Battery planning
What size solar battery does your home need?
Estimate battery capacity from the loads you actually want to run, rather than choosing a battery by panel count alone.
Solar panels and batteries solve different problems. Panels produce energy over time; a battery stores energy for later. The right battery size depends on outage priorities, daily usage, inverter power and utility pricing.
The basic battery-sizing formula
Example critical-load calculation
| Load | Approx. power | Runtime target | Energy |
|---|---|---|---|
| Refrigerator | 0.15 kW average | 12 hours | 1.8 kWh |
| Internet and devices | 0.08 kW | 12 hours | 1.0 kWh |
| Lights | 0.10 kW | 6 hours | 0.6 kWh |
| Small medical or household load | 0.20 kW | 6 hours | 1.2 kWh |
This simplified example totals about 4.6 kWh before reserve and efficiency losses. A real design must use the actual startup surge, continuous watts, wiring and transfer-equipment requirements.
Three battery goals
- Emergency backup: choose the loads and hours you need during an outage.
- Solar self-consumption: store midday solar for evening use.
- Rate shifting: charge when electricity is cheaper and discharge during expensive periods.
Battery capacity is not the whole system
Compare usable capacity, continuous output, surge output, round-trip efficiency, reserve settings, warranty throughput, temperature limits, transfer equipment and whether the system can operate during an outage. A battery with enough kWh but insufficient inverter power may still fail to start a large motor or HVAC compressor.
First estimate your household demand with the appliance-aware solar calculator. Then list the loads you would actually prioritize during an outage.
FAQ
How many batteries does a home need?
There is no universal number. Start with the appliances you want to run, their wattage, how long they must run and whether the goal is outage backup or daily bill savings.
Should a battery cover my whole house?
Usually not. Whole-home backup can require more storage, higher inverter capacity and additional electrical work. A critical-loads panel is often a simpler planning starting point.
Does a battery save money everywhere?
Not automatically. Savings depend on time-of-use rates, export rules, demand charges, battery efficiency, cycling limits and the installed cost.