A house-sized off-grid system is overkill for a shed, and a shed-sized system won't run a cabin. Here's how to size for what you're actually building.
Start from usage, not from panel size
The most common mistake in small off-grid builds is starting with "how big a panel should I buy" instead of "how much energy do I actually need per day." Add up your daily watt-hour usage first — lights, a fan, device charging, maybe a small fridge — then work backward to the panel and battery size that supports it.
Weekend cabins can lean on the battery more than the panel
If you're only there on weekends, the battery has all week to recharge between visits — that means you can often get away with a smaller panel and rely more on stored capacity, sized around your visit's actual usage plus a buffer. A full-time cabin needs the array itself to reliably keep pace with daily draw. Our off-grid cabin calculator handles both usage patterns separately.
Sheds and workshops: mind the power tool surge
Lighting and device charging are easy — a 100-200W panel and a modest battery cover that comfortably. The problem is power tools. A drill is usually fine on a small system, but anything with a real motor (a table saw, air compressor) can spike 3-5× its running wattage for a moment at startup, which is what actually determines whether your inverter can handle it — not the tool's average draw. Check any tool's requirement against the surge watts calculator before assuming a small system can run it.
RVs and vans: roof space is the real constraint
Unlike a house or cabin, van and RV solar is limited by available roof area and weight, not budget alone — you generally can't just add more panels indefinitely. The RV solar calculator factors in typical roof space limits alongside daily usage and days of autonomy, which is the more realistic way to size a mobile system than treating it like a mini house.
Frequently asked questions
Do I need a battery for a shed with just lighting?
For occasional use, a small battery still helps by letting the panel charge during the day for use after dark, but if the shed is only ever used in daylight, a simple direct-to-panel setup with no battery can work for very basic loads.
How much roof space does a typical van solar setup need?
A 400-600W array — enough for moderate daily use including a fridge, lighting, and device charging — usually needs 20-30 square feet, which fits most van and small RV roofs.