Comparison of Solar Analyst and r.sun Models to Estimate the Spatially Distributed Solar Radiation in a Mountainous Region in Iran

Abstract:

Solar radiation plays a major role in the energy exchange process between the atmosphere and earth’s surface. The spatial and temporal heterogeneity of incoming solar energy determines the dynamics of some landscape processes such as agricultural, hydrological, ecological and biological processes. Consequently, in order to understand these processes, knowledge of the spatial variability of solar radiation is crucial. At regional scales, particularly in complex topography, terrain is the major factor modifying the distribution of irradiation. Variability in elevation, surface inclination (slope) and orientation (aspect) and shadows cast by topographic features create strong local gradients of insolation which affects micro environmental factor. To account for spatio-temporal variations of solar radiation, spatially distributed DEM-based solar radiation models can be helpful. In this study, estimated daily solar radiation using Solar Analyst and r.sun solar radiation models were evaluated and compared in a mountainous region in south of Iran. The models were evaluated for different sky conditions ranged from completely overcast to clear sky conditions. The sensitivity of the models to the input, based on station data was also analyzed. Additionally, the role of the spatial resolution of the DEM has been evaluated through the use of three different resolutions: 30, 90 and 1000m. The results showed that, under clear-sky conditions, the models can estimate solar radiation favorably, but their accuracy was reduced in cloudy and party cloudy atmospheric conditions. However, the accuracy of r.sun model due to raster format of inputs was better than Solar Analyst model in presence of cloud in the sky. Regarding the role of the DEM spatial resolution, results showed that for complex topography areas, the accuracy of the estimates improves using a higher spatial resolution.