Campervans have always needed electricity to power lights, radios, fridges etc. But in the past this has meant either hooking up to an 240/220v electric hook up and paying for the privilege, or perhaps risking using the starter battery and hoping to keep enough in reserve to start the van in the morning.
The more serious campers opt for heavy leisure batteries, or even car batteries in banks under the seats or in cupboards, which are in turn recharged by the alternator when the engine is running or by a charger from the mains hook up.
But technology has changed and more and more people are striving towards self-sufficiency, shunning the electric hook up and looking towards alternatives. Battery technology has improved and the advent of led lighting and devices with good internal batteries, capable of charging from 12v cigarette lighter sockets or 5v USB style charging points is dramatically reshaping the demand for power. Likewise, super efficient 12v compressor fridges give the ability to have ice cold beers and fresh food without resorting to gas, increasingly adding to the demands placed on the batteries.
This shift towards self reliance and renewable energy has led to the advent of affordable 12v solar charging systems, that allow the camper to make use of the sun to power pretty much all of their needs. This article will cover how I added solar to our van and is by no means the only way. It is simple and any DIYer can do it, but if in doubt there are many companies that will fit these systems for you.
The first part of any install is deciding on how much power you will need. So how do I calculate the power requirements? Most electrical items have their power requirements stated on a label on the rear of the appliance and they are usually quoted in Watts (w).
There is a useful formula for any electrical system which can be manipulated if you know two of the elements, to calculate the third:
This will help you with calculating the current draw (Amps), which will in turn help you decide what wiring to use, what fuses to use and how big your leisure battery and solar panel needs to be. Current draw is expressed as Amps (A) and Power as Watts (w), with Volts (v) supplied from the battery at a notional constant 12v. For ease of calculation, I will use hypothetical easy numbers in my examples.
Step 1: make a list of all the items you wish to power from your leisure battery, with the power requirements of each – some will be in watts and some in amps. Heaters, fridges etc might state 2 conditions: heat up and steady state. Heating up (cooling down for fridges) takes the most power, but once on condition, they only use a fraction of the power. You can assume you will not be using the maximum values continuously, but the environments you are camping in will affect this: in the desert your fridge will work a lot harder.
Step 2: using the formula above as required, calculate how many amps you will consume, assuming the worst case of everything on at once.
Cookers and heaters will consume the most, but unlike lights etc. they do so for a short time as they rarely run continuously.
As can be seen above in my example and noting this is the worst case, we require 50A to be able to power everything at once.
So what size battery do we need? Battery capacity is expressed as Ampere Hours or AH for short. In simple terms, this is the number of amps the battery can supply continuously for 1 hour. A 50AH battery supplies 50A for one hour, a 150AH supplies 150A for one hour. But the 150AH battery can instead supply 50A for 3 hours. Our example above has the utilities (lights etc) consuming 10A and would run for lets say, 4 hours per day and the cooker or heater would consume 20A each for approximately 30 minutes (combined 40A), reducing significantly when on steady state, or of course being zero when not in use.
10A x 4 hours = 40AH, plus 40A for 0.5 hours = 20AH.
40Ah + 20AH = 60AH
A 60AH leisure battery would give you just about what you need, but due to inefficiencies and this not being a perfect world, it is wise to have a margin of power. As a minimum I would suggest at least 100AH, using a deep cycle leisure battery rather than an old car battery from the back of your garage. The Little Red Bus has 2 x 75AH batteries in parallel, giving us 150AH, which has so far given us enough power even in Norway. That said, we don’t run the heater through the night, but we are confident we could if required.
Some of you will wonder; “Can I power a hair dryer from my leisure battery?” Well, in short yes, but if you intend to use high power consumption units like domestic microwaves, hairdryers, blenders etc, you will need a pure sine wave inverter which converts 12v to 240v and allows the use of domestic items. However, you will need the mother of all leisure batteries to do this, as inverters are inefficient and power hungry and will deplete your battery bank faster than your solar panel will be able to recharge it. Pure sine wave inverters are a lot more efficient than the cheap inverters available in auto stores: quality costs!
There are pages of discussion on the internet regarding the pros and cons of battery types and calculations which would give you better efficiency blah, blah. I don’t intend covering them here. This is a system which works for me, but I’m no expert.
When working with electricity, disconnect all the batteries.
If in doubt, consult an electrician
In Part 2 we will discuss the solar equipment.