Output Energy Estimation of Si-Based Photovoltaic Modules Using Clearness Index and Air Mass

The output energy estimation of photovoltaic (PV) modules was carried out using contour maps as a function of average photon energy (APE), which is an index of solar spectral irradiance and module temperature ($T_{\text{mod}}$) in our previous report. This method is useful for not only crystalline Si PV modules but also thin film Si PV modules, which have a narrow spectral response. However, this method requires spectrum measurement to obtain APE using a spectroradiometer, which is not widely installed in various locations. In this study, we used clearness index (Kt) and air mass (AM), which have a strong correlation with APE and $T_{\text{mod}}$. Kt and AM can be calculated easily from irradiance, time, and location. The comparison between the output energy estimation using Kt and AM and that using APE and $T_{\text{mod}}$ was carried out. Results indicate that the accuracy of the output energy estimation using Kt and AM is as high as that using APE and $T_{\text{mod}}$. The proposed method using Kt and AM is useful for estimating the output energy of the PV modules.