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.