test in the U.S. to reach the injection phase. A year ago, Ormat Technologies Inc. (ORA) began injecting water at Desert Peak in western Nevada. Four other projects may be active by late next year, Majer said.
Blowouts and Earthquakes
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 voiced concerns that the installation may destabilize surrounding areas.
In September 2009, Seattle-based AltaRock Energy Inc. suspended a project at The Geysers due to drilling problems. Geodynamics Ltd. shut down a test in southern Australia after an uncontrolled leak in April of that year.
Not ‘Commercial’ Yet
It’s not yet certain that EGS projects can create enough steam to make them profitable, said Ann Robertson-Tait, business development manager of the geothermal resource consulting company GeothermEx Inc. While the technology has long-term potential, “there are few places where EGS can be considered commercial at present,” she said.
Proponents of EGS say it can breathe new life into geothermal fields that are literally running out of steam.
Calpine generates roughly 725 megawatts of capacity at 15 traditional geothermal plants around The Geysers, using dry steam power systems that run on vapor piped up from natural underground pockets.
Problem is, about 75 percent of the vapor is lost through condensation during the process and the steam output there today is about half its 1987 peak.
By injecting more water onto the hot rocks at The Geysers, Calpine expects to add at least 5 megawatts of capacity to an existing plant. The company may expand the use of EGS to other plants in the area if this test is successful.
Geothermal has advantages over solar and wind: It’s typically cheaper to operate and generates electricity 24 hours a day (though there’s no guarantee how much power can be produced until a well is drilled).
EGS may 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 and little steam, said William Osborn, AltaRock’s vice president of development for the project.
“The same technologies will be applicable” at sites all across the U.S., he said, “where you have high temperatures at depths everywhere, but you don’t have open cracks.”
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