Comparison of Modeled to Observed Global Irradiance

Abstract

The accuracy of a spectral, clear-sky model to predict hourly global irradiance was investigated using radiation and meteorological observations collected at the Seattle-Tacoma airport between 1 January 1988 and 31 October 1991. The model was first run using the 1976 U.S. standard atmosphere values as inputs, then using the local atmospheric conditions. Clear-sky irradiance values generated by both atmospheres, standard and local, were attenuated using local cloud cover observations for comparison with measured irradiance. Values and trends of the statistical descriptors for the two atmospheres were almost identical. Overall, the model overestimated observed irradiance by less than 6%. Cloud cover was the major source of deviation between the modeled and observed values. The close correspondence between the two model runs suggests that the U.S. standard atmosphere, in conjunction with global cloud datasets, can be used in spectral models to generate irradiance at remote locations.