Global solar radiation data are very essential for the design, evaluation, and simulation of solar energy systems. For this purpose, various empirical models for computing have been used to predict the monthly average daily global solar radiation on a horizontal surface around the world. The main objective of this article is to investigate 46 existing models and develop 4 models for estimating daily global solar radiation on a horizontal surface in Isparta, Turkey (37.47 N, 30.34 E). The collected existing models and developing models are compared on the basis of statistical error tests. According to the results, the developing model (Model 49) is showed the best estimation of the global solar radiation on a horizontal surface of Isparta by means of the R = 99.42, MPE = -0.254%, MBE = 0.00052 MJ/m(2), and RMSE = 1.3284 MJ/m(2).