Brisbane

Correct, I'm not certain but I suspect it will be all be done by calculation. Battery bank will have a digital meter and so will each of the participant houses. If your producing energy when the battery is charging your entitled to an equivalent amount for free from the battery in the other direction. When your actually consuming you can't tell where the exact power you are using is coming from but you can do calculations on the net energy movement and allocate from that.

I suspect the real benifit of the bank is actually network stability (ie preventing spikes/brownouts). A battery bank can respond to a drop in source or load in about 1ms while a generator typically takes around 100ms. This is really helpful for maintaining a healthy 240V supply when you have unstable supplies (like solar panels or wind turbines) or highly variable loads (like everyone turning on the kettle at once during state of origin half time). The whole cheaper electricity benifit is really just a way to sell it to the public.