Today is a day of looking up electrics for my motorhome. Various naysayers have been saying heating and water heating should be done with propane. The awkward sod in me says let's look at an electrical solution instead. I usually buck the trend.
The first thing I did was to check the internet for an electric shower. Low and behold, there is one at Home Depot for $103. That's affordable. Here it is! The specification is for 2.5kw which seems a trifle excessive. The amperage of the unit is stated to be 23 which means at 110v the power used is 2530 watts. Elsewhere, a Chinese supplier was offering a 300w shower. Thus I checked to see what was on offer in Britain. Britain is very happy with electric showers. The lowest rating on their B&Q website was 7.5kw. At 220v that would be around 34amps. All of that, honestly seems excessive. The goal is not to luxuriate in a hot shower for 20 minutes but simply to get clean in warm water. There's a limited amount of water available in any motor home. 2500 watts straight off an inverter with no losses at all. A 38 ah 12v battery would supply just 456 watts. It would take 5 linked together to provide enough power for that shower. This, of course, is the point where most people say "screw it" and go for propane.
A shower does not have to be hot. It just has to be warm enough not to be perceived as cold. Thus, the 300w shower might well be a solution. The next things to turn our minds to are the power consumption of the fridge, microwave and other appliances. Then we need to look into power generation using wind and or solar power.