Process — Electricity from a geothermal power plant

The diagram shows the seven-stage process by which a geothermal power plant converts underground heat into electricity.

Overall, the system operates as a closed loop running vertically between the surface and a layer of hot rock several kilometres underground: cold water is pumped down, returns as steam to drive a turbine, and is then condensed and re-injected.

The plant is deliberately built above rock that is naturally hot, with molten magma lying roughly five kilometres below the surface. In the first stage, cold water is pumped down an injection well. Deep underground, this water seeps through cracks in the hot rock, where it is heated so intensely that it turns to steam. The steam then rises up a separate production well to the surface.

Above ground, the high-pressure steam is piped into a turbine hall, where it spins a turbine connected to a generator, and the electricity produced is fed into the grid. The used steam then passes into a cooling tower, where it condenses back into water. Finally, this water is returned to the injection well and pumped underground again, so the same water is recycled continuously and almost nothing is lost.