I'm looking to do a similar setup and to have a tesla roof and 2 powerwalls installed...I intend to use a standby natural gas generator as a grid replacement during a prolonged outage during the winter... The idea is I can run the house during the day and charge the PW on the SBG then turn off the generator at night and run the house off the PW...if the sun comes out and the snow comes off the roof I can run the house off solar and charge the PW during the day...
the more I read about the way tesla operates is if the grid goes out during even a sunny day is shuts the panels off and you run only off batteries? That seams not only dumb (assuming your PV is sized to properly support the home load during the day) but an ineffective use of the panels... If the grid goes out the ATS should disconnect from the grid and the PV system and PWs should create their own grid and should power anything its connected to. Can you share drawings of how your setup is installed please?
For me the entire purpose of PV and PW and a SBG is to be up and running in any season in any grid utility outage situation. SolArk inverters with other battery suppliers can do just that.
The behavior of solar + PW is not quite what you described, and it does make sense once you work through the options. When there is an outage, the solar array cannot generate more than can be consumed. (This is also true when the grid is up, but the grid is effectively an infinite sink for purposes of residential solar power generation.) In an outage, the solar can be used either to run the home or to charge the PWs. If the PWs are full and the home load is less than the incoming solar, this will quickly become dangerous. So, one of two things happens. For older installs, the solar is shutoff completely, and the PWs run the home. For some newer installs, the systems are capable of curtailing the solar to match the home load. In the former case, this behavior only persists until the PWs are drained to a level where solar can resume. (In my case, it shuts off around 97-98% and comes back in the 92-95% range - it likely checks about every 5 minutes to see if the PWs have room for more energy.) In the latter case, the PWs should generally remain in that 97-98% range.
In either case, your system will attempt to maintain near-full batteries whenever possible (solar generation exceeds home load) but will curtail or cycle off the solar as a safety measure whenever the PWs get too full. All you lose out on in an outage is the benefits of net metering/load shifting since the grid is not available for that purpose.