Hi I have a Tesla powerwall 2 installed on my property which is 3 phase, Im going to try and simplify how the Tesla works with 3 Phase system with solar. There are several configurations that can be done. I have a 3 Phase solar inverter, when the grid goes off the inverter will not work as the supply from the powerwall is single phase unless you have 3 powerwalls on different phases. For the sake of the explanation, 1 powerwall and 3 phase inverter, the tesla uses CT clamps around all three phases which measures the power on all 3 phases. Let say the powerwall is connected to the red phase and you are using power on the blue phase the powerwall will put power onto the grid the same amount you are using, but the meter is a net meter which means instead of giving you a low export meter rate it effectively cancels out power used.