Is the transfer switch auto?
Many have an aux relay in there. Could you use that to shut off the PV.
I’m a bit unclear as to the physical layout.
Jay 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, 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 < [email protected]> 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
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
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