So far I have only done one short off grid test, and I had an issue where most of my Enphase micros went offline during the transition. 5 stayed up and charge current went to about 600 watts. I only had about 200 watts of load on the output at the time, the 5 working inverter were making about 800 watts. I did not leave it off grid long enough to run the batteries low. I am waiting for word back from Enphase on why the inverters locked out. The 5 that stayed working did not even glitch, they just kept producing with no log entry. The 11 that quit all said it was a grid frequency error. They should have gone back on after 5 minutes, I gave them close to 20, and still no good. Even after going back on grid they did not recover. And once on grid I cut the solar disconnect and turned it back on, and the same 5 plus one more came up, the other 10 didn't. I did get 3 more to come up by covering the panel to cut the DC going in, and then they came up. The other 7 dead ones were on my upper roof. They did come up the next morning after they went dark by nature.
So this was a bad test, Enphase is searching the logs, and they did admit seeing this happen before, it does seem to be a problem with the Rule 21 grid code.
I do not have much load moved into my backup panel yet for various reasons. Mainly, I am having trouble tracing the circuits, and I will have to cut house power, which means shutting down a bunch of delicate gear. I had not realized that the original solar installer moved all of my breakers, and didn't bother transferring the labels. So they are all marked wrong, and using an electronic tracer has failed. Some device in my home is putting out a noise that evidently looks like the tracer signal, causing it to keep reporting multiple breakers, even without the tracker source connected. Once I have a handle on how the loads are handled, I will decide if I need to add a load shed relay. From my calculation, I should have enough power to keep the loads up since I am not moving over the A/C or any of my shop tools. My worst case load is the Furnace blower and controls, which can hit 8 amps at 120 volt. And my old refrigerator which runs at about 5 amps at 120 volt. Beyond those, I have my main PC along with a small NAS, internet modem, router, and 2 switches. Total about 300 watts if I am not playing a graphic game. And I don't have a very serious graphics card in this machine. My second PC, which will be on the inverter does have an nvidia 660 card, is sitting idle most of the time, acting as a file store and printer server, but is used as an entertainment machine if we know we have the power to run it. And then I have one flat screen TV and the Dish Network Hopper box so we can still get new etc. if the internet goes down here. Dish coming from a satellite will keep running even if all local services quit. So until I get a solid check on the power use, I "think" I can run from 7 pm to 9 am and have some power left, but it may be tight. My current plan is to set the low battery cut off at 47 volts. If I get down there, it will cut, but then I can change it down to 44 volts, and get the system back up when there is sun. I do have a local UPS on the main PC, and I will set up a low battery alarm so I have some warning before the inverter cuts off. By my rough math, it looks like my chosen loads are going to only need about 12 KWH's and my battery should be able to supply up to 17 KWH's. To get that much power though, when I go off grid, I do need to raise my full charge voltage up to 58.5, almost 4.2 per cell, and my low batt cutoff down to 42 volts which is 3.0 volts per cell. The LG data sheet says they can go down to 2.8 volts without damage, but that is more than I want to risk.
It "Should" start up and charge from grid as long as the battery voltage is about 40 even. Worst case, I do have a manual generator and a 10 amp 14S charger I can hook up to get the battery up a bit. Once the XW-Pro will turn on, I also installed the generator socket on the XW-Pro AC2 input. I could then charge from the generator at up to 4,500 watts. That would be in the 90 amp range which is still less than 0.3C and the cells are rated to 1C continuous charge rate. The generator could go from dead to full charge in under 4 hours. But that will take nearly 4 gallons of gasoline. Any solar power I can get will help that out.
During an average day, my solar should make about 20 KWH's. Even yesterday it topped 24 KWH's. While the sun is up, my gear will consume 8 KWH's while the batteries get 12 KWH's of charge. Then during the 14 hours of dark, my gear will pull 11 KWH's. Yes, it is close if I don't shut anything down. I am looking at adding 4 panels on the garage roof. Still torn on if I should DC couple them. The Schneider MPPT units are stupid expensive though. Their smaller unit MPPT 60 150 is about $550. If I use 4 385 watt panels, I could run them in series parallel and get about 30 amps or charge current. Figure about $0.60 per watt for the panels, so $1,000 for the panels. Then add in racking and cabling, and what do I need to do about rapid shut down? I am not worried about it enough yet until I see how it works with my loads moved over and Enphase gives me a firmware update to correct the lock out issue when it goes off grid.