How to Size a LiFePO4 Battery for Home Power-Outage Backup
Make an essential-load list
List each appliance, its average power during the outage and the expected operating time. Keep starting surges and maximum simultaneous power in a separate column; energy and output power are different requirements.
Estimate the energy requirement
An illustrative 500W average load over six hours requires 3kWh at the loads: 0.5kW × 6h = 3kWh. This is a planning example, not a claim about a particular home or battery. Include cycling appliances and the intended reserve when preparing the load list.
Convert load energy into a battery estimate
For a preliminary estimate, divide load energy by the planned usable fraction and estimated system efficiency. Using illustrative assumptions of 80% usable energy and 90% efficiency gives 3 ÷ (0.8 × 0.9) ≈ 4.17kWh nominal battery energy. Replace these assumptions with the limits and measured efficiency of the proposed system.
Check current and inverter compatibility separately
A battery may have enough stored energy while its current limit is too low for the intended load or surge. Check the battery, inverter and wiring requirements together. Confirm the inverter protocol and firmware where CAN or RS485 communication is used.
Compare the system options
The 51.2V 100Ah and 200Ah catalogue models provide 5.12kWh and 10.24kWh rated energy respectively. These are rated battery figures, not guaranteed AC output energy. Confirm permitted expansion, charging time, installation conditions and essential-load wiring before final selection. For a commercial facility, provide a load profile and use a project-specific BESS design.
Explore the relevant battery ranges
Discuss your battery requirements
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