How to AC couple Enphase IQ8 w/Battery Storage to Schneider XW Pro 6848 w/rack batteries, off-grid?

AC Coupling Testing:
The XW 6848 can inject up to 140 A into the battery. With an approximate 5:1 DC/AC ratio, that gives us a max AC of about 28 A.
Any PV AC current higher than that is not possible with no backup loads. In reality, depending on the battery config and SOC it will be a lot less.

A good test would be to start with SOC about 50%, have loads on the backup panel, low solar irradiation and then turn on a substring of the PV arrays with less 20A or less and see if the IQ8's lock on and stay on and watch InsightHome and IQ gateway how the power flows.

It will take me a few more weeks before I'm ready to test all of this with a real system and I am just starting to test AC coupling with single inverters.
Adding Hoymiles micro-inverters to the inverter test mix.

wheisenburg:
Great setup with wireways! Very professional!

You could also monitor the frequency and AC voltage for any signs of FW or VV or VW by the Schneider.
You have a stacked dual Schneider XW setup, but I'm not sure the stack can handle more than 30 A max of PV power without significant consumption by loads. The master will accept the backfeed, but the slave probably not.

Interestingly, systems with a PV disconnect relay work well with IQ8's. But they do not use AC coupling with FW, VV or VW.

solar8484 said:

The iQ7 is also UL1741SA and SB compliant. The main difference is that iQ8 can be operate in grid forming mode if deployed with the iQ System Controller. So, the assumption is that iQ8's AC coupled with hybrid inverters are not setup with an iQ System Controller and never operate in the grid forming mode. Otherwise, conflict between 2 disparate grid forming inverters would certainly be problematic.

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Well when AC coupled with the Schneider acting like a grid, the micros should be able to sync to the Schneider and be in Grid following mode. Even though some of the profiles are supposed to have the Anti-islanding turned off, it still doesn't work. I actually had a choice when installing my system. I could have gone with the IQ7+ which does seem to work with AC coupling. The industry does seem really good about telling you something won't work until you've spent a lot of money on it.

DER Solar said:

wheisenburg:
Great setup with wireways! Very professional!

You could also monitor the frequency and AC voltage for any signs of FW or VV or VW by the Schneider.
You have a stacked dual Schneider XW setup, but I'm not sure the stack can handle more than 30 A max of PV power without significant consumption by loads. The master will accept the backfeed, but the slave probably not.

Interestingly, systems with a PV disconnect relay work well with IQ8's. But they do not use AC coupling with FW, VV or VW.

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Well as it turns out, I have a large 65 amp 4 pole contactor installed in my system. It is there to allow me to feed the system with a generator. Schneider says you can't run PV and Gen at the same time. It has two NO and two NC contacts (these are 4 fully separate paths not a two pole double throw). So the gen is routed through the NO to the AC2 input and the PV goes through the NC to the Inverter out. The gen AC is used to energize the contactor which has a 240 volt AC coil. This disconnects PV and connects the Gen. The Schneider has a "Aux Control Out" that can be selected to turn on based on various conditions. One of the is "Battery over X volts". I could logically "OR" these two signals together with a couple of small control relays so that the PV would disconnect on either high battery voltage or gen detected.

So to get this to work you use a profile that just produces full power without the Frequency Shifting? You still need to couple the PV output with the inverter output. If I ever do need to operate "Off Grid" for an extended period I could turn off one of the 3 strings. I have assumed that both inverters would word in parallel to convert the AC to DC and charge the battery. Do you think it is the Frequency shifting on the Schneider causing the issues or the profile on the PV inverters?

This is my first solar install. I've done some electrical work and have an engineering back ground.

I am a certified FranklinWH system designer and installer, but only to fully understand what these systems can do.
They have IQ8 installations and AC coupling is a must.
But they do not use frequency-watt shifting, only PV hard on/off. I think they need to do this so they can use the main locally required grid profile for grid-tied and off-grid without the need to switch the protocols. Having a specific protocol to make AC coupling work is not ok for regions that require a specific protocol.

Just the fact that Enphase can remotely reset the IQ system controller and get your system running again tells me that the IQ controller is actively managing the IQ8 inverters.
You can contact Eric Bentsen at Schneider and ask him about AC coupling of IQ8 inverters.
And ask him about the slave inverter if it is using the AC coupling and charging the batteries, I don't think so.

wheisenburg said:

Well when AC coupled with the Schneider acting like a grid, the micros should be able to sync to the Schneider and be in Grid following mode. Even though some of the profiles are supposed to have the Anti-islanding turned off, it still doesn't work. I actually had a choice when installing my system. I could have gone with the IQ7+ which does seem to work with AC coupling. The industry does seem really good about telling you something won't work until you've spent a lot of money on it.

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Frankly, I don't understand why people get iQ8's over iQ7's with hybrid inverters. I don't really see a way to use the extra functionality in iQ8 with hybrid inverters.

Have you asked Enphase for further help? They are typically willing to create custom profiles to help resolve AC coupling problems. I am guessing there are new profiles parameters for iQ8's that didn't exist in profiles created previously.

For now, you have a point for choosing IQ7 over IQ8, but there are others on this forum who have problems lately with AC coupling of IQ7's too.
It may depend on the firmware loaded. IQ7 and IQ8 inverters are or can be firmware upgraded to be compliant with IEEE 2030.5. These new standards require implementation of active power controls. Since Enphase knows exactly where inverters are located, they can pick and choose what get's upgraded. That's why I like Schneider so much: I can download a firmware upgrade from a list of available versions and upgrade an XW without the need for any internet connection. And to do this safely without risking bricking the inverter, I disconnect all Xanbus devices except InsightHome, disconnect the inverter from the grid and put the InsightHome external power supply on a separate UPS.

SunSpec Registry

Enphase is a supporter of SunSpec, but none of their inverters are on the certified list. Hoymiles inverters are!
Someone will crack open how it is done, or Enphase will be forced to publish it or open it up. The published API for accessing the IQ gateway does not expose any IEEE 2030.5 power controls.

Found this in an earlier document on AC coupling with XW inverters:

"Some legacy implementations of antiislanding protection on PV inverters use a grid impedance check as a mechanism to detect a failed grid. Battery inverters typically have higher output impedance compared to the grid, and this impedance might render the system incompatible."

IQ8's do work with the NFT in the IQ system controller. Intuitively, I would assume that the NFT and the Schneider toroidal transformer have similar impedances, but may be not. There is a relay between the NFT and the NFT breaker in the IQ controller, not sure what function it has, must be on during backup. What happens if the NFT breaker trips? Or is the NFT relay always open during grid operations? Then it must close before the MID disconnects from the grid.

Here is the response from product support @ Schneider Electric:

IQ7 and IQ8 AC Coupling:
Enphase has a fix for IQ7 inverters, but is still working on a fix for IQ8 inverters

Smart AC Coupling:
Smart AC coupling for stacked XW Pro inverters is under consideration, but not yet implemented.

DER Solar said:

Here is the response from product support @ Schneider Electric:

IQ7 and IQ8 AC Coupling:
Enphase has a fix for IQ7 inverters, but is still working on a fix for IQ8 inverters

Smart AC Coupling:
Smart AC coupling for stacked XW Pro inverters is under consideration, but not yet implemented.

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It would be even better if Schneider can put out a tech note on specific recommended settings (e.g. profiles) for Enphase.

Given that Enphase is working on the fix helps explain the iQ8 problem with other hybrid inverters. I would be interested to see specific info on how FranklinWH can reliably AC couple iQ8 while other hybrid inverters can't. I don't think the shutoff relay can make that much difference.

Good feedback:

Enphase is in control of the profile for IQ inverters, not Schneider. I do not think it is Schneider's responsibility to find a grid profile that works with Enphase. In my view, it should work with all profiles utilities allow in a specific regions.

All they need to do is pass UL1741 SA testing by a lab, like UL, or Intertek or ETL, and get certified. And Enphase must be UL1741 SA or UL1741 SB compliant for utility requirements in specific regions, with SA being a subset of SB. So all Inverters with UL1741 SB compliance are or should automatically be SA compliant. If it doesn't work, then either Schneider or Enphase or both are not totally compliant, my best guess? Most likely Enphase.

Let's not forget that a firmware upgrade for a Schneider XW inverter is never done OTA without your consent! You are in charge when the upgrade gets done! Not so with Enphase!

I do not know how FranklinWH is able to AC couple with Enphase IQ8's. But the PV relay is key: it is closed during normal grid operations. On a grid fault, the AC batteries have enough reserve to handle the inrush AC current from the PV. When they are full with insufficient backup load, the PV relay opens. When the battery charge drops and with sufficient load, the PV relay closes. They can work with any grid-tied inverter by presenting the AC reference for a stable micro-grid. As with any off-grid inverter, an AC battery/inverter does not need to actively provide FW, FV or VW like a utility. With UL1741 SB open standard power controls, micro-inverters , AC batteries and AC coupled inverters will be able to integrate very well in the future with these emerging open standards.

DER Solar said:

Good feedback:

Enphase is in control of the profile for IQ inverters, not Schneider. I do not think it is Schneider's responsibility to find a grid profile that works with Enphase. In my view, it should work with all profiles utilities allow in a specific regions.

All they need to do is pass UL1741 SA testing by a lab, like UL, or Intertek or ETL, and get certified. And Enphase must be UL1741 SA or UL1741 SB compliant for utility requirements in specific regions, with SA being a subset of SB. So all Inverters with UL1741 SB compliance are or should automatically be SA compliant. If it doesn't work, then either Schneider or Enphase or both are not totally compliant, my best guess? Most likely Enphase.

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I agree in principle but hybrid inverter vendors (Schneider, Outback, etc.) are stating AC coupling compatibility with UL1741-xxx compliant grid-tied inverters and Enphase micros certainly have the UL certs. So, it's reasonable to assume the hybrid inverter vendors have at least partial responsibility to ensure compatibility. Otherwise, you get rightfully dissatisfied customers like @wheisenburg.

DER Solar said:

I do not know how FranklinWH is able to AC couple with Enphase IQ8's. But the PV relay is key: it is closed during normal grid operations. On a grid fault, the AC batteries have enough reserve to handle the inrush AC current from the PV. When they are full with insufficient backup load, the PV relay opens. When the battery charge drops and with sufficient load, the PV relay closes. They can work with any grid-tied inverter by presenting the AC reference for a stable micro-grid. As with any off-grid inverter, an AC battery/inverter does not need to actively provide FW, FV or VW like a utility. With UL1741 SB open standard power controls, micro-inverters , AC batteries and AC coupled inverters will be able to integrate very well in the future with these emerging open standards.

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I understand the purpose of the relay but the reported iQ8 AC coupling problems are with the initial grid-tied inverter power ramp up well before any condition that requires frequency shift or relay shutoff. FranklinWH compatibility with iQ8 seems doubtful. A quick search also shows no example of Tesla Powerwall working with iQ8.

solar8484 said:

I agree in principle but hybrid inverter vendors (Schneider, Outback, etc.) are stating AC coupling compatibility with UL1741-xxx compliant grid-tied inverters and Enphase micros certainly have the UL certs. So, it's reasonable to assume the hybrid inverter vendors have at least partial responsibility to ensure compatibility. Otherwise, you get rightfully dissatisfied customers like @wheisenburg.

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My Solar Edge inverter is happy as a clam to AC couple to the Schneider XW pro. The issue is on the Enphase side, in my opinion.

Solar Enthusiast: Submitting a micro-inverter or hybrid inverter to UL testing with a specific firmware version required to pass testing for a specific standard is one thing, deploying a different firmware version in a region that does not require it is something else. Schneider, Outback and all micro-inverter manufacturers etc. certainly pass UL testing for a specific standard and get certified because they have to be grid compliant!

But here is the difference: they have to react to what the main grid generator, aka utility, is doing according to the standard. There is no standard how to test micro-grid compliance, i.e. the micro-inverter or the hybrid inverter takes on the role as the micro-grid defining AC reference source. Micro-grid impedance is a big unknown and probably unspecified. And that is not the objective for UL 1741 testing. It took me a while to figure this out and I may have this totally wrong.

So you can have 2 inverters, both UL1741 xx compliant, a micro-grid grid-forming reference generator and a micro-grid ac coupled "follower". Huge difference, it may work not at all, or one way, or both ways. This is what I am beginning to understand is the real issue. One participating party has to show to the other who is not in total compliance with the standard. And the standard may not even cover the non-compliant micro-grid forming detail.

Enphase has a big monopolistic advantage: they own the micro-grid forming IQ8 inverter as both an AC reference generator and as an AC coupling "follower". May be it is time for the regulators to step in!

Powerwall:
The gateway/load panel has no PV relay disconnect! But it is a nice metal load panel with a Gruner MID 200A relay and a pre-MID 200A feed-through plus an Eaton 200A optional "mutilated" busbar for either non-backup loads or backup loads, unlike the Enphase IQ controller! The Enphase IQ controller cannot support pre-MID non-backup loads if installed as the main panel!

By the way, Tesla opened up direct ordering of Powerwalls by home owners online over the weekend, 2023-03-10. There is a catch: you need a certified installer to do the install and/or final commissioning. Because Tesla infuriated and hung out dry so many installers last year, there are not many installers willing to perform an install or commissioning where the home owner has ordered the hardware! My best guess: Tesla, aka EM, will allow homeowners to perform their own commissioning. That will really get competitive! Especially if Tesla will be transitioning to more safe LiFePo4 batteries! Going to be a wild ride! One thing EM does very well except Twitter: sense which direction the wind is blowing to!

400bird said:

My Solar Edge inverter is happy as a clam to AC couple to the Schneider XW pro. The issue is on the Enphase side, in my opinion.

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You are absolutely right!

400bird said:

My Solar Edge inverter is happy as a clam to AC couple to the Schneider XW pro. The issue is on the Enphase side, in my opinion.

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Agreed but if I called Schneider sales today and asked them if the XW Pro can AC couple with Enphase what do you think they will tell me?

DER Solar said:

A common thread in backup systems which can successfully AC couple with IQ8's is the PV disconnect relay:
IQ systems controller 1 (no relay) versus IQ system controller 2 (has 64 A PV relay)
FrankinWH aGate (has a 64 A PV relay)
CSI EP Cube (has 2 relay-controlled extension ports)

solar8484: The name plate UL listing is UL 1741SA. The firmware upgrade can upgrade them UL1741SB, and that is controlled by Enphase.
Would be interesting to find out what the actual firmware is in an IQ8 versus and IQ8 with Enphase backup.

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The issue of Enphase doing something special to make their inverters AC couple when installed as part of their backup solution is an interesting one. The fact that they support a "Daylight Backup Mode" means the key "secret ingredient" is not the batteries. You need their System Controller for this. I don't have one of those but I know it serves as a central connection point for the inverters, the grid, the batteries, a generator, and the load. So maybe they have a dedicated "Grid Forming Inverter" in the controller or one specific "Grid Forming Inverter" is chosen from your PV array. I'm not sure if the controller box has a small battery in it. If it does it could continue to manage things and communicate even when there is no PV available.

If they actually install special firmware as part of the backup configuration that allows these PV inverters to work, that tends to indicate that their failure to operate when not part of a backup solution is deliberate. Never the less, it does appear that they are actually "Trying to fix this". They already have it working for IQ7s. As far as it working for Stacked Schneider Inverters, they are saying one inverter can handle PV that is 125% of the inverter rating or around 8500 watts. That should be enough for my array. If required in a prolonged outage, I could switch to a single inverter mode and just isolate the second inverter. I have some east and some west facing panels so I will never have all of my PV working at 100%. Still it will be close to the 8500 watts in the middle of summer, which is why I figured I needed two. I don't think I need two for consumption, unless I run my drier and my wall oven at the same time. Not something I would need in an outage.

solar8484 said:

Agreed but if I called Schneider sales today and asked them if the XW Pro can AC couple with Enphase what do you think they will tell me?

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I'm pretty sure Schneider would say they support AC coupling with any capable (and under 6kw) grid tie inverter. The fact that one specific brand (Enphase) doesn't work with both SolArk and Schneider says to me that the Enphase equipment is doing something funky.

wheisenburg said:

The issue of Enphase doing something special to make their inverters AC couple when installed as part of their backup solution is an interesting one.

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Enphase uses power line communication to control their micro inverters.

To AC couple with a 3rd party inverter requires testing and verifying the local grid, just like wider grid from the power company.

400bird said:

I'm pretty sure Schneider would say they support AC coupling with any capable (and under 6kw) grid tie inverter. The fact that one specific brand (Enphase) doesn't work with both SolArk and Schneider says to me that the Enphase equipment is doing something funky.


Enphase uses power line communication to control their micro inverters.

To AC couple with a 3rd party inverter requires testing and verifying the local grid, just like wider grid from the power company.

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The fact that their older inverters seem to work just fine, and other brands of inverters also work seems to indicate that Enphase has an issue, deliberate or not. There is a spec for F/W curves that their inverters should be following when AC coupled to battery inverters. Simply shutting off and refusing to work does not comply with specs they say they have implemented.

SMA systems have always used grid-forming SI with an SB in either "off-grid" or "backup" mode; in that case SB no longer performs anti-islanding.
With their latest -41 series SB, SMA's official documentation says to put it in "Rule 21" for grid backup.
But SMA America's videos have now said to use "backup" mode when SB -41 is behind SI. This suggests they too have some issues with even their own UL-1741-SA compliant GT PV inverters.

Those issues may be with anti-islanding. Although, I never had problems with that, just lack of gradual curtailment, using older UL-1741 SB. Another possible issue is curtailing to zero output, which might knock it offline for 5 minutes.

SMA also has HF (and HV) battery inverter SBS, which works with SB. In that case, it is possible Speedwire (Ethernet) is used to change settings. Haven't read comment of issues. But I suspect it sees fewer backup installations than does SI.

400bird said:

I'm pretty sure Schneider would say they support AC coupling with any capable (and under 6kw) grid tie inverter.

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That's my expectation as well and a problem. Anyone looking to decide on equipment purchase for a new system getting such info could easily make an expensive mistake (e.g. buying iQ8's vs iQ7's or SolarEdge). On the other hand, if Schneider (and other hybrid inverters) just published a list of compatible or incompatible grid-tied inverter models it could help prevent such mistakes and have more happy customers. Note, this does not mean hybrid inverter vendors need to go out and test every grid-tied inverter model. They can start with just using their customer support data.

wheisenburg said:

The issue of Enphase doing something special to make their inverters AC couple when installed as part of their backup solution is an interesting one. The fact that they support a "Daylight Backup Mode" means the key "secret ingredient" is not the batteries. You need their System Controller for this. I don't have one of those but I know it serves as a central connection point for the inverters, the grid, the batteries, a generator, and the load. So maybe they have a dedicated "Grid Forming Inverter" in the controller or one specific "Grid Forming Inverter" is chosen from your PV array. I'm not sure if the controller box has a small battery in it. If it does it could continue to manage things and communicate even when there is no PV available.

If they actually install special firmware as part of the backup configuration that allows these PV inverters to work, that tends to indicate that their failure to operate when not part of a backup solution is deliberate. Never the less, it does appear that they are actually "Trying to fix this". They already have it working for IQ7s. As far as it working for Stacked Schneider Inverters, they are saying one inverter can handle PV that is 125% of the inverter rating or around 8500 watts. That should be enough for my array. If required in a prolonged outage, I could switch to a single inverter mode and just isolate the second inverter. I have some east and some west facing panels so I will never have all of my PV working at 100%. Still it will be close to the 8500 watts in the middle of summer, which is why I figured I needed two. I don't think I need two for consumption, unless I run my drier and my wall oven at the same time. Not something I would need in an outage.

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I feel bad for you. Keep us posted on how it goes.

wheisenburg said:

Simply shutting off and refusing to work does not comply with specs they say they have implemented.

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The thing is that the iQ8 passed all required UL cert testing and works fine with the utility grid.

solar8484 said:

On the other hand, if Schneider (and other hybrid inverters) just published a list of compatible or incompatible grid-tied inverter models it could help prevent such mistakes and have more happy customers. Note, this does not mean hybrid inverter vendors need to go out and test every grid-tied inverter model. They can start with just using their customer support data.

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an N x M problem.
If the issue is grid-forming inverter impedance, maybe a standard for "gentle" anti-islanding could be defined, which battery and GT PV inverters could both be tested to.

Otherwise, it is on the installers. A big company could do more, but small ones to try a system and grow on what they learn from that customer.
Given the market penetration of Enphase, and possibly Sunny Boy & Fronius, a couple battery inverter manufacturers ought to test and guarantee operation with (some firmware revision) popular GT PV inverters.

I'm just sticking with pure SMA systems. And I've told them of one incompatibility (and older SB that didn't implement one of its documented modes.)

Hedges said:

If the issue is grid-forming inverter impedance, maybe a standard for "gentle" anti-islanding could be defined, which battery and GT PV inverters could both be tested to.

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It would be best if there is a standard for a simple but safe way to disable anti-islanding (and any other grid disturbance injection) in grid-tied inverters for *intentional* islanding. Current standards only address unintentional islanding. I imagine it could be require a transfer switch meeting certain UL standards with an output to indicate disconnection from grid, that could serve as a qualified signal to grid-tied inverters to go into intentional islanding mode.