Flash steam is the geothermal power technology in which hot underground water rapidly turns into steam when pressure falls.
Geothermal wells bring high-temperature water from a reservoir to the surface. Because the water is under pressure underground, it can remain liquid at temperatures above its normal boiling point. When the pressure is reduced in a separator, part of the water “flashes” into steam. The steam is then directed to a turbine connected to a generator.
Flash-steam plants are widely used where geothermal reservoirs contain very hot water. Some facilities use double-flash systems, reducing the pressure in stages to extract more energy from the same resource. The remaining brine may be reinjected underground, helping maintain reservoir pressure and reduce surface disposal.
Dry-steam plants use steam that arrives naturally from the reservoir, while binary-cycle plants transfer heat to a separate fluid with a lower boiling point. These names describe different plant arrangements, not different renewable energy sources.