A statistical comparative study to demonstrate the merit of day of the year-based models for estimation of horizontal global solar radiation

Abstract

This study deals with identifying whether the accuracy of the day of the year-based (DYB) models for prediction of the horizontal daily global solar radiation is as competitive as the frequently utilized models from the sunshine duration-based (SDB) and temperature-based (TB) categories. The city of Birjand, located in the sunny belt region of Iran and the capital of South Khorasan province, has been considered as a sole case study. As of the nominated categories, 12 models have been selected from the literature; then by utilizing the long-term measured data and via statistical regression techniques the models have been established and their performances evaluated through several statistical indicators. Furthermore, to identify the suitability of the DYB models for monthly mean daily estimation, new regression constants have been developed for all of the nominated models and their performances compared. The results showed the superiority of the DYB models compared to TB models, but with a minor difference the best model was from the SDB category. However, owing to accurate estimation, simplicity and more or less similar performance as SDB models, DYB models seem qualified as proper alternatives of SDB models. Although in this study the best DYB models for daily and monthly mean daily horizontal global solar radiation estimations have been recommended for utilization in Birjand, due to similar climate conditions the results are applicable for the whole South Khorasan province and its vast neighboring region.