I've enjoyed reading this thread so I figured I'd contribute to the latest discussion. I have an Ensemble system with an Encharge 10. I haven't tested off grid lately but it looks like the firmware hasn't changed since I lasted tested it. The behavior I saw was that if the battery is full and the sun is shining then initially the system uses only the batteries and no solar. Once the battery gets down to a bit of a buffer, like 96% it turns on the solar to match the load demand and stops using the batteries. From what I recall it uses power line communication to regulate the solar panels, the frequency stays at 60hz. Hope this helps!
That is how it should work from all of their white papers and online description. The idea behind it is great, and if they ever do get the cost of the Encharge batteries down, I may switch to it. Both svetz and I have seen some odd behavior from the iQ7 microinverters on the solar panels. The solar side of our systems are all Enphase with an iQ combiner. Where we differ is the storage. My backup is third party (Schneider) with no data control, just frequency shift. svetz's system (and I assume yours too) is the all Enphase gear with the Encharge and Enpower units. I almost went Encharge as well, but with the delays and the cost, I pulled the trigger and ordered my Schneider XW-Pro. I have nearly 18 KWH of Li NMC batteries on it, so it would be about the same capacity as an Encharge 10 and two Encharge 3's. I fully expect my system won't run as seamless as yours with the all Enphase solution. But some of the glitches I have seen are similar to the error svetz has also seen. Even when we don't even notice any power glitch, we have had some of the solar iQ inverters report grid stability issues.
I had several of my iQ7's go offline for 5 minutes at least twice in the last 2 months from over frequency, or grid instability, but my Schneider log shows no power issue at all since February 23 when it showed a grid frequency high disconnect. The funny thing about the 23rd, the XW switched to battery power and the Enphase iQ7's appear to have stayed working just fine. It was 6:45 PM so the sun was just about down, so it is hard to tell, and my system only shows the last 500 log entries, which is only about 5 normal days, less if there were odd errors.
Back on January 19th, I had a real power failure. The XW-Pro saw it and started grid forming before the sun came up. We also had crap weather with a lot of clouds, so I didn't get much solar. But as the day wore on, and sun did start poking through, I saw that only one iQ7 was making any power. The log showed the other 15 were all stuck in Grid Frequency out of range, even though my local grid was fine, and one of the iQ7's was completely happy and pushing about 50 wats from a grey sky. Enphase had to remote in and change the grid profile to get them back online. They have since upgraded my firmware twice, but I have not tried a power fail off grid simulation yet. The grid instability logs I saw were after the first software update, I have not seen any since the second update.
Logging into my Envoy with installer toolkit now, it shows all 16 making power, pushing 1.95 KW at 9:15 am, not bad at all. My firmware was last updated March 9, 2021 at 8:37 am running image "520-00082-r01-v04.27.04" Looking through the logs, two days ago, Apr 7, I see a few entries for "High Skip Rate" "DC Voltage Too Low" but this was at 6:37 am, I'm Guessing clouds came in and they saw just enough light to power up and then cut off again. On Apr 6 it did a few more "High Skip Rate" entries at 7:21 PM. This is as the sun goes down. All of the rest of the 500 entries are the normal power off power on each day for the 16 inverters. Without extra stuff going on, it goes back to Apr 4th as expected. So it ran this last week with no odd errors.
It looks like they are getting better. I certainly want to do a power fail test before my next real failure.