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Powering your vanlife

Making, storing, and using power wisely is important for happy vandwelling. Power issues can seem overwhelming and confusing; this article intends to lay out the basics.

Before you spend money on making/storing power in your vehicle, be sure to leverage other sources:

  • plugs at your work, church, or anywhere else you visit regularly
  • plugs at cafes and restaurants – ask for a table near an outlet
  • look for outlets at bus stops, park pavilions, etc.

It may be useful to carry a gym bag with a power strip, extension cord, and any items that need to be charged. The power strips allows you to charge many things at once, and the extension cord helps you reach faraway outlets or outlets in inconvenient places (on a wall, behind furniture).

The Big Picture

There are two generally-separate electrical systems in your vehicle1):

  • House power (coach power, leisure power) is the (usually 12v) electrical system in the living area. It runs fans, lights, etc. It's what we are discussing here.
  • chassis power is the electrical system in the vehicle itself. Starter, alternator, headlights, etc. The two are usually separate systems, except when actively charging from the alternator.2)

How much power do I need?

Only you will know that, because only you will know what kinds of electrical loads you need (or want) to run. Unlike a wall socket in a house where you can run pretty much anything you want, using power you make off-grid is a series of choices and compromises. Some things are easy to run off-grid; some things are harder and require more infrastructure, planning, and money. Some things are impractical in campervans. Car-dwelling presents additional power challenges due to limited space and charging methods.

Real-world(ish) examples

Here are some very general ideas to get you thinking:

  • Trivial to run off the cigarette lighter port while driving
  • Easy to run off a portable power pack3)
    • Phone/Tablet/small laptop (MacBook Air, Chromebook) charging while parked
    • Fan
    • Small 12v LED lights
    • CPAP - especially with humidification turned off
  • Average loads - small ($) house power system: Example: 200w of solar and 100Ah of battery.
    • Small 12v compressor fridges – they use little power and run intermittently
    • laptop charging/use during the day
    • swamp coolers (due to high power fan motors)
    • gaming laptops run off solar during the day
    • charging e-bikes, etc during the day
  • Harder and more expensive to run - substantial ($$$) house power system - 400w of solar, 200Ah+ of battery
    • Larger 12v compressor fridges (especially if they have a freezer)
    • 120v refrigerators off inverters
    • charging/using laptops at night
    • gaming consoles|laptops|PCs
    • charging e-bikes, etc at night
    • Small microwaves when used for <3 minutes per day
      • Power draw is high, but duration is short. Needs a beefy inverter.
  • Difficult and very expensive to run - Massive ($$$$$) house power system - 600w+ of solar, 400ah of lithium battery, alternator charging.
    • Cooking with electricity, which is why we use propane
      • This includes things like insta-pots, electric stovetops (resistive or induction), toaster ovens, larger microwaves, etc
    • electric coffee makers, which is why we use propane4)
  • Completely Impossible unless you're on shore power
    • Heating the van. Tens of thousands of dollars in lithium batteries will barely last a day of running an electric heater. Which is why we use propane or diesel.

Note: devices that have "wall wart adapters" may not require an inverter.

Calculating power, battery, and solar requirements

The following is a guide to calculate battery storage and solar needs. Be honest about what loads you want/need to run and how long you plan to run them. You can also check out Far Out Ride's sizing guide and their load calculator if it's more your style. Remember that you can supplement/substitute the solar system with DC-DC charging from your alternator and/or shore power.

A general guide is to have 200w of solar for every 100ah of 12v lithium battery. No one has ever complained about have too much battery capacity or too many solar panels, so rounding up is always a good practice.

Calculating your battery size

(With credit to CMDR_Schrodinger)

  • Make a list of each and every electronic device you'll be using.
    • Jot down the volts, amps, and run-time (in hours) of each device. When noting the run-times (one hour = 1, half an hour = .5, etc.), assume worst-case scenarios (ie stuck in the van on a dark, rainy day).
    • If you're using any 120 volt devices, lookup the efficiency of your inverter. It should be easily found on the manufacturer's website or with the documentation.
      • This is generally documented as a percentage. You'll want to convert that to decimal form (ie 93% = .93) Take note of this value – it'll be used in the next step.
      • Please also note that inverters are less efficient the lower your usage to max draw ratio is. In other words, if you get a larger inverter, but only use a small fraction of it's power generation, the efficiency will not be as good as advertised; get an inverter that properly fits your needs so that you're not wasting power for no reason.
  • Calculate the daily draw of each device in watts:
    • For all 12 volt devices use the equation: volts * amps * run-time
    • For all 120 volt devices, use the equation: (volts * amps) / inverter efficiency * run-time
      • The amp draw requirements for most 120v AC devices that you find printed on the label is usually the peak load, the maximum that the device could ever draw. Most electronic devices will in reality draw far less than this (although kitchen appliances will typically draw their full rated load). Getting an electrical meter socket can help you get an estimate.
  • Calculate your total daily draw in watts by adding the individual watts for each device together.
    • Assuming you'll be utilizing a 12 volt LiFePo4 battery bank and wanting a 25% buffer to protect the longevity of your battery bank, use the following equation to get your minimum battery bank capacity in amp-hours: (total daily watts * 1.25) / 12.
      • Jot the result down down – this is the minimum battery bank capacity in amp-hours that you'll need to power your devices for a single day.

Calculating Solar Size

Solar panels only operate at “peak capacity” for approximately four to six hours per day. The amount of solar power your panels can capture will depend on the angle of the panels to the sun, cloud cover, temperature, latitude, dust on the panels, etc. The amount of time you'll spend capturing that solar power will depend on latitude, season, weather, etc.

As a general estimate, assuming ideal weather conditions, but worst-case charging time, divide the result of your minimum battery bank capacity by four. This result shows how many total watts of solar you'll require to fully charge your battery bank each day.

The chances of getting the full yield out of your panels are slim to none. In the North American winter, for example, you might only get up to 50% of your panel's rated max wattage even on a clear day.

For a more exact estimate based on time/place, see this article on solar harvest modeling.

Putting it all together

An example with a 93% efficient inverter and a 12 volt battery bank (Results are rounded up):

  • Electronic Devices:
    • Laptop: 120 volts; .54 amps; 8 hours = (120 * .54) / .93 * 8 = 560 watts
    • Light: 12 volts; 1.5 amps; 6 hours = 12 * 1.5 * 6 = 108 watts
    • Phone Charger: 12 volts, .5 amps; 10 hours = 12 * .5 * 10 = 60 watts
  • Total Daily Draw: 560 + 108 + 60 = 728 daily total draw (in watts)
  • Battery Capacity = (728 * 1.25) / 12 = 76 amp hours
  • Battery bank capacity in watts = 76 * 12 = 912 watts

“Perfect conditions” solar array wattage with a four-hour peak sunlight charge time: 912 / 4 = 228 watts of solar panels.

The above calculations are for Lithium batteries; for lead chemistries, you should double both the amp-hour and solar wattage to avoid battery murder.

sources of house power

Most campervans use solar combined with another charging source, usually the van's alternator. This combination can be both cheap and highly effective5)

Pro Con
shore power (outlet) cheapest per watt
abundant power
often not available
if available you are tied to the outlet by your cord/adapter
campgrounds with outlets are more expensive
solar automatically makes power when the sun shines
makes high voltages needed to fully charge lead-acid batteries
lasts for decades
most expensive per watt
can be complex
panels are large
output drops dramatically when shaded
alternator automatically makes power when driving
about 1/10th the cost of solar for the same current output
relatively low charging voltage6)
can result in chronic undercharging
should not idle to charge
most people don't drive enough to fully charge lead-acid
alternator (ciggy port) available on all vehicles typically limited to 10A (120-150w, see this end-around).
generator can make 1000w+ of 120v
can run for days
inverter models are quieter
can be expensive ($1000+)
needs to be stored when not in use
not allowed in some areas/times

Alternator & solar charging enhance each other when used together. Adding alternator charging to solar can significantly reduce the amount of solar required to meet your needs.

Note: So-called solar generators do not generate power: they are battery banks, usually AGM or lithium. See below. Wind power is generally impractical for van use.

use patterns

  • People who can camp in driveways can cheaply run shore power to the van with an extension cord.
  • people who weekend camp can charge the batteries from shore power on their return, augmenting with alternator, solar, or generator if needed
  • people who drive hours each day (delivery, trucking, etc) may be fine with DC-DC charging alone. This also applies to lithium chemistry batteries
  • people who spend long periods camped off-grid will probably want a robust solar install
  • people who want to run big loads off-grid can do it cheapest with a generator.

storing power

Power production tends to be heaviest during the day while power use tends to be heaviest overnight. This means power needs to be stored when power is abundant so it can be used later. The most common storage for power is in a deep cycle battery bank, aka “house bank”, “house battery”, or “auxilliary battery”.7)

Pro Con
Flooded lead-acid (FLA) cheapest per Ah
most tolerant of abuse
lowest current throughput
maintenance (“watering”) required
can only use 50% of rated capacity8)
Sealed lead-acid (SLA, AGM) able to charge/discharge more current than FLA
no maintenance required
more expensive per Ah9)
cannot check or replace electrolyte
LiFePO4 (LFP) lithium very close to normal 12v ranges
available as “drop-in” replacements for lead-acid
current throughput
can be more deeply discharged than lead-acid
most expensive upfront per Ah
cannot be charged in freezing temperatures
Non-LFP lithium cheaper than LFP per Ah
current throughput
thermal runaway
voltage not well-suited for 12v systems
"solar generators" convenient relatively expensive
designed for generic needs, not your specific needs
typically slow to charge
typically limited solar input limits and performance

The battery bank is sized to meet your daily power needs and as well as any extra margin you might like.

using power

Using power is the simplest part. It's so simple the newbie may find themselves overdrawing from the available power. A low voltage disconnect (LVD) is one way to keep from overdischarging the bank.

higher bank voltages

Although 12v house banks are most common there are use cases where higher bank voltages (24v, 48v, etc) may be desirable:

  • when some big DC load demands it (DC minisplit aircon?)
  • when 12v inverter size approaches 3000w10)
  • when someone stumbles into a great deal on a higher-voltage pack (Leaf battery fell off a truck)
  • when the vehicle has a 24v alternator, as found in some commercial vehicles like buses or box trucks


  • limited options charging from normal 12v alternators ←- even more niche than the inverter market
  • requirement to buck back down for “normal” 12v house loads
  • requirement for higher solar array voltages.
trailers don't have chassis power
or doing something exotic like shallow cycling
which you will have to recharge somehow
see the pattern?
Isolators are inexpensive, and the combination allows one to run much smaller solar configurations than if one were charging by solar alone
unless b2b
“leisure battery” for our UK friends
or longevity suffers
~2x the price of FLA
sometimes seen on propaneless “all electric” setups
electrical/12v/intro.txt · Last modified: 2023/09/17 11:51 by frater_secessus