Utilisation of geothermal resources

For centuries, geothermal energy has been used for bathing, cooking and space heating. More recently, district heating, industrial processing and geothermal heat pumps have become part of the direct-use mix. Geothermal electric power generation began in Italy in 1904, with the first commercial plant operational in 1913. Presently, the total installed global capacity for direct use is 29 000 MWt, producing 76 000 GW h/year in 72 countries; the installed capacity for electric power is 9700 MWe, generating 60 000 GW h/year in 24 countries. Recent trends are to maximise the use of geothermal resources in a combined heat and power project. Geothermal resources of around 100°C have been used in binary (organic Rankine) cycle plants and then cascaded for district heating. Geothermal energy is considered to be both renewable and sustainable as a ‘green energy’ resource, but certain environmental aspects must be considered and mitigated.