Hi @SaeranVasanthakumar, no worries and thanks for the reply.
It’s possible to get up to 40 years of data in one go so it’s fairly straightforward to create an updated TMY file if needed. I’ve started processing uncertainty values although one needs to really understand what it means in this context.
On the other hand, to consider airport data as ‘real’ and reanalysis data as ‘simulated’ or ‘approximate’ is a bit of a mischaracterization I think. One way to think of it is to consider the room temperature as reported by your thermostat vs. another that takes in the thermostat reported temperature, plus a thermal imaging of the room, the location of the thermostat in the room in relation to the window, and the laws of thermodynamics etc. There is much more math involved in the latter processing but it doesn’t make it anymore unreal. NREL also recommends using gridded data over point-source data, probably because deriving radiation parameters from airport-reported sky coverage is really quite problematic (as I discussed here).
But in any case, if the models are not calibrated, it really just comes down to a matter of convenience to use the weather data that’s sufficiently correct to drive design decisions. As I like to quote, ‘all models are wrong, but some are useful.’ 