How many solar panels for a small off-grid cabin?
A small cabin using 3 kWh (3,000 Wh) a day needs about 948 W of panels at 4 peak sun hours — 3 panels of 400 W — with the energy stored in a LiFePO4 battery.
How to work it out
- Each watt of panel makes 4 sun hours × (1 − 14% losses) × 92% battery round trip = 3.16 Wh a day
- 3,000 Wh ÷ 3.16 = 948 W of panels
- 948 W ÷ 400 W = 3 panels (1,200 W)
There is no standard cabin, so this page uses 3,000 Wh a day as an example: a fridge, lights, a water pump, a laptop and phones, some TV and a microwave used briefly. Run your own appliance list through the solar load calculator first.
Adjust for your project
More options: Losses
- Panels
- 3 panels · 400 W
- Installed watts with that many panels
- 1,200 W
- Expected output per day
- 3,798 Wh
- Expected output per month (30 days)
- 113.9 kWh
Array size at other peak sun hours
| Peak sun hours per day | Solar array needed | Panels |
|---|---|---|
| 2 | 1,896 W | 5 panels |
| 3 | 1,264 W | 4 panels |
| 4 | 948 W | 3 panels |
| 5 | 758 W | 2 panels |
| 6 | 632 W | 2 panels |
What to know about cabin solar
- When do you use it? A summer-only cabin can size on summer sun. A cabin used in winter needs sizing on the worst month — in Chicago or New York, PVWatts’ lowest month is under 3 peak sun hours on a tilted array.
- Batteries for cloudy days. Two days of autonomy at 3,000 Wh a day is about 586 Ah of 12.8 V LiFePO4, or about 293 Ah at 24 V — the battery bank calculator does it.
- Go to 24 V or 48 V. At this size, a 12 V system’s currents get large. Three 400 W panels into a 25.6 V LiFePO4 battery is up to about 47 A through an MPPT controller.
- Heat and hot water need another fuel. Electric heating and water heating are far beyond a small cabin’s solar; propane or wood handles those.
For the whole system — batteries, panels, controller and inverter — use an off-grid solar system for a house as the bigger example, or the off-grid solar calculator with your own numbers. A fridge alone is on how many solar panels to run a refrigerator.
Different size? Use the full Solar Panel Calculator.
What you’ll need
- 400 W residential-size solar panelPremium price
Fewer, larger panels for a cabin, shed or ground mount. Their higher voltage usually means an MPPT controller.
See options on Amazon (opens in a new tab) - MPPT solar charge controllerMid-range price
Converts a higher panel voltage into charging current, so you can wire panels in series and lose less in the cables. Size it on output amps and maximum PV voltage.
See options on Amazon (opens in a new tab) - 12 V 100 Ah LiFePO4 batteryPremium price
About 1.28 kWh rated in a box roughly the size of a group 24–31 lead-acid battery at around half the weight. Check the BMS discharge limit and whether it can charge below freezing.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How many solar panels for a cabin using 1.5 kWh a day?
About 474 W — 2 panels of 400 W at 4 peak sun hours.
How many solar panels for a cabin used in winter (2.5 sun hours)?
About 1,517 W — 4 panels of 400 W for 3 kWh a day.
How many solar panels for a 3 kWh/day cabin with lead-acid batteries?
About 1,090 W, because lead-acid loses more in the charge-discharge round trip.
Other common sizes
- How many solar panels to charge a 100Ah battery — 3 × 100 W panels (288 W)
Sources
- National Laboratory of the Rockies (formerly NREL) — PVWatts® Calculator (opens in a new tab) — Look up the solar resource (peak sun hours) and yearly output for your own address; default system losses 14%.
- NLR (formerly NREL) — PVWatts® v8 API, NSRDB PSM V3 TMY data (opens in a new tab) — City figures on this site: fixed open-rack array facing due south, tilted at the site’s latitude, 14% system losses, queried October 2026.
- Victron Energy — Energy Unlimited (book) (opens in a new tab) — Lead-acid charge efficiency 80–95% (85% suggested as a starting value); battery energy efficiency about 75% for full cycles, about 89% in partial state of charge; inverter efficiencies above 90%.
- Victron Energy — Lithium Battery Smart manual, technical data (opens in a new tab) — LiFePO4 12.8 V: cycle life 2,500 at 80% DoD, 3,000 at 70%, 5,000 at 50% (to 80% of capacity); 92% round-trip efficiency; 12.8 V 100 Ah: recommended continuous discharge ≤100 A (1C), maximum 200 A; capacity about 20% lower at 0 °C; charge only between +5 °C and +50 °C.