I have a very Sticky situation

System
System Posts: 2,511 admin
in PV Installers Forum - NEC, Wiring, Installation #1
Problem: customer has a whole house generator/transfer switch. Also has a wind turbine which is supply line tapped before the main breaker. I am installing a 3kw system which I planned to line tap, but now is there a potential of the pv system back feeding the wind turbine system and visa versa? Both systems have their own inverters and the exsiting wind turbine inverter is to small for adding the pv. Is there a way around this problem? ANY help would be great! Thanks!!-Bill
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Re: I have a very Sticky situation

    You can't have 2 independent inverters. (PV & wind) Unless, you have a comm/sync cable to get them talking together. What's the battery bank : Voltage. Amps ?

    Is the PV Grid tie, or battery ?
    Powerfab top of pole PV mount | 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 ||
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: I have a very Sticky situation

    The wind has batteries but not sure why when he has a whole house generator. the pv has no batteries. The inverters are sunnyboy for pv and xantrex for the wind
    mike90045 wrote: »
    You can't have 2 independent inverters. (PV & wind) Unless, you have a comm/sync cable to get them talking together. What's the battery bank : Voltage. Amps ?

    Is the PV Grid tie, or battery ?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #4
    Re: I have a very Sticky situation

    I am a little confused... Is this a grid tied inverter system (at least PV + solar panels) and a whole house backup generator with an AC transfer switch?

    If these are Grid Tied systems... The GT Inverters cannot be back-driven (at least when in GT mode... Hybrid inverter systems like the XW from Xantrex have both a GT and Off-Grid mode; as well as their own AC transfer switch--and can be back driven when in the off-grid mode).

    If these are pure Grid Tie connected inverters, the only thing that could be back driven is the AC backup genset.

    And then there is a question about the AC genset... If a standard alternator, their frequency variation is generally is wider than that 60 +/- 0.5 Hz that is allowed with a GT inverter--so they will never lock.

    If the genset is a very stable geset (and some are)--then you do run the risk of back-driving the genset from the GT inverters (if GT output is greater than home AC loads) and causing damage to it.

    -Bill

    PS: I have moved your question to its own thread. -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #5
    Re: I have a very Sticky situation

    Thanks....I am new to this kind of forum with the threads and such. the Pv system is GT and I will have to check further on the wind inverter. As you said..if the both invertes are GT then the can't back feed each other?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #6
    Re: I have a very Sticky situation

    Our pleasure to help... We generally find that one thread for each poster's setup works well. There are lots of questions and answers going on and if it all relates to one setup--it keeps us from getting confused. :confused::roll:

    And yes, GT inverters can only output power, then cannot absorb/consume any energy from the line.

    If you are familiar with the terms... The AC Line network looks like a low impedance source (aka like a battery). The AC network will supply current if the load tries to take energy from the home wiring... Or, with a GT inverter, you can actually "inject current" (energy) into the AC home wiring and push the energy back out into the utility network (for use by other homes in the area).

    A GT inverter is a high impedance source (constant current source regardless of voltage--within reason--sort of the opposite of a battery).

    An off-grid inverter (and generator) is also a low impedance source and if a power source drives the AC line voltage voltage higher than the inverter/generator (such as a GT inverter), it will get energy driven back into it.

    For some off grid inverters, they actually will begin to charge the battery bank (there is no battery charge controller, so it can damage a battery bank or inverter hardware if left charging in an uncontrolled manner). For generators--the results of feeding current into the alternator is not really known.

    We have one recent thread here where a generator MFG. said it was OK if the GT inverter output was 1/2 of the connected loads (IIRC)... Obviously, most people do not controller their loads when running on the genset and looking at their solar energy output from the GT inverter (could I write that in any more confusing English :roll:).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #7
    Re: I have a very Sticky situation

    Is there a way for these two inverters to talk with each other so they don't affect one another? I will find out more about the wind inverter more tomorrow.
    Just not sure what to do. Was thinking a relay system. NO on the utility and NC on the gen side. When the gen starts to produce power it would force the coil and open the NC and not pass power. So when the utility comes back the gen still produces power until i cools and shuts off and then it would drop out. The NO coil would stay close while there is utility power. kinda redundant
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #8
    Re: I have a very Sticky situation

    Yes, you can do that with some units. Or you can put a relay (or solid state relay) in the GT inverter output line. Relay Off when generator running. Relay on when generator is off.

    If the generator does not have very tight frequency regulation--then the GT inverters will never sync with the genset in the first place (takes 5 minutes of steady/to spec. voltage and frequency before GT inverter will turn on).

    Or, put the GT inverters between the meter and the AC transfer switch and they will never back feed the generator set.

    -Bill

    By the way:
    Or, put the GT inverters between the meter and the AC transfer switch and they will never back feed the generator set.

    Yes, I am sure you know that and I am being "Captain Obvious"--But I like to make sure that all sides of an issue are discussed.

    -BB :roll:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #9
    Re: I have a very Sticky situation
    onpointnh wrote: »
    The wind has batteries but not sure why when he has a whole house generator. the pv has no batteries. The inverters are sunnyboy for pv and xantrex for the wind

    Quite a 'Swiss Army knife' system. (or maybe 'Rube Goldberg' more appropriate)

    What kind of Xantrex inverter (probably SW or XW) and what size batteries on Xantrex inverter? If wind system uses the batteries/Xantrex inverter then it is just DC pushing at batteries. What is size of generator?

    The PV's with Sunnyboy GT inverter should only be tied to grid power. It should never be allowed to push at generator. It probably won't due to gen freq accuracy but it could if gen freq was within tolerance (-0.7 Hz / +0.5 Hz of 60 Hz nominal) of GT inverter.

    Depending on Xantrex inverter type and size, the better solution for compatibility would have been a PV charge controller feeding batteries (along with wind charge controller) instead of Sunnyboy GT inverter. If it was XW inverter then it could sell back to grid the power not consumed by house loads.

    As it stands now, the PV will be useless when grid goes down.
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