A review of solar radiation on vertically mounted solar surfaces and proper azimuth angles in six Iranian major cities

To meet a part of the buildings energy demands, the buildings’ exterior walls are proper places for installation of vertically mounting solar surfaces (VMSS). In this study, using long-term horizontal global solar radiation data and the Klein and Theilacke radiation model, the solar radiation components arrived at VMSS have been assessed at different periods of the year and better surface azimuth angles have been suggested for six Iranian major cities of Isfahan, Karaj, Mashhad, Shiraz, Tabriz and Tehran. The results demonstrate that the beam and global solar radiation on non-azimuth VMSS (south walls) decline significantly in spring and summer compared to those of horizontal surface, though they are higher in most months of autumn and winter. The highest relative gains are in December, while the highest relative losses occur in June and they increase with increasing the latitude. In general, the total radiation on a vertical surface depends on its azimuth angle significantly and for each city its variation with azimuth angle is distinctive. Considering three practical azimuth angles of 0°, 45° and 90°, during the colder period (October-March) the buildings’ south walls and during the warmer period (April-September) the east and west walls (i.e. azimuth angles of 90° and −90°) are suitable ones, respectively.