Can anybody tell me where the weatherfiles that are for download on this site take their data from? for example I checked Munich and Frankfurt and both of them seem to have low solar radiation values. Munich: 979 kWh/m²a available rad (should be around 1100 - 1200 global horizontal). Frankfurt: 1037 kWh/m²a (meteonorm 1034 kWh/m²a; but this value is global horizontal, not available solar radiation).

Any Idea?