Use of an External ATS
A Sunsynk or Deye inverter does not need an external ATS, but would one cause any issues? It seems to me the inverter won’t know WHERE the grid is down, only that it is, so an external ATS won’t be “incompatible”, just redundant.
Why I ask: When my system was installed 5 months ago, I didn’t have a battery, so the entire AC side of a DC+AC combiner box was not used in favor of a simple breaker all alone in a huge metal box the size of the inverter, which was apparently all the installer had on hand. I’m adding battery storage which will require an additional breaker and perhaps a bypass switch to be added to the huge metal box. That entire box could be eliminated if the AC side of the combiner box was used. It’s prewired with protection and breakers at every stage. The ATS and a breaker would serve as an inverter bypass switch in the event the inverter needs to be taken offline for maintenance. The ATS isn’t needed. A simpler bypass switch could be used instead, but would it cause an actual problem?
This combiner box is very interesting. I’ve not seen anything like it on the internet. It comes prewired, so despite the visual complexity it’s dead simple to use as all of the connections are to terminals at the bottom: 3 PV strings in and 3 out to the inverter, Grid, Load from the inverter, a connection to the essential loads subpanel, and a direct grid connection to the inverter which bypasses the ATS. This last piece confused the hell out of me for a long time but it’s necessary since the ATS isn’t selecting between the grid and a generator, it’s not one or the other, but rather the choices are grid only or grid + inverter. The grid needs to be connected to both A and B.
One other note. In other parts of the world it would be forbidden to combine AC and DC in one box like this, but I’m in Thailand where rules are less strict. This is common here, along with (sometimes) big DC breakers for batteries.