Calpine is the largest operator of geothermal power plants at The Geysers, a 45-square-mile area in northern Sonoma County where ambient underground heat is close enough to the surface to generate steam from groundwater.
Calpine produces enough power there to satisfy the needs of San Francisco, or 60 percent of the needs of the North Coast. Mike Rogers is senior vice president of Calpine Geothermal Operations.
Q: Please describe the scale of the geothermal power generation currently occurring at the Geysers, as well as the facilities operated by Calpine in the area.
A: Calpine Corporation operates 15 geothermal power plants in The Geysers region of northern California and is capable of generating up to 725 megawatts of green energy around the clock. Unlike other renewable resources such as wind or sunlight, which depend upon intermittent sources to generate power, making them less reliable, geothermal power provides a consistent source of energy as evidenced by our Geysers availability record of approximately 98 percent in 2011.
For the past 11 consecutive years, The Geysers have continued to generate about 6 million megawatt-hours per year, which represents approximately 20 percent of California’s renewable electric generation. Calpine Corporation is the nation’s largest renewable geothermal power producer, providing 41 percent of U.S. geothermal generation.
Q: Steam production peaked at the Geysers in the late 1980s, enough to produce 2,000 megawatts of electricity. That output gradually declined in the following years, currently holding steady at 750 megawatts. What caused that decline, and what is Calpine doing to help preserve the current output?
A: Sustainable power generation at The Geysers is possible today because of two large-scale wastewater-injection projects from Lake County and the city of Santa Rosa. Together, these projects provide approximately 20 million gallons of reclaimed water per day for injection into The Geysers reservoir. The vast amount of heat in reservoir rocks efficiently converts the water into steam and supplements the production of steam from the original reservoir to Geysers power plants.
Throughout the 1970s and 1980s, vastly more steam was produced from The Geysers reservoir than was replaced by the injection of power plant steam condensate. By 1989, accelerated development had caused severe steam pressure decreases in the reservoir, resulting in lower steam production rates. This decline threatened the future sustainability of Geysers power generation.
In order to sustain reservoir pressure and steam production, The Geysers needed a large, reliable supply of water that could be used to augment injection. In 1990 a collaborative effort between Geysers operators, Lake County and the California Energy Commission identified Lake County wastewater from the southeast regional collection system as the preferred source of water. This project, known as the Southeast Geysers Effluent Pipeline (SEGEP) began construction in 1995 and delivery of wastewater to The Geysers commenced in October 1997. The original 29 mile pipeline, now lengthened to 40 miles to include effluent from additional communities in the Clear Lake area, delivers approximately 9 million gallons per day of secondary treated wastewater for injection into The Geysers Reservoir.
The success of SEGEP injection in maintaining reservoir pressure provided momentum for a similar project to bring tertiary treated effluent from the Santa Rosa area to The Geysers. In 2004, the city of Santa Rosa and Calpine Corporation partnered on constructing a 42-mile pipeline which became known at the Santa Rosa Geysers Recharge Project (SRGRP). Since 2007 SRGRP has delivered approximately 11 million gallons per day of tertiary-treated wastewater to replenish the The Geysers’ geothermal reservoir.
Calpine has also done eight steam turbine upgrades that have reduced steam consumption. These upgrades, combined with wastewater injection, have been key in sustaining the Geysers output.
Q: How have national initiatives related to renewable and clean energy affected or influenced Calpine’s efforts at the Geysers over the years?
A: In a collaborative program with the U.S. Department of Energy, Lawrence Berkeley National Labs and the U.S. Geological Survey, Calpine has drilled two experimental wells as part of an enhanced geothermal system demonstration project at The Geysers. This project involves injecting low volumes (200 to 800 gallons per minute) of reclaimed water at ambient temperatures into deepened wells, Prati State 31 and Prati 32, drilled over a hot underground dome in our Northwest Geysers steam field where temperatures reach 7,50o degrees Fahrenheit. We want to see if this technique will stimulate wells to produce more steam.
The intent is to determine how water injection affects the fracturing of hard rock with low permeability — where relatively few fractures and little steam exists — compared to the steam reservoir that feeds existing power plants. Calpine estimates that this project will produce enough electricity to power a city of 6,000 people.
We started injecting these wells in October 2011 and observed a quick response in surrounding well head pressures up to 2,000 feet away, resulting in an increase of 40 percent in well steam flow. This increase accelerated through January until pressures stabilized. The next step is to conduct flow testing in existing steam and injection wells.
Six million dollars of the cost of the project was paid by the U.S. Department of Energy, with an additional $5 million from Calpine. During this project — as is the case throughout the entire Geysers field — care is taken to monitor associated micro-earthquake activity that may be produced to determine the relationship between injection rate variations and microseismic activity.
The next step is to vary injection rates and find optimum levels, as well as to assess the impact on neighboring wells. If this project is successful, it will make an excellent case study for other geothermal sites in the U.S. and around the globe, looking for ways to extend the useful life and stimulate higher steam pressures from their legacy generating facilities.
Q: Anything else?
On April 16, the Northern Sonoma County Air Pollution Control District approved air permits for two new geothermal power plants proposed by Calpine (NYSE:CPN) for potential construction at The Geysers.
Calpine continues to actively explore long-term sales opportunities for the proposed plants’ electric output through power purchase agreements with retail electric providers or investor-owned utilities. The construction schedule for these proposed projects is dependent upon securing long-term PPAs and acquiring additional administrative permits. The Sonoma County Board of Supervisors approved land use permits in November.
Each proposed plant could be capable of producing up to 49 megawatts of power. They would be the first new plants constructed at The Geysers since 1989.
Construction of the proposed projects would create 190 local construction jobs during a 30-month build out for each project, requiring about 900,000 hours of labor. In addition, hundreds of millions of dollars in materials, supplies and services would be purchased during construction. Once operational, the proposed projects could create up to 19 new full-time jobs.
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