Influence of clearness index and air mass on sunlight and outdoor performance of photovoltaic modules

Influences of clearness index (Kt) and air mass (AM) on both the sunlight and the outdoor performance of photovoltaic (PV) modules were analyzed. The Kt and AM strongly affect the intensity of solar irradiation and spectral irradiance distribution. In this study, the impacts of Kt and AM on an index for spectral irradiance distribution of average photon energy (APE) are analyzed using a contour maps and then the impacts of the environmental factors on the outdoor performance of single crystalline Si (sc-Si) and amorphous Si (a-Si) PV modules is discussed. As the result, it was found that APE increases with decreasing the Kt and AM. Furthermore, it was found that the outdoor performance of a-Si PV modules strongly depended on APE compared to sc-Si PV modules. Thus, APE can be estimated from the contour map with the Kt and AM.