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| Fig. 1: Illustration of a binary cycle power plant. (Courtesy of EERE, U.S. Department of energy.) |
Located along the volcanically and seismically active region that spans up the pacific coasts of Australian and Asia down from the northern tips of North America to the southernmost parts of South America known as the Pacific Rim, California is home to 25 known geothermal energy resource areas, one of which is the much discussed Imperial Valley. Of the six known geothermal resource areas (KGRAs) in the Imperial Valley, four have significant amounts of usable energy: The Salton Sea, the Heber, East Mesa and the Brawley KGRA. The geothermal reservoirs associated with these particular KGRAs use a binary cycle to extract the heat instead of the dry-steam or vapor procedure used at The Geysers in northern California because the geothermal fluids in the valley are particularly scathing. [1]
Geothermal energy is the heat from the decay of naturally radioactive materials (e.g. uranium and potassium) that is transported through water conduction to the Earth's surface; approximately 42 million megawatts of heat continuously flows by conduction from the Earth's inner core outward, making geothermal energy a completely renewable and sustainable energy resource. [2] To access this natural thermal energy, industrialists drill wells miles into the earth where hot reservoirs heated by magma or molten rock reach temperatures of up to 700 degrees Fahrenheit. To get the heat energy from the water at these depths in the Imperial Valley, a binary cycle is used that pushes two fluids - geothermal fluid and a working fluid with a boiling point much lower than that of water, such as isobutene - through a heat exchanger. The heat energy from the geothermal fluid evaporates the working fluid, and the resulting vapor pushes turbines to generate electricity. Binary cycles are closed-loop systems, so the working fluid is condensed and used for future cycles and no waste is produced.
The $300 million geothermal energy business is not an immediately ostensible threat to the $1.2 billion agricultural industry that gives the Imperial Valley its economic livelihood. However, an estimated 16,000 MW potential of renewable energy, comprised of solar, wind, geothermal and biomass, lies in the valley alone, so the agricultural center that is the Imperial Valley could soon give way to the renewable energy movement. [3] This shift is already underway, as companies like San Diego Gas & Electric, which has spent the past seven years and about $100 million in the planning of a high voltage line, called the Sunrise Powerlink, that would total 117 miles and run through the heart of the alley, begin to buy government owned land. [4] In fact, there are currently 16 geothermal plants throughout the valley, ten of which are owned by CalEnergy, and the number will probably rise. [5] According to U.S. Interior Secretary Dirk Kempthorne, 90% of U.S. geothermal resources lie below federally owned land much of which could be leased to businesses soon for geothermal energy production. [6] The U.S. Department of the Interior's Bureau of Land Management (BLM) and the USDA Forest Service (FS), which issued a report in July 2009 that presented a survey of the geothermal potential of government owned lands across 12 Western states, is encouraging these leases. [7] Still, transforming the Imperial Valley into a hub for renewable energy generation will be difficult not only because agricultural workers will resist, but also and fundamentally because to function, geothermal plants built in the region will need water from the very same resource that provides irrigation for the crops: the Colorado river. [5] Water from the Colorado River is regulated by the Law of the River established in 1922; according to this law, 97% of the water that reaches the Imperial Valley is for farmers, leaving only 96,000 ML for residents and businesses, a third of which has been directed toward the geothermal industry. [5] Water in all western states is lacking, and scientists predict that in the case of the Colorado River, water supply will diminish in the coming years due to climate change. Clearly then, the drive toward geothermal, industrial excellence in the Imperial Valley could very well dry up before even getting off the ground.
© Ayana Wilson. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] D. W. Layton, "Water Supply Dilemmas of Geothermal Development in the Imperial Valley of California," J. Am. Water Resources Assn. 14, (1978).
[2] Geothermal Energy Association.
[3] B. Predmore, "Imperial Valley Economic Development Corporation Celebrates a Decade of Growth," Imperial Valley Tribune Weekly Chronicle, 25 Jan 10
[4] M. L. Wald,
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[5] S. Adee and S. K. Moore, "In the American Southwest, the Energy Problem Is Water," IEEE Spectrum, June 2010.
[6] B. Boxall, "Big Plans for Geothermal Energy," Los Angeles Times, 22 Oct 08.
[7] "Jumpstarting Geothermal Energy: Outreach to 12 Western States, Federal Agencies and the Public," U.S. Bureau of Land Management, July 2009.