Battery Backup Sizing Guide & Calculator
Understand how much battery storage you need for backup power during outages and peak-rate shifting with plug-in solar.
Why Battery Storage?
Battery storage paired with plug-in solar provides two key benefits: backup power during grid outages and the ability to shift solar energy to peak-rate hours for maximum savings.
Sizing Your Battery
Battery size depends on what you want to power and for how long. Essential loads (lights, phone charging, refrigerator, Wi-Fi) typically require 1–3 kWh for 4–8 hours of backup.
Common Appliance Power Requirements
| Appliance | Watts | Hours/Day | Daily Wh |
|---|---|---|---|
| LED Lights (5 bulbs) | 50W | 5h | 250 Wh |
| Phone Charger | 20W | 3h | 60 Wh |
| Wi-Fi Router | 15W | 24h | 360 Wh |
| Laptop | 65W | 4h | 260 Wh |
| Refrigerator | 150W | 8h (cycling) | 1,200 Wh |
| TV | 100W | 4h | 400 Wh |
Battery Sizing Recommendations
| Use Case | Recommended Size | Covers |
|---|---|---|
| Essential backup (4h) | 1,000–1,500 Wh | Lights, phone, Wi-Fi |
| Extended backup (8h) | 2,000–3,000 Wh | + Laptop, TV |
| Full day backup | 4,000–5,000 Wh | + Refrigerator, all essentials |
| Peak-rate shifting only | 2,000–4,000 Wh | Store solar for evening peak hours |
How Much Solar to Recharge
A 800W plug-in solar system in an average US location (5 peak sun hours) generates approximately 4,000 Wh per day — enough to fully recharge a 3,000 Wh battery with energy left over for direct consumption.
Connect Battery Size to the Complete Setup
Battery capacity alone does not determine outage behavior. Confirm the product's approved backup mode, supported loads, charging limits, and whether backup is provided through battery outlets or another approved configuration.
- Estimate solar and storage value for your location and assumptions.
- Check setup readiness before selecting equipment.
- Understand outage shutdown and anti-islanding.
- Compare complete plug-in solar systems.