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Electrical Engineer question: Mismatched strings of solar panels

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  • Electrical Engineer question: Mismatched strings of solar panels

    Hello all! I was wondering what would happen if you had solar panels in a system run with different strings. In this example, if you ran 1 string with 3 panels in series, and another string with 2 panels in series. If both these were going to the same Charge Controller, would things spaz out? Does the combined wattage play nice? All panels are 300w generating, so in my limited knowledge of electricity string 1 would have a 900w output, and string 2 would have 600w output... does it all just add together and the Charge controller just takes the sum total?

  • #2
    SWAG says those panels are about VOC of 35v String 1=105v and string 2=70v -- string 1&2 series 175v -- what charge controller?
    Those who do, do it!

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    • #3
      Unless the controller has dual MPPT inputs I wouldn't advise putting these two different voltage in parallel. Depending on the max voltage of the controller either wire 2s2p or, d
      epending on the max voltage of the controller
      get one more panel and wire 3s2p or 2s3p.
      Last edited by littleharbor; 03-29-2019, 10:36 AM.
      2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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      • #4
        Originally posted by motorcyclemikie View Post
        SWAG says those panels are about VOC of 35v String 1=105v and string 2=70v -- string 1&2 series 175v -- what charge controller?
        Thanks for the info, these are Schneider mppt 60-150 controllers

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        • #5
          Originally posted by DickyDck View Post

          Thanks for the info, these are Schneider mppt 60-150 controllers
          Check the VOC on your panels, if 34v or lower they can be all run in series otherwise what littleharbor said.
          Those who do, do it!

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          • #6
            Originally posted by motorcyclemikie View Post

            Check the VOC on your panels, if 34v or lower they can be all run in series otherwise what littleharbor said.


            300 watt panels will have a Voc. of 38.5 to over 39, if 60 cell panels. If 72 cell they will have a Voc. over 45, so, negative on "all in series". Don't even need to ask about lowest temps and temp. coefficients.
            2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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            • #7
              Looks like VOC is 40 on the panels,and they appear to be 60 cells per panel
              Attached Files

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              • #8
                So I have 24 panels currently, with two sets of cables running underground to two charge controllers. The panels are run in strings of three panels, 8 strings, to a combined box with 8 breakers. I have room for 4 more breakers, and basically if I can get a couple more panels to run another string that's what I'm aiming to do but I am not entirely sure if I can run strings of dissimilar numbers panels to these controllers. Nor am I positive if the controller could handle safely an addition 600w (theoretical max output from 2 additional panels) then the next potential issue is, 1 controller will have a higher input than the other but I "think" they are smart enough to work that out on the canbus/brain

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