Whole-house vs partial-circuit battery backup
Whether a battery can power an entire house during an outage depends on the battery's capacity and power rating, the home’s load profile, and the inverter and transfer switch arrangement. Both whole-house and partial-circuit backup are possible, but they require different system designs.
Partial-circuit backup
- Most residential battery systems initially support critical circuits only, such as refrigeration, selected lights, outlets and communication equipment.
- This approach uses an essential load panel and an automatic transfer switch to isolate and power prioritized circuits during outages.
- Advantages: Lower required battery capacity and cost, simplified installation.
Whole-house backup
- To supply entire household load, the battery system must be sized to meet the total power demand and capacity needed for the desired duration.
- Consider both continuous power rating (kW) and surge capacity for motors and compressors.
- Whole-house capability often requires larger battery capacity (tens of kWh) and a hybrid or capable inverter with robust transfer switching.
Factors to consider
- Peak power needs: Electric ranges, HVAC systems, heat pumps and EV chargers can require large power draw.
- Duration: How long you need the backup to last determines capacity in kWh.
- Cost: Whole-house backup is more expensive but offers greater resilience.
- Inverter and generator integration: Some setups pair batteries with backup generators for extended outages.
Design approach
- Start by measuring or estimating household peak loads and average usage.
- Decide which loads are essential for the time you expect to be without grid power.
- Work with an installer to select an inverter and battery capacity that safely handle surge demands and continuous load during islanding.
Many homeowners choose staged approaches: start with partial backup for critical loads and expand capacity later if whole-house backup becomes desirable.