Alireza Arab Solghar - Department of mechanical engineering, Scholl of engineering, Vali-e-Asr University of Rafsanjan, Rafsanjan, Iran
Azadeh Ahmadi Tajabadi - Department of mechanical engineering, Scholl of engineering, Vali-e-Asr University of Rafsanjan, Rafsanjan, Iran
Morteza Abdolzadeh - Department of Mechanical Engineering, Graduate University of Advanced Technology, Iran

One of the important parameters that affect the performance of a solar collector is its tilt angle with the horizon. This is because of the variation of tilt anglechanges the amount of solar radiation reaching the collector surface. In the present study, the monthly average daily diffuse solar radiation on a horizontalsurface was initially computed and then a standard isotropic model was exploited for estimation of the global solar radiation on inclined surfaces. Finally, themonthly, seasonal, and yearly optimum slope angles were proposed for the maximum global solar radiation.It was found that the monthly optimum tilt angle varies from 0° (May and July) to 62.3° (December), besides, the seasonal optimum slope angle is between 5.1°(spring) to 54.8° (autumn) and the optimum yearly tilt angle is 29.9° which is close to the latitude of Rafsanjan

diffuse solar radiation, inclined surface,optimum tilt angle, solar collector