Estimation of global illuminance for clear skies at Madrid

Two elementary empirical models for the dependence of global illuminance on solar elevation for clear skies are provided. The models are developed from hourly data obtained from 1 year data collected at the International Daylight Measurement Programme (IDMP) general class station at the Escuela Técnica Superior de Arquitectura in Madrid (ETSAM), and are statistically assessed with data obtained during another period of 6 months. Values of the mean bias deviation (MBD) and root mean square deviation (RMSD) of respectively less than 5% and 7% of the average illuminance measured were obtained. The qualitative dependence of global illuminance on solar elevation, common to that found by other researchers for other locations is justified, and found to be different to that given by Vázquez and Bernabeu [D. Vázquez, E. Bernabeu, Quantitative estimation of clear sky light in Madrid, Energy and Buildings, 26 (1997) 331] using data obtained at a site which is in close proximity to our station.