Performance of solar radiation models—a case study

Performance of cloud-based (Kasten) and sunshine-based (Ångström–Prescott, Garg and Garg, Sivkov) empirical solar radiation models is presented for a lowland and mountain grassland sites. Data sets utilised for the study extended from 1991 to 1994. Adjustable parameters in the models were determined. Observed monthly mean values of solar radiation K↓ and those estimated using Kasten model agreed within 2.5% for the lowland site and 13% for the mountain site, while those estimated using Ångström–Prescott relation agreed with observation within 2.5% for lowland site and 3.4% for the mountain site. The incorporation of air mass, latitude and water vapour terms into Ångström–Prescott relation did not significantly improve estimates of K↓. In general, Ångström–Prescott as well as Garg and Garg models yielded the least RMSE (<0.047) for the study sites.