Version 8: Tracker Diffuse Shading Definition: All Trackers VS Central Tracker

[Lance McGrew]

Hello,

We are curious as to how the All-Trackers Option in the Diffuse Shading Definition is calculated. Is it taking each individual tracker and calculating the shade as an average amongst the totality of the site? or is there another method. 

We are working on a site that has some segregated areas that may not experience as much shade compared to the center of our larger rectangular area.  in this instance what choice would be the most appropriate? 

The site is 440 MW. 

We have done multiple runs:

•  version 7 we obtained = 1647 specific yield
• Version 8 All Trackers = 1587 specific yield 
• Version 8 Center Tracker = 1633 specific yield 

Using the center tracker, brings us closer to the Version 7 yield however does that that equate to a more accurate and viable choice, or does the significant drop to 1587 provide a more accurate representation of our site. 

[Michele Oliosi]

Hi,

Yes, indeed, the “All trackers” option will average the shading factor tables on all the trackers in your scene. This is evaluated at 7 different tracker angles, integrated over sky directions, and then interpolation profiles are then generated. In the end, you have a profile that takes in a tracker angle and gets out a shading factor for the diffuse and albedo components.

In general, the best is to use the “All trackers” option. Since it takes the whole scene into account, it is the most representative. Besides, the “central tracker” may or may not choose the neighbors properly, i.e., it is good to check the selection automatically made by PVsyst when using this latter option. The only downside to the “All trackers” option, is the long calculation time at the “simulation initialization” stage.

[dtarin]

Custom tracker is a better option than central. It reduces simulation time and can approximate very close to all trackers; it just depends on how good of a tracker you select. Simply looking at the scene visually for a location which has a good representation of the site generally works (for larger sites), but smaller, complex sites might take some trial and error. In any case we see <0.1% delta using custom tracker compared to all trackers. 

Edited January 31 by dtarin

[Debbie]

In version 8.0.9, I found that when I run a model from version 7.4.8 that had a good "custom diffuse" tracker selected, it is now not masked correctly (it is on the edge).  Even if I go in in version 8.0.9 and select one that masks properly, after running it, it is on an edge again.  See image below.  This appears to be a bug with the custom diffuse tracker masking in version 8.0.9.  Can this be fixed?  It is not practical to always use "all trackers" for large arrays.  The problem may occur specifically when the trackers are tilted on the terrain.

This problem results in erroneous production jumps close to 1%, because the diffuse shade is only half accounted for.

Thanks in advance for the help PVsyst.

[Debbie]

Also, when I tried to switch it from "custom tracker" to "all trackers", it did not correctly save this change when running the model.  The report still shows "custom tracker" and the shade losses are still lower than the prior model because that custom tracker is on an edge of the mask.