This paper presents the temperature impacts on the performance parameters of PV systems based on measurements of two grid connected PV systems installed in different climate locations in Palestine. PV system-1 is installed in the northern West Bank, where the measured maximum module temperature varies during system operation from 30.5°C in winter to 52.5°C in summer, while PV system-2 is installed in the Jordan Valley, where the maximum module temperature varies from 35.5°C in winter to 62.6°C in summer. Measurements of a complete year obtained from PV system-1 of 4.2 kWp are analyzed to show the negative effect of temperature on the performance parameters of the PV system. At solar radiation of 800W/m2 the output power varies from 3.0 kW in the cold month of December to 2.7 kW in the hot month of July. The efficiency and the performance ratio dropped from 13.1% to 11.75% and from 93% to 84% between December and July, respectively, due to the higher ambient temperature during the summer months. The measured annual final yield amounts to 1641.1 kWh/kWp and the annual capacity factor amounts to 18.71%. The measured drop in voltage according to module temperature in PV system-2 amounts to 1.93 mV/°C-Cell.