Generac and Solar

I will be installing a Generac generator this fall and then a solar system (using IQ7 microinverters) some time next year. When I wire the house for the generator I want to go ahead and have it ready so I can easily tie to the solar system. How do I do this?


  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    The general answer is that Grid Tied Inverter (utility interactive) need a very stable source of voltage, sine wave, and frequency.

    Frequency stability is one of the biggest issues--Typically 60 Hz +0.5/-.7 Hz for utility interactive gensets. And most mechanically governed gensets are >+/- Hz (upwards of +/- 5Hz in.

    Many/most GT inverters have specifications for "acceptable" AC voltage/frequency/etc... But I have not seen any that can be "switched" between Utility/Genset AC power...

    The other big issue tends to be--Most AC Gensets can be very "unhappy" when back-fed power from GT inverters (i.e., GT inverter is outputting 3,000 Watts, House is using 1,000 Watts, genset is "expected" to absorb 2,000 Watts)...

    So--The typical setup is that the GT/UI inverters are directly to the "Grid", and AC gensets are connected "after" the AC Transfer switch (genset only sees "house loads" and does not see Utility/GT Inverter power). Normally, you cannot use your solar power with GT/UI inverters and have them reduce genset fuel usage.

    Not to say it cannot be done, but you need to ensure that you have "comparable" hardware together.

    The typical solution for residential is to use a "hybrid" inverter, a battery bank, solar array, charge controller, genset...

    The Hybrid inverter is capable of Utility Interactive/Grid Tied operation (can feed back energy to the grid from a solar array), and if the utility power fails, the Hybrid Inverter switches from Utility to Off Grid Inverter operation--Taking energy from the battery bank and solar array to power the house loads. (solar array -> solar charge controller -> battery bank). The Hybrid inverter can also manage solar/battery state of charge/genset autostart/run function.

    Batteries make the system much more expensive (batteries are not cheap)--Plus batteries wear/age out/damaged and need to be replaced every X years).

    If you do not have a lot of outages, or very long outages... Keeping it simple (no batteries, just genset for backup power) keeps things simple ... Note that "simple" is usually easier/cheaper to debug and repair.

    The "standard" GT Inverter (solar->inverter->AC mains) only "work" to reduce your utility ubill when the utilty is connected and working. During power failures, the GT Inverter shuts down (required by utility/regulations) to ensure that linemen are not electrocuted.

    There are some GT Inverters that have "backup" AC power available. Those can supply 1,000-2,000 Watts or so--When the sun is up high, and cloud free weather. If the light is reduced (not middle of day and/or clouds/bad weather), you can only run reduced loads to match the reduced solar array harvest (few hundred watts or less??).

    I am certainly not keeping up with the latest and greatest available hardware (there are some Hybrid Inverters that can run without a battery bank--Don't know how it integrates with a genset)...

    Figure out what you want for power (how much, backup power from solar/genset/batteries)--How much do you want to pay--And will you have help/professional installation and maintain or will this be more of a do-it-yourself type system?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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