The global radiation on the horizontal GHI is divided into the direct and the diffuse components: BHI (beam horizontal irradiance) and DHI (diffuse horizontal irradiance). The following models are available for this division:
With reduced correlation (in previous versions of PV*SOL® only this model was available)
Skartveit, A., Olseth, J. A., & Tuft, M. E. (1998). An hourly diffuse fraction model with correction for variability and surface albedo. Solar Energy, 63(3), 173–183. https://doi.org/10.1016/S0038-092X(98)00067-X