Solar Panel Sorting on Pallets and String Design

[aleenoor]

Hi Everyone, I am installing a 12kW system and just took delivery of 41 Canadian Solar 295W CS6K-295MS panels. I have one complete pallet of 26 Panels and 13 in a re-packaged half pallet. The full pallet has the attached sticker on the side showing the tested STC Watts of each panel. It shows that plus sorting of the panels from 299.8W to 295.7W. As you can see that the serial numbers on this sheet are not continuous and not in sequence. Also, once I looked at the panel serial numbers on modules in this pallet, they are not stacked in any sequence i.e. wattage or serial number.

Now what is the recommended best practice. Should the strings be planned with like wattage panels ? e.g. I have 4 strings of about 10 panels each. Should I cherry pick 10 panels with highest wattage and put them in a single string ? OR should I preserve the sequence of the panels as they are stacked (side-ways) on the panels.

That brings up the 2nd question. For the 2nd half pallet, I do not have this sticker with all panels serial numbers and STC wattage. However, I would assume original manufacturer's sorting sequence is preserved. How should I use these panels.OR I am over thinking it and it is all unnecessary.

2nd Question is regarding string lengths. A picture of my roof and panels layout is attached. I have 2 faces of the roof where the panels will go. The triangular hip and rectangular gable. The tilt (6:12) and azimuth (180) are identical. However, the panels marked as A will get some tree shading early in the morning and panels marked as B will get some shading due to a step b/w 2 faces , late in the afternoon.I am using 2x SMA sb 6.0-1sp-us-40 Inverters with 3MPPTs each. SMA's design tool recommends 4 unbalanced strings 13,7 and 13,8. A friend who has done his own install is suggesting 10,10,10,11.

I wanted to some guidance and opinions from all the pros over here.

Thanks a lot for your help.

[ButchDeal]

Since you are planning to do 4 separate strings each with their own MPPT. The best option would be for you to cherry pick the best modules and put them together on the least shadowed part of your roof. put the worst modules together on a string in the most shadowed part of the roof.
This would result in the most production though likely talking 1% or so.
If you only had one MPPT then balancing the strings on the one MPPT would lead to most production (this is what I did on my system).


They should have sent you a sheet for the partial pallet of modules as well. You could do a rough test of each in sunlight to compare them to each other and to some known modules from the other pallet.

[sensij]

You are looking at 4W difference between the best and worst, it really isn't going to matter. With each string on it's own mppt, the best case, if the qc data are good and represent panel behavior across all conditions (a big if), would be to match Imp as close as you can within the string. I would go with strings of balanced length.

There is an argument for putting all the shaded panels in one string, which allows the other strings to operate at full power. If you do that, I would make it the 11 panel string, so even if the bypass diodes kick in you still have enough voltage to operate the mppt.

The argument for putting only 1 shaded panel in a string is that it might hit bypass sooner, helping the other panel in the string maintain full output longer.

Again, these choices might add up to a few 00.x% annually, so no need to overthink it.

See this thread for more of the technical details of mismatch

https://www.solarpaneltalk.com/forum/off-grid-solar/off-grid-solar-panel-systems/350695-wiring-solar-panels-of-slightly-different-voltages

From whom did you end up buying them?

[aleenoor]

From whom did you end up buying them?

I bought the modules from Fortune Energy and Inverters from Soligent. Thinking on trying out the Tigo's for the few shaded panels.