I see a background import usage of typically 10-12W, or about 0.25 units per day. I think this is due to the inverter having to dynamically adjust its output in variation to load both within the house and in the rest of the neighbourhood. It drops to zero import when there is net export: i.e. the battery is full and the sun is shining, and power can't go anywhere else but export. BTW I have the smart meter now so I can watch this in close to real time!