Hydrothermal energy

Water sources for direct thermal uses range ia temperature from less than 30°C to over 90°C. Resources ia desirable locations can often be reached by simply drilling a few hundred feet into the earth. Hot water caimot be economically transported very far. AH direct thermal uses of hydrothermal energy are tied to the quantity and quaHty of nearby hydrothermal resources. 

Electric Power Generation. Hydrothermal steam and hot water resources having temperatures ia excess of about 150°C are generaHy suitable for the production of electricity (see Eig. 3a). Because electricity is easy to market and transport, it is the only product of hydrothermal energy which permits the resource to be utilized at some distance from its actual location. 

Environmental Issues. Hydrothermal energy, recognized as one of the clean power sources for the twenty-first century, is not entirely free of environmental problems. 

Direct Uses of Geopressured Fluids. Many of the uses typical of hydrothermal energy, such as greenhouse, fish farm, and space heating, have been proposed for geopressured resources, but none has been commercially developed (34). Hydrothermal fluids are widely used in enhanced oil recovery, however, to increase production from depleted oil fields. 

Fiydrothermal plants produce electric power at a cost competitive with the cost of power from fossil fuels. Besides generating electricity, hydrothermal energy is used directly to heat buildings. Across the United States, geothermal hot-water reservoirs are much more common than geothermal steam reservoirs. Most of the untapped hot-water reservoirs are in California, Nevada, Utah, and New Mexico. The temperatures of these reservoirs are not hot enough to drive steam turbines efficiently, but the water is used to boil a secondary fluid, such as butane, whose vapors then drive gas turbines. 

Zhang, R., Zhou, J., Wang, Y. (2012). Multi-objective optimization of hydrothermal energy system considering economic and environmental aspects. Electrical Power and Energy Systems, 42(l) 384-395. 

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