I note there are many different flavours of PVGIS.http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php
has two; Classic PVGIS and Climate-SAF PVGIS, and I have seen various references to PVGIS 4.
Does anyone have a view of which is considered the most accurate/best or whatever or know over which periods the data was compiled?
I am in the process of compiling sunshine hours from the Met Office historical records and want to compare it to PVGIS. There is a +7/-3.4% variation in annual sunshine hours depending on whether one takes a 40 year period (1971-2010) or a 10 year period (2001-2010). Thus I want to match sunshine records to PVGIS as best I can.