To know how much runtime your camper has, you have to start with the basics: how much each thing you switch on actually uses. Without those numbers, sizing the battery or the panels is guesswork. Here's a guide to indicative consumption for the typical appliances in a motorhome, so you can do your sums. Remember they are approximate: real consumption depends on the model (always check the data sheet for yours).
How consumption is measured
Consumption is expressed in watts (W), the power, and in watt-hours (Wh) per day, which is the power multiplied by the hours of use. For a 12 V installation, amps (A) and amp-hours (Ah) are used as well. The idea: add up what you use per day in Wh and you have the basis of your runtime.
Indicative consumption (daily use)
- Compressor fridge: the biggest consumer, usually around 300-600 Wh/day depending on size, outside temperature and use. [Note: check the figure for your specific model.]
- LED lighting: very little, in the order of 30-80 Wh/day in total.
- Water pump: it runs in bursts, around 10-30 Wh/day.
- Charging phones, tablet, laptop: 50-150 Wh/day depending on devices.
- Roof fan: low, around 50-150 Wh if you run it for several hours.
- Parking heater (fan and electronics): variable, depending on model and hours.
- Small television: 30-80 Wh depending on hours.
The big guzzlers
Beware of appliances that produce heat or cold electrically: hairdryer, kettle, toaster, electric coffee machine, air conditioning, induction hob. They use so much (hundreds or thousands of watts) that, without being plugged into the mains, they can empty the battery in minutes. For real runtime, better to avoid them or use gas. We look at this when discussing the inverter.
From the table to your runtime
Add up the daily consumption of what you genuinely use, add a margin of 20-30% and you have your Wh/day. With that, you size battery and panels. The easy way to do it is the calculator for how much battery you need, and on the move, to see real consumption in the app (monitoring consumption).
In short
Consumption is measured in Wh/day; the fridge is the biggest draw and heat-producing appliances are the big guzzlers best avoided without a hook-up. The step you can take today: note down the consumption of your three biggest draws (almost always the fridge, the inverter and charging devices); with those numbers you already have the basis for calculating your real runtime.
