Whole-Home Solar Battery Backup: Guide (2026)

Last updated: February 1, 2026

How to design a solar + battery system for whole-home backup. Sizing your battery bank, critical load panels, and automatic transfer switches.

The question isn't whether batteries are useful — it's whether they're worth the cost for your situation. A battery adds $8,000-$16,000 to your solar system, so the math needs to work. This guide helps you decide based on your outage risk, rate structure, and net metering policy.

Whole-home backup requires enough battery capacity to power all your loads — including HVAC, appliances, and lights — through overnight and overcast periods. A typical home needs 20-40 kWh of battery storage and 8-12 kW of continuous inverter power for true whole-home backup. Our database includes 43 batteries with 5+ kW output suitable for whole-home backup applications.

Key Takeaways

• Whole-home backup: 20-40 kWh battery capacity, 8-12 kW inverter power
• Essential-load backup: 10-15 kWh, 3-5 kW — covers lights, fridge, WiFi, charging
• Stack multiple batteries for larger capacity (most support 2-4 units)
• Solar recharges batteries during the day for multi-day outage resilience
• Automatic transfer switch isolates your home from the grid during outages
• Expect $20,000-$40,000 for a whole-home backup system (before tax credit)

Frequently Asked Questions

How many batteries for whole-home backup?

Most homes need 2-4 battery units for true whole-home backup. A single 8.9 kWh battery covers essential loads for 8-12 hours. For AC, electric stove, and dryer during an outage, plan for 30-40 kWh total (2-3 large batteries). Solar panels recharge the batteries during the day, extending backup duration indefinitely in sunny weather.

Can I back up my air conditioner?

Yes, but AC is the largest single load in most homes (3-5 kW running, 5-8 kW startup surge). You need a battery with sufficient continuous power (5+ kW) and peak surge capacity. Running AC drains batteries quickly — expect 3-6 hours of cooling from a single 13.5 kWh battery.