Estimation of Global Solar Radiation in the Eastern Upland Region of Taplejung, Nepal, using RadEst 3.0 Software

Understanding solar radiation distribution in each geographic region is essential for developing solar energy technology. This research estimates daily global solar radiation (GSR) at Eastern Upland, Taplejung, Nepal (27.35° N, 87.69° E, 2840 m) using RadEst 3.0. It incorporates seven meteorological parameters: rainfall, maximum and minimum temperatures, solar radiation, maximum and minimum humidity, and average wind speed, for 2020, 2021, and 2023. Four different models, Donatelli and Bellocchi (DB), Campbell and Donatelli (CD), Bristow and Campbell (BC), and Donatelli-Campbell-Bristow-Bellocchi (DCBB), are used for calculating radiation. In evaluating the models' performance, we utilized various statistical methods, such as coefficient of determination (R2), mean bias error (MBE), mean percentage error (MPE), correlation coefficient (r), root mean square error (RMSE), and mean error (ME). Parameter fitting (PF) calibrates all four models by maximizing R2, minimizing CRM, and RMSE. In 2020, 2021, and 2023, the annual mean GSR values were 15.0 ± 0.31 MJ/m2/day, 14.6 ± 0.28 MJ/m2/day, and 15.9 ± 0.31 MJ/m2/day, respectively. The maximum GSR values recorded in 2020, 2021, and 2023 were 29.2 MJ/m2/day, 32.0 MJ/m2/day, and 30.0 MJ/m2/day, respectively. Similarly, R2 was found to be 0.64, 0.64, and 0.65 in 2020, 2021, and 2023 respectively in the CD model for the three years which are larger than all other models. The CD model offers the most accurate global solar radiation (GSR) estimates in this area. This article recommends implementing a comprehensive program to promote and require using renewable energy resources (RES), especially solar energy, across eastern Nepal.