Ingenuity Turned the Geysers into a Powerhouse

The first thing to know about the Geysers is that they are, in fact, not geysers at all. Geologically, a geyser is a spring that accompanies a cavern of volcanically heated rock; when the water boils, a jet of steam mixed with water erupts at the surface, none of which happens at the 45 square mile site about 70 miles north of San Francisco.
 
According to historian Susan Hodgson, the first American survey party to the area killed a marauding grizzly bear, and one of the surveyors, William Bell Elliot, went to a nearby town to report the incident and describe an area he called “the Gates of Hell,” with vents of steam and vapor raising from the ground. He called the formation “geysers,” and the name stuck even though the geologically heated vapor seep is technically a fumarole.

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The hot rocks, heated by a blob of magma that forced its way toward the surface, and its resulting vapors and hot springs have been a source of wonderment for centuries. Today, however, the site is known more for its connection to electric generation. The Geysers is home to 18 power generating stations that tap steam produced by the geological formation; together, the steam turbines generate as much as 1.5 GW of electricity for use in California.
 
That accounts for nearly 40 percent of the installed geothermal power capacity in the United States. 

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The success of the Geysers site traces back to Unit 1, the first commercially viable geothermal power plant in the United States, which ASME listed as an Engineering Landmark in 1985. But that innovation would not have been possible without some false starts to point the way.
 

Spa treatment 

The native Americans of Northern California knew about the fumaroles in what are now Lake, Sonoma, and Mendocino counties and considered them to be vested with healing powers.
 
“The Indians were using it, and what they did that was so smart,” Hodgson said. “They crisscrossed the area with trails, and everybody was allowed to come in use the geothermal facilities. Instead of fighting over them, everyone was welcome.”

European settlers in the mid-1800s also believed that hot springs and their waters laden with sulfates and borates could treat many ailments, and within a year of Elliot’s “discovery” of the Geysers site, tourists began flocking to the site. By 1854, Archibald Goodwin opened the Geysers Resort Hotel to cater to elite tourists. It was a success, Hodgson said, even though getting to the remote location from San Francsico required two ferry rides, two train trips, and a wagon ride up a steep and twisty road to the top of a mountain. One written account stated that the passengers cowered in fear as they saw “the yawning chasms that threaten death” just beyond the wheels of the wagon.

“There isn’t that much rain up there and it’s very, very dusty,” Hodgson said. “So, when the stagecoach reached the hotel, a man with a feather duster would greet the guests and dust them off.”

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By 1877, some 3,500 names had been entered on the register of the hotel. According to historical accounts, Theodore Roosevelt, J.P. Morgan, William Howard Taft, and Albert Edward, the Prince of Wales, visited the site.
 
The heyday of that resort was short-lived, though it lived on for decades as a local attraction. But the hot rocks and the dry steam that escaped from them eventually drew the attention of entrepreneurs. In 1921, local businessman John D. Grant drilled a borehole that exploded like a volcano, Hodgson said. A second one drilled in 1922 was more successful Grant captured the hot, dry steam, which registered 62 pounds per square inch of pressure. Directing it to two reciprocating, steam-engine-driven turbine generators, the output of the well produced 35 kW of electricity for the Geysers resort. 
 
Grant’s project was successful for a time, Hodgson said, but the minerals in the water that attracted bathers wound up fouling the power equipment. Together with a glut of cheap oil from West Coast petroleum companies, the geothermal plant couldn’t compete.
 
In the immediate aftermath of Grant’s attempt, a pair of geochemists from the Carnegie Institution of Washington went to the site to study dissolved chemicals in the water, the effects of the steam production, and other issues. Their report, Hodgson believes, eventually may have found its way into the hands of B.C. McCabe of Magma Power Company. 
 

New era

Building off Grant’s experience and taking advantage of newly developed technology, such as centrifugal separators to remove rock dust carried along by the steam, McCabe drilled a new geothermal well in 1955. Able to extract consistent amounts of high-temperature steam, McCabe negotiated with the local utility Pacific Gas and Electric to supply a steam turbine to generate electricity. This was Geysers Unit 1, which began operations on September 25, 1960.
 
The turbine of Unit 1 was designed for 100-pounds-per-inch, 350 °F steam, though copper parts in the interior were removed due to fear that hydrogen sulfide mixed in the steam would degrade them. 

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The Unit 1 was by necessity small, producing only 11 MW. After the experience of John Grant in the 1920s, there was no reason to make a large investment until the technology could be proved to work. Within a few years, however, another steam turbine was added, and by 1968, two more began operation. Especially in the aftermath of the energy crises of the 1970s, geothermal power was seen as both cost-effective and clean. 
 
Developers continued to drill wells through the Geysers site, bringing steam to the surface, running it though pipes to steam turbines, and then piping condensed steam and cool water back to the well for reinjection. These pipes crisscross the rugged terrain, connecting wells and power stations.

Today, some 22 geothermal power stations operate in the Geysers area, though Unit 1 was decommissioned in the 1990s. Altogether, the site produces enough electricity for about 1 million homes in northern California.
 
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In the late 1990s, the site began to suffer water shortages, according to Danielle Matthews Seperas, manager for government and community affairs at Calpine, the energy company that now operates 17 of the generating stations at the Geysers. 
 

Recharge and replenish  

“When we first took over the Geysers, our goal was to make it more efficient, because at the time there was a severe decline,” she said. 
 
At the same time, local municipalities were running into difficulties meeting environmental standards for disposing of their treated wastewater. In a stroke of insight, Calpine started a project where it piped treated effluent to the site for use in cooling the power plants and reinjecting the water back into the geothermal well.

Two pipelines, each over 40 miles in length, deliver 20 million gallons of secondary or teriary treated wastewater from the communities of Clear Lake and Santa Rosa to the Geysers. 
 
“The Lake South Lake County effluent pipeline project brought in recycled waters from nearby communities that we could use to replenish the reservoir. Running two separate systems like that was a lot to manage and we were learning how the projects work,” Matthews Seperas said. “The project is 25 years old and operations are going strong. The community benefits because they now have a responsible way to discharge, and we are using the water efficiently.”
 
The future for the Geysers seems bright. The need for carbon-free electricity has never been greater, and unlike wind and solar power, the geothermal wells at the Geysers operate around the clock. While it is difficult to vary the steam output of the geothermal wells to match the varying demand from California consumers, Calpine is adding a battery storage facility to the Geysers, on the site of a decommissioned steam turbine. 
 
“It is an efficient way to use the facilities, the roads, the transmission equipment, everything,” Matthews Seperas said.

Jeffrey Winters is editor in chief of Mechanical Engineering magazine.