Yes, that’s the way to do it. I suppose there is still the chance, however, that the grid could still be present, but the transfer switch is still in off-grid mode (like if the main breaker is turned off for some reason). That could still result in AC coupled solar backfeeding a generator if close attention is not paid to the relay coil source relative to all disconnects in a system.
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 Tue, Jan 27, 2026 at 1:07 PM William Miller <[email protected]> wrote: > The design relies on a relay relaxing upon *loss* of grid voltage. This > is fail-safe. > > Furthermore, Enphase can be configured to send an email if production is > lost so if the system fails as it should, in the no-production state, > someone gets notified. > > > > William Miller > Miller Solar.com > 805-438-5600 > www.millersolar.com > > > On Tue, Jan 27, 2026 at 9:17 AM Jason Szumlanski via RE-wrenches < > [email protected]> 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 < >> [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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