Average kWh per day. A small off-grid cabin often runs 3–8; a full house 15–30.
Average per day for your area. Autofill from a state below if unsure.
Optional — sets the peak-sun-hours field to that state's average.
Rated watts of a single panel (common residential panels are 350–450 W).
How many cloudy days the battery bank should carry on its own. 2–3 is typical.
Lithium discharges deeper (≈80%) than lead-acid (≈50%), so it needs less capacity.
The array size is your daily energy use divided by your location's peak sun hours and an overall system efficiency of about 75% (inverter, wiring, soiling, and temperature losses). The battery bank covers your chosen days of autonomy at a usable depth of discharge — about 80% for lithium and 50% for lead-acid. Selecting a state fills in its average peak sun hours from our state data.
These are planning estimates; a real design also weighs winter sun, surge loads, and charge-controller sizing. To compare states on raw solar resource and off-grid rules, see our best states for off-grid solar guide.
Divide your daily energy use (in watt-hours) by your location's peak sun hours and an overall system efficiency of about 75%. That gives the array wattage; divide by your panel wattage for the panel count. A 10 kWh/day home at 4.5 sun hours needs roughly 3 kW of panels — about eight 400-watt panels.
Peak sun hours are the number of hours per day that sunlight averages full strength (about 1,000 W/m²). It's not the same as daylight hours. Most US states fall between 4 and 6.5; you can autofill your state's average above.
Size it for your daily use times the number of cloudy days you want to ride out, divided by the usable depth of discharge — about 80% for lithium and 50% for lead-acid. More autonomy means a bigger, costlier bank, so most off-gridders pair 2–3 days of storage with a backup generator.
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