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Thread: Solar - Generator connection

  1. #11
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    Quote Originally Posted by Chamuit View Post
    Are there any code issues? Or are they just operational?
    I am not aware of any direct code violation. If there is, I would guess it would be in 702 or 705. Note that this would be perfectly fine with the right equipment and/or controls.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  2. #12
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    Quote Originally Posted by electrofelon View Post
    I am not aware of any direct code violation. If there is, I would guess it would be in 702 or 705. Note that this would be perfectly fine with the right equipment and/or controls.

    Thanks. I didn't see anything that would prohibit the hook up to be arranged that way. I did call Generac and they said that the unit attach is not designed to work with solar. They do have models (controllers) that would work with solar like this.

  3. #13
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    Somewhere in 705 it says that interactive sources must be 'compatible'. One could make the case that is a violation here.

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    There's nothing in the NEC that says you can't connect a generator in parallel with a PV system, which is good because there are cases where it is the desired design. Remember 90.1(B), the purpose of the code is safety, not keeping the equipment working. That's the job of the system designer or engineer.

    Having a generator and PV in parallel is not a guarantee that one will damage the other, it just creates the condition under which one can damage the other. Under the right conditions these two can get along fine, but those conditions are not usually maintained if they are not designed in.

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    Quote Originally Posted by pv_n00b View Post
    There's nothing in the NEC that says you can't connect a generator in parallel with a PV system, which is good because there are cases where it is the desired design. Remember 90.1(B), the purpose of the code is safety, not keeping the equipment working. That's the job of the system designer or engineer.

    Having a generator and PV in parallel is not a guarantee that one will damage the other, it just creates the condition under which one can damage the other. Under the right conditions these two can get along fine, but those conditions are not usually maintained if they are not designed in.
    Well said. For example, a Sunny Boy, Sunny Island, and generator system can work really well off grid because the SI arbitrates between the SB and the genny, throttling back the SB when the batteries are full and the loads are less than the available output from the SB.

  6. #16
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    Quote Originally Posted by pv_n00b View Post
    There's nothing in the NEC that says you can't connect a generator in parallel with a PV system, which is good because there are cases where it is the desired design. Remember 90.1(B), the purpose of the code is safety, not keeping the equipment working. That's the job of the system designer or engineer.

    Having a generator and PV in parallel is not a guarantee that one will damage the other, it just creates the condition under which one can damage the other. Under the right conditions these two can get along fine, but those conditions are not usually maintained if they are not designed in.
    Remember that PV already operates in parallel with a generator. It just so happens to be called “The Grid”. Remember also that all grid-interactive PV is designed to disconnect when “The Grid” goes outside of specification, which is actually rather tight. Very few non-inverter generators can hold frequency and voltage well enough to keep an inverter running.
    Julie in Austin

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  7. #17
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    But, unlike a small discrete generator, the grid can sink significant power when needed. It gets redistributed to non-local loads and/or causes the generators feeding the grid to reduce their output.

    Sent from my XT1585 using Tapatalk

  8. #18
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    Quote Originally Posted by tallgirl View Post
    Remember that PV already operates in parallel with a generator. It just so happens to be called “The Grid”. Remember also that all grid-interactive PV is designed to disconnect when “The Grid” goes outside of specification, which is actually rather tight. Very few non-inverter generators can hold frequency and voltage well enough to keep an inverter running.
    That hasn't been my experience. I used to teach an off grid lab at ImagineSolar with a Sunny Boy, a Sunny Island, and a run-of-the-mill Generac generator. The SB ran just fine when the SI was in pass-through mode with the genny as the grid.

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    Quote Originally Posted by ggunn View Post
    That hasn't been my experience. I used to teach an off grid lab at ImagineSolar with a Sunny Boy, a Sunny Island, and a run-of-the-mill Generac generator. The SB ran just fine when the SI was in pass-through mode with the genny as the grid.
    If the generator is able to produce a stable enough voltage and frequency signal the anti-islanding logic in the Sunny Boy won't know it doesn't have an actual grid. It's definitely possible, especially with larger generators where the rotational mass helps to stabilize things, but extremely unlikely with crappy "alternator generators" like what you buy in a Blue or Orange store for a few hundred bucks.

    I don't know how SMA's anti-islanding logic works, but the usual approach is to try changing the grid frequency. If successful, the inverter assumes it's islanded and MUST trip. If not, the inverter will continue to run so long as the generator is within voltage and frequency for the rest of the intertie requirements.
    Julie in Austin

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  10. #20
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    Quote Originally Posted by GoldDigger View Post
    But, unlike a small discrete generator, the grid can sink significant power when needed. It gets redistributed to non-local loads and/or causes the generators feeding the grid to reduce their output.

    Sent from my XT1585 using Tapatalk
    So long as the PV system's output is less than the loads, the generator will back off the same as if the connected loads were reduced.

    Automatic grid controls are actually pretty trick -- the more the instantaneous imbalance is too much supply, the faster (in very tiny amounts) the generators rotate, converting excess power into additional rotational energy, increasing frequency. The rise in frequency is detected causing some of the generators to reduce output. When the imbalance goes the other way, the deficiency is met by rotational energy in the generators being converted to electricity and a lower frequency. That frequency drop is detected and those same generators increase their output.

    Each grid has its own "inertia" -- in the Texas (ERCOT) grid, a change of supply or demand of 450MW produced a frequency change of 0.1Hz under normal conditions.
    Julie in Austin

    Born to brew, forced to work ...

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