By Peg Mitchell / SanDiego350
Burning less coal, oil and gas is not only something we must do, but something we can do. Nature gives us a variety of renewable energy sources, and the technology to tap into them is getting better all the time.
Climate change makes the news often for a variety of reasons, from the multiple impacts we have been witnessing locally — drought, record-breaking temperatures, mudslides, fires — to the President’s issuance of the “Clean Power Plan” to the Pope’s encyclical. But ultimately climate change discussions must focus on economically viable solutions.
We are fortunate to live in a state that has ample natural non-fossil-fuel resources to provide electricity for our citizens. Not only do we have an abundance of sun to power solar generation, but we have a reliable steady-state resource right in our backyard: the Salton Sea Known Geothermal Resource Area in the Imperial Valley.
The geothermal fields near the Salton Sea are the hottest, most prolific resource in the U.S. The reservoir is part of our major fault system near the end of the San Andreas fault. Lateral slip occurs as the North American and Pacific plates slide past each other. This movement forms a “spreading basin” creating natural geothermal reservoirs.
The energy in the reservoir is heat, continually produced from the magma below the Earth’s crust. As seismic action occurs, the rock covering is broken up allowing water to circulate, become heated and naturally rise to the surface. It is this type of action that causes such natural phenomena as geysers and hot springs. Thousands of feet beneath the earth’s surface, the temperature of this water can be as high as 700 degrees Fahrenheit.
In general, geothermal production wells are drilled to tap this hot, hyper-saline water deep in the earth. The superheated liquid naturally rises so no pumping is required. At the surface, the superheated fluid is flashed into steam and used to drive turbines to generate electricity. This has been done in the Salton Sea area by several different companies since 1982 when the first of now 11 facilities began operation.
Since the first facility opened, however, the technology has continued to advance. Earlier plants were problematic and their processes were criticized for extensive water use, greenhouse gas emissions from parts of the process, and similarities to the dangerous method of hydraulic fracturing used today for oil and gas extraction. Newer plants, such as the John Featherstone Facility built by EnergySource which began operating in 2012, have mitigated most of these issues making it a truly clean, continuous, renewable baseload resource, producing energy day and night, every day of the year.
What makes this next-generation geothermal plant a distinct improvement is its “triple flash” process. Three production wells have been drilled down to precisely targeted existing fractures. No explosive “fracturing” of rock (as is done in the fracking of oil and gas) was required. The hot fluid naturally rises, so no fossil fuel driven pumps are needed to get it up the well bore. Once on the surface, the super-hot water enters a separator where its pressure is reduced causing much of it to vaporize and “flash” into high-pressure steam.
The steam is cleaned in scrubbers and de-misters before being sent directly to the turbine for generation while the remaining fluid flows to a second vessel, a “standard–pressure crystallizer” where an additional amount of standard-pressure steam is produced. This step repeats yet a third time, with each step generating and sending cleaned steam to the turbine as the temperature of the fluid decreases. This process maximizes the amount of energy captured and used for direct generation thereby enhancing efficiency while dramatically minimizing the use of fresh water compared to other processes.
One technical challenge that has been turned into an asset is that the region’s geothermal fluid is approximately 75% water and 25% dissolved solids which contain significant amounts of valuable minerals including lithium, manganese and zinc. Once the steam potential is exhausted in the three-step flash process, a clarifier technology removes an iron-rich amorphous silica by-product to minimize the potential of scaling and corrosion, one of the most challenging hurdles in the early development of the Salton Sea resource. One enormous potential side project under exploration is the capture and reuse of the minerals which are important to battery and energy storage technology. Finally, the remaining fluid, about 80% of the original volume, is sent back into the ground, again using natural pressures in the loop.
Imperial County contains the largest known undeveloped geothermal resource in California and possibly the world with the potential to produce 2,965 megawatts (MW). Yet the total maximum amount currently available from the eleven existing facilities at the Salton Sea is only 395 MW, and an additional 200 MW produced from three other locations in Imperial County. For comparison, the San Onofre Nuclear Power Plant, now decommissioned, produced 2,200 MW.
Right now, San Diego Gas and Electric does not purchase a single MW of this renewable resource located so close to San Diego. The Featherstone plant discussed above sells 100% of its output to Arizona because of how power purchase agreements are costed when auctions take place. Geothermal advocates have argued that the California Public Utilities Commission’s rules for estimating the costs of renewable energy sources put geothermal at a disadvantage relative to solar and wind.
They also point out that geothermal does not receive some of the subsidies and tax breaks that these other renewable technologies do. For example, the Featherstone plant pays approximately $3 million a year in taxes to the local government.
Geothermal facilities can also provide other economic benefits to local communities. Because the plant is a baseload plant requiring human operators, each plant creates permanent jobs – the Featherstone plant employs 33 full-time professionals, and it employed over 200 workers during the drilling and construction phases. Because geothermal is considered “mineral rights” there are also royalty payments paid to local landowners for mineral leases. According to the Geothermal Energy Association, “geothermal operators are the largest or second largest taxpayer in their respective counties.”
We will need all of the renewable energy technologies. Geothermal can be an important part of that mix. It provides a very useful kind of electric power, which is available 24 hours a day, 365 days a year. Using advanced technology, geothermal can minimize greenhouse gas emissions and water use on a small land footprint. It can also provide a much needed by-product, lithium, without the need for separate mining facilities, while supplying permanent jobs and a significant revenue stream for the community. Just when we absolutely must find ways to stop using fossil-fuel, geothermal energy is a large-scale, economically feasible, renewable energy source our region should seriously consider.
Images provided by Vince Signorotti of EnergySource from a presentation given on Borrego Energy Day, April 11, 2015.
Peg Mitchell, is a member of SD350 who works mainly on anti-fracking issues.