Inverter suggestion for 5.7 kw, 3-phase system

nepalm
nepalm Registered Users Posts: 5 ✭
in Grid Tie and Grid Interactive Systems #1
I designed a 5.7 kw commercial system which includes 30 Evergreen 190-ESL and an SMA SB6000. There are three strings of 10 and seems to be perfect on paper.

The utility comes back and says they do not allow a multiple inverter configuration just in case one phase goes down and there could be an imbalance. I spoke with a tech at SMA and he said there are thousands of commercial installations across the country configured this way.

Has anyone run into this situation with their utility? If so, how did you get around it? As far as I know, there isn't a 3-phase inverter small enough to handle a <6 kW system.

thanks in advance for any help!
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: Inverter suggestion for 5.7 kw, 3-phase system

    we have run into this before and no further knowledge of any results are known to us on the matter in the following thread,
    http://forum.solar-electric.com/showthread.php?t=4760&page=2
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #3
    Re: Inverter suggestion for 5.7 kw, 3-phase system

    I believe their comment for your system is regarding the 120/240 VAC split phase system.

    The older UL standard (as I recall) just required 240 VAC across the inverter (two wires and a green wire ground).

    The current UL standard requires the neutral wire to the inverter now... And the inverter monitors the neutral relative to the other two legs... So if the inverter/home lost the neutral, the inverter would shut down the 240 VAC output (there is no current on the neutral for the standard Xantrex et.al. GT inverters (2kw and larger)--as I understand, so there cannot be a "single phasing" on a 120/240 VAC circuit).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: Inverter suggestion for 5.7 kw, 3-phase system

    ok, if i misread this i'm sorry, but he mentioned 3 phase in the thread title.
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  • solartek
    solartek Solar Expert Posts: 69 ✭✭✭✭
    #5
    Re: Inverter suggestion for 5.7 kw, 3-phase system

    I thought the Xantrex GT series of inverters could be configured to handle 3 phase systems and would communicate with each other to make sure that if one phase went offline the others would also.

    A-ha. Found the link for it here. Yep, if you connect up the communications network between multiple Xantrex GT inverters you can force them all to disconnect if any one phase goes out so that you don't have an unbalanced situation.

    Maybe SMA offers the same thing for their SB inverters.

    Scott.
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #6
    Re: Inverter suggestion for 5.7 kw, 3-phase system

    That's new on the Xantrex GT's since I was involved, good to see that feature.

    For the OP, may not help as for this to work you need three inverters and each inverter would have it's own solar input.

    I also think you have an issue on your strings, 10 panels in a series string will not be enough voltage for normal operation, regardless if its the Sunnyboy or the Xantrex GT's and Evergreen I believe is no only making 12V nominal panels ( 18V vmp ~ 25C ), the odd ball voltage ones have been discontinued
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  • System2
    System2 Posts: 6,290 admin
    #7
    Re: Inverter suggestion for 5.7 kw, 3-phase system

    I have encountered this while designing a large system (~750kw) with SMA SB inverters. This may be a problem for utilites because, yet again, they are "unfamiliar" with PV and are used to prime movers where you would not normally lose a single phase.

    I don't see what the issue is since if a single utility phase went down, then all the inverters on that phase would turn off so basically you would have the same situation as without the PV. The only way around this would be a large and expensive relay with voltage sensors that would disconnect the entire array if this were to happen.

    It looks like the euro version of the SB has a 3-phase feature where you connect a communication cable between the three and they work in unison (http://download.sma.de/smaprosa/dateien/7418/NetzSMC-UEN084110.pdf). But I am not aware of the US version having this.
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