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12V Power & Solar Calculator

List what you run at camp to see how many amp hours you use in a day, how long your battery lasts without charging and how much solar it takes to keep up.

What you run

Use the watts or amps on the label of your own gear. A fridge only runs part of the time, so enter the hours its compressor runs, not 24.

Quick add (typical figures, edit to suit)

Battery and solar

Your power budget

Daily use0Ah0 Wh at 12 V
Battery lasts–Enter your battery size
Solar to keep up0WTo cover a full day’s use
Your solar makes–Enter your panel size

Add what you run to see your power budget.

An estimate. Real use changes with the heat, how often the fridge is opened and how the panel is aimed.

How the 12V power calculator works

  • Daily use: watts × hours for each item, added up. Amps are converted at 12 volts (watts = amps × 12). Amp hours = watt hours ÷ 12.
  • Battery lasts: battery capacity × the usable share ÷ what you use in a day, less whatever your solar puts back.
  • Solar: panel watts × hours of full sun × 0.7. The 0.7 allows for heat, dust, panel angle and losses in the cables and controller.

The quick-add figures are typical values to get you started. The label or manual of your own fridge, lights and chargers is the better source, so change them to match.

Looking for gear? See our off-grid power reviews and the Kings solar comparison.

Common questions

How do I convert watts to amps on a 12V system?

Divide watts by 12. A 60 watt appliance draws 5 amps at 12 volts. To get amp hours, multiply the amps by the hours it runs: 5 amps for 2 hours is 10 amp hours.

How much of my battery can I use?

A common rule of thumb is to use about half of an AGM or other lead-acid battery, and around 80% of a lithium (LiFePO4) battery. Check what your battery’s maker recommends and change the usable figure in the calculator to match.

Why does my solar panel make less than its rated watts?

The rating is measured in ideal test conditions. At camp, heat, shade, dust, the angle to the sun and losses in the cables and controller all cut the output. The calculator allows for a 30% loss, and you set the hours of full sun for the season and place.

Related on AdventureKit

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Kings Solar Comparison: Which One Belongs in Your Kit?

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