Dynamic global-to-direct irradiance conversion models

Abstract

This paper presents two models for converting hourly global into hourly direct beam irradiance based on a new parameterization of insolation conditions (Perez et al. 1990a). This parameterization does not require any additional input data than those already contained in a global irradiance time series but attempts to better utilize available information. The models are capable of using surface dew-point temperature as an additional input when this is available. The models are derived statistically from a large multiclimatic experimental data base. The two models differ technically but should be functionally equivalent: The first is a correction to the physically based DISC model(Maxwell 1987); the second consists of a set of simple linear relationships. Validation results are presented in reference to three existing models (Maxwell 1987; Erbs et al. 1982; Randall and Whitson 1977). The validation benchmarks consist of root mean square and mean bias errors as well as the ability of the models to recreate the skewness and kurtosis of actual direct irradiance distributions.