Solar irradiance estimation models and optimum tilt angle approaches: A comparative study

The importance of needing for renewable energy sources is completely clear. The sun is one of the biggest and most reliable sources and two types of major devices for extracting energy from it, are solar cells and collectors. The produced energy by these devices extremely depends on solar irradiance which means by increasing of irradiation, the out coming energy will get high. This paper is going to review some of the main models of irradiance estimation and two main approaches of detecting optimum tilt angle. In the last part of the paper these models compared and the optimum tilt angle for major cities of Iran calculated and finally four relations expressed to compare results of four common models, Perez, Hay, Gueymard and S&O (Skartveit and Olseth).