IN CONVENTIONAL LIFE we got used to almost limitless electricity being only an outlet away. We rarely thought about how much power our stuff consumed until we blew a fuse, tripped a circuit breaker, set something on fire, or got the electrical bill.

But living off-grid means living without the grid that delivers the mighty river of excited electrons. We nomads have to provide our own electricity if we want it.

So among the frequently asked questions from those preparing to live in a vehicle are, “How much solar and battery capacity will I need?” and, “Will this amount of electricity be enough to run this, this, this and this?”

How to figure it out

Somewhere on every electrical device there’s a label listing how many Watts it draws when in use. Some appliances use more at startup to get all the parts moving or to bring things up to temperature. Some cycle on and off to maintain temperature settings. But anyway, the Watt rating on the device is a suitable place to begin figuring power usage.

For actual real-world wattage draw numbers, you can plug your AC-powered things into a Kill-A-Watt meter. If you already have a power station, its meters will also give you that information — and for your DC-powered devices as well. (But you want to know how much power you’ll need so you can get a sufficiently powerful power station, so… yeah, the Kill-A-Watt.) 

Go though all the electrical things you want to use in your rig and write down their Wattage. Then estimate how much time each day you will be using the thing. A few seconds for a blender? A few hours for a slow cooker? All day for a heater or air conditioner? When in doubt, round your numbers up. Compare your numbers to this chart.

For example, you might use a 300W mini cooker for 15 minutes twice a day. Three-hundred Watts uses 25Ah per hour, so 12.5Ah for a half hour. 

Another example: a 700W microwave for 3 minutes (5% or 1/20 of an hour). Divide the 58.33 Ah that 700W would use in an hour by 20 and get 2.9Ah.

A CPAP machine with a humidifier uses about 90W. So 100W for 8 hours is 66.67 Ah.

According to Kill-A-Watt, charging my laptop draws 44W. My 20,000mAh battery pack draws 18W when charging. My hot spot draws 15W. My phone draws 13W.

Finally, add up the Amp hours to get your estimated daily use.

Amp hours versus Watt hours

After doing all that arithmetic, you might need to do more. If you’re assembling your own electrical system using lithium batteries, you’re in luck. Those batteries are not only rated in Amp hours, you can also use almost all of those Amp hours between recharges.

If you’re using deep-cycle lead-acid batteries (AGM’s for example), they are also rated in Amp hours. However, you can use only half of those Amp hours between recharges, otherwise you will ruin the batteries. So you’ll need twice as many Amp hours to do the same job as lithium batteries.

As for power stations (which also use lithium batteries), they’re rated in Watt hours. Because, reasons. You can use this handy online converter to get figure out the equivalent Amp hours.

Something else to take into account

Let’s say you use up most of your electricity in a typical day and you’re going to recharge your system with solar the next day — while still drawing electricity for your daily uses. This is like trying to fill a bucket with a hole in the bottom. Is power going out faster than it’s coming in? And the situation is worse during periods of less sunlight. So you would need greater Amp hour capacity. Or a faster way to recharge. Or you could reduce your usage.

Reality check

If your calculated electricity use is higher than you had expected, you have to decide whether you want to spend what’s necessary for a system that will produce enough electricity (with some to spare) or whether you’ll give up some of the stuff on your electrical device wishlist. Sunlight is free, but not the system needed to turn sunlight into refrigeration, dinner, heat, cool air, entertainment…