Many factors determine the percentage of parasitic load of the geothermal power plant. Domestic consumption accounts for about 20–25 per cent of total production in low-temperature geothermal power plants. As a case study, the ratio of a 1 MW grid-connected PV system to the internal consumption of the Sultanhisar GPP-2 and its effect on increasing the efficiency of the system have been examined. The current production of the power plant has been modeled thermodynamically with the parameters taken from the plant, and the efficiency of the system has been calculated. Sultanhisar GPP-2, which operates at a geothermal well temperature of 140.2°C and a net efficiency of 6.28%, has a domestic consumption to production ratio of around 25%. The installation of a 1 MW PV system is expected to produce 2140MWh per year, equivalent to 7% of the internal energy consumption.