PVSYST 7.4.0 changes in Shadings: Electrical Loss acc. to strings

[Sergio Jimenez]

Hi all.

With the recent update of PVSYST to the 7.4.0 version I have see that the shading electrical losses are too much higher comparing with the previous version.

Launching the same simulations of a PV plant (using the same parameters and the same Near Shadows scene, the shadings losses goes from -0.34% (in 7.3 version) to -3.41% (in the version 7.4). Could it be a possible bug? Is is possile to the new version overestimate this kind of losses? Near and far shadow losses factors change too but the value are similar this only happens with the shading electrical losses.

Thank you very much.

[Michele Oliosi]

This is likely not a bug but part of the feature. But we would need to see your scene to be sure. First of all, I would recommend checking the two following posts

https://forum.pvsyst.com/topic/3085-electrical-shading-losses-in-versions-73x/

https://forum.pvsyst.com/topic/3312-electrical-shading-losses-partition-model

In version 7.3, the electrical shading losses were oftentimes underestimated. Now the partition model tends to overestimate irregular shadings, which is what it was originally intended to do. For irregular shadings (not just mutual shadings), you should use the fraction for electrical effect to mitigate this overestimation.

[Sergio Jimenez]

Hi Michele.

Please find attached the .shd in the next link https://we.tl/t-4wzvKGvVZt

I will check the post mentioned.

Thank you very much.

[Michele Oliosi]

The following types of shading patterns were typically neglected in version 7.3, and are accounted for in version 7.4 (somewhat overestimated when they are irregular, i.e. not a long mutual shading like in screenshot #2). All of these shadings are due to the topography and should not be neglected, i.e. version 7.4 should be more accurate (albeit somewhat overestimated) than version 7.3.

Since these shadings are partly irregular you could consider a factor for electrical effect somewhere around 80-90% to mitigate the overestimations, but it will be very hard for us to give you aprecise value that fits the whole scene: there are many different shading instances on the scene.

[Sergio Jimenez]

Thank you very much!, I will try to adjust the electrical effect.

Kind regards.

[Joe Hollingsworth]

@Sergio Jimenez I have seen similar results. A shading scene I am using (with terrain and single axis tracking) Electrical loss acc. to strings jumped from -0.13% in v 7.3 to -3.56% in v7.4. 

[mtamm3]

I am seeing this same thing as well. Near Shading and Electrical losses jumped significantly between v7.3.4 and v7.4.0. @Michele Oliosi is there any other way to mitigate this besides adjusting the electrical effect factor? I already have the electrical effect factor at 70%. 

[Michele Oliosi]

Probably 7.3.4 was underestimating the losses in your case. I am not sure there's a solid reason to go back to a situation where the losses were underevaluated. But you can always reduce the shading factor further, even though we don't recommend it.

[Ubers83]

Hi, I also noticed the same thing after updating from v7.3.1 to v7.4.3. Very significant increase in the Electrical Loss acc. to strings for one of the 3D models I'm working on. If you're using topography, it's worth mentioning that you need to be very careful with your backtracking management too.

[Michele Oliosi]

Indeed, 7.3.X was significantly underestimating the losses in some situations. 7.4.X is much better, although we will make a further adjustment for trackers in version 7.4.6.

[laurahin]

We haven't seen large changes in the electrical loss yet in our (admittedly limited) use of v. 7.4, which includes variants with significant terrain.  Is it possible that the differences as great as 3% aren't attributable to the modified shading loss algorithms per se but to automatic selection of a different diffuse shading reference tracker when rerunning in the higher version?  We definitely have seen elect. loss differences that great depending on the location of the reference tracker in an array.

Edited March 18 by laurahin

[Michele Oliosi]

Hi !
Diffuse shading should be completely independent of electrical shadings. I don't think that can happen.

[laurahin]

Bummer.  It seemed like a good idea at the time.