This study investigated the effects of dust deposition and ambient air temperature on the performance of a thin film photovoltaic module under real outdoor conditions in the humid harsh climate of Egypt. The experimental study investigated the effect of dust deposition and the effect of ambient air dry bulb temperature on the performance of the PV module. Theoretical study predicted the temperature of the PV panels at various metrological conditions in different locations inside Egypt. The study experimental results show that dust deposition has a significant effect on Isc current, while is has less effect on Voc voltage. Dust effect becomes more significant on cloudy days more than on sunny days. The PV modules must be cleaned regularly every 4 days and directly after a dusty storm. The ambient air dry bulb temperature has a significant effect on Voc voltage, while it has less effect on Isc current. The theoretical models results were compared with the experimental results, and good agreement were found. The theoretical results show that the Crystalline PV panels are more affected by the ambient air dry bulb temperature rather than the thin film PV panels