Offgrid/Ongrid PV sharing

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  • MAGNUMCJ
    Junior Member
    • Nov 2023
    • 5

    Offgrid/Ongrid PV sharing

    Hello, new here. Hopefully I picked the right forum. I have a situation I'm looking for advice on from those more familiar with solaredge equipment.

    Given the following layout of my system I have added a backup offgrid system. Reason is the Solaredge works great with a present grid but is obviously worthless with grid down. The intent here is during a grid down event my electrical system is disconnected from the grid connection via the main utility disconnect. (Ignore the amp rating as that is what code required me to install but the grid transformer can't even supply that much) Then the backup system is turned on (manually, not automatically). The hope is (not tested fully yet) is that the voltage from the offgrid system will enable the Solaredge system to supplement. The rest of the time the backup system is not used.

    Main issue and the advice I need is I was not aware at the time of design the limitation of sharing solar panels. So the dashed proposed solar panel connections will not work. that leaves limited ways to charge the batteries. Current thought is to use the supplement AC current from the solaredge system to power the chargeverter from the farms "local grid". this seems maybe possible but still not ideal.

    so I'm looking for advice, ideas, solutions on this issue.
    I've done electrical for 30 some years, but the last 25 some odd years has been focused more on electronics and automation food production systems/process. so I'm familiar with the basics of electrical work, but maybe not as familiar with differences in solar system.
    Thanks in advance.


    solar layout 2.png
  • solardreamer
    Solar Fanatic
    • May 2015
    • 452

    #2
    Originally posted by MAGNUMCJ

    Main issue and the advice I need is I was not aware at the time of design the limitation of sharing solar panels. So the dashed proposed solar panel connections will not work.
    What's the issue with the PV connection?

    Comment

    • MAGNUMCJ
      Junior Member
      • Nov 2023
      • 5

      #3
      I cannot use the pv's to feed the solaredge and the eg4 inverter no. 1 at the same time. so in backup mode the pv through the solaredge puts juice to the system but not charge the batteries. essentially that would be two mppt charge controllers hooked to the solar array in parallel.

      Comment

      • azdave
        Moderator
        • Oct 2014
        • 765

        #4
        Originally posted by MAGNUMCJ
        The hope is (not tested fully yet) is that the voltage from the offgrid system will enable the Solaredge system to supplement. The rest of the time the backup system is not used.
        I'm far from an expert in the latest tech but all non-hybrid grid-tie inverters that are legal for use in the USA are designed to operate only if they detect that the grid is up and running. They are intentionally designed that way for safety. You cannot so easily fool a grid-tie inverter into operating without a valid grid connection by simply feeding it power from a generator or by using the converted power of an off-grid system.

        More info:
        Dave W. Gilbert AZ
        6.63kW grid-tie owner

        Comment

        • solardreamer
          Solar Fanatic
          • May 2015
          • 452

          #5
          Originally posted by MAGNUMCJ
          I cannot use the pv's to feed the solaredge and the eg4 inverter no. 1 at the same time. so in backup mode the pv through the solaredge puts juice to the system but not charge the batteries. essentially that would be two mppt charge controllers hooked to the solar array in parallel.
          The diagram shows SolarEdge and EG4 each having a PV input DC switch. In the OP, you indicated the EG4 is backup power only used when the grid is down. That suggests PV power is not used by both inverters at the same time. If so, in grid outages, you just turn off the SolardEdge PV input switch and turn on the EG4 PV input switch then you will have all PV power going to the EG4. While on grid, you would have the opposite switch settings.

          Comment

          • MAGNUMCJ
            Junior Member
            • Nov 2023
            • 5

            #6
            Originally posted by solardreamer

            The diagram shows SolarEdge and EG4 each having a PV input DC switch. In the OP, you indicated the EG4 is backup power only used when the grid is down. That suggests PV power is not used by both inverters at the same time. If so, in grid outages, you just turn off the SolardEdge PV input switch and turn on the EG4 PV input switch then you will have all PV power going to the EG4. While on grid, you would have the opposite switch settings.
            doesn''t work that way to my knowledge. each solar panel has an optimizer on it that won't let the panels have any output unless they are connected to the solaredge converter. communicates with dh485 thru the solar cables.

            Comment

            • MAGNUMCJ
              Junior Member
              • Nov 2023
              • 5

              #7
              Originally posted by azdave

              I'm far from an expert in the latest tech but all non-hybrid grid-tie inverters that are legal for use in the USA are designed to operate only if they detect that the grid is up and running. They are intentionally designed that way for safety. You cannot so easily fool a grid-tie inverter into operating without a valid grid connection by simply feeding it power from a generator or by using the converted power of an off-grid system.

              More info:
              https://www.solarpaneltalk.com/forum...-a-grid-outage
              there is a good point I hadn't thought of in that thread link. if the solar system generates more current than the load I am currently running, bad things could happen. hmmmm....

              Comment

              • solardreamer
                Solar Fanatic
                • May 2015
                • 452

                #8
                Originally posted by MAGNUMCJ

                doesn''t work that way to my knowledge. each solar panel has an optimizer on it that won't let the panels have any output unless they are connected to the solaredge converter. communicates with dh485 thru the solar cables.
                That's the explanation I was asking for. Does the EG4 8xxxEX supports AC coupling? You need one that supports AC coupling with frequency shifting control (e.g. EG4 18K) then it should work with SolarEdge AC output.
                Last edited by solardreamer; 11-16-2023, 05:32 PM.

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