how it works

Deep underground there are hot rocks, fluid, and permeability (the ability for fluid to move between rocks).

These are the three key components of geothermal energy generation. They can exist either by natural or artificial causes.

To create energy, fluid must flow through the hot rocks, absorbing their heat. That fluid then is drawn up through wells to the earth’s surface. This heat energy is converted to steam, which drives turbines that produce electricity before it is re-injected into the wells.

There are 3 main types of geothermal power plant technologies:

1. Dry steam. Uses hydrothermal fluids that are already mostly steam. These are the oldest types of plants, first used in Italy in 1904.

2. Flash steam. Fluids at >360F are pumped from underground and travel under high pressure to a low pressure tank at the earth's surface. This sudden change in pressure causes fluid to "flash,” into vapor. That vapor drives a turbine, which drives a generator to create electricity.

3. Binary cycle. Use lower temp geothermal resources. The geothermal reservoir fluids never come into contact with the power plant's turbine units. They pass through a heat exchanger with a secondary (binary) fluid which flashes into vapor, which drives turbines to create electricity.

   
   

As of 2023, geothermal makes up about 0.4% of US utility-scale electricity generation.