CLIMATIC EVALUATION OF MODELS THAT PREDICT HOURLY DIRECT IRRADIANCE FROM HOURLY GLOBAL IRRADIANCE - PROSPECTS FOR PERFORMANCE IMPROVEMENTS

This paper presents a comprehensive evaluation of recent models designed to predict direct from global irradiance on a short time step basis. Three models are selected for the present evaluation. These were proposed by Erbs et al., Skartveit and Olseth, and Maxwell. Model validation is performed against a large array of experimental data: A total of over 60,000 global and direct data points from 14 sites in Europe and the United States. Environments range from humid oceanic to desertic, including humid continental, high altitude, subtropical, and polluted. It is found that specific models are better adapted to certain climatic types than others. However, each model is found to have a "generic" insolation-dependent error pattern across all climates. This error pattern may be deterministically corrected and yield substantial performance improvement without additional input data. © 1990.