Size an off-grid solar setup
Cabin, van, or shed — daily watt-hours turn into panel watts and battery capacity.
Tools used in this guide
The job
An off-grid system has to make what you use on an average day and store enough for the days the sun doesn't show. The two outputs are array watts (make) and battery watt-hours (store).
Use, sun, autonomy, losses
Enter daily consumption in Wh, your panel's rated watts, and peak sun hours for the location. Add days of autonomy, depth of discharge (lead-acid 0.5, Li-ion ~0.9), and a system efficiency for wiring and inverter losses (~0.75 typical).
Worked example
Using 2,000 Wh/day with 5 sun hours and 0.75 efficiency needs a 533 W array — three 200 W panels. Storing 2 days at 0.5 DoD needs an 8,000 Wh battery — e.g. ~667 Ah at 12 V.
Where it stops
Average sun hours hide winter — size for the worst month, not the annual mean. Cold panels perform better, hot panels worse; shading and tilt aren't modeled.