I would think there is no way to fully avoid consuming a bit of grid power here and there. I can only talk for my system, but my smart meter reader (that sends the real time data into HEMS) has a bit of a delay and the output of my battery is limited to 800 W anyway (local legal regulation). So if a high power device is in use (like a kettle or washing machine), there will be always some grid power entering my system, although theoretically I produce enough solar energy throughout the day. But it's the peaks that require some grid power.