MIDDLETOWN, Calif. -- Geothermal plants in The Geysers area north of the Napa Valley have tapped steam fields to produce electricity since the 1960s. The 350-degree steam rushes more than 1,500 feet up from the earth, spinning turbines that create a constant flow of electricity.
But mismanagement of the steam fields beneath the hilly northwestern California region that straddles the Sonoma and Lake county lines has led to a large decline of pressure - and a drop of more than 50 percent in the amount of power the plants produce.
The geothermal decline comes as California already faces short supplies of hydroelectricity from the drought-ridden Pacific Northwest and growing competition for megawatts from other power-starved states.
State power grid managers estimate they're losing about 900 megawatts of geothermal electricity due to the gradual depletion of the steam fields. That's enough power for roughly 675,000 homes.
"They just overproduced. It is a renewable source of power, but it's renewable over geologic time," says Katherine Potter, a spokeswoman for Calpine Energy, which owns 19 of the 21 geothermal power plants in The Geysers region, which incidentally has no geysers.
The first electricity produced by tapping into pockets of steam trapped in the earth made its debut in 1904 in Larderello, Italy. That plant, rebuilt due to World War II damage, is still operating. The first U.S. geothermal plant was a small operation at The Geysers built in 1962.
Steam fields are created when water flows through fissures in the rock deep in the earth and is heated by hot magma. Geothermal plants tap into that pressure and use it to spin turbines. The plants' cooling towers release plumes of white steam, which can be seen for miles on a clear day.
While The Geysers is a unique geologic formation called a dry steam field, there is the potential for thousands of megawatts of geothermal power from other regions that could use the more common "wet steam" process, said Karl Gawell, executive director of the Geothermal Energy Association in Washington D.C.
Wet steam plants tap into superheated water in the earth, separate the steam and use it to power generators. The water and the condensed steam is pumped back into the earth.
CalEnergy Corp. owns 10 power plants in Imperial County that produce about 330 megawatts of power, enough for about 247,500 homes. Those plants and others like them haven't seen a decline in pressure like Calpine's plants.
Geothermal energy is second only to hydroelectricity as a continuous, cheap source of power, said Jan Stewart, Calpine's public relations manager.
The plants in The Geysers reached their peak power production in the 1980s, producing about 2,000 megawatts of electricity - enough to power about 1.5 million homes.
At that time, about 30 companies were involved in various geothermal ventures in the area and didn't work together, Stewart said.
"The resource wasn't being managed properly. As a result, it was a very fractured environment," she said. "If one plant shut down, the steam would be vented to the atmosphere, instead of being rerouted to another plant where it could be used."
In the 1960s and '70s when The Geysers got started, there was "a real wildcatter's mentality" among power generators, said Rich Ferguson, energy chairman for Sierra Club California.
"Basically, they took out the water in the form of steam faster than Mother Nature was putting it back in," he said.
The available steam declined, and the area now puts out about 850 megawatts, sufficient power for roughly 637,500 homes.
Since then, geothermal engineers have learned more about managing the resource, Ferguson said.
The superheated, self-contained system at The Geysers has no water running through it.
"The Geysers is unique worldwide. There really aren't other dry steam fields," Gawell said. "In effect, there was never a sustainable level of production, you always would have depleted it eventually. It's like a giant pressure cooker. As soon as you put the first straw in, you began to deplete the resource."
Calpine is experimenting with replenishing the steam fields by pumping treated waste water back into the earth. It began three years ago, when Lake County stopped pumping its treated waste water into Clear Lake.
Now, more than 8 million gallons of treated waste water is returned daily to the earth. The experiment appears to be working - power output is up 68 megawatts.
"People like the stewardship that Calpine provides now," Ferguson said. "Calpine has taken on as a long-term goal to make that sustainable."
Calpine is building a 50-mile pipeline to Santa Rosa and plans to pump another 11 million of treated waste water daily from that city. The company expects that will boost production another 85 megawatts.
Even with the new project, power grid managers say they're planning for diminishing geothermal electricity.
"We've lost a considerable portion of their output due to the decline in the output of the steam," said Jim McIntosh, director of grid operations for the Independent System Operator. "All supplies are very important to us at this point."
The plants are relatively low-maintenance once they're running - only one engineer staffs each of the 19 Calpine plants in The Geysers.
But geothermal plants are more expensive to build than natural gas-fired power plants, Gaywell said.
"It's like choosing between two identical cars - one is $10,000 and the other is $30,000, but the $30,000 car comes with a lifetime supply of fuel," he said. "People are shortsighted on investments and it takes more money upfront to build geothermal."
Most geothermal resources are on public land, lengthening the building process because more permits are needed, Gawell said.
Two new plants are in the application process in California.
Researchers estimate there are 2,500 megawatts of untapped geothermal resources in Nevada, Gawell said. Idaho, New Mexico and Oregon also have sites that could be tapped, he said.
"Many of these sites were looked at in the '80s, but then nothing happened because in the '90s natural gas was too cheap to meter," he said.
Ferguson said the state spent $540 million over the last four years on incentives for renewable energy projects, including geothermal, solar, wind and biomass, and he expects the plan will be renewed when it expires in December.
"We think there will be an equivalent amount of money," he said. "All the technologies have to compete against each other, but geothermal should do pretty good."
On the Net:
Geothermal Education Office: http:geothermal.marin.org
California ISO: http://www.caiso.com
Calpine Corp.: http://www.calpine.com
Geothermal Education Office: http://geothermal.marin.org
|There are three types of geothermal power plants. Here's a look at how they work:|
- Dry steam: Such plants are rare, producing steam and not hot water. The Geysers region is the world's largest dry steam field. Steam from the earth is piped to the power plant, where it spins turbines to create electricity. After the remaining steam condenses back to liquid, it is returned to the earth.
- Wet steam: This type of geothermal plant is more common. There are several such plants in Southern California. Hot water and steam are brought to the surface, separated and the steam is used to power turbines. The water is returned to the earth as is the condensed steam.
- Binary: These plants use hot water and steam from the earth to heat another liquid, such as isobutane, which has a lower boiling point than water. That liquid's steam is used to power turbines to make electricity. When the steam cools and becomes liquid it's returned to the tank and reused. This type of system is self-contained and has no emissions.