OP here, thanks for the replies again. So it does seem like the design is arbitrary and there is no hard criteria where they will deny a whole home backup request.
In my original application, I specified that I did not own an AC or EV (since I do not) so those loads should not have been taken into consideration. On Tesla's own website, they specify that for scroll-type ACs, 2 Powerwalls are sufficient as long as the LRA was <139 (
What Does Powerwall Back Up | Tesla Support). Therefore, for a standard home without AC or EV, I do not see the reasoning behind recommending 3 Powerwalls. I will email my rep to ask for the design details behind that decision.
- For those who have 2 Powerwalls, was the AC slow-start part of the Tesla install?
- For those with Partial Home backup, at what stage do you get to specify which circuits go in the backup subpanel, and which circuits will be left in the main panel? Specifying which combination of circuits can be backed up and which ones cannot would also have helped me arrive at a decision but Tesla did not specify.