Steam propels a turbogenerator producing electric current.

The average power output from a HDR geothermal power plant ranges from tens to hundreds of megawatts. The big advantage of this source of electricity is that it can generate power 24 hours a day independently of actual weather condition.

The source of heat for a hot dry rock geothermal power plant is a region of impermeable rock in economically accessible shallow depths, heated from bellow by magma up to several hundred degrees Celsius. This region is reached by drill and then fractured by pumping pressurized water (this is called stimulation) or by microexplosions. Growth of the fractures during stimulation is typically monitored by mapping the locations of microseismic events. The cracks in the rock are filled with circulating water, which creates a large heat-exchange system. During routine energy production, the injection pressure is maintained at just below the level that would cause further pressure-stimulation of the surrounding rock mass, in order to maximize energy production while limiting further reservoir growth.

A drill hole that reaches the HDR reservoir. At first it is used for reservoir creation by pumping pressurized water. This hydraulic stimulation creates a large interconnected array of joint flow paths within the rock mass. In operation, fluid is injected through the injection well at pressures high enough to hold open the interconnected network of joints against the Earth stresses, and to effectively circulate fluid through the HDR reservoir at a high rate. Heated water is then pumped out of the HDR reservoir by a production well. After transferring its heat to the power plant, cooled water is injected back to the reservoir. The injection well is about 3 km deep. In the Otaniemi geothermal project in Finland drilling has reached a depth of 4.6 kilometers.

Steam coming out of the turbine needs to be cooled and condensed. Depending on the location of the geothermal power plant, cooling is done either by water from a river or sea if available, or by cooling towers with a natural or forced draft.

The water in contact with hot rock could contain various dissolved minerals. These could be harmful for the turbine, so the heat from the water pumped from HDR reservoir is transferred to the secondary circuit in the heat exchanger. This is typically a set of tubes in which circulating secondary-circuit-water is heated by water from a well flowing around them. The heated water turns into steam which is led to the turbogenerator and then is cooled in a condenser and flows back to the heat exchanger.

The HDR pressure-stimulated region is accessed by one or more production wells pumping hot water back to the surface. The location of the production wells is so that it ensures the best circulation through the reservoir. The temperature of the outgoing water ranges from around 180°C to 350°C.