On the generation of hourly shortwave radiation data on tilted surfaces.

In this paper we describe a method for computing hourly values of global radiation on inclined planes at any desired location. Fundamental to the computations are a 10 year series of global radiation and temperature measurements from 64 weather stations in Switzerland. As a first step, the monthly mean values are interpolated to any desired location. Hourly values are then generated stochastically on the basis of the interpolated monthly values. Using additional models, the hourly values of horizontal global radiation are transposed to inclined surfaces. This strategy involves a number of newly developed models, of which those for interpolation, and inclusion of skyline profile in calculating radiation on inclined surfaces, are the most important. The individual models are combined in a single comprehensive procedure. This was briefly validated, showing that coupling the independent models leads to satisfactory results, and confirming the validity of the chosen approach. Although the methods and models were checked for Switzerland, they are based on components that have been tested over a wide range of geography.