Hi,
Can Anyone confirm me if I can Use one string comprised of 6 panels and a second string comprised of only 4, connected to the same MPPT Charger ? Lets assume all panels are alike, first string will produce 200W at 240V and the second 1360W at 160V
Thankx
Hi, I have a similar set up, but not quite... although it seems to me the "issue" is alike.
Any advice would be much appreciated !
I plan 2 strings of 4 panels (in series) each. The strings are to be connected in parallel to a MPPT charge controller (or possibly 2 PPT's, when this would be advantageous) .
So quite a "classic" set-up. PS: I'm in the south of France...
But due to a wall on the east side (panels are facing S), the 2 parallel strings get a different shading in the morning hours (till about 10:30 AM). Especially in winter when sun only rises quite low on the horizon. This sadow will influence both arrays differently, creating more shadow on 1 array, than I will get shadow on the other. Thus I have different output on the 2 strings.
Surely the issue disappears when i get full sunlight after 10:30 AM !
I'm only looking for the best solution to cover the morning hours in winter season.
Would it be more advantage to connect each string to a "dedicated" MPPT ? Instead of connecting 2 strings to 1 MPPT ?
set up would be in combination with a MultiPlus.
Many thanks
Hi @Cadoxa
No, don't do that. The mppt needs to track a 'common' string mpp, and if they're far apart will still likely work, but won't work very well.
Then you'll need to ensure you don't exceed the max string Voc of the particular chosen mppt. 6x in a single string way well be too much anyway.
So you'd need to match string lengths, and with 10x in total, maybe 2S5P would do. That may be borderline if you're charging 48V batts in poor light. 5S2P might work on a 250/ mppt.
If you could be more specific with panel data, mppt and Vbat we could try to help further. Or run your data through this: https://mppt.victronenergy.com/
Hi John,
Thanks for your answer. Here is the real world scenario;
My roof only has space for 16 Panels. The panels I'm using are LG´s 340W all alike.
My MPPT charger is a 250/100 MC4 (takes 3 strings). Inverter Charger is a Victron Quattro 8000, and the battery pack is a 48v LifePo4 (connected both to the inverter and MPPT charger.
At the roof, I created three strings two of them with 6 panels (2000w / 240v) and one with 4 panels (1360w / 160v).
The question is; is there a problem connecting this 4 panel string to the MPPT Charger, along with the other two ? and Why ?
Best
Carlos
Yeh, real world scenarios are good. :)
Firstly, your 250/100 (great unit) may only have 3x pairs of MC4 plugs, but they're just a convenience thing, and link within to a common bus. The number of strings it can handle isn't related whatsoever, perhaps the main consideration there is the rated max A per MC4 plug (30A from memory).
So with 16x panels, wire them 4S4P (just double 2x strings into 1 of the MC4 pairs). That would be a 'perfect' setup for you. Run it through that link I provided to check. (I did have a look at typical LG panels)
And for fun, run a 6x string through the calculator too with the temp data of your panels, and you'll likely find it won't recommend anything Victron as it may destroy the mppt.
It's all about having the same mpp on each string so that output can be maximized over all of them.
I'm guessing that your real issue is the 'max 3 strings limit' into the mppt. Which doesn't exist.. nope, doesn't exist..
Hi John,
I run my configuration through the Victron calculator and it suggested the 250/100 mppt with no problems. My only doubt is; can I use the two 240v strings connected in parallel with the 160v string? If so, how could this compromise the performance of the whole system ?
Share your thoughts ...
Best
Carlos
It's all in the letters 'MPPT'. Have a look through this whitepaper at the V vs W curves: https://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf
Your own panels will have a unique curve, but of similar shape. Let's say your panels have a Vmp of 35V, so a string of 6x means Wmax is at 210V. That's higher than the Voc of your 4x string, so the 4x string would act as if in open circuit and produce no power. In practice, a single mppt would weight the best combo, but the potential power would be seriously reduced.
You may well have good reasons for wanting/needing a 4x string, and if so would get far better results with a separate mppt just for that string.
Why not do 4s4p to a combiner box and then only 2 cables to the mppt ?
