Cabin Solar Sizing Guide: How Much Do You Need?

A plain-English walkthrough to size your panels, battery bank, and inverter — no engineering degree required.

Sizing an off-grid system comes down to one question: how much energy do you use in a day? Once you know that, everything else — panels, battery, controller, inverter — follows. Here's the whole process in four steps.

Step 1 — Add up your daily energy use

List every device, multiply its wattage by the hours you run it, and total the watt-hours (Wh). For example:

LED lights: 40W × 5h = 200 Wh
12V fridge: ~50W averaged × 24h = 1,200 Wh
Laptop + phones: 60W × 4h = 240 Wh
Water pump, fan, TV, etc.: ~400 Wh

That sample cabin uses roughly 2,000 Wh (2 kWh) per day. Tally your own devices the same way.

Step 2 — Size your solar array

Divide your daily Wh by your peak sun hours (typically 3–6, use a low number for winter), then add ~20% for losses and aging:

Array watts = (Daily Wh ÷ Sun hours) × 1.2

For 2,000 Wh at 5 sun hours: (2000 ÷ 5) × 1.2 = ~480W, so a 400–600W array fits. In a low-sun region, lean toward the higher end.

Step 3 — Size your battery bank

Store 1–2 days of use so you can ride out cloudy weather. For LiFePO4 (which you can safely discharge deeply), divide daily Wh by your battery voltage:

Battery Ah = (Daily Wh × Days reserve) ÷ Battery voltage

For 2,000 Wh, 1 day reserve, 12V: 2000 ÷ 12 = ~167Ah, so a 200Ah LiFePO4 bank gives a comfortable day of backup.

Step 4 — Size your controller and inverter

Charge controller: divide array watts by battery voltage, add 25% headroom. A 480W array at 12V ≈ 40A, so a 40A MPPT controller fits. Inverter: add up the watts of everything that might run at once, plus surge headroom for motors — most cabins land at 2000–3000W.

Quick Reference

Recommended System by Cabin Type

A starting point — always check against your own daily-use total.

Cabin Type	Daily Use	Array	Battery (12V)	Inverter	Suggested Kit
Shed / hunting cabin	~0.5 kWh	100–200W	100Ah	1000–2000W	100–200W kit
Weekend cabin	~1 kWh	200–300W	100–200Ah	2000W	300W kit
Seasonal cabin	~2 kWh	400–600W	200Ah	2000–3000W	400–600W kit
Full-time cabin	~3–5 kWh	600–800W+	300Ah+	3000W	800W kit

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Not sure? Round up. Solar panels and lithium batteries are easy to add later, and a little extra capacity means fewer dark evenings and less generator time. Start with a complete cabin solar kit sized to the table above.

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Questions

Solar Sizing FAQs

How do I calculate my cabin's daily power use?

List each device, its wattage, and the hours you run it per day. Watts × hours = watt-hours (Wh). Add them up for your daily total. A small LED bulb might be 10W × 5h = 50Wh; a 12V fridge might be 50W averaged over 24h = ~1200Wh. Sum everything to get your target.

How many peak sun hours does my location get?

Peak sun hours are the equivalent hours of full-strength sun per day, typically 3–6 depending on region and season. Sunnier southern areas average more; northern or winter conditions average less. Use a conservative number for your worst season so the system still works in winter.

Should I size for the worst-case season?

Yes, if you use the cabin year-round. Winter has fewer sun hours and shorter days, so a system sized only for summer will fall short in December. Size panels and battery for your lowest-sun month, or plan to supplement with a generator in deep winter.

What if I get it slightly wrong?

Build in margin and you'll be fine. Oversize panels by ~20% to cover cloudy days and aging, and size your battery for 1–2 days of reserve. Both panels and lithium batteries are easy to add to later, so start with a sensible buffer and expand if needed.