Ac coupling enphase to a Xantrex XW for battery backup

System
System Posts: 2,511 admin
in Advanced Solar Electric Technical Forum #1
Has anyone ever AC coupled enphase micro inverters to the sub-panel of a battery system using the Xantrex XW? What I am trying to accomplish is having battery backup and being able to use the Enphase system during periods of utility outage.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #2
    Re: Ac coupling enphase to a Xantrex XW for battery backup

    XW will shut down if your load consumption falls below the PV/Enphase power output.

    XW will think you hooked its ACout to grid.

    It probably will not damage XW.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,641 admin
    #3
    Re: Ac coupling enphase to a Xantrex XW for battery backup

    The only missing point is that using the Enphase to power the XW can result in the XW charging the battery bank... All is good--except there is no charge controller in the the circuit at this point.

    Most likely, the batteries will charge until they hit the maximum bank voltage programmed into the XW--and the XW will shut down the AC output.

    If this is a long term setup--you need to look at some way to limit charging on the battery bank... Either by inhibiting the Enphase (relay in AC output) or a shunt load + controller on the battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #4
    Re: Ac coupling enphase to a Xantrex XW for battery backup

    XW inverter/chargers loaded with the latest firmware (so-called "1.5") now support AC-coupling. :cool:

    The architecture is grid-tie inverter manufacturer agnostic, so networking between the XW and the grid-tie inverters is not required. Accordingly, this feature should work with the Enphase inverters.

    AFAIK, the key "requirement" is that the system's total PV array size (i.e., STC Watts) should not exceed the XW's nominal power rating. For example, a single XW6048 can handle an array of up to ~6 kW.

    HTH,
    Jim / crewzer
    Sr. Sales Application Engineer
    Schneider Electric Renewable Energy Business Unit (x-Xantrex)
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #5
    Re: Ac coupling enphase to a Xantrex XW for battery backup

    Where does the PV grid tie inverter power go if light ACout loads?.

    I see a few choices.

    1) let the ACout voltage increase. Assume GT-inverter will disconnect.

    2) dump it to batteries, possibly over charging them.

    3) XW could move its inverter frequency a bit, outside of normal grid tolerance, to cause the GT-inverter to shutdown when its power is not needed for ACout loads or battery charging.

    #3 would seem to be a viable solution, but would bring up another question. What happens if you also have a generator operating on AC2 input and a PV inverter tied on ACout?
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #6
    Re: Ac coupling enphase to a Xantrex XW for battery backup

    Frequency shift (#3) is the heart of the control strategy. GT inverters typically won't sync up to "regular ol" generators (i.e., non-inverter types), but I'll have to dig into this a bit more.

    Regards,
    Jim / crewzer
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #7
    Re: Ac coupling enphase to a Xantrex XW for battery backup

    I guess in the case that a generator was connected, and within freq spec of grid tie, and power not needed, XW could just open relay to AC2 (gen) and do the freq offset to shed the GT inverter.

    Thanks for info. I alway want to understand any side effects.

    RC
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  • System2
    System2 Posts: 6,290 admin
    #8
    Re: Ac coupling enphase to a Xantrex XW for battery backup
    RCinFLA wrote: »
    I guess in the case that a generator was connected, and within freq spec of grid tie, and power not needed, XW could just open relay to AC2 (gen) and do the freq offset to shed the GT inverter.

    Thanks for info. I alway want to understand any side effects.

    RC

    Xantrax does have a technical bulletin on AC coupling and its XW does work but it is an on / off situation I wish it could taper charge the batteries.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #9
    Re: Ac coupling enphase to a Xantrex XW for battery backup
    Sun stuff wrote: »
    Xantrax does have a technical bulletin on AC coupling and its XW does work but it is an on / off situation I wish it could taper charge the batteries.

    Use an additional diversion load controller and dump load ?
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,917 ✭✭✭✭✭✭
    #10
    Re: Ac coupling enphase to a Xantrex XW for battery backup
    Sun stuff wrote: »
    Xantrax does have a technical bulletin on AC coupling and its XW does work but it is an on / off situation I wish it could taper charge the batteries.

    If you really want an XW and batteries then you might as well just make it simple and use the XW-80-600 controller and keep it simple. Disconnect your solar input from the grid tie and connect it to the new controller. That is one of the main reasons it was developed BTW.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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