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Remote transfer switch (isolation switch) on hybrid system

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  • Remote transfer switch (isolation switch) on hybrid system

    Hi,

    I'm planning a PV system with around 9000 watts of panels that will be placed on the roof of an outbuilding (pole barn). It will usually be grid-tied, but this will be a "hybrid" system with at least some battery backup to be able to run when the grid is down. For various reasons, I pretty strongly want the inverter and batteries to also be in the barn. To cut to the chase before explaining further details, my main question right now is whether there is a viable (and economical) inverter/system that would let me put a "remote transfer switch" a fair distance from the inverter, in the basement of the house near where the critical loads panel would be, rather than needing to add a second electrical line between the house and barn (one from grid to inverter, one from inverter to critical panel).

    I call it a "transfer switch", but really it would just be the "isolation switch" to separate the critical loads panel from the grid. I'm not sure what that's called when it's not built into a hybrid inverter. Logically it seems plausible and doable, but the question is whether something exists on the market that would fit the need. SolarEdge StorEdge seems to support this concept with their "Backup Interface" device which is physically a separate unit from the inverter. But with the StorEdge only working with the expensive LG RESU battery, I'm not inclined to go that way.

    If I can find suitable products, I believe the diagram would look basically like this. I'll call this the "Remote" option:




    But if not, and I need to add another electrical line between the buildings, then I believe it would look like this. I'll call this the "Round trip" option:




    To elaborate on some details / questions:
    • The distance between the main panel in the house and the barn panel (where the inverter would also be) is about 160+ ft
    • I do have conduit space available between the buildings, so it wouldn't be out of the question to run the 2nd line, but, I'd of course like to save money on the wire, and I don't like the idea of the voltage drop that is incurred (with the Round trip option) during normal times when the grid is up and the current needs to travel from the house main panel to the barn, through the hybrid inverter, and then back to the house to the critical loads panel. Round trip of ~320ft instead of what "could be" ~6ft with the right equipment.
    • With the Round trip, I'm not aware that this causes any code concern, but it does seem unusual to have a circuit leaving the main house, to another building, and then re-entering the house, powering a subpanel. Done correctly, it doesn't seem like this would be a problem, but if you're aware of something I'm not, let me know.
    • For reference, if I were to use the "Round trip" option, a couple of the inverter options I have my eye on would be the Sol-Ark 8K and a PAIR of Phocos PSW-H 5K or 6.5K since those are 120V only, but can be paired for split phase, and they seem more economical. But they don't have as much built-in like DC disconnect, AFCI, GFCI, and the 5K lacks UL 1741, not sure yet if that matters. The Phocos also isn't rated for as cold of temperatures as the Sol-Ark, so I would need to insulate a room and potentially give a bit of heat now and then, which I may want to do anyway for the batteries' sake.
    So there's a bit of extra info there than the core question, if anyone wants to chime in on inverter options. I'm not expecting you to design the system for me, nor have I given enough info for you to do so, but wanted to get some input on this high-level direction if possible, since I'm not turning up much on this "Remote" option.

    Thanks much.
    Last edited by cm21; 06-07-2022, 09:26 PM. Reason: fix images

  • #2
    Transfer switches are always a hassle.
    BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

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    • #3
      I don't see any diagrams.

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      • #4
        Just blank pages
        BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

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        • #5
          Originally posted by solarix View Post
          Just blank pages
          Interesting. Those diagrams were showing earlier today.

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          • #6
            Sorry for all the trouble. I think I finally got it. The Dropbox links I was using evidently had "expired"... the ones I used now should be permanent. I edited the original post. Let me know if it still has a problem.

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            • #7
              Hybrid inverters have their own integral transfer switches. You could use line powered relays or contactors to emulate some remote transfer switches, but I think the design of hybrid inverters precludes a simple arrangement, as they have to protect the linemen at all costs.
              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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