A new theoretical approach of black flat-plate solar collector considering the glass cover as a participating media taking into account the absorption and emission within a glass cover is presented. Two kinds of glasses commonly used as cover for such system, clear and low iron, have been studied. The glass material is analyzed as a non-gray plane parallel medium subjected to solar and thermal irradiations in one-dimensional case using the Radiation Element Method by Ray Emission Model. The optical constants of the complex refractive index, 160 values of real part (n) and imaginary part (k), of a clear and low iron glasses proposed by Rubin covering the range of interest for solar and thermal calculation have been used. The CPU times for predicting the thermal behavior of a solar collector using non-gray models were found to be prohibitively long. Therefore, suitable semi-gray models have been proposed for rapid calculation. In order to compare the thermal performance of solar collector having low iron glass as a cover with the solar collector having clear glazing, the previous result concerning the clear glass cover will be presented again. It has been also shown that the instantaneous efficiency of the solar collector with a low iron glass cover is higher than the efficiency of the system with clear glass cover,