OK Cool.
The point of the thread is that I'm trying to learn how stuff works so that I can make informed decisions about what to buy. I see good deals on (apparently) good-quality used microinverters on eBay. When I weed through all the videos, it seems microinverters just change DC to AC and dump it into a panel.
For microinverters you would look for 1741SA ones, those will support frequency shift shutoff (and I guess ramp-down but i don't believe in the value of that vs just shutting off). Otherwise you are stuck with really clunky older ways to shut off.
And 1741SA microinverters have been on the market for a while.
Lower powered microinverters command a better savings IMO.
You are not eligible for 30% tax credit when used, so factor that in.
I like microinverters in a new build if you have a lot of small roof planes, or want to simplify away from DC wiring. Otherwise hybrid string inverter is better. Microinverters also have developed faster than solar charge controllers (more volume / money in it)
The caveat is that these tend to be people who have ponied up 10's of thousands of dollars and had a professional install including an agreement with POCO so that they can dump energy into the main load center and not have to worry about backfeeding.
In my state it's pretty straightforward to DIY grid tie agreement. $150 for interconnect, $200 for permits, $400 for plans, is what it cost me.
My basic understanding of the microinverters is that they have an "anti-islanding" feature that means if the grid goes down, they sense the power loss and stop injecting power (with the exception of the new microgrid forming setups).
All grid-tie inverters have anti-islanding, yes. In the absence of an interconnect agreement I'm not sure it's worth getting a grid-tie string inverter, as opposed to microinverters, to learn and play with. Since grid tie strings require rapid shutdown (if you want to be 100% code compliant), need DC wiring technique, and are less scalable in terms of reducing number of panels. There's minimum voltage for MPPT to activate and minimum number of series in string for the RSDs.
WRT trying a small system. I think an AIO is best since it forms a grid and does not have a chance to backfeed. You might consider a hybrid with grid connection air gapped; you can reuse this when you get an interconnection agreement. Like the SRNE and Growatt hybrids, which have 1741 certifications at a $1500-2000 price point.
However, these hybrids may not have a strict off-grid mode, which is why you want the air gap. Some hybrids do have strict off-grid mode which can be directly tied to grid.
Looking at my diagram I see now how the 220v microinverters wouldn't work in that scenario, but for hypothetical purposes, assume that I had parallel AIO's, feeding each leg of the load center. Would it provide the feedback the 220 microinverter was looking for?
In this case you need properly parallel stacked AIOs, since that ensures the voltage are synchronized in frequency and phase. This is just as important as AC coupling capability. Randomly shifting phases can blow up equipment plugged into that panel, and confuse or blow up the microinverters. AIO without AC coupling can blow up the AIO.
It's MUCH easier these days to just buy a split-phase inverter. Stacking 120V for split phase is only recommended in a pretty limited set of cases. So the preoccupation with 120V micro setup is kind of oddball
With the 110 grid tie microinverters, my understanding is that the peak voltage is slightly higher than the nominal peak voltage coming into the load center (per this video:
Same applies for 220V (also the system is 120/240 not 110/220)
110 grid tie with all the safety features such anti islanding. Is there a technical limitation preventing a connection to a load center as I sketched? Trying to understand where the magic device is that makes a turnkey enphase system work but that renders a single IQ7 essentially worthless for any purpose other than expanding an existing enphase system.
I'll probably not cover all the potential issues with 110, since it's pretty uncommon. Off hand, you can't power the loads on the other leg directly; you'll need an autotransformer to shift the power across. You double the wiring / have higher losses if you want a balanced system (so usually with 240V micro you just have a string that spans both legs, and that's it for a house. Easy. 120V micros means you have to plan it like a 3phase european or american commercial set up. Not rocket science, but also harder to find help with).
The magic device is the grid forming, AC coupling capable battery (like an IQ5), in combination with the Microgrid Interconnection Device, the System Controller. The System Controller has an ATS that will disconnect from grid before sending grid forming signals to the microinverters. It also has a neutral forming autotransformer to convert the 240V only microinverters to a 120/240V system. When on-grid, you use the utility transformer to do this (IE, you send 240V out your service ,to that transformer, then any neutral current you need is created here and sent back to your house)
