This paper presents an energy performance analysis of three different photovoltaic (PV) modules technologies under Izmit, Kocaeli weather conditions in Northwest of Turkey. Some comparative analyzes were conducted for showing solar energy potential of Izmit, Kocaeli. For this purpose, by using crystalline (c-Si), multi crystalline (mc-Si) and cadmium-telluride (Cd-Te) modules, three on-grid photovoltaic power systems (PPS) were installed on the rooftop of the Engineering Faculty at Kocaeli University These PPSs were monitored from October, 2013 to December, 2014. In order to determine the energy performances of PV modules and PPSs, normalized energy of systems, performance ratios (PRs), mean array efficiencies (MAEs) and capacity factors (CFs) were calculated. The results show that due to the low dependency on weather changes, MAE of Cd-Te arrays result in higher value than that of the other arrays. Changes in PRs of c-Si and mc-Si arrays are lower than Cd-Te arrays within the measurement period and mean values of PRs are 83.8%, 82.05% and 89.76% for mc-Si, c-Si and Cd-Te arrays, respectively. Since Cd-Te array has the highest CF during all months, Cd-Te array can be accepted as more reliable array under Izmit climatic condition. On the other hand, one of the outcomes of this study is to reveal the solar energy potential of Izmit by on-site measurements. So, it is shown that contrary to measurement taken between 1985 and 2006 from 156 stations by General Directorate of Renewable Energy (GDRE) and Turkish State Meteorological Service (DMI), Izmit has more solar energy potential by rate of 23.79%. (C) 2015 Elsevier Ltd. All rights reserved.