Our system has 15.4KW of solar panels and 4 PowerWalls, and provides about 50% of our home power for the year.
We're currently under a Free Nights plan, providing us free electricity between 9PM to 9AM, and charging us $.20/KWh between 9AM to 9PM.
Our system is configured for Advanced Time-Based Control in Cost Saving mode with 35% reserve for unplanned power outages and 9AM-9PM set as peak with 9PM to 9AM as off-peak.
In 2019 (before solar panels), we used 42.6MWh of electricity.
Last year, with the solar panels/PWs, we reduced that to 19.5MWh of grid power (reduced EV charging due to COVID also helped).
Of that, we used only 4.3MWh of grid power during the peak period (9AM-9PM). If we had been under the free nights plan for the entire year, we would have reduced our annual electricity cost from $4.7K to $1.2K.
During the peak period (9AM-9PM), the system will power our house as much as possible from solar or PowerWalls, charging the PowerWalls with excess solar, and then sending excess solar power to the grid when the PowerWalls are full.
During the off-peak period (9PM-9AM), while you would expect the system to stop using the PowerWalls completely - that's not what happens. Instead, the software appears to project how much solar power will be generated the next day, and will draw power from the PowerWalls overnight to make space to store the excess solar power for the next day.
Most of the time, this seems to work OK - and it's probably better to discharge/charge the PowerWalls some each day, than letting them sit at close to full charge for days...
Though I wish there was a setting to turn this "feature" off and run grid-only during the "off peak" period - when the off peak grid power is free...