Adjustment of the clear sky coefficients for the transmission of solar radiation under the ambient conditions in Fortaleza

Abstract

This research article presents the transmittance of direct solar radiation calculated using the clear sky model and measurements made in the city of Fortaleza. To estimate the clear sky coefficients needed in the model, correlations available in the literature for the ratio of an hour’s radiation to the standard clear sky radiation for that hour were used. The calculated values for the transmittance to direct solar radiation and the clear sky model were used in a non-linear statistical procedure to estimate the coefficients needed. The data used in the statistical procedure were for the year 1997 and, even though the new coefficients represented well the direct transmittance in the year 1997 and 1998, a definite change cannot be suggested at this time, as data for other years are needed.