Solar + Powerwall: Lights have started flickering when off-grid

[aesculus]

What I don't understand is why some of my digital clocks run fast during backup. Initially I chalked it up to the frequency shift due to solar generation control. But lately I've had some outages where the solar wasn't producing much and the Powerwalls weren't fully charged. Some of my digital clocks still ran fast.

Clocks aside. I know the PWs will start to increase the frequency when they become full. Not sure when it starts but I have heard starting at 90% and certainly kicks in at 95% big time. I also don't know whether they adjust based on actual solar production or some setting that Tesla made based on our solar install base, or worse yet just some fixed figure based on % charge. Does anyone know for sure exactly how the frequency shift algorithm works?