I have tried to calculate solar radiation (whole year with monthly interval) for Portugal from an ESRI grid (27m DEM) in Arcgis10. It seems to work, however it takes much more than a week and in the meantime there was an energy failure. I use ArcToolbox/Spatial Analyst Tools/Area Solar Radiation.
I have cut the dem so as to have only the south of Portugal in the hope that the processing would be faster. However, ArcGIs 10 crashes after a few minutes and I get the error: "Background processing has encountered a serious error and is unable to continue. Contact ESRI". I have also tried in Arcgis 9.2 and I get the same message.
It simply seems not to like the cut dem.