Luminous efficacies of global and diffuse horizontal irradiances in a tropical region

This paper reports results of a study on characteristics of luminous efficacies of tropical global and diffuse horizontal solar irradiances using observed data from a daylight measurement station located in the southern area of Bangkok, Thailand (latitude 13.58°N and longitude 100.44°E). Mean hourly values of the efficacies and their frequency distributions are first presented. Through scatter plots, variations of the efficacies are then presented for different sky conditions covering from cloudy to clear skies. From our results, the pattern of variation of tropical global efficacy is noticed to be distinct from those in high latitude region. In this study, two all-weather models are developed empirically for predicting values of the tropical global and diffuse efficacies. The models are evaluated for their performances against some selected existing models. The results show that the proposed models predict well the tropical efficacies and outperform all other evaluated models.

► Luminous efficacies of tropical solar irradiances are reported.
► Tropical global efficacy varies distinctly from those in high latitude regions.
► Two empirical models are proposed for the tropical global and diffuse efficacies.
► The proposed models predict accurately the tropical efficacies under various skies.