MEASUREMENTS AND MODELS FOR TOTAL SOLAR IRRADIANCE ON INCLINED SURFACE IN ATHENS, GREECE

This article presents a comparative assessment of tilted irradiation m odels, using hourly measurements of total solar irradiation on a surfa ce tilted 50 degrees and oriented south in Athens. Detailed measuremen ts on inclined surfaces are carried out at the National Observatory of Athens and are unique in Greece. Twelve sky diffuse submodels are use d with four albedo submodels to estimate the global irradiation on the tilted surface from data on the horizontal plane. Root mean square er rors (rmse) and mean bias errors (mbe) are used to determine the intri nsic performance of each diffuse tilt/albedo submodel combination. GUE YMARD, HAY, REINDL, and SKARTVEIT-OLSETH diffuse tilt submodels are fo und to have the best overall performances, in conjunction with either one of three albedo submodels (constant albedo, seasonally varying alb edo, and anisotropic albedo). The PEREZ model's performance was below expectations, probably due to the particular atmospheric environment o f Athens. The anisotropic and seasonally varying albedo submodels do n ot improve the performance of the four better diffuse tilt models (com pared to their performance using an albedo fixed at 0.2) for the moder ately tilted surface investigated in this article.