Binary cycle experiment as one of the Organic Rankine Cycle (ORC) technologies has been known to provide an improved alternate scenario to utilize waste energy with low temperatures. As such, a binary geothermal power plant simulator was developed to demonstrate the geothermal energy potential in Dieng, Indonesia. To better understand the geothermal potential, the laboratory experiment to study the ORC heat source mechanism that can be set to operate at fixed temperatures of 110 °C and 120 °C is conducted. For further performance analysis, R245fa, R123, and mixed ratio working fluids with mass flow rate varied from 0.1 kg/s to 0.2 kg/s were introduced as key parameters in the study. Data from the simulator were measured and analyzed under steady-state condition with a 20 min interval per given mass flow rate. Results indicate that the ORC system has better thermodynamic performance when operating the heat source at 120 °C than those obtained from 110 °C. Moreover, the R123 fluid produces the highest ORC efficiency with values between 9.4% and 13.5%.