Uncertainties in Clear-Sky Solar Irradiance Modeling Induced by the Limited Availability of the Atmospheric Parameters

In the recent years, great progress has been made in developing terrestrial and satellite-based networks for the measurement of atmospheric parameters, which serve as inputs in clear sky parametric models. However, some parameters may still be missing from the model input due to small temporal sampling or lack of in situ data. This paper presents a case study on the accuracy of the clear-sky solar irradiance estimation by a parametric model, when the availability of inputs is limited. The study was conducted with high-quality radiometric and atmospheric data recorded by the INOE-Magurele station, Romania. Seven different scenarios were studied. In each scenario the clear-sky solar irradiance model was run assuming that certain parameters are missing from the input. The results quantitatively confirm the dominant role of aerosols in establishing the accuracy of solar irradiance estimation under clear sky conditions. The unavailability of the measured Ångström turbidity coefficient may lead to a twofold/threefold increase in the uncertainty of direct-normal/diffuse solar irradiance estimation.