The main objectives of this study are to assess the degradation of power, voltage and current for photovoltaic (PV) modules in predicting temperature and soiling based on five-month measurements. This study aimed to present simple experimental models for estimating the temperature and effects of dust on PV power generation. Results demonstrated that soiling short-circuit current loss underestimates the real soiling power loss by approximately 8%, and this value rises with the increase in dust density. The soiling rate during the week of dust deposition was 0.3% per day and during the final week was 0.15% per day. Results indicate that the polynomial model from the second degree is more accurate than the linear and power models for evaluating the influence of dust on PV systems in the case study. The results suggest that such analysis is required to arrive at a realistic estimation of the best cleaning time in PV power plants.