Tacklebox ’n Tools

Cabin Solar & Battery Sizer Calculator

List what you run at your hunting camp or cabin and get the battery bank, solar panels, charge controller, inverter and generator that keep it going, for weekend trips or full-time living.

How to use it

  1. Tell it how you use the cabin. Weekends with the cabin empty all week, or every day. Then pick the season you need it to work in.
  2. List what you run. Start from an example camp, then change the watts and hours, remove what you don't have and add the rest.
  3. Pick your batteries. Lithium or lead-acid, your system voltage, and how many cloudy days to ride out.
  4. Read the results. Battery size, solar watts, charge controller, inverter, whether you need a generator, and what to buy.
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Your setup

An example is loaded to start. Change any field and the results update. Simple shows the essentials. Detailed adds inverter idle draw, a solar table for every season, where the power goes and the math.

View

Your cabin

How you use it
days
A Friday-to-Sunday trip is about 2 days of use.
Size for the worst month you'll be there. Hunting season is often the darkest.

What you'll run

Picking an example replaces the list below. Then edit anything.

Watts are typical figures from published charts. The label on your own gear beats any estimate. AC means it plugs into a 120 V outlet through an inverter.

An inverter left on uses power even with nothing plugged in. Victron lists 15 to 20 W for its 12 V, 3,000 VA models, which is 360 to 480 Wh a day. We add 15 W all day when this is checked and you have AC gear.

Your batteries

Battery type
days

How the numbers are worked out

Daily use

Each item uses watts × hours a day × how many watt-hours (Wh) a day, the formula the Department of Energy uses for appliance energy. If you leave the inverter on all day with AC gear, we add 15 W × 24 hours = 360 Wh for its idle draw, the low end of the 15 to 20 W Victron lists for its 12 V, 3,000 VA models.

Watts come from published charts and spec sheets, listed under Sources. Items marked "estimate" are typical values. Use the label on your own gear when you can.

Battery bank

The bank has to carry you without sun for 1 day + your cloudy days if you're there every day, or your whole stay + your cloudy days for a weekend cabin, since the panels only refill it between trips.

Lithium (LiFePO4): Wh needed ÷ 0.8, so you use about 80% of it. LiTime rates its 12 V 100 Ah battery at 1,280 Wh and 6,000 cycles at 80% use.

Lead-acid (AGM or flooded): Wh needed ÷ 0.5 × 1.2. Backwoods Solar's battery worksheet uses no more than half the bank and adds 20% because lead-acid ratings run optimistic. A 12 V 100 Ah lead-acid battery is counted as 1,200 Wh.

Battery count is rounded up to whole 12 V 100 Ah batteries, wired in series to reach 24 or 48 V.

Solar panels

Panel watts = daily Wh ÷ (sun hours × 0.75). The 0.75 is our planning allowance for wiring and charging losses, heat, dirt and imperfect aim, the same number our other calculators use. NREL's PVWatts model starts from 14% system losses.

Weekend cabin: the panels get all week to refill one stay, so we use daily Wh × days per stay ÷ 7 in place of daily Wh. Anything left on while you're gone eats into that.

Sun hours are rounded from NREL-based maps. Northern Arizona Wind & Sun notes that designers size for the worst months, and much of the U.S. gets 4 sun hours or less in December.

Charge controller amps are panel watts ÷ battery voltage, rounded up to a common size. Check the controller's own panel-watt and voltage limits, which are listed for each one on our store page.

Inverter and generator

The inverter has to run all AC gear under 500 W at once, plus your single biggest item of 500 W or more, since things like a coffee maker, microwave and saw are usually run one at a time. Gear with a motor or compressor can pull several times its running watts for a moment at start-up, so leave headroom for those.

We suggest a generator when you run a 1,000 W or bigger load, or when you size for late fall and winter sun, for cloudy stretches. Its running watts should cover your biggest load. Running watts and run times for each generator come from the maker's spec sheet.

What it leaves out

  • Inverter conversion losses on AC gear. Check your inverter's efficiency rating.
  • Shade from trees, which cuts output a lot more than the 0.75 allowance.
  • Cold weather, which cuts battery capacity. Lithium also can't be charged below 32 °F unless it has low-temperature protection or a heater.
  • Batteries getting older. Plan a little extra if you want the bank to last years.

Planning estimates. Heat and cook with propane or wood, not solar. A generator always runs outside, at least 20 feet from the cabin with the exhaust pointed away, as the CPSC and CDC advise, and keep battery CO alarms inside. Fuse every battery cable close to the battery, and have a licensed electrician do or check any 120 V cabin wiring. Our cabin solar guide and generator vs solar guide go deeper.

Sources