Solar Illumination and Estimating Daylight Availability of Global Solar Irradiance

Abstract

In this article, it is aimed to determine the daylight availability and luminous efficacy of global irradiance for Izmir, which has Mediterranean climatic conditions. Daylight availability and luminous efficacy were put forward by using existing valid models, including Aydinli Model, Perez Model, and IESNA Model. Yearly exterior illuminance levels have been estimated by the use of hourly data of the Meteorological Station of Solar Energy Institute. The models were compared in consideration with their luminous efficacies. Monthly average hourly exterior daylight illuminance levels estimated by Aydinli Model, Perez Model, and IESNA Model were put forward for Izmir. Frequency distributions of luminous efficacies (lm/W) for hourly values calculated by these theoretical methods were evaluated. The frequency distributions were examined in consideration with the reference value referred to in the literature. Yearly correlations between hourly average daylight illuminance by Aydinli Model, global illuminance by Perez Model, daylight illuminance by IESNA Model, and measured hourly global solar irradiance were established and determined to be able to estimate daylight availability data for Izmir. According to these correlation equations, it is shown that the linear correlation coefficients (R²) are 0.9536 for Aydinli Model, 0.9994 for Perez Model, and 0.9747 for IESNA Model. Finally, the potential of daylighting and the feasibility of natural lighting systems for Izmir were evaluated according to these results.

Keywords:

• daylight availability
• global solar irradiance
• luminous efficacy

Acknowledgment

The authors gratefully thank Mr. Sirri Aydinli (Berlin Technical University) for providing us with the estimation methodology of illumination.

Notes

^a No direct sun; E _DN = 0.