From my point of view as a PG&E NEM customer, you can only save as much money with a PowerWall as you currently pay at your annual true-up. If you are currently Net $0 true-up but are a net user of kWh, then a PowerWall won't save you anything. I have a small 4.32kW DC solar system and average about $800/year energy charges due at true-up. Rate arbitrage by either capturing my own solar during Part-Peak or actually charging the batteries during Off-Peak, then using the batteries to avoid any Peak period usage could save me up to that much on my annual true-up. If you interconnect batteries, you have to sign a special agreement. I don't know the conditions of that agreement, so I don't know if you're actually allowed to discharge into the grid during peak period without a signal from the utility that it is needed. Clearly the rate tariffs need to be modernized to fully account for people who have distributed storage and generation.