Solar and battery sizing for an off-grid cabin using 8 kWh/day
A full example for a small cabin where winter sun and backup margin matter more than annual average output.
Technical feedback wanted: if the winter sun-hours, loss factor, or backup-day assumption looks off, copy the result summary or share link and send a correction.
Load and weather assumptions
- Daily energy use: 8 kWh/day
- Winter sun assumption: 3 peak sun-hours/day
- System loss factor: 25%
- Backup target: 48 hours at the average cabin load
- Battery chemistry: LiFePO4 at 90% DoD
Sizing result
PV array
3.6 kW
Nominal battery
21.5 kWh
Inverter planning
3-5 kW
PV array formula: 8 kWh/day divided by 3 winter sun-hours divided by 0.75 system efficiency = about 3.6 kW. Battery formula: the 0.33 kW average load x 48 hours is 16 kWh delivered; adjusting for 92% inverter efficiency, 90% DoD, and 10% reserve gives about 21.5 kWh nominal.
Open the editable calculators
This example is meant to be edited and challenged. Share the result if you want a second set of eyes on the winter assumptions.