• There is chassis power (your van's electrical system) and house power (your power setup for charging and running things). They are separate except when intentionally combined, as when charging from the alternator.
• As with money, using power is much easier than making/storing power.
• Only you can know how much power you will require; there will be math. Luckily it is the kind of arithmetic we learned in grade school.
• it is easy to make some power offgrid. It is challenging to make substantial power, and/or to make it consistently in all conditions.
• house power systems are DIY (made from selected components) or pre-made (“power stations”, “solar generators”). Regardless of your choice, ensure you understand your own needs, ability to charge, and capabilities¹⁾ of the products you are considering.

about these summaries

There are two generally-separate electrical systems in your vehicle²⁾:

• 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.³⁾

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.

See daily power requirements

Here are some very general ideas to get you thinking:

• Trivial to run off the cigarette lighter port while driving
  • phone and tablet charging - can also be charged from a USB battery pack.
  • laptop charging
  • ⇐100w loads from small inverters. Note that most small, inexpensive inverters are modified sine wave and not appropriate for all loads.
  • very small loads (like a cellphone) might be run off the ciggy/USB port without the engine running.
• very small loads like phone charging can be run off USB power bricks. See this testing video by Project Farm. Recharge the brick[s] from the cigarette lighter while driving, at cafes, etc.
• Easy to run off a small portable power station⁴⁾
  • Phone/Tablet/small laptop (MacBook Air, Chromebook) charging while parked
  • Fan
  • Small 12v LED lights
  • CPAP - especially with humidification turned off
  • Note: there are power stations available in all the sizes described below.
• 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
  • roof vent
  • 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
  • air conditioning, which is why we go where it is cooler
  • electric coffee makers, which is why we use propane⁵⁾
• Effectively Impossible unless you're on shore power
  • Heating the van with electric space heaters. 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.

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.

(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.

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.

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.

Most campervans use solar combined with another charging source, usually the van's alternator. This combination can be both cheap and highly effective⁶⁾

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.

• 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.

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⁾

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

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.

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
• when wiring and solar charge controller expenses need to be reduced

Challenges:

• 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.

• hoping, wishing, or daydreaming instead of doing the math
• failure to consider all loads
• belief that electrical outlets will be easy to find and free to use
• failure to consider the time it takes to recharge a bank
• relying on marketing rather than product specifications
• DIY: belief that all components have to be from the same brand
• Pre-made: belief that a “power station” is the default solution to every answer. People were vandwelling for decades before power stations were invented and marketed.