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

Abstract

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 (Tmod) 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 Tmod. 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 Tmod 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 Tmod. The proposed method using Kt and AM is useful for estimating the output energy of the PV modules.