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Pérez transposition model, PVsyst vs. satellite database


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Hi all,

SolarGis uses the Perez transposition method to pass the irradiance from GHI to Glob.Inc (POA).

Does PVsyst have any advantage in terms of accuracy? I mean: is 'Pérez transposition method' applied first and then the 3D model, shadows and horizon are applied or does the model itself also use the information from the geometry where the plant is located?

Glob.Inc. (POA) output of PVsyst is more accurate than GTI (POA) SolarGis?

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If SolarGIS uses the Perez model, it should have the same accuracy as PVsyst id the input data (Ghi and Dhi) are the same. 

Now you should be aware that the transposition model highly depends on the diffuse component. I don't know what is the diffuse model used by SolarGIS, but if you want to do a close comparison you should use the same input data (Ghi and Dhi) in hourly values.

In PVsyst, the horizon shading is taken into account before applying the transposition. Then the GlobInc (POA) is evaluated without any other perturbations.

The 3D irradiance models (shadings, IAM, etc) are applied on the GlobInc, DiffInc and AlbInc issued from the transposition.







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  • 8 months later...

Hello André,

When you say "the horizon shading is taken into account before applying the transposition" would that mean that, loading a horizon profile for the site is always needed to balance out this diffuse contribution on the GlobInc calculation so that, when comparing against GPOA measured onsite with in-plane pyranometers (Gmeas) and calculating performance there are comparable figures from theory (Egrid/GlobInc) to reality (Eactual/Gmeas)? This of course, under the ideal scenario when the same weather conditions and system performance would happen.

I do not get to understand how this horizon shading is taken by PVsyst when no profile is loaded, since GlobInc result does not vary if there is one or no file from any source. Does it estimate it or calculate internarlly once the site coordinates are set by reading internal databases? 

Thank you. Regards.

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