Alameda in pictures: The Geysers
Alameda in pictures: The Geysers
A few hours north of San Francisco, in the Mayacamas Mountains, sits the world’s largest geothermal field. The Geysers steam field covers more than 2,000 acres and provides electricity to thousands of Californians, and Alameda Municipal Power owns a significant share of its output.
The utility took more than 60 customers and staffers on a tour of one of The Geysers’ power plants Friday, leading a pair of tour buses through the Bay Area fog, the vines of wine country and a winding maze of steam and water pipes to the Northern California Power Agency plants.
The plants generate electricity by mining superheated steam from porous rock as far as two miles below the Earth’s surface and using it to power turbines that create electricity. Alameda Municipal Power gets 17 percent of the 100 megawatts of power the plant produces. A megawatt is typically considered enough electricity to power 1,000 homes.
Twenty-two percent of Alameda Municipal Power’s output in 2013 came from “green” power sources, its power content label says. It says the utility didn’t get any of its state-eligible renewable power from geothermal sources in 2013 and 4 percent of its power from those sources in 2012; spokeswoman Rebecca Irwin said that since the utility is generating more green power than the state requires, it is selling the power to the State Department of Water Resources for the next few years. The money will go back into the utility's effort to expand its green power projects.
PG&E drilled the first commercial wells at The Geysers in 1960, and a host of other companies soon followed. The agency – which includes 15 public agencies, including Alameda Municipal Power – entered purchase agreements with Shell in 1977 and 1980, buying out the company’s steam leases in 1985. Its plants are on property owned by the federal Bureau of Land Management.
The agency built its first plant in 1983 and a second one in 1986. The plants are encircled by a network of twisted 30-inch pipes – built with bends to mitigate spikes in pressure – and smaller pipes that carry water back into the ground, plus a cooling system that pumps 60,000 gallons of water per minute and storage for the mercury and hydrogen sulfite pulled from the steam (prior to the fields’ use for energy production, they were home to mercury mines).
But the year after the second plant was completed, the amount of steam power companies pumped out of the ground dropped by 18 percent – a catastrophic decline, according to one of the plant’s engineers. While the heat source producing the steam was still at full force, the steam itself turned out to be a finite resource that was being exhausted – largely due to the fact that most of it dissipates into the air as exhaust.
Power companies mining The Geysers cut production in an effort to slow the loss of steam pressure. That reduction, combined with an agreement with Lake County to pump millions of gallons of treated wastewater mixed with lake water into the field to create more steam, has slowed the losses to between 1.5 percent to 2 percent a year, plant staffers said.
But this past year, that solution faced its own challenge in the guise of California’s drought. For the first time since the wastewater agreement was put in place, in 1997, the lake the power plant is drawing some of its water from fell below the level county officials sought to maintain. That slowed the flow of water to a quarter of what it had been before the drought.
Nevertheless, the plants’ engineers projected that they will be viable until 2040 – and probably beyond that date.
“We’ll provide power as long as people want it,” he said.