Off-grid, and still charged

It depends entirely on what you run, which is why any number someone gives you at a campfire is useless. The method is fixed: add up the watt-hours you use in a day, divide by the peak sun hours you actually get in the season and place you camp, and add roughly 30% for system losses. A laptop and lights is a very different system from a 12V fridge and a satellite dish running all day. Our calculator does the arithmetic.

Not daylight hours. A peak sun hour is one hour of full-strength sun, with a day's weaker light converted to that equivalent. Arizona in June is around 6 to 7. The Pacific Northwest in December can be under 2. Size for the worst month you intend to camp in rather than the annual average, or your system works beautifully in July and quits in November.

Usually, because rated capacity is not usable capacity. Draining an AGM below about 50% wrecks its life, so a 100Ah AGM realistically gives you 50Ah. Lithium is comfortable down to 20% or lower, so a 100Ah lithium gives you 80Ah or more, and it lasts far more cycles. Price per usable amp-hour, not per rated amp-hour, is the comparison that matters. The catch is cold.

It will not accept a charge below freezing, and forcing it causes permanent damage rather than a temporary problem. Many batteries now include a low-temperature cutoff that refuses the charge to protect the cells, which saves the battery and still leaves you without power on a cold morning. Heated banks solve it properly. This catches out more people heading north or up in elevation than any other single thing.

Bigger than the running total suggests, because motors surge on startup. An air conditioner that runs at 1,400W can demand 3,000W or more for the instant its compressor kicks in, and a generator that cannot survive that spike trips and everything stops. Size for everything running plus the single largest startup surge, then add headroom. Our generator tool works it through.