Solar Panel Sizing Basics for Off-Grid Systems
How peak sun hours, daily energy use, and system efficiency determine the panel wattage you need.
Sizing solar starts with your daily energy budget in watt-hours (Wh). Add up everything you plan to run—lights, fridge, pumps, chargers—and multiply watts by hours of use per day.
Peak sun hours
Panels are rated at full sun (1,000 W/m²). Real locations average fewer equivalent hours per day. Many US sites see 3–6 peak sun hours depending on season and latitude.
Required panel watts ≈ daily Wh ÷ (peak sun hours × system efficiency). Efficiency captures inverter loss, wiring, dust, and temperature—often 75–85% for good installs.
Add margin
Cloudy weeks and battery aging mean you should oversize 20–30% beyond the calculator minimum. Pair panel sizing with a battery bank calculator for complete off-grid planning.