Solar energy can be recognized as one of the most promising renewable energy sources, especially in subtropical regions. Along with other forms of renewable energy sources (i.e. winds, geothermal, sea waves and biomass), it has a great potential for a wide variety of applications because of its abundance and accessibility.

Solar systems, like any other system, need to be operated with the maximum possible performance. This can be achieved by proper design, construction, installation, and orientation. Nevertheless, the performance of a solar collector is highly influenced by its orientation (with respect to the Equator) and its angle of tilt with the horizon (with respect to the ground). This is due to the fact that both the orientation and tilt angle change the solar radiation reaching the surface of the collector. Taking into consideration that designing an installation to yield maximum annual energy helps to minimize the necessary installed capacity and reduce the cost of equipment. To achieve this, solar collector must be mounted at right angles to the sun’s rays. Ideally this is achieved by mounting the collector on a two-axis tracker that continuously tracks the sun by the hour and through the seasons. In practice, however, the method is quite cumbersome and inconvenient. Thus, the majority of installations are with fixed mountings. Therefore, it is often practicable to orient the solar collector at an optimum tilt angle, Bopt and to correct the tilt from time to time. For this purpose, one should be able to determine the optimum slope of the collector at any latitude, for any surface azimuth angle, and on any day of the year.

The main objective of this proposal is to develop simple and easy ways for finding monthly, seasonal, half-yearly and fixed optimum tilt angles for any location in the world on the basis of theoretical and experimental results of the contributed in this project articles. The influence of azimuth angle on the value of optimum tilt angle should be demonstrated on different regions in the world.