Off-grid is a completely different design problem from grid-tied solar. There's no utility to fill the gaps — every component has to be sized for the worst day, not the average one.
The core difference: worst-case, not average
A grid-tied system can undersize slightly and the grid quietly covers the shortfall. Off-grid can't do that. Every component gets sized against your worst realistic sun day and your longest expected cloudy stretch, which is why off-grid systems are almost always noticeably larger and more expensive than a grid-tied system built for the same household usage.
Worst-case sun hours are typically 55-65% of your location's annual average. Run your own numbers — including your specific worst-case assumption — in the Off-Grid System Calculator.
The three components you're actually buying
Panels sized for your worst sun day, not the average — see above.
Battery sized for your target days of autonomy — how many consecutive low-sun days you want to survive without any generator. 2-3 days is standard for most climates; regions with extended overcast stretches sometimes go 4-5. This is usually the single most expensive part of an off-grid build, since usable battery capacity multiplies directly with autonomy days. Full detail in our battery storage guide.
Inverter (and charge controller) sized not just for your average load but for the surge when multiple appliances — a fridge compressor, a well pump — start at once. Undersizing here is the most common off-grid mistake; check your real numbers with the Inverter Size Calculator and Charge Controller Sizing Calculator.
What it realistically costs
Off-grid budgets vary enormously by target usage:
- Small cabin (2-4 kWh/day) — modest panel array, small battery bank, often no generator needed.
- Small off-grid home (6-10 kWh/day) — meaningfully larger array and multi-day battery bank; a backup generator is common.
- Full off-grid home (12+ kWh/day) — the largest jump, since battery cost scales directly with both daily usage and autonomy days.
Battery is usually the line item that surprises people most — get a real installed-cost estimate, not just a per-kWh sticker price, from the Home Battery Cost Calculator.
Cable sizing matters more off-grid
Off-grid systems typically run at low DC voltage (12-48V) between panels, charge controller and battery — at low voltage, the same power requires much higher current, and voltage drop becomes a real efficiency loss if cable is undersized. Check your specific runs with the Solar Cable Size Calculator before wiring anything.
Frequently asked questions
How much does it cost to go fully off-grid with solar?
A small off-grid cabin might need $10,000-$20,000 in panels, battery and inverter; a full off-grid home with 10+ kWh/day usage and multi-day battery autonomy often runs $40,000-$80,000 or more, largely driven by battery size.
Do I need a backup generator if I have solar and battery?
Most off-grid systems keep a small backup generator for the rare multi-day low-sun stretch beyond their battery's designed autonomy — it's usually cheaper than oversizing the battery bank for a once-a-year event.