Off-grid solar size calculator
Add your daily loads. Get the panel count, battery bank Ah, inverter rating, and charge controller amps — worst-month sun hours and derating handled.
Once you know your system size, matched off-grid solar kits: 400 W class for weekend cabins, 1,000 W+ class for full-time off-grid.
The inverter turns battery DC into household AC. Size it by what runs at the same time — plus the startup surge of the biggest motor.
The charge controller sits between panels and battery. Size it by array watts ÷ battery voltage — and pick MPPT above ~200 W.
Have a battery already? Here's how much panel it takes to recharge it in a day — after sun hours and charge losses.
Sizing a whole bank from scratch instead? Use the battery bank sizer.
How off-grid solar sizing works
Everything flows from one number: daily watt-hours. Panels must replace that number every sun-hour day — array watts = daily Wh ÷ sun hours ÷ ~0.75 system efficiency (wiring, charge controller, battery round-trip, panel heat and dust). The battery bank must carry you through sunless days: bank Wh = daily Wh × days of autonomy ÷ max depth of discharge. LiFePO4's 80% usable depth is why it wins on-paper capacity math even before cycle life.
Typical daily-load reference
| Load | Watts | Hrs/day | Wh/day |
|---|---|---|---|
| Energy Star refrigerator | 150 | 8 (cycled) | 1,200 |
| LED lights, cabin (10 bulbs) | 80 | 5 | 400 |
| Laptop + phone charging | 100 | 6 | 600 |
| 12 V water pump | 60 | 0.5 | 30 |
| CPAP machine | 40 | 8 | 320 |
| Starlink / internet | 60 | 12 | 720 |
| TV | 100 | 4 | 400 |
| Microwave | 1,000 | 0.25 | 250 |
| Induction cooktop (per burner) | 1,500 | 0.75 | 1,125 |
Draw figures are published manufacturer/DOE typical values. Anything with heat in it (cooking, water heating, space heat) is what blows up solar budgets — propane or wood wins there in 2026 economics.
Sun hours cheat sheet (worst month)
| Climate | Peak sun hrs/day |
|---|---|
| US Southwest (AZ, NV, NM) | 5–6 |
| US Sun Belt average | 4–5 |
| Pacific Northwest winter | 1.5–2.5 |
| Northeast / Midwest winter | 2–3 |
| Northern Europe winter | 0.5–1.5 |
Guides
What size solar system for an off-grid cabin?
Worked examples from a weekend cabin to a full-time homestead — panel counts, bank sizes, and where the budget actually goes.
How many solar panels to charge a battery?
The 100 Ah to 400 Ah recharge math for 12/24/48 V banks — and why winter changes the answer by 3×.
Battery bank sizer ↗
Sizing the storage side in depth — LiFePO4 vs AGM bank builder with parallel-string planning. Generator backup? GeneratorSizer has the fuel-side math.