Efficiency of Geothermal Power Plants: a Worldwide Review

The conversion efficiency of geothermal power developments is generally lower than that of conventional thermal power plants. Confusion can be found in literature concerning the estimation of this conversion efficiency. Geothermal power plants conversion efficiency estimates that is based on the enthalpy of the produced geothermal fluid can be the most desirable for use during the first estimates of power potential of new wells and for resource estimation studies. The overall conversion efficiency is affected by many parameters including the power plant design (single or double flash, triple flash, dry steam, binary, or hybrid system), size, gas content, parasitic load, ambient conditions, and others. This work is a worldwide review using published data from 94 geothermal plants (6 dry-steam, 34 single flash, 18 double flash, 31 binary, 2 hybrid steam-binary and 1 triple flash plants) to find conversion efficiencies based on the reservoir enthalpy. The highest reported conversion efficiency is approximately 21% at the Darajat vapour-dominated system, with a worldwide efficiency average of around 12%. The use of binary plants in low-enthalpy resources has allowed the use of energy from fluid with enthalpy as low as 306 kJ/kg, resulting in a net conversion efficiency of about 1%. A generic geothermal power conversion relation was developed based on the total produced enthalpy. Three additional, more specific, relationships are presented for single flash / dry steam plants, double flash plants, and binary plants. The conversion efficiency of binary plants has the lowest confidence, mainly because of the use of air cooling, which is highly affected by location and seasonal changes in ambient temperature.