The Solar Powered Tent

Sunrise OffgridI had thought about going to the Sunrise Offgrid festival for three years and this year was the one I finally picked up my bed and walked, using public transport to get from North-Cornwall to North-Somerset. Actually, I was amazed for an ‘off grid’ festival quite how many people chose to go by car, but that is another story.

When you are camping on foot, you basically have to carry everything you are going to need and don’t have the convenience of a vehicle to move and store things for you. I changed my tent and sleeping bag to more compact versions to lighten the load.

Five days is quite a long camp for me, so I needed some kind of electric supply to run my tent light and charge my mp3 player which is essential to me when camping at a family festival full of screaming babies and noisy children, music and activity at any time of the night, with thin, fabric tent-walls. So I decided I needed to make my tent solar powered.

I do have a mobile phone but only used it every couple of days to assure my partner that I was OK and hadn’t been eaten by the natives. It didn’t need recharging as it was nearly always off.

Now I was a total failure at Physics at school, where I might have learnt more about electrical circuits. They wouldn’t even let me take the ‘o’ level, having scored 2% in the mocks for getting my name right. In fact I can even remember my Physics report which was, age 15 ‘a hopeless case I fear’ and age 16 ‘I have nothing further to add’. Taking my right to reply right now I would like to say: ‘shit teacher, made no effort whatsoever to engage creative and imaginative child in his subject’.

Sorry, digression over, these things have to come out. I had in my possession a dozen solar powered garden lights which I stripped down for their components. Solar powered garden lights are one of those things that are cheaper to buy than their components singly. Not only are there solar cells in each but switches, light sensitive switches, battery containers and LED lights. They come with rubbish batteries and it’s one of the wonders of consumerism that it is cheaper to replace these lights than buy decent batteries for them.

Solar powered tentThere are instructions online on how to strip down one of these garden solar lights. Even with my own dodgy physics background I managed to wire up twelve of the solar cells. I wired up three sets of four solar cells in serial and then wired those three sets together in parallel. I mounted these on a piece of plastic taken from an empty gallon tomato feed container, as shown in the image. I made holes through and wired on the inside. The plastic folds up concertina-like for compact transport.

Now I don’t quite get amps yet, but put this circuit onto volt meter to show nearly 10 volts in full sun, dropping to around 6 in cloudy weather.

I had read about blocking diodes online. Apparently you put a resistor in the circuit to stop the batteries discharging to the circuit once the sun goes in, but I haven’t done this yet. I just pull the plug out before dark until I have learnt a bit more about resistors.

I had also read about a voltage regulator being needed on the USB outlet to drop the maximum voltage of 9 volts coming in (from the solar panel) to 5 volts needed to charge my mp3 player. But I decided to do this with a 3 way switch. The solar panel charges the batteries with the switch in the central position. I then unplug the panel and switch one way to charge the USB socket at 4 x 1.2 volt fully charged AA batteries ( 4.8 volts) which seems to do the job alright, even with the mp3 player in use. If I left the panels on in full sun, the high incoming voltage might break the mp3 player.

Switching the other way opens the circuit to the tent light, which also has its own on-off switch. This is made from a cheap cupboard light in which the 3 x AA 1.2 volt batteries had died.

Now I realise that this is a laughably simple circuit for some of you nerdy types out there, but for someone who wasn’t even allowed to take their Physics ‘o’ level, it was quite an achievement. And when I ran my mp3 player dry on the first night camping by falling asleep with it on, I was able to recharge the next day using an AA battery bank charged from a solar panel on my tent, made from recycled materials. And when I fell asleep with the tent light on the following night, I was able to recharge the batteries again during a very overcast and rainy day.

And what better place, you might think, to successfully test my first real, home-made-from-recycled-materials, solar-powered tent gadget than at the Sunrise Offgrid Festival.

simonthescribe writes and publishes articles, books and websites themed around living a sustainable life in tune with nature.

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