Shadings in single axis tracker with backtracking in PVsyst 6

[unilhexio]

Hi,

I'm simulating a single axis tracker system wih backtracking in PVsyst 6. The scene only contains the trackers: no buildings or shading objects. When PVsyst is computing the shadings diagram, the ressult is no shadings, as expected.

But in the final report, a 2% of near shadings losses is shown. It never happened to me in the previous PVsyst v5 version. In fact, I have been simulating this project in v5 correctly. What can be the problem?

Thanks in advance.

[unilhexio]

In the following picture, the near shading for single axis tracker N-S with backtracking is shown. There are not any other shading object, as can be seen in the diagram below:

http://sia1.subirimagenes.net/img/2013/09/26/130926104851235384.jpg

In the following picture, the loss diagram is shown:

http://sia1.subirimagenes.net/img/2013/09/26/130926104850599410.jpg

I know that it is not necessary to draw the scene. As it is mentioned in PVsyst help "As there are no shadings (except when the sun is behind the plane), the 3D construction is not really necessary. The "Orientation" dialog is sufficient for fully defining a Backtracking system for the simulation. "... but the result is different if I define only the orientation dialog:

http://sia1.subirimagenes.net/img/2013/09/26/13092610542830347.jpg

In PVsyst v5 both simulations lead to the same results. This is an inconvenience if the 3-D must be done if we have any other shading object in our scene.

[André Mermoud]

This is not a bug.

This is an update of the shading loss calculation.

Even with backtracking (where you don't have any shading losses for beam component), you can have shading losses on the diffuse as well as on the albedo.

This is now taken into account since the version 6.10. The previous calculations were not quite correct.

See the FAQ How is calculated the Shading loss on Diffuse for tracking systems?

And also the post Additional Tracker shading loss in 6.10

[unilhexio]

Ok.

Thererfore, I understand that it is a more accurate calculation to do the simulation by constructing the 3-D scene instead by defining the "Orientation" dialog.

In my opinion, the text from PVsyst help that I have quoted before (Near shadings: Backtracking strategy), may be improved taking this into account.

Thanks a lot for your reply!