I think my POCO interconnection agreement does require a disconnect outside. With my AHJ I think the microinverters cover the rapid shutdown requirement but I'll check back with them.
Most places require an external disconnect. And it's also something EG the fire department cares about.
Microinverters cover rapid shutdown under NEC, however there's a question here on the specifics of how it's triggered. With microinverters the low level mechanism is always the same -- cut the AC feed so it can't see grid anymore. But where you put the breaker/switch for that is the question.
I mainly wanted to make sure there wasn't an additional breaker box that was needed for safety or function before going to the MSP - which sounds like Enphase does call for.
Some random reasons you would want a combiner subpanel:
- organizing cables
- lots of branch circuits, and AHJ is anal about how they interpret 120% rule (branch circuits need to be on opposite end)
- might be easier to monitor combined solar output with energy meter if you put one CT on combiner feeder vs snaking multiple branch circuits into the same CT. I have both setups in my system.
- 705.12 min-maxing
In the past (like, 2011 or 2008) the combiner simplifies most 705.12 calculations. Nowadays it only simplifies some less common calculations.
Currently I'm looking at Hoymiles or APsystems microinverters. I'd get a gateway/monitoring so I'll look over their install manuals to see how they need to be hooked up.
I haven't looked at APsystems. I use Hoymiles. I have their monitoring and installed to their rules.
Hoymiles monitoring (DTU or DTU-S) is all wireless based, so they don't need a combiner box like Enphase which is power line communications based. (The Enphase combiner probably has some CTs in it or something as well for various purposes).
I have two hoymiles branches going into an inside combiner (this was from an installer). And another two hoymiles branches going into distribution subpanel (inside as well; this was my self-install). But my POCO/AHJ allows us to cut off the whole house on shutdown, lol. Some places require independent solar shutdown.