The Earth's Heat: A New Power Source (1970)

current short-term energy crisis (SN: 11/14, p. 379), the long-term finiteness of fuel resources and the increasing success of environmentalists in stalling the building of new generating plants are causing utility engineers to look more and more to geothermal reservoirs as a possible source of electrical energy. Tapping these naturally occurring pools of hot water beneath the earth's surface would cause few of the pollution problems created by conventional or nuclear generators and could supply huge quantities of energy. Most geothermal development to date has been in nations such as Japan and Italy where there is a shortage of fossil fuels. But the picture is changing rapidly. The United States has not been so hungry for sources of energy other than fossil fuels or the atom, says an Interior Department official. With the increasing emphasis on environmental pollution, however, a new attitude is developing toward geothermal power, he says. Engineers who once scoffed at it as a pipe dream are now taking a second look. And the increased interest is reflected in activity such as the formation of new companies devoted to geothermal prospecting, as well as in new interest by giant energy firms. United States Tax Court has declared geothermal resources eligible for a percentage depletion allowance of the kind that has made oil companies the envy of other energy producers. Another large stimulus has come from a report this year from the University of California at Riverside. report concerns itself with a single geothermal site, California's Imperial Valley (SN: 2/1/69, P. 113). It indicates that if the geothermal resources there were fully utilized, 20,000 to 30,000 megawatts of electric generating capacity could be installed. Other nations-both those traditionally interested in geothermal power and some newcomers to the fieldare also taking a new look at geothermal resources, and the Soviet Union is now carrying out wide-scale mapping of temperature gradients to discover the best areas for geothermal prospecting. source of geothermal energy is the molten rock, or magma, in the earth's interior. When underground water comes into contact with the magma, hot water and steam are produced. Among the conditions necessary for the existence of a tappable source of geothermal energy are a large chamber of magma relatively close to the surface and large and porous underground reservoirs with channels connected to the heat source. Where these conditions exist, as in Imperial Valley, wells of a depth within the means of current technology will produce geothermally heated water. There is also a possibility, not yet fully confirmed, that the geothermal energy might be a self-renewing resource. Dr. Robert W. Rex, director of the UC study, estimates the average cost of the thermal energy to be about two cents per million British thermal units, compared with the 20 to 30 cents and more that energy from fossil-fuel or nuclear sources costs. Capital costs involved in developing this energy for power would probably be comparable to those for ordinary fossil-fuel plants. same turbinegenerator arrangement would be used. Substituting for the boiler of fossil-fuel plants and the reactor and heat exchanger of nuclear plants would be wells and flashing units that would collect the hot water and steam from the geothermal reservoirs and convert it to the clean, dry steam-with no condensed water in it-necessary for electric generation. Imperial Valley geothermal resource became more attractive when the salinity of most of the geothermal reservoirs was shown to be lower than earlier thought. brine, largely sulfate free, of those portions of the Imperial Valley sources not near the Salton Sea has a relatively low salt content of 1.5 to 2.5 percent. In the ground, the brine has a temperature of 500 degrees F. and a pressure of about 2,000 pounds per square inch. About 20 percent of this brine can be converted in flashers to the hot, dry steam needed for power production. But there is enough heat in the remaining brine to distill about 90 percent of it into fresh water before the dissolved solids begin to precipitate in the residue. leftover, highly concentrated brine can be pumped into wells isolated from the useful geothermal reservoirs. With full use of the capacity of the Imperial Valley resource, it might be possible to produce 5 million to 7 million acre-feet of fresh water annually from the wells-a valuable by-product for irrigation and other uses in the water-short lower Colorado River Basin. Generally speaking, any thermal electric power plant is most useful for producing base-load power, or meeting constant demand. It takes a long time to heat up a boiler and turbine, and the PG & E