Why is the working fluid in a binary cycle plant kept in a closed loop?

In a binary cycle power plant, the working fluid—typically a substance like ammonia or hydrocarbons—is kept in a closed loop to facilitate a continuous, efficient energy conversion process.1

The system operates by using geothermally heated water to transfer thermal energy to the working fluid through a heat exchanger. Because the working fluid has a lower boiling point than water, it vaporizes upon absorbing this heat and drives the turbine to generate electricity. By maintaining a closed loop, the vaporized fluid can be recondensed after passing through the turbine and piped back to the heat exchanger to be reused, ensuring the cycle remains self-contained and efficient. This design allows the plant to generate power from lower-temperature geothermal resources that would otherwise be insufficient for traditional steam-based generation.1