Methods to estimate global and diffused luminous efficacies based on satellite data

This paper presents universal models and constant values to estimate luminous efficacies for each of global and diffused solar radiation on a horizontal surface. They are applicable to all sky conditions and are based on satellite derived data available via web servers. Solar radiation data from ten locations in Europe and North Africa was used to obtain three global and diffused functions for luminous efficacy (K) against solar altitude (alpha), cloud amount (C), and sky clearness index (k(t)). All were used to estimate illuminance for the ten originating locations; for four locations based on satellite data; and for a further five based on measured data. A statistical assessment showed that the best models are K against alpha. Comparison between results from the proposed models and those produced using three published models for both cases, indicate that the former produce more accurate estimates of luminous efficacy. Constant values also showed very reliable results, especially for the diffused case. The satellite based approach makes daylight data available in locations remote from current measurement sites. (C) 2011 Elsevier Ltd. All rights reserved.