Challenges to expanding geothermal energy include long project development times, the risk and cost of exploratory drilling and undesirable environmental effects. Geothermal energy entails higher risks than most other renewable forms of energy because of the geological uncertainties of developing reservoirs which can sustain long-term fluid and heat flow. It is difficult to fully characterize a geothermal reservoir prior to making a major financial commitment. Another potential challenge for hot dry rock is the large quantity of water required in the process. A small 5-MW plant could use 8.5 ML of water per day, while a full-scale commercial plant could use ten times that amount.
Various countries with geothermal resources have devised policies to underwrite risks at both the reservoir assessment and drilling stages. For these countries, it would be impossible to attract private investment without these measures. Some aquifers can produce moderately to highly saline fluids that are corrosive and present a potential pollution hazard, particularly to fresh water drainage systems and groundwater. Re-injection and corrosion management are, therefore, important.
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