Geothermal power plants have the potential to produce reliable, low-cost, baseload electricity. Three basic types of geothermal power plants are currently in operation: single-flashing, double-flashing and binary power plants. For single-flashing power plants brine temperatures from 220° C to 140° C have been used and 250° C to 160° C have been used for double-flashing power plants. The work on flashing type power plants focuses on optimized flashing chamber temperature and pressure to determine specific power generation and finding efficiencies. For binary power plants brine temperatures between 180° C and 120° C have been used and butane is used as the secondary working fluid. Power generation and efficiencies are calculated by considering the heat exchanger design points. Entropy generation for each power plant has been calculated to determine the thermally inefficient and more irreversible processes. It is found that binary power plants generate the lowest entropy; highest rate of conversion of thermal energy into mechanical power. The double-flashing and the single-flashing plants generate highest entropy. The binary power plants have been observed to produce the maximum power at lower brine temperatures, and on the contrary, the single-flashing power plants did not. These calculations prove entropy generation can be used as the powerful tool to analyze and optimize geothermal power plants.