Optimum tilt angle and orientation for solar collectors in Assiut, Egypt

Abstract

One of the important parameters that affects the performance of a flat plate solar collector is its angle of tilt with the horizontal. This is due to the fact that the variation of tilt angle changes the top loss coefficient and the amount of solar radiation reaching the absorber plate. Also, concentrating solar collectors must be oriented to track the sun so that beam radiation will be directed onto the absorbing surface. A mathematical model was developed for calculating the total radiation on a sloped surface. The model was then used to determine the optimum tilt angles for a flat plate collector and the optimum tilt and surface azimuth angles (orientation) for concentrating solar collectors in Assiut, Egypt on a daily basis, as well as for a specified period. These optimum angles were found by searching for the values for which the total radiation on the collector is a maximum for a particular day or a specified period. The results show that changing the tilt angle eight times in a year is necessary to maintain the total radiation on the collector in Assiut near its maximum value. This achieves a yearly gain in total radiation of 6.85% more than the case of a flat plate collector with a fixed slope of 27°, which is equal to the latitude angle of Assiut. Also, it is observed that changing the hourly surface azimuth angle twelve times and the tilt angle six times in a year for a concentrating solar collector maintains the total radiation near its maximum value (found by changing the surface azimuth and tilt angles daily to their optimum values). This achieves a yearly gain in total radiation of 29.18% more than the case of a concentrating solar collector facing south at fixed tilt equal to the latitude angle.