ABSTRACT
Solar energy is the world's most abundant permanent source of energy. The amount of solar energy intercepted by the planet Earth is a tiny fraction of the solar radiation emitted by the sun. The projection of the sun's path on the horizontal plane is called a sun-path diagram. Such diagrams are very useful in determining shading phenomena associated with solar collectors, windows, and shading devices. Accurate determinations of the hourly solar radiation received during the average day of each month are a prerequisite in different solar energy applications. In the early 1950s, Whillier introduced the utilizability method to analytically predict the performance of active solar collectors. This method used a simple formulation to estimate the mean hourly radiation during each hour of an average day of the month, based on the ratio of the hourly to daily irradiation received by a horizontal surface outside of the atmosphere.
