Off-grid calculator
How many nights can you camp before the battery runs flat? Enter what's in your van and what you run each day. The sign updates as you go.
How it works
Battery. Usable energy is capacity in amp-hours × nominal voltage × the share you can safely use: 90% for lithium (12.8V nominal) and 50% for AGM or gel (12V). Starting charge scales that down if you leave a powered site part-charged.
Solar. Panel watts × peak sun hours × 0.75, which allows for heat, panel angle, dust, cable and controller losses. Peak sun hours used: clear summer days 6; spring or autumn, mostly sunny 4.5; southern winter 3; overcast or heavy shade 1.
Driving. Hours driving × charger amps × 13.6V × 0.9. A DC-DC charger tops up the house battery from the tow vehicle while you drive.
Appliances. Watts × hours a day. Anything marked 230V runs through the inverter, which loses about 12% as heat, and a switched-on inverter draws around 15W even when nothing is plugged in.
Days. Usable battery ÷ (daily use − daily charging). If charging covers what you use, the answer is "indefinitely", as long as the weather holds. Read How to size batteries and solar for the full method.
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