[RE-wrenches] Will IQ8 microinverters backfeed a generator during grid interruptions
Dave Angelini Offgrid Solar
offgridsolar at sti.net
Tue Jan 27 10:02:28 PST 2026
The failsafe for me offgrid, is the owner has to know how to do these
things. I say bye bye if they are not capable. Sleep really well with
the independance concept.
Dave Angelini Offgrid Solar
"we go where powerlines don't"
[2]https://offgridsolar1.com/ [3] [2]
e-mail offgridsolar at sti.net
text 209 813 0060
On 2026-01-27 9:14 am, Jason Szumlanski via RE-wrenches wrote:
> I don't like to install anything that isn't failsafe for this purpose,
> so if it relies on a NC relay opening upon receiving generator voltage,
> I usually won't consider it because the relay can fail. And if the
> relay fails, there is no indication of that (other than the adverse
> effects that might happen).
>
> That's just my opinion, but I can understand fringe scenarios where
> there just isn't a way to get the solar connected on the line side. As
> long as the customer signs off on the risks, I would do it, but
> cautiously.
>
> 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 Mon, Jan 26, 2026 at 4:41 PM Howard Scot Arey via RE-wrenches
> <re-wrenches at lists.re-wrenches.org> wrote:
>
> Interesting. Somebody else recommended a web-based version of what you
> did. You were ahead of the times. I might pursue this with the web
> option...not the radios. Same concept - different technology.
>
> Thank you.
>
> Howard "Scot" Arey
> Owner, Solar CenTex
>
> NABCEP PV Installation Professional
> TECL 29755
> 254-300-1228
>
> -------------------------
>
> From: William Miller <william at millersolar.com>
> Sent: Monday, January 26, 2026 3:28:04 PM
> To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
> Cc: scot.arey at solarcentex.com <scot.arey at solarcentex.com>
> Subject: RE: [RE-wrenches] Will IQ8 microinverters backfeed a generator
> during grid interruptions
>
> Friends:
>
> I had the same problem: Enphase arrays on an outbuilding which was
> connected to the generator side of a transfer switch. I had no
> independent power path from the grid to the outbuilding so the Enphase
> had to be connected to the load side of the transfer switch. When the
> large generator was powering the facility and the sun was out the
> generator acted wonky (unstable voltage).
>
> My solution was to buy a transceiver set (National Control Devices
> MlrXR2x). I powered one radio from the grid side of the transfer
> switch and the other radio controlled a contactor on the remote Enphase
> feeders. When the grid goes down the contactor opens.
>
> The radios were inside of two buildings and the reception was
> borderline. I augmented the included 900 mHz rubber duckies by
> replacing them with panel antennas from Pasternak. So far the system
> is operating as intended.
>
> If anyone wants details let me know.
>
> William
>
> William Miller
>
> Miller Solar
>
> www.millersolar.com [1]
>
> CA License C-10 77398
>
> From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On
> Behalf Of scot.arey--- via RE-wrenches
> Sent: Wednesday, January 21, 2026 12:45 PM
> To: RE-wrenches
> Cc: scot.arey at solarcentex.com
> Subject: Re: [RE-wrenches] Will IQ8 microinverters backfeed a generator
> during grid interruptions
>
> 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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[1] http://www.millersolar.com/
[2] http://members.sti.net/offgridsolar/
[3] https://offgridsolar1.com/
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