Comparison of two model systems for the calculation of the solar irradiance on shaded, arbitrarily orientated surfaces
Eckhardt, Klaus; Bigalke, Klaus
In its guideline 3789, part 2, the VDI (Verein Deutscher Ingenieure - German Association of Engineers) presents methods that allow the calculation of hourly values of the global irradiance on arbitrarily orientated surfaces. In the present study, these approaches are compared to an alternative combination of previously published models for different partial stages of the simulation that have been implemented in a program called METSUN. It is shown that measurements of the global radiation and of its components can be better reproduced with METSUN than with the approaches of the VDI guideline. Furthermore, the alternative model combination is more flexibly usable. The VDI guideline imperatively requires observations of the degree of cloud cover. With METSUN, however, also sources of information that provide values of the global irradiance on an unshaded horizontal plane can be used as starting point of the calculations, for example measurements of the global radiation at a nearby meteorological station. It is shown that this can increase the reliability of the results.