Grid-tie with generator

stumpy40
stumpy40 Solar Expert Posts: 35 ✭
in Grid Tie and Grid Interactive Systems #1
What are the options if any to have a generator installed to run house if and when grid is down during storms with a grid-tie system installed?

I understand a PV system will back feed a generator possibly killing it over time if not right away. The array would most likely come on with generator, although excess power would have to go somewhere.....hence ruining generator.

What about a separate panel with critical loads only that the generator can power. Possibly installing transfer switch between main and sub(critical loads) or (would there be a way to power entire house also)so that array and grid aren't affected by generator and critical loads
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #2
    Re: Grid-tie with generator

    Unless you have a really nice and stable generator (such as an inverter/generator set), as I understand, it is highly unlikely that the inverter will see 5+ minutes 60 Hz +/- 1% accuracy required for GT inverter to activate.

    So, you are left with needing to decide how many circuit and which circuits you are going to power from the genset...

    Either you will create a separate "protected" powered subpanel with 6-12 circuits (or whatever) behind a transfer switch (AC Grid or Genset power).

    The GT Breakers would then be installed in the "non-protected" main panel so they only see AC Grid power...

    Otherwise, you would still need to put a transfer switch ahead of the main panel and make the whole main panel as a protected circuit (solar PV and all) and bet on the fact that the genset will not be stable enough for the GT inverter to lock on.

    How big of genset and how many loads do you want to power?

    By the way, I am a big believer in using as small as genset as practicable. Large generators just gobble the fuel like there is no tomorrow... Natural Gas can cost $1-$2 per hour for a typical home genset--Let alone the storage issues for having enough gasoline, propane, diesel storage for extended run-times.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • stumpy40
    stumpy40 Solar Expert Posts: 35 ✭
    #3
    Re: Grid-tie with generator

    Thinking of just a small one also. Just to power critical loads...few lights, fridge, etc.
    Thought entire house at first, but since came to my sense.
    So if a transfer switch was installed between array panel(house) and sub(critical loads) in theory I could have a genset power just that sub without fear of anything else being live?

    I do believe that the genset could turn on the GT's...even if for a few seconds I would imagine could be harmful. According to SMA they state it is very possible.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #4
    Re: Grid-tie with generator

    The purpose of the transfer switch is to Isolate the genset from the AC mains. Basically a big A/B switch with the subpanel on the common output.

    Are you going to use a manual or automatic transfer switch/genset? The nice transfer switches are not cheap (automatic generator cycling once a week, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • stumpy40
    stumpy40 Solar Expert Posts: 35 ✭
    #5
    Re: Grid-tie with generator

    Auto if I can....just in case wife is at the house and I'm not. Needs to be as simple for her as possible. haha
    If anything 1 switch for her to close to isolate to protect array.

    I just need to figure how a ATS installed would be done......everything is in a gutter on the house. The solar is line side tapped, don't have room for anything.
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  • SolarLurker
    SolarLurker Solar Expert Posts: 122 ✭✭
    #6
    Re: Grid-tie with generator

    To solve some of your space issues Kolhler makes a integrated Service panel/transfer switch. This makes for a tidy install, you can even shed two circuits if need be.

    Also, APC make a 20 amp protected load panel that has a integrated load shedding feature. If you view honda Generators website, you find a nice little video on how the unit works.

    This device also allow solar input.

    If you have a SMA inverter you could also consider the addition of a sunny island to create you own mini grid, and use both a generator and solar.
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  • stumpy40
    stumpy40 Solar Expert Posts: 35 ✭
    #7
    Re: Grid-tie with generator

    That's good stuff...thanks.
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #8
    Re: Grid-tie with generator

    There are brand-new charge controllers that will handle the high voltage of a GT PV system, allowing it to be used during outages to charge a battery bank. Here is one: http://forum.solar-electric.com/showthread.php?t=9810
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #9
    Re: Grid-tie with generator
    techntrek wrote: »
    There are brand-new charge controllers that will handle the high voltage of a GT PV system, allowing it to be used during outages to charge a battery bank. Here is one: http://forum.solar-electric.com/showthread.php?t=9810
    The OP did not mention battery backup, just PV and a generator. In reality, that would be two separate systems, as others have said, with the PV on the main service and the generator on a protected loads panel.
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