Bifacial System, bifacial panels, E/W orientation, tilt 90°(vertical planes). What is a negative array losses??

[Eduardo]

Dear all,

I was researching vertical panel simulations. I'm simulating a system with 43,6 kWp, bifacial panels, E/W orientation, tilt 90°.

 Bifacial configuration include the option "Use unlimited sheds 2D models".

Distance between panels (pitch) and Height above are design specifications. Shed width is based in height of panels. The albedo was selected according to PVsyst tables that relate soil type. Image 1 as reference

My specific question is about the results, since the "losses array" returned a negative value (indicating a supposed gain? which doesn't make sense) which is not expected. Can you tell me what this means? Or possible causes for this supposed error? image 2 as reference.

Thank you in advance for your attention, I look forward to hearing from you.
Sincerely, Eduardo.

 

Image 1

Image 2

3D model:

Image 3

[Michele Oliosi]

The calculation of the normalized production and losses is based on monofacial systems. Indeed, for some bifacial systems, and in particular vertical bifacial which have a large bifacial yield, the effective irradiance is higher than the front-side incident irradiance. In the diagram or in the array losses label, you therefore get negative values. The diagram does not really work in this case, actually.

The results are however correct, it's just the definition of array losses which is not adapted.