Man has utilized the natural heat of the earth for centuries. Worldwide direct use of geothermal currently amounts to about 7,000 MWt, as compared to 1,500 MWe, now being used for the generation of electricity. Since the early 1970s, dwindling domestic reservoirs of oil and gas, continued price escalation of oil on the world market and environmental concerns associated with coal and nuclear energy have created a growing interest in the use of geothermal energy in the United States. The Department of Energy goals for hydrothermal resources utilization in the United States, expressed in barrels of oil equivalent, is 50 to 90 million bbl/yr by 1985 and 350 to 900 million bbl/yr by the year 2000. This relatively clean and highly versatile resource is now being used in a multitude of diverse applications (e.g., space heating and cooling, vegetable dehydration, agriculture, aquaculture, light manufacturing), and other applications requiring a reliable and economic source of heat.