Albedo shading component calculation

[ClaireWest]

Hi, how is the albedo shading component (ShdALss) calculated? I have read the help pages on this topic but i am still not clear how this functionally works, sorry.

https://www.pvsyst.com/help/project-design/shadings/calculation-and-model/index.html

https://www.pvsyst.com/help/project-design/shadings/calculation-and-model/treatment-of-the-albedo-component.html#far-shadings

Why does the albedo shading loss have this profile on a clear-sky day (single-axis tracking system): ?

TIA

[Linda Thoren]

Hi,

The shading calculation is indeed explained in the second link you have attached. In general, the higher the tilt, the higher the albedo contribution. Most of the albedo contribution will directly be lost (you see that the albedo loss is indeed following the albedo contribution) since we assume that only the first row is "seeing" the albedo, so that the albedo shading factor will be (n-1)/n (n = number of sheds). The albedo loss is a significant contribution to the global shading losses.

[ClaireWest]

Thank you. Is that a fair assumption that only the first row is "seeing" the albedo? With typical GCR ~40% or lower there will be sun hitting the ground between the panels by early to mid morning. E.g. in my snip above (36% GCR), at 8am only 65% of the ground is shaded and at 9am only 48% is. So the albedo shading factor should be ~35% and ~52% during these times?

[ClaireWest]

Sorry, the albedo shading factor should be *~65% and *~48% during these times, not sure what happened there

[Linda Thoren]

Hi,

Indeed, today the ground reflection between rows is only considered for bifacial systems. In general, this contribution is very low with sheds and trackers systems, but becomes more important with high tilts and large pitch and crucial with vertical East-West bifacial systems.

The calculation of the ground reflection of the front side involves an accurate definition of the ground, its albedo, the geometry, and the full calculation of the ground points view factors. 

So, the ground reflection of the front side is considered for bifacial systems since all of the needed parameters are already defined, but neglected for monofacial systems. The only way to run a simulation including the ground reflection for the front side for a monofacial system today, would be to alter the PAN file (activating the bifaciality and put the bifaciality factor to 0) and run a simulation with the bifacial parameters, though everything except the ground reflection on front side will be 0 given the bifaciality factor of 0.  

In the following help page, the reflection on the ground is further discussed:
https://www.pvsyst.com/help/project-design/bifacial-systems/bifacial-systems-results.html