Coupling satellite images with surface measurements of bright sunshine hours to estimate daily solar irradiation on horizontal surface

Satellite images are heavily used for the estimation of solar irradiation at the Earth's surface. The accuracy yet should be improved to attain more reliable input values for the use of all types of solar energy systems. This paper presents two new alternative approaches to increase the estimation accuracy of daily solar irradiation by coupling the satellite images with surface bright sunshine hour measurements. Two different approaches are described for the estimation of global solar irradiation on daily base, by using the data for some locations in Turkey and Germany. These approaches are compared with the estimation of a satellite model (HELIOSAT), Angstrom models and ground measured daily global solar irradiation by using regressions and error analyses. For nine out of ten stations the relative RMSE values of the proposed models slightly decrease in the range of only 2% in comparison with the direct satellite model for the daily global solar irradiation. The results obtained for the new approaches did not considerably improve the performance of the satellite model. However, it is possible to recommend new coupled approaches to estimate daily global solar irradiation because of their simpler calculation procedure. The results are encouraging for the future works to use long and short-term satellite image data together with the surface measured data to estimate the solar irradiation values.