Transposition factor pvsyst5 and 6

[klerindias]

Hello,

i just did for same location and same meteorological data PVGIS-SAF compare of transposition factor:

PVSYST5:

http://img841.imageshack.us/img841/5568/transpositionalfactorpv.jpg

and here PVSYST6:

http://img11.imageshack.us/img11/5568/transpositionalfactorpv.jpg

Why is this diffrence?

and dont know why in both examples is diffrence 1kWh/m2.

Between this 2 cases is like 2 weeks diffrence.

But even 1kWh/m2 shouldnt have so big influence on tilt?

Regards

[André Mermoud]

In the version 5, the default transposition model is the Hay model.

In the version 6, it is the Perez model.

Now these are models (with their uncertainties), not the reality !

The Perez model is known for giving slightly higher transposed values (by 0 .. 2% according to climates, plane tilts, etc).

However please observe that these optima are very broad: a difference of some few degrees (with the same model) represent a very little irradiation difference.