How does a binary cycle geothermal power plant work?

A binary cycle geothermal power plant operates using a closed-loop system that separates the geothermal fluid from the power-generating turbine. Unlike other designs, the geothermal water never comes into direct contact with the turbine.12

The process functions as follows:

• Heat Exchange: Geothermally heated water is extracted from underground and passed through a heat exchanger.1
• Energy Transfer: Within the heat exchanger, the thermal energy from the geothermal water is transferred to a secondary "working fluid"—typically a substance with a lower boiling point than water, such as ammonia or hydrocarbons.12
• Vaporization and Generation: The heat causes the secondary working fluid to vaporize. This pressurized vapor is then used to drive an electrical generator turbine.12
• Recirculation: After passing through the turbine, the working fluid is recondensed and piped back to the heat exchanger to repeat the cycle, while the cooled geothermal water is injected back into the ground.12

Because this is a closed system, binary cycle plants produce no air emissions. This technology is particularly valuable for utilizing lower-temperature geothermal resources.21