This paper provides an accurate modeling method for the photovoltaic panel using Matlab software. The mathematical model discusses the effect of the environmental factors on PV panels. The model based on specifications given on the manufacturer’s plate, a previous Simulink model was developed using Matlab code, to include the effect of humidity on the solar cell performance and efficiency. In the previous work on P-V characteristics, the temperature effect is discussed adequately, without mention the humidity side effects. In this paper, the effect of humidity on the fill factor and efficiency of solar cells is discussed. The conclusions come with many side effects of the humidity on the solar cell, which is the sediments trapped by water molecules, and energy loss due to the reflections of light from the condensed water surface. In addition to the heat carried by moister. The effect of this kind of heat has been studied through calculating the enthalpy of the moist air, and feel like temperature). According to this model and in Silicon solar cell, the lost energy due to reflection was equal to (Gave=842.0175 w/m2) on average. Due to this loss, solar cell current and voltage will be different. All these effects lead to a decrease in the fill factor and the efficiency of the solar cell, because of a reduction in the absorbing energy.