According to the U.S. Energy Information Administration (EIA), the average household uses 900 kWh per month, or 10,800 kWh per year. This means that the average power required per day is 30 kWh. Now, when sizing a grid-tied solar battery system for daily use, you will need a system that can deliver up to 30 kWh, or possibly more on peak usage days. However, if you also want the system to provide off-grid backup battery storage, then you would typically choose 3 to 5 times the daily average, or 90 to 150 kWh. This should provide ample storage for full system autonomy in the event of an extended outage of 3 to 5 days. Combine battery storage with a PV solar panel system to ensure you will have renewable power to charge your batteries.