This is an old revision of the document!
It's not hard, but it does require paying attention and being realistic about what you will actually power in the van.
The primary goal is how to figure out your daily power requirement. We will do this step by step and end up with watt-hours (Wh, see below).1)
All electrical appliances (aka loads) have labels/stampings on them2) that describe how much power they draw.
Watts are only half the story. We need to know how long the doodad will be run.
NOTE: some loads, even if plugged in 24/7, cycle on and off. A good example is a compressor refrigerator. A common rule of thumb is that a fridge will run the compressor ~1/3 of the time. So you would use 8 hours instead of 24 hours for that load. (24 / 3 = 8).3)
It may be easiest to do this in a spreadsheet where you can see all the loads at once, and twiddle numbers to see how it affects your daily power requirements. Here's a simple example:
The numbers in green were calculated automagically by the spreadsheet.
The more accurate your estimate the easier it will be to build a system that meets your needs on your budget.
Individual loads in the van will be either
Loads run off inverter will draw more power because of inverter losses4). The inverter specifications will say exactly what this the efficiency rate is, but for our purposes we will assume 90% (i.e. 0.9).
To get a more accurate estimate when can enter this efficiency rating into the spreadsheet, divide loads into DC/AC, and let the spreadsheet do the work for us:
The number is yellow is the inverter efficiency. I typed that in one spot so the spreadsheet could refer to it as often as it needs to.
A couple observations: