10.3 Geothermal power generation
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within the underground and not during ordinary circulation and thus production of the hot geothermal fluid. In seismic unstable areas, this microseism may produce small earthquakes before the natural event. However, this situation is very unlikely to occur as such sites would not be chosen due to their history or would be eliminated at least after the stress has been detected at site. For this reason, also the slightest acoustic signals are recorded, which occur when rocks burst during stimulation /10-1/. Due to the relatively low temperatures, varying between 150 and 250 °C, the efficiency of geothermal power generation is relatively low when compared to conventional power plants. This is a result of the high quantities of waste heat to be released into the atmosphere and thus pollute the environment. However, if there is a certain demand for low-temperature heat in the locality of the power plant, the heat might be used to substitute other environmental harmful heat provision systems (e.g. coal oven). Furthermore, waste heat could also be returned into the underground. Geothermal generation facilities are characterised – compared to other power plants based on renewables and conventional energy carrier – in general by little land demand depending on the reservoir and generation conditions only. Additional space is required for the pipelines that transfer the geothermal fluid from the well head to the power plant. In the case that the pipes are installed aboveground they also affect the landscape visually. Additional space is required for cooling towers and power stations. However, these space requirements do not differ essentially from those of fossil fuel-fired power plants. For normal operation, altogether only very few environmental effects can be expected. From the current viewpoint no significant detrimental effect on humans and the natural environment is likely to occur. Malfunction. Due to the salt and mineral contents, in case of a malfunction, minor environmental impacts may result from heat transfer medium leakage at the earth ’s surface (i.e. hot water or hot steam). However, the environmental impacts are low compared to those observed in the volcanic areas of the earth. Further environment impacts may result from a possible pressure relief of the heat transfer medium within the power plant (due to a malfunction (e.g. leakage) of the circuit). Small amounts of gases may be released; however, such a release can be prevented by appropriate safety measures which are well known from the conventional power plant technology /10-1/. As for any other technical plant, environmental impacts are thus by all means possible; however, they are always limited to a restricted area and do not have global effects. From our current knowledge they only have very little impact. End of operation. To prevent unwelcome environmental impacts, at the end of operation the wells need to be properly sealed to permanently exclude penetration of harmful substances from and to the earth ’s surface and to prevent a hydraulic short-circuit of various subterranean layers. Disposal of plant components, in