I had the same idea - store energy from the solar panels that would otherwise feed onto the grid and then use that energy later at night etc. I had a couple of ideas to achieve that -
1. Ensure everything on mains will operate OK on DC. Put a diode in series with live and put the 20 or so lead acid batteries in series and loads after that. When the batteries are fully charged, the house runs only on batteries, when they are flat they will charge from mains (assuming the solar array is supplying). At night if the batteries are flat AND there's no solar, everything can run on mains through the diode with the batteries disconnected.
2. High current battery charger connected to mains charges a 10kWh battery bank during daytime, 500w GTI powered from the batteries runs during the night to make sure the small loads never use paid electricity. Problem is that it's the fridge / freezer which is on at night and that uses high power for short periods of time.