PVsyst v6.84: I am importing measured irradiance data from a tilted global POA pyranometer (GlobInc aka GPI). I would expect Mod GlobInc to exactly align with the Mes GlobInc that I am importing; however, this is not the case.
The first measured GlobInc value is 446.7 W/m^2. Upon importing, I look at the modeled GlobInc value at the same timestamp. GlobInc (Hay model) for the same tilt and azimuth is 416.0 W/m^2. So, there is a 7% deviation b/w Mes and Mod GlobInc at this timestamp (at times the deviations are larger than 7%).
The deviations are notably larger at the edges of the day (morning/afternoon) compared to around solar noon.
I have set PVsyst to use the Hay transposition model per the following post:
Another note: For both Hay and Perez, it reports albedo = 0.2 for GlobInc; however, there is no option to define albedo when importing custom measured irradiance. Should albedo be a user input to the custom data import tool?