What I Learned at the Geysers

November 2009
by James Schwab

Every year the Northern California Power Agency takes state legislative staff on tours of their facilities. As a legislative aide to State Senator Elaine Alquist, who represents much of Silicon Valley, I was excited to see the emerging technologies being employed a short drive from the State Capitol. The Geysers do not disappoint. The facilities sit on mountain tops, connected to a network of pipes that is reminiscent of a screen saver. The staff are friendly and were obviously proud to display their hard work and ingenuity. I highly recommend a visit.

The Geysers, a geothermal field, is the largest in the world, covering 30 square miles across the sparsely populated Mayacamas Mountains in Sonoma and Lake counties.

Underground illustration of how geothermal works.

Geothermal fields are naturally occurring areas where super heated magma pushes close to the earthʼs surface and the heat boils trapped groundwater that seeks a pathway through fractures in the crust. Most of these areas are located near boundaries of tectonic plates which criss-cross the earth. Just west of the Geysers the Pacific Plate dives under the North American Plate fracturing rock underneath and sending heated water and steam to the surface.

This remote area currently supplies over 5% of the stateʼs electricity needs and generates an amount of power equivalent to more than 60% of the entire northern coastal region from San Francisco to Oregon.

Among the handful of providers that operate at the Geysers, our group visited the Northern California Power Agencyʼs (NCPA) site. The NCPA has integrated a number of green technologies into a very sophisticated renewable energy system.

Attempts to capture the geothermal energy for electricity generation began in the 1920s but did not become viable until commercial operations began in 1960. Today there are over 400 production wells at the Geysers producing 800 megawatts (MW) of electric power.

A close up of the geothermal towers. The cooled steam pours over the side to be re-injected back into the geothermal field.

The NPCA site we visited has 70 production wells drilled one to two miles deep into the geothermal field to capture steam at 490 degrees F, and pressures up to 500 psi. Geothermal energy can be produced at anytime of the day, the Geysers generally produce energy 95% of the time. Compared to wind and solar which operate about 30% of the time. However, it is not the steam that makes Geothermal renewable, it is the heat.

Geothermal systems typically draw the heat and steam from the underground reservoir faster than nature can replenish. Over time, the water and steam reserves along with the power production decline. This creates a need for water to be injected back down into the reservoir. However, as water is a scarce resource in California the increasing need of geothermal plants to inject water could lead to problems with other state and local needs.

The NCPA sight faced this problem in the 1990ʼs and found a solution to two different environmental problems with a single integrated system. NCPA needed a new, reliable source of water for injection and the local sanitation districts needed a home for their treated waste water effluent.

NCPA joined with the Lake County Sanitation District to begin operation of the worldʼs first wastewater geothermal injection system. An average of 6,000 gallons per minute are collected from Lake County water treatment facility and pumped 26 miles through the Southeast Geysers Effluent Pipeline (SGEP) for injection.

In the first 12 years of operation over 35 billion gallons of wastewater has been injected into the geothermal reservoir. By 2007 this process created 100 MW of power that would have otherwise disappeared with the declining water reserve.

However, this was not the end of the innovative technology that came out of the first wastewater geothermal injection system.

The SGEP requires 4.3 MW of electricity, which has traditionally been bought from PG&E. However, projected PG&E rate increases would create escalating costs to the geothermal electricity. To cut down on long term costs, the NCPA applied and received an $8 million grant from the California Solar Initiative to build two 1 MW solar systems. The solar arrays, comprised of solar photovoltaic panels are engineered to track the movement of the sun. Using solar to power the waste water system contains the cost of the geothermal energy, decreases NCPAʼs carbon footprint, and diverts billions of gallons of effluent water that would otherwise go into Clear Lake.

The solar array is not the only green innovation at the Geysers. To gain additional power from each well, NCPA installed small turbine generators 1800 feet down into each water injection well. The turbines generate electricity from the effluent waste water as it drops down the pipes and activates the generators.

The generator is a standard submersible electric pump modified to turn backwards in order to change the mass of flowing water into power. Water injected into the top of the well at a rate of 1350 gallons/minute falls about 100 feet into a 1700 foot column of water which forms the “head “of the small hydroelectric system. This technology adds about 250kW of capacity to the system, although by late 2010 NCPA hopes to increase that to 500kW. NCPA is the first geothermal producer to use such a technology.

The Geysers is on the cutting edge of an emerging green technology and growing industry. However, the conditions that make the Geysers such a prolific energy producer are rare. Current US capacity is about 3,000 MW, which is comprised of a few dozen plants scattered over seven states. However, there are about 130 more geothermal plans in different stages of development that represent about an additional 4,000 MW.

The geothermal towers that generate the power. The hot geothermal steams shoots up, turning the turbine and creating power.

A more common form of geothermal energy comes from ground source heat pumps GSHP, which are central heating and/or cooling systems that pump heat to or from the ground. They use the earth as a heat source in the Winter, and as a heat sink in the Summer. They are designed to take advantage of the moderate temperatures in the ground to boost energy efficiency and reduce the operational costs of heating and cooling systems.

In 2007 MIT studied GSHP and estimated US potential that 100GW could be created by 2050 if sufficient research and development (R&D) funds were available. The R&D funds would be used to bring deep earth technologies called “enhanced geothermal systems” (EGS) to commercial readiness. They estimated that EGS could comprise 10% of US energy output by 2050.

The MIT study created strong interest in EGS in both the private and public sector. The 2009 American Recovery and Reinvestment Act provided the US Department of Energy with $350 million for geothermal development, $140 million of which would go towards “shovel ready” projects.

Geothermal energy is not a single solution to our renewable energy demands, but it is a very important part of an overall portfolio. It has its advantages over wind and solar because geothermal energy can be produced almost 24 hours a day. However it has its disadvantages as well, because prime locations for geothermal energy production are few and far between.

The solar array near Middletown that will power the pipes from Clear Lake that will re-inject water to the geothermal reservoir.