Watch what happens after sunset
Cooling, hot water, cooking and vehicle charging may overlap. Review representative days for evening energy and simultaneous loads. Moving flexible heating or charging into daylight changes the battery’s task. Sizing against total daily consumption ignores energy already supplied directly by solar.
Separate daily use from backup reserve
Energy intended for evening use can follow the household routine; energy reserved for outages cannot all be spent beforehand. Specify the reserve, backed-up circuits, phase requirements and whether solar can recharge the battery during an outage. Check cloudy periods separately instead of assuming a full charge every day.
Check the expansion conditions
Future vehicles or new appliances may justify asking about expansion. But expandable does not mean any battery can be added at any time. Verify model compatibility and limits on mixing ages or batches. Bills, the existing inverter model and a critical-load list will produce a better proposal than asking whether 10 kWh is enough.
Further reading: www.energy.gov
This article supports early project discussions. Final configuration depends on site conditions.