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| Fig. 1: The Geysers Geothermal area, north of San Francisco, California, is the world's largest dry-steam geothermal steam field. (Courtesy of EERE - U.S. Department of Energy.) |
Located north of San Francisco, in north of Calistoga lies the largest complex of geothermal power plants in the world. Operated by Calpine - a major Texas power company - the forty-five square miles complex that comprises the Geyser is reported for being responsible for a net generation of 725 megawatts of electricity (which is enough to power a city of the size of San Francisco). [1] Since the State of California requires that all of its energy units have a certain fraction of "green" energy in their annual portfolios, the Geysers are also of highly political importance. Thus, we are left wondering if the costs reported for the extraction of the Geysers natural energy and their true economically standing is in fact hidden. Furthermore, one should be concerned with the future implications of this resource and its perspectives. [2]
Geothermal energy is derived from the earth's natural heat. It originates mostly from the radiation decay of minerals, however it can also be attributed to the original formation of the planet. More specifically, in the Geysers, the magma that usually is found in the depths of Earth is believed to be a mere four miles beyond the earth's surface, especially around the Pacific Rim. The heat from this molten rock radiates to the layers of rock above heating water through the pores and fractures of the hot rock. As a consequence, a small amount of the heated water can ascend to the surface resulting in geysers. At the region located between the Sonoma and Lake County Border, the heated water boils to steam, and is trapped beneath a layer of unfractured rocks. In order to create energy, wells are dilled through the rock that originally traps the steam, which is then piped to fifteen operating Calpine power plants in the area. Then, after the cleansing of the steam, it is put to work in order to create electricity. [3]
According to self-divulgated data, the Geysers operated by Calpine are currently responsible for the production of 725 megawatts, which means that it provides California with approximately 63.5 × 1012 joules per day. [2] However, as of December 31, 2010, according to self-divulgated data, the Calpine Company's generation potential included approximately 5,241 megawatts of base load capacity from its Geysers Assets and cogeneration power plants. The reason as to why not all of the Geysers potential has been fully explored as of now lies on economical matters. After all, even though it is exempt of fuel costs fluctuations, the capital costs required are significant, especially the ones related to drilling and exploration of deep resources. It was reported that a typical well doublet that can support only 4.5 MW could cost up to 10 million dollars with a 20% failure rate. [4]
It is a known fact that the Geysers operated by Calpine are easily the most developed geothermal field. Just for comparison: Nevada's geothermal plant has a power capacity of 454.4 megawatts, and the Imperial Valley's capacity is approximately 600 megawatts. [5-7] Furthermore, the Geysers' importance in state of California has been constantly increasing, especially due to some new measurements made by both the Calpine Company as well as the California government itself.
Recently, there has been a discussion of Calpine investing over 700 million dollars on the Geysers. The project would include two new power plants capable of producing 98 megawatts. This idea is very much in pair with California's goal of producing more power from renewable source. The expansion would reportedly take place in the north of the existing complex, on 6,200 acres of state and private lands within The Geysers known as geothermal resources. [4] However, the construction of said expansion still requires the approval of the county's zoning board.
The future of the Geysers is also prominent if we verify the current political background. As of March of 2011, there is great incentive for the passing of a bill that would make the utilities to provide 33 percent of their power from renewable sourced by 2020. Before, laws required utilities to generate 20 percent of their electricity from clean sources by 2020. [2]
With the geothermal injection and production activity in the Geysers, there has been an increasing concern related to induced seismicity activity. The volume of seismicity is determined by the volume of the rock considered capable of building up stress and forces that act in order to deform the natural state. At The Geysers, it is claimed that one of the main causes to the seismicity activity in the area is the injection of water to prevent pressures in the steam reservoir to fall to uneconomic levels. [8] Research, indeed shows that the Geysers are very active and thousands of micro-earthquakes (magnitude<3) are recorded every year in the area in which it is operated, probably due to its activity. Furthermore, it is important to point out that the magnitude appears to be increasing with additional injection. However, the larger earthquakes (greater or equal to 3) seem to be the same every year, which leads us into the conclusion that the seismicity activity for larger magnitudes does not seem to be related to the geothermal activity. [9]
Even though geothermal energy can be very important, it is also essential to determine the energy dissipated in this kind of power source. First, we can examine the loss of energy that occurs due to the heat dissipation in the pipes and the geyser casing, which can be related to the following equation:
where qlosses is the heat loss in Watts/m2, Th is the water temperature inside the geyser in degrees Celsius, Tambient is the air temperature outside the geyser in degrees Celsius), t is the thickness of the insulating layer in meters, k is the thermal conductivity in W/m °K, and h is the surface heat temperature coefficient in W/m2 °K.
Now, we will determine the energy dissipated at the mid-ocean ridges, where we can find the black smokers, a type of hydrothermal vent found on the seabed. They customarily resemble black chimney-like structures that emit a cloud of black material. The black smokers typically emit particles with high levels of sulfur minerals, or sulfides. They are produced in fields hundreds of meters wide when vey hot water from Earth's depths comes through the ocean floor. This water is rich in dissolved minerals from the crust, most notably sulfides and when it comes in contact with cold ocean water, many minerals precipitate, forming a black chimney-like structure around each vent. This dissipation can be calculated by the following equation:
where rate is the rate of sea-floor spreading measured from rocks on either side of the ridges (in meters per year), thickness is the thickness of the ocean floor rock (in meters) and heatfussion is the heat of fusion of the lava in joules per cubic meter.
It is interesting to observe that from this formula people conclude that most of Earth's geothermal flow comes from this ridges. [10]
The Calpine Geysers are extremely important politically and economically to the state of California. Although there is some speculated relation with seismic activities in the region where it is located, we can agree that its significance as a great source of "green" power surpasses all the negative aspects of its production.
© Cibele Montez Halász. 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] E. Douglass, "Calpine to Pump up Its Geothermal Power Source," Los Angeles Times, 31 May 07.
[2] R. DiPippo, Geothermal Power Plants: Principles, Applications, Case Studies and Environmental Impact, 2nd Ed. (Elsevier/Butterworth-Heinemann, 2008).
[3] W. E. Glassley, Geothermal Energy: Renewable Energy and the Environment (CRC Press, 2010).
[4] P. McGreevy, "California Assembly OKs Increased Green Energy Requirement," Los Angeles Times, 30 Mar 11.
[5] A. Herndon, "New Life for Power Plants Losing Steam, Bloomberg Businessweek, 13 Oct 11.
[6] B. Predmore, "Imperial Valley Economic Development Corporation Celebrates a Decade of Growth, Holtville Tribune, 25 Jan 10.
[7] S. K. Sanyal, "Cost of Electric Power from Enhanced Geothermal Systems - Its Sensitivity and Optimization," GRC Trans. 33, 245 (2009).
[8] L. Rybach and M. Mongillo, "Geothermal Sustainability", Geotherm. Res. Council Trans. 30, 1083 (2006).
[9] N. Deichmann and D. Giardini, "Earthquakes Induced by the Stimulation of an Enhanced Geothermal System Below Basel," Seismol. Res. Lett. 80, 784 (2009).
[10] Geothermal : the Clean & Green Energy Choice for the World (Geothermal Resources Council, 1998).