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Joining strings the right way

  • 28-10-2022 2:04pm
    Registered Users Posts: 2,222 ✭✭✭

    I have a Solis 6kwh hybrid with 2 strings, one with 12 panels and the second with 9 (335w panels)

    Looking at adding 3 extra panels to the second string but I would like to join this string in the attic and I want to do it right.

    You can see the existing string into the fireman switch (left) and then the cable going to the inverter port (right)

    My plan is to bring the 3 panel string here and connect it to the fireman's switch free port and then the output cable and bring it to the inverter.

    Then at the inverter unplug the 9 panel string

    And connect both 9 and 3 panel strings to a pair of these:

    Is that right? Wrong? Before you ask I can't get to the 9 string to link in the 3 on the roof so I need an inside job 😁


  • Registered Users Posts: 21,316 ✭✭✭✭ELM327

    Make sure they are the same panels in the same orientation, sounds like the best option is to join probably in series the way you intend - mind that the voltage is within spec too.

  • Registered Users Posts: 2,222 ✭✭✭SD_DRACULA

    The panels are the same orientation yes and while the new ones are 350w they are part of the same family and voltage/amps are the same. Might put optimizers on them but there are 0 in stock in Ireland at the moment.

    So the 9 are in series, the 3 will be in series as well but I am just unsure about joining them at the inverter using those MC4 joiners.

    Is that safe? Last thing I want is to blow the panels/inveter.

  • Registered Users Posts: 196 ✭✭UID0

    Those joiners are for parallel connection. If you connect your existing 9 panel string in parallel with the new 3 panels, at a minimum you will get no power from the new panels, and you could potentially get no power from the old panels or damage the new panels.

    You need to connect the 9 panels in series with the new panels. As you can't do this on the roof, the easiest way is to run the new positive and negative cables down and, in the attic, disconnect the positive from the old string from the fireman's switch and connect it to the negative from the new panels and then connect the positive from the new panels to the fireman's switch.

    Before doing it, make sure the voltage is within spec for the inverter. It probably is, given your other string already has 12 panels on it. Optimisers shouldn't be needed once the panels aren't shaded at any point.

  • Registered Users Posts: 64,693 ✭✭✭✭unkel

    @SD_DRACULA - "The panels are the same orientation yes and while the new ones are 350w they are part of the same family and voltage/amps are the same"

    That's impossible, the voltage and amps can't be the same, otherwise they'd be the same wattage 😁

    Don't mix up panels on one string, or the whole string is dragged down to the output of the lowest panel. Could still be ok, as long as you are aware...

  • Registered Users Posts: 2,222 ✭✭✭SD_DRACULA

    That was my next question so this is spot on - in my mind joining them did not sound right (still connected in series due to not having + to - connected)

    Yes there will be some shading on the 3 but it might only be at a point when the sun doesn't do much and is quite low, will need to wait and see.

    Differences are minute so let's call it the same for this exercise 😁

    I think I'll be ok if I lose the 15w from the new panels.

    Also, does anyone know of a courier I can use to get the gear from the North? Got quoted some silly prices for delivery.

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  • Registered Users Posts: 64,693 ✭✭✭✭unkel

    Aye that's fine, you'd just lose the 15W from the one new 350W panel, as your whole string will run at the same max current that the old 335W panels can give

  • Moderators, Home & Garden Moderators Posts: 5,752 Mod ✭✭✭✭graememk

    Cant use the Y Splitter as that would add the new panels in parallel to the existing string. Different voltages, and too much current to the inverter.

    What you can do is "patch it in"

    Unplug the say the positive from the string at the fireman switch, Plug the Negative from the new string into the original string positive and then the positive of the new string goes into your fireman switch.