NASSA overestimation in irradiance

[Konstantina]

Dear Andre,

usually data derived from satellite overestimate the irradiance value such as NASSA in PVsyst. The reason for that is the larger errors that take place much often and the quality control which is much harder in these cases, or I got it all wrong ?

Thank you!

[André Mermoud]

I don't know from which source you estimate that the satellite models overestimate the data.

They have their own accuracy, with a MBE (mean bias error by respect to ground measurements) which may be either positive or negative.

And in hourly values, the RMSE (root mean square difference) is competitive with terrestrial measurements as soon as you are at more than 20 km of the measuring station.

Please have a look on the document

"Five satellite products deriving beam and global irradiance validation on data from 23 ground stations (IEA)",

Pierre Ineichen, 2011, Research report of the Institute for Environmental Sciences, University of Geneva.