Modelling solar radiation on tilted surfaces and determination of the optimum tilt angle

Understanding the solar energy incident on inclined surfaces is essential for optimising the design and efficiency of solar systems such as photovoltaic panels, solar thermal collectors, and passive building components. The study examined all variables influencing global solar energy on a horizontal plane and a 30° south-facing inclined surface, using established extraterrestrial radiation equations, solar time corrections, and models of anisotropic diffuse radiation. Additionally, realistic meteorological data were used to simulate typical annual variations under both clear-sky and average atmospheric conditions. Results showed that the 30° south-facing surface receives significantly more solar radiation during winter and early spring than a horizontal surface, mainly due to the lower solar altitude and better orientation towards the sun. In summer, the differences diminish as the sun is higher in the sky. The analysis emphasises that accounting for direct, diffuse, and reflected radiation is crucial for accurate estimates of solar energy incident on inclined surfaces. Achieving maximum solar energy absorption, optimal system efficiency, and effective system planning requires selecting the appropriate tilt angle, especially in areas with abundant solar resources.