Global comparison between all sources: the figure shows a comparison between all available sources, for 12 locations in Europe. All values are by respect to the Meteonorm values (PVsyst internal default).
Except the first green bin, which shows the difference of Meteonorm by respect to the average of all other sources (excluding Helioclim 2005).
We can observe some trends:
We cannot say which source is the more representative of the reality (and which reality? - no one is of course able to foresee the future climate).
Meteonorm often gives lower values than the average. This means that simulations with default values in PVsyst will be rather conservative, and give prudent results for the final yield of the customer’s systems.
Except at Barcelona, very little differences between Meteonorm “old” (1961-1990) and “new” (1981-2000) data.
PVGIS seems to be one of the more compatible with Meteonorm data.
Also, when available, the WRDC data are well representative of the Meteonorm data.
Satellight data seems to overestimate the average by 5 to 10% (except in Berlin and Roma).
The Helioclim data response seems to be chaotic. Especially the 2005 values (Helioclim-2 hourly file) are very high over the other data, by a factor which is not compatible with the 2005 irradiance (see below for Geneva).
Satellight data: for other sites in Europe, the Satellight data are always far over the Meteonorm ones, with one exception in Berlin. This exception is not attributable to the Meteonorm value; as we can see on the global comparison plot above, the Satellight data for Berlin are significantly below the other Satellight data. We don’t have any explanation for that.
Climate evolution: we avail of a homogeneous sample of continuous measurements from the same source (ISM - Swiss Institute for Meteorology) for Geneva, from 1981 to 2007.
This shows that at Geneva, the annual dispersion stayed far below 5% with only 3-4 exceptions during 20 years, but increased significantly since 2003. This is of course not necessary valid for other sites in Europe!