Just a little food for thought based on my experience:
I originally tried to put a UPS between my wall outlet - which is backed up by the whole-house battery - and my gadget closet devices.
While testing this setup, I found out that, in case of off-grid operation (initiated manually or because the grid power is down), my system works as follows::
- when the solar system is charging the whole-house battery (<100% charge) everything is fine
- when there’s no solar power, the battery is providing power to the house - including the gadget closet - as expected
- when the battery is fully charged (and the excess power from the solar system has nowhere to go) the gateway for the whole-house battery shuts down the solar system.
This seems to be done by increasing the frequency from the (US-)normal 60Hz to around 66Hz.
The frequency increase triggers my UPS to go into a what-the-hell-I-lost-mains-power mode and starts running the gadget closet from the UPS battery only, i.e. it doesn’t keep the UPS powered or charged from the wall socket.
This means that my gadget closed devices don’t use the whole-house backup any more and run out of juice in less than 3h while the whole-house battery would last 15h
Hope that this layman’s description makes sense somehow (it’s been almost 2 years since I did that, so I might be a little fuzzy on some of the details).
I read a around a lot in quite a few forums and the most-often recommended approach was to get in touch with the battery/gateway manufacturer (Tesla in my case) and ask them to reduce this ‘signalling frequency’ from 66Hz to something
- high enough that my solar system (Enphase) would still understand and shut down solar production
but - low enough for my UPS not to trigger the what-the-hell-I-lost-mains-power mode.
This is where I called it a day and just removed the UPS.
Not necessarily how every system works, I guess, but in my case, it would have been very counter-productive 