I am lucky enough to have a dad who is an electrical engineer. He planned and installed all the electrical systems in the Carabane. He's the one who really should be writing this post- but I am going to try to explain everything in layperson's terms!
Production, consumption and storage
I want to come as close as possible to self-sufficiency. In terms of electricity, self-sufficiency is a function of 1) how much power I consume 2) how much power I can produce 3) how much power I can store.
So to reduce the power consumption to the maximum, I decided to heat via gas (and not electricity). I do not have a kettle, a vacuum cleaner, television, or microwave. The electrical load is therefore reduced to : the fridge, LED lighting, charging my phone, laptop and other portable devices, 3 ventilation fans (stove, heater, and toilet), and a hand blender in the kitchen.
We calculated the power use to be about 1 kwH per day. The fridge takes about half of that- it's by far the largest consumer.
Next, the amount of power I can produce using a photovoltaic panel depends on the panel size, the panel efficiency, the panel orientation, and the weather (hours of sunlight). Using an estimation of around 1000 hours of sunlight per year (an estimate for Switzerland, although it varies a lot from one region to another), we calculated that I would need a 360 watt panel, well-oriented for maximum sunlight, in order to theoretically produce as much power as I consume. I say theoretically because those 1000 hours of sunlight are not spread evenly throughout the year.
The amount of power I can store is purely a question of battery size. We decided not to plan for multiple days with no sunlight or backup power, and pick a battery that is sized for the power consumption of one day. Well, really two days, because to make the battery's life longer you aren't supposed to drain the power under 50%. 1060Wh/d ÷ 12V = 88.3Ah working capacity ÷ 0.5 (50%) discharge duty cycle = 177Ah. So we picked a battery with a capacity of 170 amp-hours.
AC/DC and 12v / 220v
The solar panel produces direct current (DC) at 12 volts. Most appliances designed for caravans use 12v. I tried to keep the most of the circuits at 12v, as there is less loss and is less dangerous. There are only two outlets where the direct current passes through an inverter to produce the standard 230v AC current.
So there are two breaker panels, one for the 12v circuits and one for the 230v circuits.
Wiring
After the design came the actual wiring. Each plug, switch, and light was hooked up with a cable, grouped at a 'terminal strip' and then connected to the breaker panels in the utility closet behind the caravan. I was very impressed by my dad's work in the utility closet, because he managed to hook up all the different pieces correctly and neatly.
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