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 < [email protected]> 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 <[email protected]> > *Sent:* Monday, January 26, 2026 3:28:04 PM > *To:* RE-wrenches <[email protected]> > *Cc:* [email protected] <[email protected]> > *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 > > CA License C-10 77398 > > > > *From:* RE-wrenches [mailto:[email protected]] *On > Behalf Of *scot.arey--- via RE-wrenches > *Sent:* Wednesday, January 21, 2026 12:45 PM > *To:* RE-wrenches > *Cc:* [email protected] > *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 <[email protected]> on behalf > of Jason Szumlanski via RE-wrenches <[email protected]> > *Sent:* Wednesday, January 21, 2026 2:33 PM > *To:* RE-wrenches <[email protected]> > *Cc:* Jason Szumlanski <[email protected]> > *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 < > [email protected]> 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 < > [email protected]> 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 < > [email protected]> 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 > > [image: cid:[email protected]] > > > > _______________________________________________ > List sponsored by Redwood Alliance > > Pay optional member dues here: http://re-wrenches.org > > List Address: [email protected] > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > There are two list archives for searching. 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When one doesn't work, try the > other: > https://www.mail-archive.com/[email protected]/ > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > http://www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > http://www.members.re-wrenches.org > > > _______________________________________________ > List sponsored by Redwood Alliance > > Pay optional member dues here: http://re-wrenches.org > > List Address: [email protected] > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > There are two list archives for searching. When one doesn't work, try the > other: > https://www.mail-archive.com/[email protected]/ > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > http://www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > http://www.members.re-wrenches.org > >
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