The Optimum tilt angle of a solar panels or collectors is crucial to be considered when determining the parameters that affect the performance of them. A mathematical model is used to determine the optimum tilt angle and calculating the solar radiation falling on a south facing surface on a daily, monthly, seasonally, semi-annually and yearly basis. The results show that daily and monthly adjustments of the solar panels or collectors for most of the emirates of the UAE can receive about 20 % more solar energy than the case of a solar panels or collectors fixed on a horizontal surface. While seasonally and semi-annually adjustments can receive about 18% more solar energy. I.e. that it is worth to change the solar panels or collectors 12 times yearly (monthly) or at least 2 times in a year (semi-annually). The yearly optimum tilt angle for the most of the emirates of the UAE is about 23°.