Near Shadings: Irradiance loss

[Kebby]

I have noticed a large different in results from identical models run in v6.12 and v6.18. The only obvious change i can see is that:

6.12: Models used Transposition Perez Diffuse Measured

6.18: Models used Transposition Perez Diffuse Erbs, Meteonorm

This leads to:

6.12: -3.0% Near Shadings: irradiance loss

6.18: -1.9% Near Shadings: irradiance loss

Ultimately this leads to an increase in PR of 0.9%, is there an explanation for this change between these versions?

[André Mermoud]

For the shading loss changes:

If your system involves unlimited sheds: in the version 6.13 to 6.18, there were an error when reading the VCi file.

The plane tilt used for the evaluation of the shading effect on the diffuse part was not read correctly, which underestimated the shading loss.

This error didn't occur with new calculation versions, or if you opened the "Orientation" dialog before the simulation.

This problem has been corrected in the version 6.19.

On the other hand, the diffuse model is the same in both cases: just the denomination on the report has been changed.

"Measured" was used previously for any values read on an hourly file (whatever the origin, which is not known by PVsyst).

Now for most meteo data, the diffuse is indeed issued from a model. Therefore this denomination is not correct.

In the new versions we have tried to put some more accurate description when we have an idea of the origin of the data.

When creating synthetic data (which uses the Meteonorm algorithm), the diffuse is constructed by the Meteonorm software, using a Liu-Jordan or similar (Erbs) model.