For those of us in sunny (ish – I live in the UK, there are limits) countries, who like to go away in our vehicles and who use 12 volt electrical items, solar charging is now possible. In fact, it is quite easy with a small amount of reading and hopefully this article will help.
- You have a battery that I’m going to call the leisure battery but you can call it a second battery or camping battery. It powers your various camping related items but is not designed to run large appliances like heaters or disco units!
- You want to charge that up for free from the sun so that you are not tethered to an electrical socket on each camp site.
- List all equipment that you have in your vehicle that needs powering from 12 volts
- Check on the equipment or in the manual (which is probably online too and you can magnify the text easier!) for the wattage or the amperage. Make a note of each one in a list.
- Think about how often you use each item in each day and be realistic.
- Think about when you camp.
Now, convert the amps to watts by multiplying by 12 if you only noted the amps.
Otherwise list each item like this:
- Fridge uses 60 watts and will be in use for 8 hours per day on average when in the UK. That makes 480 watt hours per day.
- Lights are 2 watts each and I use 4 of them making 8 watts. In use for 2 hours each. Total is 16 watt hours.
- I use 2 USB sockets that are 7.2 volts and 2 amp which is a maximum of 14.4 watts. Total of 3 hours per day. That is 44 watt hours.
Then add up all those little watt hours to get a total for the day. In this example I get 540 watt hours. It doesn’t really matter what that means, just get the number!
In the UK I think we can get 6 hours of sunshine per day in the summer and 4 hours in spring and autumn (fall). Your country may be different and your feeling might be different.
You then take the total watt hours, in this case 540 watt hours and divide that by the number of hours of sunshine (aka charging) to get the number of watts of input charge you need to counteract the discharge. 540 watt hours divided by 6 hours is 90 watts.
Therefore to replace the lost charge I need a solar panel that has an output of 90 watts. If you need more than 100 watts, consider more than one panel.
The solar panel itself
They come in 3 main flavours, choose the type you prefer!
- Briefcase – these pack away and get stored unused when travelling. They can plug into the cigarette lighter that connects to the correct battery.
- Solid frame free standing panel – these can either be inclined towards the sun and stood on the grass when you are pitched or could be mounted on the roof of your vehicle. They tend to be the least expensive.
- Flexible and semi-flexible – these tend to be the most expensive and will be the focus of the rest of this article. They can be permanently attached to your vehicle.
We purchased a 100 watt solar panel that is “semi flexible” meaning it is about 2mm thick and bends a little but bending too much will break it. We used a Biard panel but other manufacturers are available and the price was around the £130 mark for the supply only of just the panel but this was in 2015.
We then purchased a used roof rack and connected it at the back of our bay window to the roof gutters with a little modification as roof racks are generally lower and narrower than a Bay window needs! It did cost £4 ($6) though!
As an expedient, we laid the panel on the grass upside down, laid the roof rack on the panel also upside down and gaffer taped the two together. It was a plan for a couple of months before glueing the panel to the Dormobile roof and 3 years later it is still gaffer taped!
There are two cables coming out of the solar panel and remember they are live except in the dark so tape them up / ensure the ends are not able to create a short circuit
The clever box in the middle
You cannot just wire the solar panel to the leisure battery – bad things will happen. You need a box in the middle that will stop the leisure battery sending its charge out through the solar panel into the night. It stops the solar panel over charging the leisure battery so far that it explodes. You need to avoid that. This clever box is called a regulator or solar controller and comes in 2 main types – PWM (pulse width modulated) and MPPT (maximum power point tracking). The PWM is less efficient at getting power out of the panel into your battery but is generally a lot cheaper. MPPT would be recommended if you camp outside summer as it is more efficient in less than full sunny days or if you have more than one panel.
The clever box for us was a cheap PWM controller that was about £10 / $15 and has just 3 lights. Charging, discharging and battery health (green is good, flashing is full, red is bad).
We dropped the solar panel cables down the air vent at the back so that there are no new holes on the van and therefore no chances of a water leak! Then got the wires up next to the spare wheel inside the vehicle as the controller is easier to see and that engine bay can get quite warm.
The leisure battery has two new wires, leisure battery positive to the hole on the regulator for battery positive. And then battery negative to regulator battery negative.
Then the solar controller should give you a light on the box.
Next I connected the solar cables – positive first as it is always live in daylight – to the solar controller / regulator. Now my controller had a light saying it was charging.
Then I checked the voltage coming from the controller to the leisure battery – I was getting over 13 volts! It works! I used a dedicated wire directly to the battery rather than using the chassis as it seemed to keep the regulator a little happier with its lights, I don’t know why!
Erm, that’s it
Now I have a solar panel permanently on the roof, always charging from dawn until dusk even on the move. The regulator means that even with the engine running and the split charge working, we do not over charge the leisure battery and it works even under the car port in the winter keeping that battery going until spring time.
Total cost of solar system £160. Cost of replacing the leisure battery every year £120. Saving on electricity per night at a camp site is up to £10 per night. This system seriously pays for itself in no time.