Battery Storage
How to Size a Solar Battery for Backup and Daily Savings
Mar 23, 2026•9 min read
Battery sizing is not guesswork. You must define your outage goals and calculate both power (kW) and energy capacity (kWh).
kW vs kWh
kW is instant power (how many appliances can run at once). kWh is stored energy (how long they can run).
| Appliance | Starting Power | Running Power | Daily Energy |
|---|---|---|---|
| Refrigerator | ~1200W | ~200W | 1.5-2.0 kWh |
| Wi-Fi + Router | Low | ~20W | ~0.5 kWh |
| LED Lights (10) | Low | ~100W | ~0.5 kWh |
| Central AC (3 ton) | Very high | ~3500W | 15+ kWh |
Sizing Checklist
- Define backup objective (critical loads vs whole home).
- List required circuits from main panel.
- Calculate surge and continuous load.
- Account for usable DoD and seasonal recharge.
Common Mistakes
- Expecting one battery to power full house loads.
- Ignoring compressor startup surges.
- Not planning for winter production.
Barre Wool Solar LLC can help calculate the right battery size for your system.
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Office Address: 910 Boston Post Rd E, Marlborough, MA 01752
Owner: Michael J Staiti
Email Address: team@barrewoolsolarllc.com