The honest answer is: it depends on what you run, and when. A cabin with a few LED lights and a phone charger can live on a couple of panels. A cabin with a full-size fridge, a well pump and a microwave needs a real system.
The good news is that sizing is not guesswork. Four numbers get you there. If you prefer to skip the math, plug your appliances into our cabin solar calculator and come back here to understand the result.
Step 1: Add up your daily energy use (watt-hours)
Every appliance has a power rating in watts (W), usually on a label or in the manual. Multiply it by the number of hours you use it per day to get watt-hours (Wh). Add everything up.
Here is a realistic weekend cabin:
| Appliance | Watts | Hours / day | Wh / day |
|---|---|---|---|
| LED lights (4 bulbs) | 40 | 5 | 200 |
| Energy-efficient fridge (average draw) | 45 | 24 | 1,080 |
| Wi-Fi router | 10 | 24 | 240 |
| Laptop + phone charging | 60 | 3 | 180 |
| Water pump | 300 | 0.5 | 150 |
| Total | 1,850 |
Now add about 20% for losses in the inverter, wiring and battery: 1,850 × 1.2 ≈ 2,220 Wh per day.
Fridge tip: a fridge doesn’t run constantly. Its compressor cycles on and off, so use its average draw, not its maximum. If you can, measure it for a day with a plug-in energy meter.
Step 2: Find your peak sun hours
Panels are rated under ideal lab sunlight. “Peak sun hours” converts a real day’s sunshine into the equivalent number of those ideal hours. It varies with your location and season:
- Cloudy northern winter: about 2.5 hours
- Northern US: about 3.5 hours
- Most of the US: about 4.5 hours
- Sunny south: about 5.5 hours
- Desert southwest: 6+ hours
Use the value for the worst month you plan to use the cabin. For a year-round cabin, that is December or January.
Step 3: Size your solar panels
Real panels produce less than their label because of heat, dust, shading and the angle of the sun. A safe rule is to count on about 75% of the rated power.
Solar watts needed = daily Wh ÷ (peak sun hours × 0.75)
For our cabin at 4.5 sun hours: 2,220 ÷ (4.5 × 0.75) ≈ 658 W, so around 700 watts of panels. In practice that’s seven 100 W panels, or two 350–400 W panels.
Step 4: Size your battery bank and inverter
Battery bank
Decide how many days you want to get through without any sun. Two days is a sensible default for a cabin.
For lithium iron phosphate (LiFePO4) batteries, which you can safely use down to about 10% charge:
Battery Wh = daily Wh × days of backup ÷ 0.9
2,220 × 2 ÷ 0.9 ≈ 4,900 Wh. To convert to amp-hours, divide by the system voltage:
- At 12 V: about 410 Ah (for example, four 12 V 100 Ah batteries in parallel)
- At 24 V: about 205 Ah
Lead-acid batteries should only be used down to about 50%, so you would need almost twice the capacity. That’s the main reason most new off-grid builds use LiFePO4.
Inverter
The inverter turns battery power into household AC. Its continuous rating must cover everything that could run at the same time, with some margin. Our appliances add up to about 455 W, but the fridge and pump draw a surge when their motors start. A 1,000–2,000 W pure sine wave inverter gives comfortable headroom.
Putting it together: our example cabin
| Component | Size |
|---|---|
| Daily energy use | ~2,200 Wh |
| Solar panels | ~700 W |
| LiFePO4 battery bank | ~410 Ah at 12 V (or ~205 Ah at 24 V) |
| Inverter | 1,000–2,000 W pure sine wave |
| Charge controller | MPPT, sized for your panel array |
At this size, a 24 V system is worth considering: it halves the current, so the cables can be thinner and the system runs cooler.
Prefer a ready-made kit? Complete off-grid kits bundle panels, an MPPT controller, an inverter and batteries that are already matched to each other. Compare the kit sizes against the numbers you just calculated.
See off-grid kits at Eco-Worthy
Common mistakes to avoid
- Sizing for summer. A system that’s perfect in July can run dry in January.
- Forgetting standby loads. Routers, inverters and chargers draw power 24 hours a day. They add up.
- Undersizing the battery. Panels refill the battery; the battery is what you actually live on at night and on grey days.
- Ignoring surge. Pumps, fridges and power tools can trip an inverter that’s sized only for their running watts.
- DIY wiring beyond your comfort zone. Low-voltage DC systems still carry serious current. For permanent installations, have an electrician review the design and check local permit rules.
Next step
Run your own appliance list through the cabin solar calculator. It does all four steps above in a few seconds.
Frequently asked questions
- How many solar panels do I need for a small cabin?
- A weekend cabin running LED lights, a small efficient fridge, a router and device charging typically needs around 2 to 2.5 kWh per day, which works out to roughly 600 to 800 watts of panels in most of the US. Your number depends on your appliances and your winter sun, so run your own list through the calculator.
- Can I run a cabin on solar without batteries?
- Not if you want power at night or on cloudy days. Without batteries, the system only produces electricity while the sun shines. The battery bank is what makes an off-grid cabin usable after dark.
- Should I use a 12V, 24V or 48V system?
- 12V is simplest for small systems (under about 1,000 watts of panels). For larger cabins, 24V or 48V halves or quarters the current, which means thinner, cheaper cables and better efficiency.
- Do I size for summer or winter?
- Size for the season you will actually use the cabin in. If you visit in winter, use your winter peak sun hours: the days are shorter and the sun is lower, so you need more panel wattage for the same energy.