The 'Binary' method of deriving electricity from geothermal energy
With binary technology, underground reservoir waters of lower temperatures are used for flashing. Heat from geothermal water is transferred to a second (binary) liquid, which flashes into vapor upon heating, and that vapor is used to drive turbines. (With dry steam technologies - a much rarer fuel source but the one used in the world's largest geothermal power plant at The Geysers in northern California -- highly pressurized geothermal vapor is used directly to drive a turbine.)
