A simple model for sky radiation measurements

Abstract In the proposed model the sky hemisphere as a radiating source has been replaced by a single point radiating source and a diffuse background. The point source produces insolation H on a horizontal surface, its beam coming from direction (α,ϕ), α being the azimuth and ϕ the zenith angle. The diffuse radiation comes from all directions equally and produces insolation D on a horizontal surface. For estimating all four parameters H, α, ϕ and D of the model, a four-segment photo-cell was developed and tested. The method is suitable for calculating the optimal orientation (azimuth and tilt) of a solar collector, depending on local conditions.