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    #16
    Originally posted by iwire

    In the next few weeks I should be installing a 75 KW PV system that will be tied into the utility. Any 'extra' power will be sold back to the utility.
    Bob, do you mean a 7.5KW?
    A 75KW is one serious power plant!

    I've done a bunch of 5KW and one 15KW. I can't imagine a 75KW! How big is the roof!?!?!?
    Dave

    "Don't wire like my brother"

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      #17
      Yeah Bob, know that, backfeeding power to the utility has rules, but many inverters support it. The inverter has to have anti-islanding provisions, so that when utility power is out, the inverter stops, so as not to present a shock hazard to PoCo folks.

      But... the OP wants the inverter to operate without utility power to feed critical appliances. In many installations the PV system is just connected to a breaker in the panelboard, as thats all that is needed. But in this case that wont do. Either the inverter has to have separate supply in and load out terminals, and the inverter has internal relaying so that it can isolate the utility terminals whilst feeding downstream equipment, or an external relaying mechanism is needed, and the inverter has to be dual mode (inter-tie / standalone) with external control to switch between modes.

      Many inverters cannot handle this arrangement, which is why I am interested in what the inverter is.

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        #18
        Originally posted by davedottcom
        Bob, do you mean a 7.5KW?
        A 75KW is one serious power plant!

        I've done a bunch of 5KW and one 15KW. I can't imagine a 75KW! How big is the roof!?!?!?
        75 KW, about 280 panels.

        They are also bidding a 750 KW system at a school.

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          #19
          Originally posted by dbuckley
          But... the OP wants the inverter to operate without utility power to feed critical appliances. In many installations the PV system is just connected to a breaker in the panelboard, as thats all that is needed. But in this case that wont do. Either the inverter has to have separate supply in and load out terminals, and the inverter has internal relaying so that it can isolate the utility terminals whilst feeding downstream equipment, or an external relaying mechanism is needed, and the inverter has to be dual mode (inter-tie / standalone) with external control to switch between modes.
          You make it sound like rocket science, some switching is all you need and it is also covered by 690.61.

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            #20
            Originally posted by iwire
            You make it sound like rocket science, some switching is all you need and it is also covered by 690.61.
            Actually, anti-islanding mechanisms to comply with UL 1741 (which is basically what 690.61 requires) is rocket science, and most folks have no idea how it works.

            And yes, "some switching is all you need", but you still have to get a grid intertie inverter to start up whilst it is islanded, which is exactly what it doesn't want to do, in compliance with 690.61...

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              #21
              Originally posted by dbuckley
              Actually, anti-islanding mechanisms to comply with UL 1741 (which is basically what 690.61 requires) is rocket science, and most folks have no idea how it works.
              I don't know how many of the things I wire 'work' it does not bother me, I don't build them and I have no trouble reading the instructions that come with them regarding their connections to the buildings electrical system.

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