6.5kw solar system with a 20kw briggs standby generator

jer19545
jer19545 Registered Users Posts: 4
i have a 6.5kw solar system by sunpro, & a 20kw briggs straton natural gas standby generator. the question is when the power goes out & the solar is producing electricity, will the generator transfer switch crank the generator? i've been told yes, no, & maybe. anybody out there know for sure? thanks john

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: 6.5kw solar system with a 20kw briggs standby generator

    Welcome to the forum John.

    The only one who can tell you if your gen will automatically start when the power is out is the installer. Or possibly not as this should have been outlined for you to begin with.

    There are several different types of system. For example if this is a straightforward grid-tie system when the grid goes down the inverter stops producing; the generator starts and supplies all power. It will not be coupled to the solar.

    But if this is a hybrid system then when the power goes out the batteries take over. If they get too low the gen should start to provide both load power and charging. In some cases such a system could have "gen support" where the inverter and generator can both provide power, although given the generator size this would likely be unnecessary.

    The transfer switch doesn't "crank the generator" per se; it will provide a signal to the gen that grid power has been lost and it should start. When it has the transfer switch will engage the loads to the generator. This is if it is auto-start.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: 6.5kw solar system with a 20kw briggs standby generator

    Welcome to the forum John!

    First question... Your 6.5 kWatt solar system is a Grid Tied Inverter based system (solar panels + GT Inverter, no battery bank).

    These system work in parallel with the Utility Power... When you have 120/240 VAC and 60 Hz power, the GT inverter "syncs" with the AC mains and simply pumps energy into your home's power lines--Which goes to support local AC appliances, and if there is extra power, goes out the AC mains and turns your utility meter "backwards" (assuming you have a Utility Net Metering agreement and the correct utility meter).

    If you lose utility power, the GT inverter system will shut down too. No AC utility power, no GT solar power.

    Now--You toss in an AC generator. You have two places that the generator transfer switch can be installed relatively to the GT Inverter's connection.

    The "standard" installation would be:

    AC mains + GT Inverter -> Transfer Switch -> Generator + "protected loads" (loads that the generator runs.

    A second method would be:

    AC mains -> Transfer Switch -> Generator + GT Inverter + "protected loads" (loads that the generator runs.

    The AC mains would go down (so with GT solar), then the transfer switch starts the genset and then connects the sub panel with the protected loads. Generator voltage/frequency, if withing the GT inverter's specification, will allow the GT inverter to sync and start feeding power to the grid... And then the fun begins...

    First, the voltage/frequency/waveform needs to be qualified and stable for >5 minutes by the GT inverter before it turns on. The frequency is +/- 0.5 Hz or so--And many generators can drift outside of that frequency tolerance range... So, the GT inverter may never "turn on" if the generator frequency wanders too much (not all generators can hold these tight frequency tolerances).

    Second, the GT inverter turns on and starts feeding ~5-6 kWatts or so into the protected sub panel. If your loads are greater than the GT inverter's output, all is "OK". However, if the loads are less than the GT inverter's power output, the extra power will try to "run backwards" through the generator. That is not a good thing.

    The generator could over speed (and shut down the GT inverter for fine minutes/fault the genertor), could over voltage (shut down GT inverter for five minutes/fault generator), or start feeding current backwards through the alternator/regulator (and possibly let the magic smoke out of the generator).

    At this point, I do not know if a good/safe/reliable method to make a pure GT Inverter + Generator play together unless you are going to somehow actively manage your loads to prevent the GT inverter from backfeeding your genset.

    There are other methods that can be done to make solar+generator play together nicely... But that usually involves a "Hybrid" AC inverter (GT+off grid capable AC inverter) and battery bank. This can be expensive and may not be cost effective if your power failures are rare/short term.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jer19545
    jer19545 Registered Users Posts: 4
    Re: 6.5kw solar system with a 20kw briggs standby generator

    thanks, one question when the power goes out the gt inverter stops producing a/c, the generator starts producing a/c, the gt inverter knows not to produce a/c till the commercial power is restored? how?????????
  • jer19545
    jer19545 Registered Users Posts: 4
    Re: 6.5kw solar system with a 20kw briggs standby generator

    sorry, i didn't answer your first question. gt inverter, no battery. i'm going to assume the gt inverter will tie in to the line side of the transfer switch & the generator to the load side.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: 6.5kw solar system with a 20kw briggs standby generator
    jer19545 wrote: »
    thanks, one question when the power goes out the gt inverter stops producing a/c, the generator starts producing a/c, the gt inverter knows not to produce a/c till the commercial power is restored? how?????????

    It all depends on where the GTI connects to the wiring:

    GRID --- GTI ---- TRANSFER SWITCH/GEN INPUT ---- LOADS

    Grid goes down, transfer switch changes loads from grid & GTI to gen output.
  • jer19545
    jer19545 Registered Users Posts: 4
    Re: 6.5kw solar system with a 20kw briggs standby generator

    right now, the generator & transfer switch are not yet installed, the GTI is connected to a 30amp 240v breaker in the mail breaker panel. the question is when the generator & transfer switch is installed, will i connect the GTI to the line side of the transfer switch. i have a licensed electrician that will connect the generator, i'm just tiring to get me head wrapped around this install. i'm looking for the questions to ask the electrician. thanks john
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: 6.5kw solar system with a 20kw briggs standby generator

    You don't want the GTI to connect to the generator as per Bill's explanation.