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Personnel Profile: Larry Sessions

Tell me about the Geysers.
We generate geothermal power, which is a renewable source of power. The Geysers provide about 25 percent of the state’s renewable energy. There is a lot of emphasis these days with wind and solar. I guess because of the rarity of geothermal there is not a lot known about it. We’ve got 15 power plants in the Geysers. It’s a couple hours north of San Francisco. We have about 825 megawatts that are generated continuously. With wind and solar it tends to fluctuate, depending on whether the sun’s out or when the wind is blowing. But geothermal is a nice base load energy, so we’re getting that renewable energy 24 hours a day around the clock, 365 days a year. It covers about 45 square miles up there. We’ve got about 400 wells, which is a combination of producing wells and some injection wells. The whole process of being able to take steam out of the ground, and then as we’re depleting the steam but not the heat, we put water back in ground, reheat it, and make more steam. That steam then goes through turbines connected to generators, and we generate electricity for the grid.

One of the neat things is in the early days, probably late 80s/early 90s, everybody was saying The Geysers is dying. It seemed to be declining. But then we looked into ways to fix that. Our cooling process is evaporative cooling. It’s kind of a swamp cooler. All that steam we were condensing was going into our cooling towers and evaporating into the atmosphere, so the water wasn’t going back in the ground. So we partnered with some local communities, first with the County of Lake, and brought in treated wastewater, which we were able to put back into the ground and regenerate steam. The larger one was Santa Rosa. So we’re coming from Lake and Sonoma Counties, taking about 20 million gallons a day, continuously. The cities were up against environmental issues where they don’t want to put that water back in rivers and streams. We needed it to refuel. It was a definite win-win between industry and community.

If this is such an old, well-understood technology, why is it so rare?
If you look at a world map, you have to find places where the Earth’s crust is relatively thin, where that hot magma is relatively close to the surface. It’s still several miles down, but it’s close enough to heat up where you find these fractured rock formations under the Earth where it traps water. That pressure finds its way to the surface as steam. The wells are anywhere from one to two miles deep. Through an infrastructure of pipes and valves, we take that to the plants. There’s a significant risk to developing geothermal: high upfront costs of drilling and establishing your wells. But then once they’re drilled, it’s just a matter of maintaining them. Your going forward cost is competitive in the energy market.

To what extent is there untapped geothermal potential in California and the nation?
We’re working to expand The Geysers to the northwest region. There are areas that are deeper and hotter, but we believe there is enough steam there to build at least two more plants. Further north, up around Eureka, there’s the Glass Mountain area where we know there is enough steam trapped in the Earth that could be somewhere in the neighborhood of 300 to 500 megawatts.

Geothermal is pretty much located along the West Coast in what they call the Pacific Ring of Fire. It goes across to Japan, New Zealand, Australia. You’ve got a lot of heat in those areas. Then you see some of it in Europe, in Iceland.

Are there federal or state policy changes that would help you guys?
A lot of it is permitting issues. For instance, Glass Mountain is primarily native Indian lands, sacred territory. We believe the thermal process to be a fairly small footprint, kind of unobtrusive and out in the middle of nowhere so no one is going to see it. Obviously it’s very environmentally sound. We don’t understand why there are so many hassles to allow us to move forward and develop that. Any way the state could step in and make that process easier would be beneficial.

Are oil and gas industry players standing in the way?
I don’t think so. They know we can’t impact the nation. Some places like California, New Mexico, Nevada, some placed in Utah. But obviously we’re not going to push them out and take over the world because there is just not enough geothermal available. Oil and gas have found that a lot of their waste products, have a significant amount of hot water. There are geothermal processes like binary or flash that allow us to take their waste water and generate power from that.

What does a geothermal plant actually look like?
If you’re familiar with any power plant, it’s very similar to a traditional steam plant. The difference is in most steam plants you either have a combustion turbine or a boiler where you burn coal or gas, and run that heat with a series of tubes to boil water into steam. Mother nature is doing that for us. You’ve got steam coming out of the ground. It then is directed through a rotating turbine that spins at 3600 RPM, coupled to a generator at 60 cycles a second, which is the U.S. standard for electrical generation. We take down from a transformer out onto the power grid. You’ve got a lot of plant equipment, pumps and fans and blowers. The biggest thing people misconstrue is steam on a cold day. When you look up in the hills and you see steam or smoke rising, that’s just the heat vapors rising off our cooling towers. It takes a tremendous amount of water circulating through a condenser to put it back in the ground.  

You’re looking at a room about this size [hotel lobby maybe 60 feet on a side] to house the turbine and generator. In a traditional power plant, you’re looking at a whole other structure used to heat up [water] and make steam. Whether you’re burning coal or gas or oil, that’s a tremendous facility in itself. The plants are actually very small. The steam fields, because they’re so connected, cover hundreds of miles of pipes and roads.

The pipe going into the ground, the surface casing going down about 500 feet, is about 20 inches in diameter, getting smaller and smaller. The average well bores are probably about 8.5 to 10 inches in diameter. It will run down to probably about two miles. They directionally drill, so they can actually pinpoint the location where they want to draw steam from. If you ever come to the Geysers, you’ll see a series of wells right in a row, but their down-hole locations could be up to a mile apart.


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