| Summary: | Natural surface manifestations of geothermal energy, such as hot pools, steam vents, geysers, etc., have been known since Antiquity, but the significance of natural steam in terms of economic development has been grasped only in recent years. Individual geothermal fields occur under a great variety of geological conditions, but they all have in common a deep magmatic source, an aquifer in a highly permeable reservoir rock heated from below, and an impermeable cap-rock which prevents the escape of the accumulated steam in significanr quantities. The geological enviromncnt of eight selected fields is described in order to illustrate their common and individual characteristics. Exploration methods such as those used for oil, gas and minerals have been applied to surface and subsurface study of geothermal fields. However, new specific methods have also been devised, which are increasingly employed. Particular drilling methods and problems are described. An indication of average costs is also given. The main utilisation of geothermal energy is electric power generation. The total installed capacity will quadruple from 385 MW in 1960 to approximately 1,600 MW by 1975. Production costs per kWh compare favourably with those obtained by the use of conventional fossil fuels. At present, important geothermal power plants are in operation in Italy, Japan, New Zealand and the U.S.A., while production on a smaller scale is going on in Mexico and the U.S.S.R. Natural steam is also harnessed for district and greenhouse heating, especially in Iceland, for cooling and air conditioning, as well as for various agricultural and industrial applications in many countries. Future utilisation trends point to an increased and more efficient electric power generation. The counties which are currently small producers will intensify the use of their vast geothermal resources, and in the next decade several developed and developing countries will join the list of present power producers. More intensive geothermal steam utilisation in ...
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