Selector Switch Between CC and Micro Inverter?

CanemanCaneman Solar Expert Posts: 71 ✭✭✭✭
Could a selector switch be wired between a charge controller and an enphase GT micro inverter? Switch to "1" and the PV feeds to the charge controller, switch to "2" and the PV feeds the enphase GT. The purpose would be to have a PV system that is GT for "normal use", but have the capability to switch to the battery bank for emergency backup power when the grid is down. Can this be done safely and effectively?

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Selector Switch Between CC and Micro Inverter?

    Yes, you can.

    Since the Enphase will shut down with a power outage you could switch its panel input to a charge controller and use the 200 +/- Watt panel to recharge a battery of about 160, maybe 200 Amp hours at 12 Volts.

    Keep in mind the microinverter is not meant to be wired up this way and you may have trouble getting such an install past inspection. But from a purely technical standpoint it would work. And yes you could "gang" multiple panels together (more wires, more switches). Also, you will no doubt need an MPPT type controller as the panels of this size almost invariably are not "standard for battery systems" Vmp.
  • BB.BB. Super Moderators, Administrators Posts: 29,327 admin
    Re: Selector Switch Between CC and Micro Inverter?

    Note--There is a very good chance that you will have to switch both solar panel + and - wires--The GT Inverter standard requires "ground fault" detection/shutdown--and an "extra" +/- connection could cause the Enphase to shutdown until the "faults" are removed.

    If this was done with a larger central GT inverter type--They frequently have ~1 amp fuses to detect "ground faults" and you would need to replace the fuse if it pops (some GT inverters may require some reset procedure or even a service call to reset the ground fault).

    I have no clue what the Enphase units will do (they probably are sealed units--so a replaceable fuse would seem to bit odd ball for there product).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Selector Switch Between CC and Micro Inverter?

    Bill;

    It's my understanding that the micro inverters are exempt from this DC ground-fault regulation as they are considered "an AC device" due to there being "no significant wiring run" from the panel to the inverter.

    All of which goes in the trash can the minute you install a "significant wiring run" to provide the tap for the battery charging controller.

    Hence my concern that the OP may run in to some regulatory problems.

    Probably voids the inverter warranty as well. :roll:
  • CanemanCaneman Solar Expert Posts: 71 ✭✭✭✭
    Re: Selector Switch Between CC and Micro Inverter?

    Thank you... i am not sure if this would pass inspection either, but I was just curious if it would work...

    So, do I need a switch on the PV + and -, or will just one + switch work?

    I was thinking an MC4 Y connection could be added on the + PV side of the inverter, then wired down to the switch that goes to the CC... to charge batteries just flip the Inverter breaker open, then close the switch going from the PV to the CC... could this work?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Selector Switch Between CC and Micro Inverter?

    Discounting the ground-fault stuff, at a minimum you need a single pole double-throw switch to change the (+) of the panel from the microinverter to the charge controller. Merely "piggybacking" the controller to the panel when the inverter is down may not work, as it might interfere with operation of the controller (the micro will periodically try to fire up and detect AC present so long as it has panel power).

    Someone else here did a similar install with a conventional GT inverter, tapping a section of the array to supply a charge controller when needed. It was a bit complex. This is why Xantrex came up with the 600 Volt controller, which is more than a bit pricey. But then so is a complete hybrid GT inverter set-up like the XW or Sunny Boy, which is why people keep trying to AC couple their conventional GT systems to small battery-based inverters (with varying degrees of success and headaches).
  • CanemanCaneman Solar Expert Posts: 71 ✭✭✭✭
    Re: Selector Switch Between CC and Micro Inverter?

    OK, so what I need is a SPDT switch on the + PV line so it is either going to the CC or the GT micro Inverter...
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Selector Switch Between CC and Micro Inverter?
    Caneman wrote: »
    OK, so what I need is a SPDT switch on the + PV line so it is either going to the CC or the GT micro Inverter...

    Yes. That would be minimum. And of course you'll have to parallel the negative side (but you shouldn't have to switch it). Keep in mind that from a single PV there can be a lot of V-drop before you get to the charge controller if you have a long wire run (often the case with roof arrays and having to fit the controller in the house somewhere).
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Selector Switch Between CC and Micro Inverter?
    Bill;

    It's my understanding that the micro inverters are exempt from this DC ground-fault regulation as they are considered "an AC device" due to there being "no significant wiring run" from the panel to the inverter.

    Your understanding is incorrect. Enphase inverters have GFDI protection (it's internal, electronic, and resettable) and I know of no reason they would be exempt from NEC requirements. The NEC does not yet distinguish requirements for micro inverters on any issue. Separately sold micro-inverters do not qualify as an AC module if there is exposed DC wiring of any length. Article 690 does not use the phrase "AC device" or 'significant wiring run', as far as I can remember.
    All of which goes in the trash can the minute you install a "significant wiring run" to provide the tap for the battery charging controller.

    Well, no, there's nothing to go in the trash can. However, the OP's proposal probably violates the listing of the Enphase (or other) micro-inverters, thus indeed jeopardizing inspection requirements and warranty.
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Selector Switch Between CC and Micro Inverter?
    Caneman wrote: »
    OK, so what I need is a SPDT switch on the + PV line so it is either going to the CC or the GT micro Inverter...

    I'd recommend a DPDT switch that switches both the +PV and -PV. For one thing, I've heard that enphase grounds the positive side of the PV circuit. If so that would cause a dead short if you ground the negative side on the charge controller. I think you're better off insuring that the two systems remain completely isolated from each other.
  • BB.BB. Super Moderators, Administrators Posts: 29,327 admin
    Re: Selector Switch Between CC and Micro Inverter?

    Assuming J.Ben is correct--You have to look for switches that are "Break before Make"... Some are "make before break" and that could lead to ground faults/other shorts if the wrong type of switch/relay is used.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • st2288st2288 Registered Users Posts: 9
    Re: Selector Switch Between CC and Micro Inverter?

    I am thinking about doing the same thing with the Y-cable. Do you have any luck?
    Thanks
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