Inconsistency Near shading and electrical losses results

[YASMINA]

I am working on a project with 3D shading scene imported from the software helio (file h2p), I did the following simulations:

  Case  1 (variant VC9).  Including all shading objects (Results: near shading = 3.89% ;  Electrical shading loss= 3.19% )

  Case 2 (variant VCA). Enabling only shadow between trackers, exluding other objects shadows  (Results: near shading = 0.77%   ;  Electrical shading loss= 0.108% )

  Case 3 (variant VCB). Exluding the shadow between trackers but including the other objects (Results: near shading = 0.75%   ;  Electrical shading loss= 0.06% )

  Case 4 (variant VCC). Excluding all shadow objects and the trackers shadow too (Results: near shading =  0.71%  ;  Electrical shading loss= 0%  )

  Case 5 (variant VCD). Repeat again case 1 after excluding all shadow and then enable all of them again (Results: near shading = 0.8%   ;  Electrical shading loss= 0.167%  )

The questions are:

  A. The 0.71% obtained as results of case 4, It is due to which shadow? the fact is that all shadows objects were disabled!

  B. The sum between loses of case 2 and case 3 should be the same as the case 1 results? if it is so, the results are not the same (for near shading is 0.77% (case 2)+0.75% (case  3)=1.52% so it is diffrent from 3.89% (case1).

   C. The Case 1 and Case 5 are exactly the same but, why the results are differents?

   D. Moving from case 1 to the other cases, the avarage axis tilt changes from -0.4º to -0.5º, but the only action done was enabling or disabling objects/trackers shadows

 

Many thanks in advance for your help.

Yasmina.

[André Mermoud]

I had a look on this project.

In the first simulation, there is indeed an error. The first shading factor table calculation was not correct, it did not take the Backtracking strategy into account. This sometimes arised with the versions up to V 7.2.17  (where this bug was corrected).  You are indeed using a rather old version 7.2.14  (April 2022); you are advised to update to the latest version. 

 

For the next versions the table was re-calculated  correctly, and leads to linear shading losses of the order of 0.75%.

This loss is mainly due to the mutual shadings on the diffuse part.  See the help  “Project design > Shadings > Calculation and Model > Diffuse losses with tracking systems”.

In usual cases this contribution is about 2 to 3%, because it also includes the shading loss on the project’s albedo component, which is completely invisible from the trackers in the field (100% loss).  But in your case you have put the albedo = 0 in your project,  so that this loss is not accounted here. However the final result is correct as the albedo contribution is also not taken into account in the transposition.

 

NB: Your question A: for trackers, the mutual shading loss on diffuse is calculated in a specific part, independently of the simulation, and doesn’t take the option “No shadow casting” into account. This is the reason why it is apparent in the variant  VCC.

Question B: In the VCB, supposed to exclude the mutual shadings of trackers, this contribution is indeed calculated as explained above. Therefore the shadings of VCA and VCB should not be added. The contribution of the other objects (trees) is completely negligible in such a system.

Question ? As explained the VC9 is erroneous. The recalculation updates the shading factor table and is correct.