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PostPosted: Tue Oct 15, 2019 12:35 am 

Joined: Wed Oct 23, 2013 12:36 am
Posts: 31
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:

viewtopic.php?t=40/

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?


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PostPosted: Mon Oct 21, 2019 8:12 pm 
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Joined: Tue Oct 18, 2016 3:31 am
Posts: 223
That article is quite old. Perez is the default transposition model. Using measured diffuse irradiance will result in higher transposition accuracy for GlobInc.


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PostPosted: Tue Oct 22, 2019 12:08 am 

Joined: Wed Oct 23, 2013 12:36 am
Posts: 31
Thanks @solarguru but the deviations I reported are larger (>10%) using Perez vs. Hay

I am interested to hear PVsyst's opinion on this

There are no issues reported for the imported measurement data however the PVsyst POA does not match the imported values


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