ENERGY SOURCES, cilt.25, ss.637-649, 2003
In this study, empirical correlations were developed to establish a relationship between the daily diffuse fraction (K-d) and the daily clearness index (K-T) for the city of Izmir in Turkey. Hourly global and diffuse radiation measurements on a horizontal surface were performed in the Solar-Meteorological Station of the Solar Energy Institute in Ege University over a 5 year period from 1994 to 1998. The present models were then compared to the 16 models available in the literature in terms of the widely used statistical indicators, namely, correlation coefficient (R-2), main percentage error (MPE), main bias error (MBE), root main square error (RMSE), and the t-statistic (t-stat) combining the last 2 errors. It may be concluded that the present models predict the values of Kd as a function of KT for Izmir better than other available models, while all the models tested appear to be location-independent models for diffuse radiation predictions, at least for Izmir.