Unusual results in the modeling of bifacial vertical PV

[sofya]

I came across unusual results when modeling a solar power plant. 2 rows of 4 modules at a distance of 4 meters from each other. They are located in the far north. I can't interpret the shading graph. Shouldn't it be symmetrical about noon? The hourly production schedule is also unclear. The gap in the mine should be at noon (when the sun is shining into the end of the panel). But here it is strongly shifted, and the output gradually decreases in the evening.

[Michele Oliosi]

Hi,

Thanks for reaching out on the forum. The main difficulty is that front side and backside are modeled differently in PVsyst.

Starting with the shadings in the iso-shadings diagram, these shading factors are only applied to the front side. This is why the shading just shows up on negative azimuth side, which must be the front side in your case. The backside shadings are applied differently: they are inherent to a view factor model. 

The back side is mainly modeled as defined in the System > Bifacial system window. There, you should activate a bifacial model, and make sure albedo coefficients are consistent with the front side ones (found in the project settings). The structure shading factor should be chosen as zero to match what happens on the front side (unless there is some component clutter in the backside, cables, combiner boxes, etc). Moreover, I'd recommend choosing a mismatch loss factor in the Bifacial system window equal to the front side's electrical shading loss. This latter factor will appear in the loss diagram if you choose a fitting model in Near shadings: either the partition model (according to module strings) or the module layout model (detailed electrical calculation).

[sofya]

Thank you very much! It’s not obvious that additional configuration of the bifacial modules is required. I thought it was enough to select them in the system.