in this paper, a test methodology is proposed to study and analyze the factors that affect Photovoltaic system's performance involving dust accumulation and tilt angle. Literature has shown that a number of studies have studied the effect of dust accumulation on the PV modules performance. However, the relationship between the dust accumulation and tilt angle in real time study is not cleared yet. As the dust is inversely proportional with tilt angle, this work investigates the optimum tilt angle to maximize the output power gained from the PV system. To achieve that, eight PV panels are installed as study cases in Aswan, desert environment example. Different tilt angles with different cleaning scenarios are executed. Test bench is built with data monitoring to measure continuously the result data. Generated power is measured and then, an equation for the average reduction of output power is extracted. The expected generated power from the derived system and the measured system are compared and results show a good matching.