Higher Institute for Applied Sciences and Technology, Damascus, P. O. Box 31983, Syria.
The performance of a solar collector is highly dependent on its tilt angle with the horizon. The variation of tilt angle changes the amount of solar radiation reaching the collector surface. Meanwhile, is the rule of thumb, which says that solar collector should be orientated towards the Equator with a tilt equal to latitude, is valid for high latitudes region? Thus, it is required to determine the optimum tilt for Equator facing collectors. In addition, the question that may arise: how many times is reasonable for adjusting collector tilt angle for Equator facing collectors? A mathematical model was used for estimating the solar radiation on a tilted surface, and to determine the optimum tilt angle and orientation (surface azimuth angle) for the solar collector at any latitude. This model was applied for determining optimum tilt angle in the high latitudes zone in the Southern and Northern Hemispheres, on a daily basis, as well as for a specific period. The optimum angle was computed by searching for the values for which the radiation on the collector surface is a maximum for a particular day or a specific period. The solar radiation on the collector surface of optimum tilt angle, of latitude tilt angle and of null tilt angle was calculated for a particular day or a specific period. The results reveal that changing the tilt angle 12 times in a year (i.e. using the monthly optimum tilt angle) maintains approximately the total amount of solar radiation near the maximum value that is found by changing the tilt angle daily to its optimum value. This achieves a yearly gain in solar radiation up to several times of the case of a horizontal surface depending on the latitude value.