Photovoltaic systems convert only a small amount of incident solar insolation into electrical energy while the rest is dissipated into heat. The increase in the PV cell temperature decreases significantly the electrical efficiency by about 0.5% for each 1 degrees C rise. Hence, it is necessary to keep the module temperature at low values to improve the efficiency and to minimize the thermal degradation effect. In this research paper, a passive cooling system was developed to mitigate the overheating of PV modules in order to enhance their performance. The developed cooling system is based on water evaporation and the capillary action of the burlap cloth that was attached directly to the rear surface of the module. Thermal and electrical characteristics of the modules (with and without cooling) were investigated experimentally under outdoor conditions during summer days of a hot climate region. Experimental results showed that a PV module temperature reduction of 20 degrees C (26%) was achieved with the help of the developed evaporative cooling system leading to an important increase of 14.75% in the electrical efficiency. The results also revealed the high effectiveness of the developed cooling system in the reduction and the maintaining of a uniform temperature distribution over the PV module throughout the day. Furthermore, this cooling system has many advantages such as being environment-friendly, low investment cost and low water consumption 0.39 L/h.