BACKUP POWER
How Many Kilowatt-Hours of Battery Backup Does My Home Need?
Size home battery capacity from essential loads, runtime, surge demand, usable capacity and conversion losses.
Add the watt-hours needed by each essential load, then divide by the battery’s usable fraction and system efficiency. A 3,000 Wh essential-load plan divided by 0.85 usable capacity and 0.90 efficiency requires about 3.9 kWh of nameplate battery capacity, before extra reserve.
- ✓ Energy need = watts × hours
- ✓ Separate nameplate from usable capacity
- ✓ Check peak and starting watts too
Build the load budget first
For every essential device, multiply watts by expected operating hours. For cycling appliances, use measured daily kWh. Add the energy values to create a watt-hour budget; divide by 1,000 for kWh.
Adjust for real system limits
A battery should not be assumed to deliver every nameplate kWh to appliances. Apply the manufacturer’s usable-capacity figure and expected conversion efficiency. Add reserve for uncertainty, cold conditions, aging and a longer-than-expected outage.
- Separate essential from optional loads
- Model one night, one day and multi-day scenarios
- Check continuous and surge power
- Include inverter standby consumption
Whole-home backup needs professional design
Electric heating, air conditioning, water heating and cooking can rapidly increase capacity and power requirements. Hardwired backup, transfer equipment and solar integration should be specified and installed by qualified professionals under applicable codes.
Use the EnergyBillAnswers calculator for an initial essentials estimate, then validate appliance measurements and system ratings before purchasing.
Actual energy use and product performance vary by equipment, conditions and installation. Confirm measurements and manufacturer specifications. Qualified professionals should handle permanent wiring and transfer equipment.