Shading losses and tilt losses

Hi all,
Im trying to obtain two things:

1) The losses with respect to optimal angle and azimuth. I've been doing parametrics analysis but the results im obtaining (28º as optimal) are way off of those given by PVsyst (35º) and PVgis (37º). 
2) In case of having multiple rows, the losses from self shading. In PVsyst, is quite straight forward but in SAM I've done another parametric analysis but the resutls doesnt match the ones given by PVsyst. 

If you have any idea how can I do this or why is it wrong I'd really appreciated.

Many thanks.

Hi Miki,

One possible explanation of the difference is that there are inconsistent inputs between the two models. There are some published comparisons between SAM and PVsyst on the PV Validation page of the SAM website: sam.nrel.gov/photovoltaic/pv-validation.html .

If you are optimizing the tilt angle to maximize total annual output, I would expect both models to give similar results, assuming you are using the same weather data and input parameters for both.

Best regards,
Paul.