Electrical Loss According to Strings lower with First Solar modules

[Rachel Hamilton]

Hi PVsyst forum!

 

I have just completed two PVsyst models with the intention of comparing the near shading losses and I had a question about the electrical shading loss observed on one of them. The main difference is that one variant was modeled with Jinko Solar JKM400M-72HL-V modules and the other with First Solar FS-6480-P. Obviously given the difference in DC size, the overall array DC size is different and the module count is slightly different also. However, factors like the pitch, table spacing, etc, are the same between the two. I opened the same shading zone without modifying any of the area limits or any shading features, and all I did after switching the modules was change the table from "by sensitive area" to "modules" and then set the tables to 2x6 in portrait (the same between both variants), and then re-populated the zone. The First Solar modules are longer than the Jinko Solar modules in the portrait dimension by 16mm, so given that the pitch is the same, the First Solar configuration is slightly more compressed. The string partitions were set such that there are 2 strings in height for each row, and the electrical loss is set to 80%. 

This is the loss profile for the Jinko Solar version:

This is the First Solar version:

The general shading losses are almost the same, but can anyone help me to understand why the electrical losses are so different? As I mentioned, the First Solar configuration is the one that is more compressed. Also, I realize that the shading losses overall are extremely high--this system is located on a steep north-facing hill with a substantial treeline around the site, so losses in this range are expected. 

Any insights would be helpful. Thank you!

Rachel H. 

[Michele Oliosi]

In terms of simulation, if the parameters are similar, the losses should be similar. Trying to get the two values to agree I would suggest the following:

First of all a few things to check:

• If you are using the "fast" mode i.e. using the table, go to both shading factor tables (Near shadings > Table) and click on recompute. We have seen a few bugs where an incorrect older shading factor table was not recomputed automatically.
• If you can, use the "slow" mode (recomputed at each simulation step) and check whether the discrepancy still exists. Sometimes the shading factor table doesn't have enough resolution especially with complicated shadings.
• Nothing beats a visual check. You can use the shading animation for a day in winter to visual differences for a day in winter for example. Electrical shading losses are in yellow. You may find that shadings have different patterns in the two variants.

If the differences persist, there may be another external reason / bug / parameter choice not listed above. You can send both projects at support@pvsyst.com we'll gladly have a look.

Now I should make a comment about first solar modules vs Jinko Solar JKM400M-72HL-V and partitioning in general:

• The two modules have very different technologies, and they respond to shadings in different ways. Jinko solar is a half-cut cells module and when in portrait, you should partition it with two partitions (in height) per module row.
  On the other hand First Solar modules are thin film modules that are quite resilient to shadings as well. When installed in portrait, they will not suffer much from inter-row shadings. If shadings are only inter-row I think they advise to deactivate electrical shading losses, by using "linear shadings" instead of "according to strings" in PVsyst. Since you have other shading objects such as trees etc, which give more vertical shadings, I would suggest keeping the "according to strings" and lowering the fraction for electrical effect, for example to 30%.
• I would suggest sending them (First Solar people) an email for detailed guidelines, I am not too sure of how to determine a good fration for electrical effect in this case. Maybe someone on the forum has some info for First Solar modules in complex shading situations ?
• In general for partitioning, you can check the help page: https://www.pvsyst.com/help/shadings_partitioninstrings.htm we will be updating these pages again soon, but they already offer some guidelines for partitioning.

[dtarin]

The reason for the difference in electrical loss is because the string lengths are longer for the c-Si modules compared to the FS. After modifying the JKM partition as Michele noted, the elec. losses will come also come down for that module. 

I would evaluate how much shading is due to the trees compared to row-row to get an idea of whether or not you should include any electrical loss for the FS modules. Run a model with and without trees and compare the near-shading loss only (turn off electrical effect). Also run the shading animation in the shade scene throughout different times of the year to understand the shading patterns on the modules due to trees. If there is a lot of E-W shading from trees and there is a significant contribution, then including an electrical effect makes sense, and as michele noted, it should be low. 

Also, your jinko module should have an LID loss. 

Edited June 2, 2023 by dtarin

[dtarin]

Actually disregard the first comment, I see you are using the same table sizes for both. Check how you defined the partition area in each variant.

Edited June 2, 2023 by dtarin