Transposition model, GlobInc gain

[Fernando Martins]

Dear PVsyst team,

I am working in some projects where I can see a high GlobInc gain using default Perez model.

Basically, the model is giving numbers higher than ClearSky model calculated by Nrel guidances (gain of transposition ~26%).

When using Hay model, the result is more than 1% lower than Perez model and the results (see the picture) raised an alert on that topic, once simulations we received from providers presented lower gain when compared to ours (maybe a local installation issue?).

I would like to confirm if the difference in the models are consistent and if Perez model in latest version is really reliable.

[André Mermoud]

The Perez model calculation has not been changed.

It is well-known that the Perez model has a higher gain that the Hay model. For fixed planes the difference may be of the order of 1%, depending on the tilt of course.

Here you have probably a tracking system, perhaps with backtracking. This difference of 1.6% seems indeed high, but is probably reasonable. Please check that all other parameters of your simulation are quite identical.