Accuracy of Solar Resource Assessments on the Basis of Publicly Available GHI Databases
Abstract
The “true” long-term Global Horizontal Irradiation (GHI) for a given location is normally unknown. Thus, the selection of the most appropriate, publicly or commercially available dataset or the application of a corresponding data handling approach is a key challenge and task when assessing the site-specific GHI solar resource. Based on reference data obtained from Baseline Surface Radiation Network (BSRN) as well as the German and Dutch national weather services, a database and approach benchmarking including 63 locations in Europe – mainly Germany and the Netherlands - and 1 location in North Africa has been conducted. For publicly available databases and various arithmetic means, a typical relative Root Mean Square Error (RMSE) of the long-term annual GHI of ±1.8 % to ±7.2 % has been found. Regarding inter-annual variability, the corresponding range is ±0.4 % to ±4.0 %. In both cases, the arithmetic means typically achieve smaller relative RMSE, thus suggesting a greater reliability for Solar Resource Assessment purposes.