It looks like you are close to balancing out your usage with your production.
In an outage situation if you have excess solar production it is "spilled" unlike when the grid is on where it sent there.
That day includes charging my car, and some whole house AC. Those would both be optional during a grid outage. I have a separate AC in my TV room that is on the Powerwall. The main house AC is not.
Last year, before Powerwalls, PV covered 71% of my usage. It would have been 92% without charging my EV.
I have a LEAF, my next door neighbor has a LEAF, across the street has a Bolt. I could let them charge if I can see that I will have excess PV. (My former employer, Enel, refers to that as a virtual battery.)
The one row you are showing says you used about 3 kWh more than you produced. If this is a typical day you are consuming about 1.3 kW/hour. You indicated that your "idle" use was around 800 watts. This means during other hours your usage is higher than 1.3 kW. How much of that easy to shed load if you were aware that there is an outage? If you know there is an outage would you consume 30 kWh in a day? If you are naturally going to be inside your typical production (27 kWh) then easiest thing to do overnight during an outage is nothing.
Typical day for July... lots of PV, and some AC. That day includes a 9 kWh EV charge, usually, it is only 3-4 kWh.
If your Powerwalls and solar are wired to dedicated generation panel and your have separate load center it would with breaker that controls it you could shutdown your loads with one switch throw while maintaining the ability have your Powerwalls be charged automatically.
TL;DR; if I was in your shoes I wouldn't complicate things by trying to shutdown the Powerwalls during an outage.
Yes. Thank you for your consideration in such detail.
Without the whole house AC and charging my car, I will probably have plenty of PV production.
I'll just forget about the grid outage, and let the system run. (except maybe charging my neighbor's LEAF.)
If I think I am in trouble, I will flip a breaker to disconnect the house, and not touch the Powerwalls.
I just expected that there was a button in the app to force standby.