Investigating the Dependence of Optimal Orientation of Flat Solar Collectors on Latitude and Climate Types Under Clear Sky Conditions

This study investigates the daily dependence of the optimal angle of a flat solar collector on geographical latitude, climate type, and altitude under clear sky conditions. Hottel′s model is primarily used to mathematically describe the clear sky condition. In addition, this paper considers three other clear sky models. It is shown that the dependence of the optimal tilt angle is very close to Hottel′s model prediction. Although the paper mainly considers the direct beam energy, it is shown that the inclusion of sky diffusion irradiation only slightly changes the results. The results show that the climate type does not significantly affect the optimal angle. In contrast, the geographical latitude has a drastic effect on the optimal tilt angle. The plot of the optimal tilt angle versus latitude forms a straight line, whose slope moderately depends on the day of the year and is typically close to unity. In contrast, the line intercept significantly depends on the day of the year. When the effects of atmospheric attenuation and climate are neglected, analytical results show that the optimal tilt angle, in terms of latitude, follows a linear relationship. The intercept depends on the day of the year. In addition, the daily maximal beam energy received by the solar collector, when oriented at the optimal tilt angle, is evaluated for each day of the year. The total annual beam energy is a decreasing function of the absolute value of the latitude and has the maximum value, which depends on the altitude, at the equator.