Friday, April 25, 2008

Basic campervan solar

Here's the very, very minimum you can put on your van. This is if you just want to keep your battery topped up over the winter- this is what's referred to as "trickle charging". As it sounds, you're just going to get a little bit of power literally trickling in. Depending on how big your batteries are, then you might be able to charge the phone for a bit, have the internal lights on for a bit, or even listen to the radio, again for a bit - but don't rely on it. All the power from the panel is going to go to the battery - by it's very nature, solar power is intermittent, it comes and goes during the day, then goes totally at night. So put the power into the battery, then take it out from there to ensure a constant supply.

Maplin are widening their range of solar products, starting from little personal pocket chargers to some fairly large ones - they're not necessarily the most efficient products, and you might be able to get better deals elsewhere if you know where to look, but Maplin are everywhere, and often run promotions. Check out their Alternative Energy section. You can also find all kinds of stuff on eBay.

What you get depends on how much you're prepared to spend, you get what you pay for.

All solar panels are "rated" (eg classified) in Watts. A watt is a measure of power. Technically, it's the ability to generate 1 joule per second. A joule? Pleasingly, a joule is the energy required to throw an apple up 1 metre in the air. So the Watt rating is how much power you can theoretically obtain from the panel. It's probably not going to be able to throw an apple very high though.

The battery you're going to be plugging into is going to be 12 volts. The current going in and out is measured in amps - the rule is that current equals watts divided by volts. So, in a 12v system, to find out what the current going in is going to be, divide the rated power in watts by12. As a reference point, mobile phones seem to draw about 0.5 amps when charging.

Maplin and eBay panels at the moment (April 2008) seem to start at 1.5 or 2.4 watts, both for about £15, then about 5w for £30-40. But bear in mind that this is theoritical maximum, and it's pretty unlikely you're ever going to see that. So our budget panels will give us ...

Watts Amps
1.5 0.13
2.4 0.20
5 0.42

feel the power! Even if you have a 5 watt panel in maximum conditions at midday with the angle right and everything, you're not going to be able to directly charge a mobile phone. But you will stop your battery going flat.

Installation of these panels is incredbily easy - just stick the panel on the roof, and run the cable down to the battery. Depending on what you've bought, you often get 2 big crocodile, like in jump leads. Attach each lead to the correct battery terminal (red for positive, black for negative), and that's it - you've got power! One thing to note - you've created an electrical circuit, with power being collected during the day from the solar panel, and sent down to the battery. Unfortunately, this is a 2 way process - at night, the power is going to flow back the other way. Unless you want the panel to heat the night sky, either make sure you unplug it at night (hassle, and you'll forget), or get a panel with a blocking diode (it'll say on the box).

Above 5w, you're going to need extra bits, but that's all you need to get started!

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