“…Therefore, days in zone III are the hardest to predict, and days in the zone CI are the easiest, as they are clear sky days with low variability. All the GHI measurements used in this work are available at (Segarra-Tamarit et al, 2020) to facilitate the reproducibility of this research. Furthermore, as the archive of GHI estimates at http://msgcpp.knmi.nl only stores the last three years of data, the matrices used in this work are also provided within this repository.…”