An off-grid solar system — one with no utility connection at all, common in cabins, sheds, and some tiny homes — is really four components sized to work together, not one product you buy. Undersizing any single piece bottlenecks the whole system, so it's worth understanding each one before shopping.
The four components
- Solar panels — convert sunlight into DC power; sized to your daily energy need divided by realistic sun hours
- Charge controller — regulates power flowing from the panels into the battery bank, preventing overcharging
- Battery bank — stores energy for use when the sun isn't out; sized for your daily use times your desired days of autonomy (backup during cloudy stretches)
- Inverter — converts the battery's stored DC power into the AC power most household devices and outlets need
Sizing it step by step
- Add up your daily watt-hour use. List every device, its wattage, and hours of use per day — the same exercise as sizing a power station, just for continuous off-grid living rather than an outage. Our free wattage calculator handles this for a standard appliance list.
- Size the battery bank for autonomy. Multiply daily Wh use by the number of cloudy/low-sun days you want to cover without recharging (2-3 days is a common target) to get your minimum battery capacity.
- Size the panels to recharge that daily use. Divide your daily Wh need by your location's realistic peak sun hours (commonly 4-6/day) and derate by roughly 25% for real-world losses — that gives your minimum panel wattage.
| Daily use | Battery bank (3-day autonomy) | Panel array needed |
|---|---|---|
| 500 Wh/day (small cabin, lights + devices) | ~1,500 Wh | ~250-350 W |
| 1,500 Wh/day (fridge + lights + devices) | ~4,500 Wh | ~700-1,000 W |
| 3,000 Wh/day (multiple appliances) | ~9,000 Wh | ~1,400-2,000 W |
These figures are planning starting points, not a substitute for sizing your specific device list — seasonal sun-hour swings, panel angle, and shading all shift the real numbers meaningfully. For a permanent off-grid install, working with a solar installer to validate the final sizing is worth the cost given how much is riding on getting it right the first time.