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  • Mismatched wattages on solar panel installion.

    Hi all,

    I'm building an off grid system, it comprises of 18 260w matched panels, they run at just over 30v. The inverter charger I have handles a maximum input of 145v and 5kw. My intention was to have two lots of five panels and two lots of four wired in parallel, then series them to make 120v input. Will the uneven wattages cause any issues?

    Thanks in advance, Mike

  • #2
    Originally posted by Mookie30 View Post
    Hi all,

    I'm building an off grid system, it comprises of 18 260w matched panels, they run at just over 30v. The inverter charger I have handles a maximum input of 145v and 5kw. My intention was to have two lots of five panels and two lots of four wired in parallel, then series them to make 120v input. Will the uneven wattages cause any issues?

    Thanks in advance, Mike
    For a true MPPT type CC the wattage per string should not matter except being too low for the bigger inverters that require a minimum voltage to start up.

    I guess my question to you is what is the battery system voltage and what is the make and model of your inverter/charger?

    4680watts is a big system and can generate almost 98 amps even for a 48V battery system.

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    • #3
      My batteries are 24 units of 2v PowerSafe 1300aH at c20 AGM type, wired for 48V. My inverter charger is 80a solar charging, 5kw constant supply with a 10kw spike. The system is designed to be overkill for my power needs as I want to add car charging in the next year or so. My charger is MPPT and takes a minimum of 60v to start up.

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      • #4
        If a string of 5 panels generates 150V then you will exceed the max input rating of 145V. There should be some type of paperwork with that charger showing the best way to wire your panels to it without exceeding any limits.

        I also think that with only 80 amps of charging it will be short to take care of a 1300Ah battery system. You should have about 1/10th the Ah rating (130A) to charge it. 80 amps will get you only a C/16 charge rate which is not good for the batteries.

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        • #5
          You cannot wire 5 panels in series with your controller. , 3 maximum. You used the wrong controller, you should be using a 600 VOC controller, would have saved you thousands of dollars..

          Now you need 6 strings of panels requiring a lot of wire and very expensive Combiners and fuses. That mistake will cost you a lot of money. Good news is you can use all 18 panels.

          Smart money would be to use a 600 volt controler, and make two stings of panels with 9 in series using a lot less wire and smaller wire, and no expensive combiners and fuses required.

          Good Luck. You are going to need it as you discover more expensive mistakes you have made like charging your car with an off grid battery system. You will be paying ten times more for electricity than you have to. A ICE car would be less expensive and less polluting than what you will be doing. Wait until you figure out AGM cost you 400% more than FLA. You will be buying new batteries in two or three years. I could have saved you $6000 minimum.
          Last edited by Sunking; 09-11-2018, 05:56 PM.
          MSEE, PE

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          • #6
            Originally posted by Sunking View Post
            You cannot wire 5 panels in series with your controller. , 3 maximum. You used the wrong controller, you should be using a 600 VOC controller, would have saved you thousands of dollars..

            Now you need 6 strings of panels requiring a lot of wire and very expensive Combiners and fuses. That mistake will cost you a lot of money. Good news is you can use all 18 panels.

            Smart money would be to use a 600 volt controler, and make two stings of panels with 9 in series using a lot less wire and smaller wire, and no expensive combiners and fuses required.

            Good Luck. You are going to need it as you discover more expensive mistakes you have made like charging your car with an off grid battery system. You will be paying ten times more for electricity than you have to. A ICE car would be less expensive and less polluting than what you will be doing. Wait until you figure out AGM cost you 400% more than FLA. You will be buying new batteries in two or three years. I could have saved you $6000 minimum.
            I think you misinterpreted the OP. What I think he was trying to do is make 2 groups of 5 in parallel, and then make 2 groups of 4 in parallel, put those al 4 of these groups in series.. That would give him 4 groups of panels in series, hence the 120V string is he talking about. Obviously the problem is that the whole series parallel array would be current limited by the groups of 4 in parallel.

            I'm not recommending this, but I believe that is what he meant.

            Andy
            EE, NABCEP

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            • #7
              Originally posted by PVAndy View Post
              I think you misinterpreted the OP. What I think he was trying to do is make 2 groups of 5 in parallel, and then make 2 groups of 4 in parallel, put those al 4 of these groups in series.
              Perhaps, but I cannot even follow what you are saying, and I do not think the OP even knows what he/she is saying. Only way to get 120 volts is to use the Vmp of 4 panels in series. However both you and I know that cannot be done with a 150 volt controller. The controller can only handle 3 panels in series at best, and that may still be over the Voc input limit of the controller because 260 watt panels Voc before temp comp is at a minimum of 40 volts. So if the OP lives where there is a winter season, 3 in series could be too many panels.

              The main point I am making, is for a system of this size requires using a 600 volt Charge Controller to make it cost effective. Yeah sure a 600 volt controller cost almost twice that of a 150 Voc controller, but will save you thousands of dollars in equipment material, and labor to work around the problems a 150 Voc controller brings to the table. It is an expensive mistake and asking for more complex maintenance/repair problems. A mistake a uninformed DIY or amateur would make. He has a lot more nasty surprises waiting for him to discover.

              Last edited by Sunking; 09-11-2018, 11:04 PM.
              MSEE, PE

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              • #8
                There is still going to be a 60 or 80 amp limit on most controllers. The PT100 has 100a limit, they seem reliable, but it's only been out 2 years
                http://www.magnum-dimensions.com/pt-...rge-controller Maximum PV operating voltage 187 VDC



                Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                solar: http://tinyurl.com/LMR-Solar
                gen: http://tinyurl.com/LMR-Lister

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                • #9
                  Umm, Sunking
                  Last edited by Mookie30; 09-12-2018, 03:06 AM.

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                  • #10

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