This paper develops a semi-empirical model to calculate direct solar shortwave irradiance on a horizontal surface for any cloudiness condition. The model is based on radiative transfer simulations combined with empirical relationships; it makes use of the global solar irradiance, experimentally...

Using experimental data collected at Uccle (Belgium) in 1980, new relations are proposed which allow the spectral density distribution of diffuse solar radiation on a horizontal surface to be estimated for clear skies, as a function of the commonly measured broadband global and diffuse solar...

Several years of measured data for 17 European locations have been used to develop models for estimating monthly mean daily values of diffuse radiation (Hd) from combinations of the following: clearness index, sunshine fraction, and solar declination. Two models giving the highest correlation...

The classical equation of Liu and Jordan for estimating the monthly mean hourly to daily diffuse ratio (rd) was tested for applicability to locations in Spain. While the model predicts the rd ratios and the monthly mean, hourly diffuse (Id) values accurately at low hour angles close to solar...

In the present work we have modelled mean hourly values of the luminous efficacy of direct solar radiation for clear skies in Madrid using solar elevation as the only independent variable. Models of the polynomial type, similar to those given by different authors, and a model for the direct...

Three models for the luminous efficacy of direct solar radiation on a horizontal surface, valid for all sky conditions, have been developed in the present work, and two of them are proposed. In all the models a function for the direct luminous efficacy for all sky conditions relative to the...

Studies on the spatial distribution and temporal variation of solar radiation in Spain have been carried out. Detailed maps are prepared on the geographical distribution of total and diffuse irradiation, clearness index, diffuse-to-total ratio, and percentage of possible sunshine values for the...

The recently published Olmo model estimates global irradiance on inclined planes. It only requires the horizontal global irradiance and the sun’s azimuth and elevation as input parameters. As a consequence, it does not contain empirical coefficients that need determination for each location....

Several years of measured data on global and diffuse radiation and sunshine duration for 40 widely spread locations in the latitude range 36° S to 60° N are used to develop and test models for estimating monthly-mean, daily, diffuse radiation on horizontal surfaces. Applicability of the...