The performance of 14 models for estimating hourly diffuse irradiation on inclined surfaces was investigated. In order to obtain solar radiation data for this investigation, equipment for measuring solar radiation on inclined surfaces facing to the north, south, east and the west at different tilted angles to the horizontal surface (30 degrees, 60 degrees and 90 degrees) were constructed and installed at two tropical sites in Thailand, namely Nakhon Pathom (13.82 degrees N, 100.04 degrees E) and Ubon Ratchathani (15.25 degrees N, 104.87 degrees E). Radiation data encompassing different periods of 1-4 years were used in this work. Diffuse irradiance measurements at different tilted angles were compared with various model algorithms. Results show that the Muneer and Gueymard models have comparable performance in terms of root mean square difference (RMSD) and these models give the lowest RMSD, as compared to that of the other models. (C) 2016 Elsevier Ltd. All rights reserved.