A global model for monthly mean hourly direct solar radiation

This paper introduces a worldwide applicable model for estimating hourly portions of monthly mean daily direct solar radiation intercepted on the horizontal surface, as a function of actual solar elevation, daily maximum solar elevation and latitude. The model fits well (R > 0.99) pyranometric data measured at stations from practically entire Northern Hemisphere (0 < phi < 70 degrees). Application of the model using independent data sets, including one station from the Southern Hemisphere, leads to the acceptance of the model worldwide. Model is not sensitive to the local climate differences or interannual variability and it represents an ultimate solution for daily topographic solar radiation modelling without site-specific or latitude-specific hourly radiation data. (C) 2000 Elsevier Science B.V. All rights reserved.