Discrepancies between PVSyst and SAM results for vertical E/W bifacial systems

[Hadi Hammoud]

I am interested in modelling vertical E/W bifacial PV systems in locations in the Netherlands. To validate my simulation results, I am comparing the yield results between SAM and PVSyst for the same system and meteo conditions. After running an extensive number of simulations, the results showed significant diffferences between the two software's outputs. Moreover, the observed error exhibited a peculiar pattern. For a conventional south-facing system with low to moderate tilt (around 30 degrees), the results are in close agreement (less than 1% error). However, when moving towards east-facing configurations with high tilts, the results start consistently diverging, reaching up to 70% deviation for an east-facing vertical system. 

I am concerned about these results and I am having difficulties pinpointing the source of these discrepancies. So, I am seeking the help of whoever has experience in modelling east-facing vertical systems in PVSyst. I would appreciate any insights from people who have experienced such issues before. Also, I would be grateful if you could point me to some actual use cases or applications of E/W bifacial system modelling in PVSyst. 

Thank you in advance!