A simple general luminous efficacy model of global irradiance

This paper reports on the development of a luminous efficacy model of global horizontal irradiance. The model is intended to be both simple and applicable to multiple locations. Two sets of measured data were applied toward the development and evaluation of the model. The first set was used to derive the luminous efficacy model. The second set was then used to compare the model predictions with measurements. The proposed luminous efficacy model involves, as the main influencing variable, the Clearness Factor, which is an original derivative from the Clearness Index. Two further variables (Humidity Ratio and the solar altitude) are included in the model formulation. The paper includes the result of the statistical analysis of the relationship between the model predictions and the measured data from the second set of empirical data.