The earliest design for a geothermal power plant is the dry steam power plant. Still used today, the dry steam power plant uses the steam directly from the underground geothermal reservoir, or well. The steam comes up from the well and turns the turbine.

The most common design for today’s geothermal power plants is the flash steam power plant. They extract very hot water from underground wells and pump it to the surface under high pressure. The hot water is converted to steam which turns the turbine.

If the temperature of the underground water is less than 350°F, then a binary cycle power plant is used. Water is pumped to the surface so it can heat another fluid that has a lower boiling point, like a hydrocarbon. Steam from the second fluid is used to turn the turbine.