It is entirely apparent that an accurate estimation of global horizontal solar irradiance (GHI) does not guarantee an accurate estimation of its fundamental components. This basic perception motivates the present study, which evaluates the ability of the clear-sky solar irradiance models to accurately partition GHI into beam and diffuse components. Diverging from the traditional perspective, the diffuse fraction is assessed as an appropriate quantifier for the fractional part of GHI estimated by a clear-sky solar irradiance model as being diffuse. Acting as a quantifier, the diffuse fraction has the merit of isolating the uncertainty induced by aerosols in estimating the diffuse solar irradiance. The results of evaluating various clear-sky solar irradiance models show that many models consistently experience similar errors under high atmospheric turbidity. A strong influence of the atmospheric aerosol loading on the dissimilarities between the accuracies in estimating diffuse fraction and the corresponding diffuse solar irradiance is noticed. Our analysis of uncertainties in estimating the diffuse solar irradiance appears naturally as a sum of two terms: one encapsulating the ‘intrinsic’ error of the model, as quantified through errors in global solar irradiance, and the other encapsulating the aerosol modeling errors, as quantified through errors in diffuse fraction. For small atmospheric aerosol loading, the intrinsic errors of the model are dominant, while for high atmospheric aerosol loading the accurate modeling of the aerosols effect on GHI becomes critical.