How to Size a Power Station — Load Math for a Fridge, a CPAP and a Camp Kitchen

Not what you might run. What you will.

The most common sizing error is including a kettle "just in case". A 1,500 W kettle for ten minutes is 250 Wh — a quarter of a 1 kWh unit for one cup of tea. Decide now whether that is a real requirement, because it changes the answer enormously.

Our worked example is a two-night car-camping trip:

• 12 V compressor fridge
• Two phones
• One laptop, evenings
• LED lantern
• CPAP machine

The number on the label is usually the maximum draw, not the average. For anything with a compressor or a thermostat — fridges, coolers, heaters — the running average is far lower because the unit cycles on and off.

Typical figures, which vary by model:

Watts × hours = watt-hours. That is the whole of it.

Our two-night trip, over 48 hours:

Two immediate observations, and both are typical.

The fridge is nearly two thirds of the budget. It is the only thing running all 48 hours. In almost every camping power budget, refrigeration dominates — so if you can live out of a cool box for one of the two nights, you halve your requirement.

The CPAP is the second largest item, and it would be the largest if the humidifier were on — 1,120 Wh instead of 560.

Here is the step almost everyone misses, and it is the reason this site exists.

A power station rated at 1,000 Wh does not give you 1,000 Wh. Independent testing puts real delivery between 75% and 93% of the rating, with most units at 84–87%.[1][2]

So you cannot buy a unit rated at your requirement. You must divide:

Rated capacity needed = watt-hours required ÷ 0.85

For our example: 3,350 ÷ 0.85 = 3,941 Wh rated.

If the unit you are considering has an independently measured figure, use that instead of the 0.85 estimate. That is always better than an assumption, and it is why we publish measured figures for every unit we cover.

3,941 Wh rated is a large unit — the EcoFlow Delta Pro 3 class, at 4,096 Wh rated and 3,790 Wh measured usable.[3] For a camping trip that is excessive and expensive.

So revisit the assumptions, which is what the exercise is for:

With a fridge for one night and a pair of 100 W panels, you are into the 2 kWh class — the Jackery Explorer 2000 v2 at 1,710 Wh measured, or the Bluetti Elite 200 V2 at 1,910 Wh.[4][5]

Without the fridge at all, a 1 kWh unit covers it comfortably.

Continuous output. Capacity is the size of the tank; output is the size of the pipe. A 2 kWh unit rated at 800 W will not start a 1,000 W kettle regardless of how full it is. Check the continuous watts against your single largest simultaneous load.

Surge. Motors — pumps, compressors, power tools — draw several times their running wattage for the first fraction of a second. A fridge averaging 52 W may pull 800 W to start. Surge ratings are published but, on this site's evidence, not always reliable: one test of the Bluetti Elite 200 V2 recorded a shutdown at 3,140 W against a 3,900 W lifting claim.[6]

If you intend to recharge from panels, run a second calculation — your daily use against your daily input.

Panels rarely produce their rating. We assume 75% of nominal in clear conditions, so two 100 W panels deliver about 150 W. Over a seven-hour useful solar window that is roughly 1,050 Wh a day.

If your daily consumption is 1,675 Wh, two panels do not keep up. You need four — and then you must check that your unit will accept four, because several cap at 400 W.[7]

More on this in solar recharge in practice.

Once you have your number, the full ranking lists every unit by independently measured usable capacity, so you can match it to a real product rather than a rating.