Geothermal plants use heat from the depths of the Earth to produce renewable electrical energy. Our planet’s internal temperature increases gradually the closer we get to its core. This increase in temperature, called the geothermal gradient, is on average about 3° every 100 meters of depth, but in some areas – under certain geological structural conditions – this is much higher, with temperatures of 250-350°C at depths between 2000 and 4000 meters.
How Geothermal Plants Work
Through the fracturing of rock layers, heated water and steam from heat sources (for example, magma ascent from low depths and/or the thinning of the earth’s crust) rise to the surface, where they are intercepted by geothermal extraction wells. The steam from the wells is then conveyed into pipes, called steam pipes, and sent to operate a turbine, where the energy is transformed into mechanical rotational energy.
The turbine axis is connected to an alternator rotor that, by turning, transforms the mechanical energy into alternating electrical energy, which is then transmitted to a transformer. This raises the voltage value to 132,000 volts and puts it into the distribution grid.
The steam coming out of the turbine is returned to a liquid state in a condenser, while the non-condensable gases in the steam of the subsoil are dispersed into the atmosphere only after specific treatments are done to break down the main pollutants, like hydrogen sulfide and mercury (Hydrogen Sulfide and Mercury Abatement Systems, AMIS). A cooling tower allows the water produced by the condensation of the steam to be cooled: at this point the cold water is either used in the condenser, to lower the temperature of the steam, or is injected into deep rock with injection wells, to initiate a new production cycle of renewable energy.