[RE-wrenches] Will IQ8 microinverters backfeed a generator during grid interruptions

Wed Jan 21 15:39:47 PST 2026

Hi Scot -

I would think that the easiest solution is to just tie the solar into the
utility side of the ATS. I understand that is what you are trying to avoid.
Otherwise, you could set up the PV system in non-export
<https://enphase.com/download/power-export-limit-iq7-and-iq8-series-microinverter-systems>,
but that would negate potential NEM or utility excess energy credits, if
they exist in your neck of the woods. Otherwise I think it is potentially
bad news to backfeed a generator! I just had an electrician call me on a
site where this happened and it caused voltage instability on the site.

Best, August

On Wed, Jan 21, 2026 at 12:47 PM scot.arey--- via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Thanks but I'm just trying to grid-tie a small Enphase array without ESS
> where the point of interconnection is on the customer side of the
> generator/ATS.
>
> Trying to use existing wires in place to simplify and lower costs...but
> the generator is my constraint because I need the PoI to be on line side of
> the ATS.
>
> *Howard "Scot" Arey*
> *Owner, Solar CenTex*
> 254-300-1228
>
> ------------------------------
> *From:* RE-wrenches <re-wrenches-bounces at lists.re-wrenches.org> on behalf
> of Jason Szumlanski via RE-wrenches <re-wrenches at lists.re-wrenches.org>
> *Sent:* Wednesday, January 21, 2026 2:33 PM
> *To:* RE-wrenches <re-wrenches at lists.re-wrenches.org>
> *Cc:* Jason Szumlanski <jason at floridasolardesigngroup.com>
> *Subject:* Re: [RE-wrenches] Will IQ8 microinverters backfeed a generator
> during grid interruptions
>
> I should have also noted that Enphase DOES allow use of a generator with
> its System Controller 3G, and supposedly the inverter, battery, and
> generator sources can all power loads simultaneously, so I could be wrong
> about how the IQ8s work. That said, Enphase has strict pairing
> specifications and an approved generator list. They seem confident in their
> ability to limit backfeed to the generator in this scenario.
>
>
> Jason Szumlanski
> Principal Solar Designer | Florida Solar Design Group
> NABCEP Certified Solar Professional (PVIP)
> Florida State Certified Solar Contractor CVC56956
> Florida Certified Electrical Contractor EC13013208
>
>
> On Wed, Jan 21, 2026 at 3:16 PM William Bryce via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
> If the AC coupled exported energy is more than the generator produced
> energy, it can destroy the generator controller.
> That is why most AIO inverters have a relay on the dedicated AC coupling
> input. It will open the relay if the inverter sees generator power.
>
> The MNP AIO will allow both inputs, but will open the relay if the AC
> coupled power increases to 20% of the Generator input (firmware dependent).
>
>
> On Wed, Jan 21, 2026 at 2:27 PM Jason Szumlanski via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
> Enphase IQ8 microinverters will absolutely leak some power back to the
> grid when set to a no-export grid profile. How much, and if that is
> detrimental to the generator is another question. I suspect if the
> generator is large enough relative to the PV array, the impact will be nil,
> but I would not take the risk.
>
> I don't think the fast switching really does the trick in terms of not
> exporting. That function relies on the consumption CTs connected to the
> Gateway, which in turn communicates with the microinverters. Aside from the
> CTs not being totally accurate, I don't see how that communication loop
> could be fast enough.
>
>
> Jason Szumlanski
> Principal Solar Designer | Florida Solar Design Group
> NABCEP Certified Solar Professional (PVIP)
> Florida State Certified Solar Contractor CVC56956
> Florida Certified Electrical Contractor EC13013208
>
>
> On Wed, Jan 21, 2026 at 12:09 PM scot.arey--- via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
> Good day,
>
> I many years ago watched the fast-switching capabilities of the IQ-8
> microinverters to produce only what demanded of the MI, and wondered if it
> might have application in a grid-tied system that is served by a
> whole-house generator.
>
> We have the opportunity to install grid-tied-only array of 24 IQ8 but all
> the MIs will be on the customer side of an auto-transfer switch and
> generator. We want to leverage using existing building wiring to carry the
> solar and all solar sizing meets the 120% rules.
>
> But I know that grid-tied solar on the customer load-side of the transfer
> switch means no place for full solar power production to flow to when the
> grid is not available...but  then I thought back to that fast switching
> capability: is there a way to ensure the IQ8 don't backfeed a generator
> when it is operating for a grid anomaly?
>
> I suspect the answer is "are you nuts???" but that video of capability got
> me thinking, "why not?" and if not, how is it - what tells the MI to cease
> production? - when it is within a full and proper ISC/ESS system design?
>
>
>
> *Howard "Scot" Arey*
> *Owner, Solar CenTex*
>
> NABCEP PV Installation Professional
> TECL 29755
> 254-300-1228
>
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