In this paper, the thermal effects of solar panels are investigated experimentally and computationally on the efficiency of an Unmanned Air Vehicle (UAV) in laminar and turbulent flows. At first, the impact of temperature on output power and efficiency of an eFlex 30 Wp solar panel is studied. Then, the surface temperature and output voltage of two different types of solar panels, a flexible and a solid panel, are measured under a heat lamp. The heat lamp provides the radiation and raises the temperature of the solar panels. A thermal camera and laser thermometer are used to measure the surface temperature of the solar panels. Considering a tilt-rotor UAV as a case study, an energy balance is modeled for the wing of UAV, which is assumed as a flat plate. Applying the Blasius boundary layer for laminar flow and 1/5 power law for turbulent flow, it is shown that there is skin friction drag changes on the top surface of the solar panel due to its dark blue color. In order to validate the results of the proposed model, a thermal-fluid study is carried out on the NACA 2412 airfoil through COMSOL to see whether changing the surface temperature on the solar panel relates to skin drag reduction. The results indicate that an increase in the surface temperature of the solar panel will decrease the output power and efficiency to a maximum of 8%; while this increase in temperature reduces drag by up to 10% in laminar flow. This research shows that despite the reduction of efficiency and generated power by solar panels with increasing the surface temperature on top of a UAV, the aerodynamic efficiency can be improved with drag reduction in laminar flow.