Solar energy can be converted to electrical energy by means of two methods: the first one is a direct method with photovoltaic (PV) systems and the second is an indirect one by solar thermal power generation. The main disadvantage of the PV systems is the high sensitivity of the output electrical characteristics to their temperature surface. The increase of the surface temperature leads to reduce the power output according to its power temperature coefficient. For this purpose we have to locate the zones where the PV systems can work efficiently as high as the standard test condition (STC) efficiency. The aim of this research is to determine the surface cell temperature of a working PV system under real operational and environmental conditions (Load, Solar radiation and ambient), further to evaluate the electrical behavior of PV systems and to estimate the failure of their function. The experiment has been carried out in order to measure the following parameters: output power, surface temperature, solar radiation, ambient temperature and wind speed. An experimental model has been designed and built up in the Solar Energy Laboratory at the Department of Mechanical Engineering, in Brack. Brack City is located at 27.6 degrees N and 14.2 degrees E, 600 km away to the south from Tripoli (Capital). According to the results of the experiment, the maximum cell's surface temperature reached 125.4 degrees C in 6/5/2003 at 2:30 PM. The solar radiation was around 896 W/m(2). The percent of the failure of the power was found to be 69% of the nominal power at STC. This is why we have to be careful concerning the use of PV cells for Multi-Mega-Watts power generation, especially, which classified as hot regions, in most of the Arabic countries, especially in those which are classified as hot regions, such as North Africa and South Asia.