What Size Solar System Do You Need for an Off-Grid Cabin?

Step 1: Add up what you'll run

The Department of Energy's formula is the one to use: watts × hours used per day = watt-hours (Wh) per day. Find the watts on each item's label, guess the hours honestly, and add it all up.

LED watts from DOE's lighting guide (a 9 W LED replaces a 75 W bulb). Fridge draw from OutdoorGearLab's steady-state tests of 12 V compressor coolers. Pump draw from the Shurflo 4008 data sheet (2.2 A at open flow, up to 6.8 A near shut-off). TV from Champion's wattage chart. Starlink from its equipment specifications. Inverter idle from Victron's datasheet figure for the MultiPlus-II 12/3000.

A few things this table teaches:

• A 12 V compressor fridge is cheap to run. OutdoorGearLab measured steady draws of about 6 to 11 W on the good ones. The thermoelectric-style coolers in the same test (Cooluli, Wagan and Igloo Iceless) pulled about 46 to 62 W, five to ten times more. Skip thermoelectric on solar.
• The standard Starlink dish is a big load. Starlink lists 75 to 100 W on average for the Standard kit and 25 W for the Mini. Eight hours of the Standard is 600 to 800 Wh.
• Turn the inverter off when you're not using it. Victron lists 15 to 20 W of no-load draw for its 12 V, 3,000 VA MultiPlus models. Running 12 V lights, pump and fridge straight off the battery avoids that loss.
• Big heat-making loads don't belong on a small system. Champion's chart lists a coffee maker and a microwave at 800 W each, and most plug-in space heaters are labeled 1,500 W. Run those on a generator, or use propane.

Step 2: How many batteries

Your battery bank has to carry you through the nights and any cloudy days. How much of the battery you can use depends on its type:

• Lithium (LiFePO4): plan on using about 80%. LiTime rates its 12 V 100 Ah battery at 1,280 Wh and 6,000 cycles at 80% use, so a 100 Ah lithium gives you about 1,000 Wh.
• Lead-acid (flooded or AGM): plan on using about 50%. Backwoods Solar's battery worksheet uses three days of storage and never more than half the bank.

Battery Wh needed = daily Wh × days without sun ÷ usable fraction. Here's how the two camps work out for a two-day stay with no help from the sun:

Lithium: daily Wh × 2 days ÷ 0.8. Lead-acid: Backwoods Solar's worksheet, daily Wh × 6 ÷ 12 V × 1.2 (three days at 50%, plus 20% for optimistic ratings).

Lead-acid costs less up front but weighs much more and lasts fewer cycles. Our lithium vs AGM guide goes through the trade-offs.

Step 3: How many solar panels

A panel's watt rating is what it makes in perfect lab sun. In the real world, use this:

Panel watts needed = daily Wh ÷ (sun hours × 0.75)

Sun hours means the equivalent hours of full sun your spot gets in a day. The 0.75 is our planning allowance for wiring and charging losses, heat, dirt and less-than-perfect aim. It's the same number our calculators use.

The key is choosing the right month. Northern Arizona Wind & Sun, using NREL's maps, says designers almost always size for the worst case, December and January, and that much of the U.S. averages 4 sun hours or less in December. For a hunting cabin used in October and November, plan on 2.5 to 4.5.

If you're at the cabin every day. Panel watts = daily Wh ÷ (sun hours × 0.75). Shade from trees cuts output a lot more than this.

In a Northern Arizona Wind & Sun forum thread on sizing a weekend cabin, experienced owners advised that panels are the cheap part, so buy more than the math says. One Vermont owner found his three 125 W panels fine in summer but needed three 250 W panels and a bigger controller to get through December. Our solar placement guide covers aim, tilt and shade.

Try your own numbers in the Cabin Solar & Battery Sizer Calculator. It uses this same math, for weekend or every-day cabins.

The weekend cabin advantage

Most hunting camps sit empty during the week. That's good news for your panels. If nothing is running while you're gone, the panels get all week to refill what you used over the weekend.

Example: the comfort camp uses 1,170 Wh a day for two days, or 2,340 Wh a week. Spread over seven days of sun, that's about 335 Wh a day. At 2.5 sun hours, that's roughly 180 W of panel instead of 625 W.

The catch: the batteries now have to hold the whole weekend by themselves, plus a cloudy day, so don't skimp there. And anything left on while you're gone eats into the refill. A forum member's cabin batteries kept getting run down by a security camera and a DSL modem that stayed on all week.

Batteries in an unheated cabin

Hunting season is when cabins get cold, and cold changes the rules for both battery types.

Lithium

LiTime rates its 12 V 100 Ah battery to discharge down to −4 °F but to charge only at 32 °F and above. REDARC explains why: charging lithium below freezing causes lithium plating, which permanently cuts its capacity, and the damage adds up each time. REDARC's best charging range is 41 °F to 113 °F.

That's a real problem in a cabin with panels on the roof. On a sunny 20 °F morning, the panels will try to charge a frozen battery. Some lithium batteries, like that LiTime model, have no low-temperature protection. Protect yours one of these ways:

• Buy a battery with built-in low-temperature charge cutoff, or a self-heating battery.
• Use a charge controller with a battery temperature sensor set to stop charging below freezing.
• Keep the battery in the warmest part of the cabin, in an insulated box. REDARC also suggests a warmer mounting spot.

Lead-acid

Lead-acid can be charged in the cold, but Battery University warns the electrolyte can freeze and crack the case, and it's more likely when the battery is low. Leave lead-acid full when you lock up. A forum member points out a full flooded or AGM battery stays happy cold if the panels keep it topped up.

The rest of the system

The Department of Energy lists what a stand-alone system needs besides panels: batteries, a charge controller, power conditioning (an inverter for 120 V), safety equipment and meters.

• Charge controller. It sits between the panels and batteries and keeps the batteries from overcharging. MPPT controllers get more out of panels in winter than cheaper PWM ones.
• Inverter. Only needed for 120 V things like a TV or Starlink. Size it for your biggest load, and turn it off when you don't need it. Our Inverter Run Time Calculator shows how long your bank runs a load.
• System voltage. Higher voltage means less current for the same power, so smaller wire. A 1,200 W load is 100 A at 12 V but 50 A at 24 V. Small camps do fine at 12 V, and bigger ones often step up to 24 V.
• Wire, fuses and a disconnect. Size wire for the current and the length of the run with our Wire Size Calculator, and fuse every battery cable close to the battery.
• 120 V cabin wiring falls under the electrical code. Have a licensed electrician do it or check it.

Compare panels for a cabin roof on our solar panels page, and batteries on our lithium batteries page.

Questions people ask

How many solar panels do I need for a hunting cabin?

For a basic camp with LED lights, a 12 V fridge and phone charging, about 250 W of panel covers late fall if you're there every day, and less if it's a weekend cabin that charges all week. Add Starlink, a TV and an inverter and plan on 400 to 650 W.

How many batteries do I need for an off-grid cabin?

Enough to cover your whole stay plus a cloudy day. For a basic camp that's two 12 V 100 Ah lithium batteries, or about 270 Ah of lead-acid.

Can solar run a refrigerator at a cabin?

Yes, if it's an efficient one. A 12 V compressor fridge uses roughly 200 Wh a day once cold. A thermoelectric cooler can use five to ten times that, and a full-size household fridge also needs an inverter big enough for its starting surge.

Can I heat my cabin with solar?

Not with a small system. A plug-in space heater is usually 1,500 W, which would drain a 100 Ah lithium battery in under an hour. Use a vented propane or wood heater, and keep CO alarms in the cabin.

Is 12 V or 24 V better for a cabin?

12 V is simplest for small camps and runs 12 V fridges, pumps and lights directly. For bigger inverters, 24 V halves the current and the wire size.

Can I leave batteries in the cabin over winter?

Yes, with care. Leave lead-acid full so it doesn't freeze. For lithium, make sure nothing can charge it below 32 °F, and turn off every load you don't need while you're away.

Is a portable power station enough for a hunting cabin?

For a basic camp, often yes. A 1,000 to 2,000 Wh power station with a couple of panels can cover lights, a 12 V fridge and charging, and you can take it home between trips.