Geothermal energy is the energy coming from the Earth sub-surface.
The energy of the earth's crust comes from the initial formation of the planet (for 20%) and the radioactive decay of certain elements (for 80%), the lifespan of this energy is counted in billions of years (as the sun). The deeper you go, the higher the temperature.
This thermal energy can be used directly, or it can be converted into electrical energy if conditions permit.
Direct use and electricity :
Different uses :
High enthalpy geothermal energy : for electricity production. Usually exploited in volcanic and active tectonic geological contexts, it is also called high temperature geothermal energy. Geothermal fluids are generally above 150°C.
High temperature geothermal energy can also be developed in other geological contexts such as the Massif Central or Alsace in France, but also elsewhere in Europe, at depths ranging from 2500m to 5000m.
Low and medium temperature geothermal energy : warm resources between 30° and 150°C, mainly used for district heating and some direct industrial uses. Widely used in the Paris Basin in France (world's largest concentration of geothermal plant for district heating).
Very low temperature geothermal energy : houses and buildings' heating with heat pumps (vertical or horizontal geothermal probes).
On the production side :
+ Primary energy, 24h/24 availability, all year
+ Reliable and predictable production, not intermittent (baseload energy)
+ Power plant factor capacity between 75% and 95%, about 6570 to 8322 hours/year
+ Decentralized energy with a neutral impact on existing power grids (not intermittent)
+ Geothermal reservoir has long life (40 to 50 years minimum)
On the environnemental side :
+ Clean and renewable energy
+ No greenhouse gas nor air pollution
+ Low land easement
+ Available everywhere, with high concentration in some location (volcanoes, magmas)
+ Alternative energy to coal and oil&gas capacities (which have more greenhouse gas emissions)
+ Energy security and independance for territories or countries, no external supplies
Land easement of different energy power systems
compared to geothermal (source: Islandbanki)
Furthermore, geothermal power plant development can have some drawbacks, but they are well controlled.
During the well drilling phase, the rig can cause noise. In the Paris basin where more than 80 geothermal wells were drilled in the last 30 years, developpers has always reduced this temporary nuisance with adequat means.
Very low magnitude induced seismicity (not felt) is possible during operation, depending on the encountered geological setting. Seismic monitoring system can reduce these events by modulating the power plant production. Developpers should therefore inform the public and integrate it into this kind of project.