Abstract The present study investigates the variation of hourly global solar radiation for inclined surfaces. We have measured the data for horizontal surface and different south-facing (γ = 0°) inclined surfaces at Lucknow (Latitude 26.75°, Longitude 80.85°), Uttar Pradesh, India. These inclined surfaces data have been compared with the estimated tilted results from measured horizontal data using circumsolar model, the isotropic model suggested by Liu and Jordan [1], and the two anisotropic models by Klucher [3] and Hay [2]. Statistical error tests are also performed for the critical analysis of the models. The comparative study of the model validates the performance of isotropic model for all inclined surfaces.