PVsyst 7.2.17 PVC Scene Backtracking

[David]

Hi,

The release notes for patch 7.2.17 say, "the first simulation of imported PVC scenes with backtracking now takes backtracking into account."  I was wondering if you would be able to clarify why it says the "first simulation?"  Does backtracking with PVC scenes not work properly after the first simulation? I attached the release notes below. 

Thank you!

David

[Michele Oliosi]

Hi, yes I can give more specifics.

Basically depending on the order in which you access the different windows when defining your system, it could happen that the shading table was computed without backtracking, even though you had selected backtracking in the orientation window.

This happened more specifically whenever you used an imported PVC scene, because the trackers were not assigned the "backtracking flag" during import, and only by refreshing the shading window and/or recomputing the shading factor table the flags were updated.

The impacted simulations were those that had an incorrect shading factor table, and where the "fast" option was selected, i.e. the calculation of shadings according to the table. The "slow mode" with the hour by hour evaluation was not affected. By the time of the simulation the all backtracking flags were set correctly.

Now this specific error is solved.

[dtarin]

If the user selected a backtracking pair under the backtracking management menu prior to computing the initial shading table, is there still a possibility for this to occur? Typically I do not generate the shading table from the shading menu, and instead have it compute during the simulation process. Is there any difference? One last question, what is the approximate error in % you are seeing? 

Edited August 15, 2022 by dtarin

[Michele Oliosi]

The error is the backtracking gain over tracking without backtracking, so 1% in general-few% max.

Note that the error was actually quite easy to spot for relatively flat terrain. Indeed, when you activate backtracking you should expect few losses in the shading factor table.

Indeed, I am not sure about this case (selecting the backtracking pair). Additionally if you did not generate the shading table previously there is a chance the error had been avoided. I will double check this situation and get back to you.

*Edit: if you select the backtracking pair, the backtracking seems to have been well activated (confirmed each time for a few tries).

*Edit 2: If you generate the table only at simulation the issue was unfortunately the same.

NB: these errors have been corrected in v7.2.17

[dtarin]

Thanks, Michele. 

[David]

Thank you!