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  • Grid tie system with generator

    I am getting ready to install a 19kw solar field and the customer wants to add a stand by generator to the system. I came up with a way I think should work just wanted to see if it makes the most sense or if there is another way. The customer has a 400 amp meter enclosure that feeds 2-200Amp breakers already installed from factory that makes meter enclosure( Millbank Brand). 1 of the 200amp breakers feed the house and the other feeds the barn. The idea i came up with was take the 200amp breaker that feeds the house and use that to feed the 200amp Automatic Transfer Switch (ATS) and then feed the wire that already goes to the house. Then from the Solar field I would feed the inverter that would feed the breaker panel in the barn. By doing this I will be only feeding the house with the generator because that is where the crucial circuits are at and then the solar panels would power the house and barn when utility power is on. I have never installed a solar field and stand by generator before but this was the best thing i came up with with the equipment that is already installed at the location. Would there be any other ways I could install this better or if the customer wanted both the barn and house powered by generator in a power outage event

  • #2
    Welcome to Solar Panel Talk, PGKCONST!
    You have the right idea, even if some of the wording of your description is wrong.
    The inverter output will be connecting to grid and when grid power is up it does not make a lot of sense to try to specify which loads the GTI is or is not feeding.
    Depending on where the GTI is located and how much current it is producing it may make sense to feed it into the garage subpanel or the main panel or even make a supply side tap to the incoming lines ahead of the main breaker.
    The key thing is that you do not want the GTI to try to be active while the generator instead of the grid is your power source.
    To make sure of that you need to connect the GTI anywhere upstream (toward POCO) from the transfer switch. So in the scenario you describe the one place you cannot connect it would be into the main panel.
    There is another design consideration for the generator connection, however:
    If you are using an automatic transfer switch (ATS) rather than an manual transfer switch (MTS) the National Electrical Code (NEC) requires either that the generator is capable of driving all normal loads at the same time or that there be automatic load shedding circuitry that can reduce the house load to be less than or equal to the capability of the generator. Some people choose a manual transfer switch instead to avoid this additional expense. Others instead set up a critical loads sub panel off the main which does not include large loads such as electric heat or A/C and feed that subpanel from the ATS.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      What size generator? The 400 amp service does not really mean anything. If I were doing this I would temporarily install Load Demand meter for a week to see what the peak load demand really is. It may just turn out to be something like 15 to 20 Kw. If that is the case a 20 Kw genny, ATS, and 500 gallon LPG tank and no rewiring anything. Beats the heck out of wiring a Emergency panel and rewiring everything.
      MSEE, PE

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      • #4
        Originally posted by Sunking View Post
        What size generator? The 400 amp service does not really mean anything. If I were doing this I would temporarily install Load Demand meter for a week to see what the peak load demand really is. It may just turn out to be something like 15 to 20 Kw. If that is the case a 20 Kw genny, ATS, and 500 gallon LPG tank and no rewiring anything. Beats the heck out of wiring a Emergency panel and rewiring everything.
        +1
        But in all cases connect the GTI upstream of the transfer switch.
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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        • #5
          Originally posted by inetdog View Post
          +1
          But in all cases connect the GTI upstream of the transfer switch.
          Well of course silly.

          MSEE, PE

          Comment


          • #6
            Originally posted by inetdog View Post
            Welcome to Solar Panel Talk, PGKCONST!
            You have the right idea, even if some of the wording of your description is wrong.
            The inverter output will be connecting to grid and when grid power is up it does not make a lot of sense to try to specify which loads the GTI is or is not feeding.
            Depending on where the GTI is located and how much current it is producing it may make sense to feed it into the garage subpanel or the main panel or even make a supply side tap to the incoming lines ahead of the main breaker.
            The key thing is that you do not want the GTI to try to be active while the generator instead of the grid is your power source.
            To make sure of that you need to connect the GTI anywhere upstream (toward POCO) from the transfer switch. So in the scenario you describe the one place you cannot connect it would be into the main panel.
            There is another design consideration for the generator connection, however:
            If you are using an automatic transfer switch (ATS) rather than an manual transfer switch (MTS) the National Electrical Code (NEC) requires either that the generator is capable of driving all normal loads at the same time or that there be automatic load shedding circuitry that can reduce the house load to be less than or equal to the capability of the generator. Some people choose a manual transfer switch instead to avoid this additional expense. Others instead set up a critical loads sub panel off the main which does not include large loads such as electric heat or A/C and feed that subpanel from the ATS.

            If i understand what your saying then it is exactly what I was thinking. I might not have explained what my plan is well enough the ATS will be getting power from the 1 of the 2 200amp breakers in the 400amp meter box so the house will be the only thing ran off the generator when power is down. The second 200 amp breaker feeds the panel in the barn that is where I would hook the inverter so then when the power does go out the breaker box in the barn will have no power and the ATS will sense there is no power and start generator to feed the breaker box in house but not the barn breaker box. Am i thinking correctly or will this not work?

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            • #7
              Originally posted by Sunking View Post
              What size generator? The 400 amp service does not really mean anything. If I were doing this I would temporarily install Load Demand meter for a week to see what the peak load demand really is. It may just turn out to be something like 15 to 20 Kw. If that is the case a 20 Kw genny, ATS, and 500 gallon LPG tank and no rewiring anything. Beats the heck out of wiring a Emergency panel and rewiring everything.

              I have already done a load survey and like you said a 20kw will work fine. I wasn't really planning on rewiring much at all I just have to take the wire that feeds the house and move it to the ATS and then feed the ATS from the breaker in meter box and the generator will power the whole house in case of power outage.

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