Determination of the monthly, seasonal, semi-yearly and yearly optimum tilt angles of flat plate solar collectors in Kashan

The orientation of the flat solar collectors affects the amount of solar radiation received and absorbed by them. In this study, the optimum tilt angles of flat plat solar collectors in Kashan for the fixed monthly, seasonal, semi-yearly and yearly adjustments have been determined. If the solar calculations are based on the measured data, they produce more accurate results however in many parts of Iran like Kashan the solar data are not measured. Due to similar climatic conditions of Kashan and Isfahan, in this study the long term measured solar data of Isfahan have been utilized for calculating the optimum tilt angles. Also for making comparison, other estimated values have been used also the optimum tilt predictions of some general correlations proposed by several researchers have been obtained. The comparison stated the weakness of some existing correlations and the validity of the results obtained in this study. The results indicate that for the optimized use of solar energy it is necessary to adjust the tilt at least once in every month and the maximum and minimum slope angles are 60° for Azar and zero for two months of Khordad and Tir, respectively. The optimum tilt for the fixed seasonal adjustments in Spring, Summer, Autumn and Winter are 3°, 14°, 53° and 48°, respectively and for the fixed semi-yearly adjustments in the first and the second six months of the year are 9° and 51°, respectively. Also the fixed annual optimum tilt is 29°, which is very close to the latitude of Kashan (33.59°).