The objective of the current paper is to evaluate the performances drop of a photovoltaic system composed of a new PV module conception without EVA encapsulation. After three years of operation under harsh atmospheric condition at Green Energy Park research facility, in the mid-south of Morocco, the system shows an energy drop around 1.8kWhe in one of its strings. For this reason, an inspection (in-situ and at the lab level) to evaluate and detect the source of this energy drop has been done using the IV-Curve, IR thermal and Electroluminescence. Results show that the Performance Ratio (PR) of the affected string reaches 13%. Besides, two modules from this last one showed a degradation rate (Rd) greater than 4.12 %. It has been found that the main cause of this energy drop is due to the presence of breakages and crack at the modules cells. Those deceases are caused by a bad manual cleaning, as well as, for the nature of the modules, without EVA protection against the mechanical shocks.