Sustainable management of geothermal resources

Geothermal energy is a renewable, environmentally friendly energy-source most often associated with volcanic activity, hot crust at depth in tectonically active areas or deep and permeable sedimentary layers. The energy production potential of geothermal systems is primarily determined by the pressure decline caused by production. Sustainable management of a geothermal resource involves utilisation at a rate, which may be maintained for a very long time (100-300 years). Overexploitation of geothermal systems mostly occurs because of poor understanding, due to inadequate monitoring, and when many users utilise the same resource without common management. Careful monitoring and modelling, as well as energy-efficient utilisation, are essential ingredients in sustainable management. Reinjection is also essential for sustainable utilisation of geothermal systems, which are virtually closed and with limited recharge. The Hamar low-temperature geothermal system in the volcanic lava-pile of Central N-Iceland and the geothermal resources in the sedimentary basin below the city of Beijing, P.R. of China have been utilised for decades. They are examples of geothermal resources, of highly contrasting nature, which may each be managed in a sustainable manner. The sustainable potential of the Hamar system is estimated, through modelling, to be greater than 40 kg/s of 65°C water