TL;DR . There was a huge delay of ~5 months between the installation of the first and second PW2 units.
Long Story
I had started this project in Dec 2019. Installer got permit and that was all I heard from them till 5/14/20. The shutdown in the Bay Area prevented battery installs was the claim. I also read a SJ Mercury news where apparently the installer had almost gone out of business! I had prepaid the entire balance in Dec 2019 to get the 30% ITC federal tax credit. So I probably would have lost a lot of money but luckily they weathered the shutdown.
So one day they schedule me for the install Nov 3, 2020. The installer apparently didn’t know I wanted whole home backup. Apparently the salesman thought I had meant whole inside home and not the outside like the HVAC. I was confused as I thought whole home backup was everything to do with the home. So once that was clarified, no big deal I thought. The installers install one PW2 and then tell me there’s a problem backing up the HVAC. I did not have a solar ready main panel. It had no service disconnect and although it was 200A rated, the bus bar could only handle max 100A breaker which wasn’t big enough to backup the whole home. They needed to put in a 150A breaker in the main panel and transfer all the breakers to a subpanel next to the Gateway 2. My current main panel could not support a 150A breaker on the bus bar.
In my displeasure and confusion, I stupidly told the installers not to come back to install the second PW2 and instead come back after I upgraded the main panel. I was frantically calling the project manager and salesman to schedule the main panel upgrade. They ended up subcontracting out the upgrade and then there was a concern around the upgrade because my gas riser is not 36 inches away (like only 24 inches) from the main panel. Luckily, they were able to get approval from PG&E for a like-for-like upgrade (200A rating but now with a 225A bus bar). The upgrade was performed in end Jan 2021. So another 3 months blown there. But ok I had a brand spanking new 200A/225A busbar main panel with a service disconnect so I was happy. The electricians also did an amazing job patching my home stucco because the texture was an exact match.
The battery installation continuation was then scheduled for Feb 1, 2021. The day before, the project manager tells me they don't have a battery because procurement had given it away for another install and that they have to order another one from Tesla. Around this time, I think the PW2 were hard to come by. It took another 2 months (Apr 2021) until they finally got the second PW2 unit.
The remainder of the install (Mar 30, 2021) went smoothly except they had some delays in ordering the 150A breaker. For some reason they only had a 125A breaker but they said they would install the 150A breaker after the city inspection Apr 7, 2021. City inspection went smoothly and they then installed the 150A breaker.
All in all, the process from Dec 2019 -> Apr 2021 had a lot of bumps and setbacks and more $$$ spent. However, now that I am staring at the energy flow and stats of the PW2s in the Tesla app, it was really worth the trouble!