The high installation costs of photovoltaic (PV) systems are the most important obstacle in the spread of systems; that's why various studies are carried out on the optimization of PV systems today. Thus, PV systems can be optimized in terms of criteria such as inclination angle, PV module number, module type, module construction structure, and inverter. Different user-friendly software is used to design PV systems. Such software estimates energy production using climate data and provides

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... ic data accordingly. However, the reliability of these data varies as the productivity of photovoltaic systems depends on climatic conditions. In this paper, it is aimed to evaluate the effectiveness of PV*SOL, PVsyst, RETScreen, and PVGIS software, widely used in the solar energy sector, under the climatic conditions of Kocaeli province. A 5,1kWp roof-top PV system installed on Kocaeli University Technology Faculty building is simulated with these programs to reveal which software is more successful in predicting real energy production data. According to comparison, PV*SOL and PVsyst are evaluated as the most reliable software since the yields obtained are the closest to the real energy values.