Mix and match panels

I have 4 KC 170 panels connected to form a 48v system. I am now going to add 4 KC 175 panels for a second 48V string. Was told by the retailer that mixing the 2 sizes would not cause any issues. Wondering if it would not be better to use 2 of each in a 48v string or let the MX60 sort out the difference between the 4x175 and the 4x170 string.

Comments

  • BB.BB. Posts: 27,699Super Moderators admin
    Re: Mix and match panels

    My 2 cents worth... There is so little difference between the output Vmp output voltages (0.2 volts per panel), that I would not worry about it at all.

    I would just wire up the new panels in the easiest method for you (probably, just adding a new parallel string and don't bother messing around with the existing wiring.

    Certainly, there will be no damage or problems from either mix and match or paralleling. The differences are within normal manufacturing tolerances.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • crewzercrewzer Posts: 1,832Registered Users, Solar Expert ✭✭✭✭
    Re: Mix and match panels

    I agree with Bill; you just need to keep the appropriate module specs close.

    When connecting modules in series, you want to match the Imp specs fairly closely, and the Voc and Vmp specs just add up. When connecting modules (or series strings) in parallel, you want the Vmp specs to match fairly closely, and then you just add up the Isc and Imp specs for each string.

    My hybrid two-string array might serve as an example. Each string consists of four BP SX-60’s (configured for 8.4 Vmp x 7.12 A Imp), one Kyocera KC-120 (16.9 Vmp x 7.10 A Imp), and one Sharp 123 (17.2 Vmp x 7.16 A Imp), all connected together in series. The Imp’s of the various modules are all close enough, so each string is rated at 67.7 Vmp x ~7.1 A Imp. The two strings in parallel make for an array rated at 67.7 Vmp x ~14.2 A Imp.

    The array works fine… the key is to get the numbers close.

    HTH,
    Jim / crewzer
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert ✭✭✭
    Re: Mix and match panels

    You can parrallel the strings and won't have any issues
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Mix and match panels

    the retailer was right so just add it in parallel to your present pv configuration, but to be sure you understand that the new pvs shall still need their own wiring/fusing to go to the controller as you don't want to up your voltage drops.
  • System2System2 Posts: 6,290 admin
    Re: Mix and match panels
    niel wrote: »
    the retailer was right so just add it in parallel to your present pv configuration, but to be sure you understand that the new pvs shall still need their own wiring/fusing to go to the controller as you don't want to up your voltage drops.

    Original wiring was put in to be ready for 4 strings of four panels. Had to spread out the panel purchases to take best advantage of the tax breaks.

    Thanks for the advice. They are going up on the roof today.
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