Tuesday, April 29, 2008

Mo' power!

Mo' Power! the war-cry of the micro-generator - however much power you've got coming in, you always want more.

Previously, I looked at the most very basic, budget system - 5w, straight onto the battery. This produces at most half an amp, which will make sure that your battery has more of a chance of starting if you've been parked up for a while, but nothing more.

If you're going to spend any length of time in your van, going to be using the lights, pump, radio or charging your phone, then you want something with a little more oomph. Unfortunately, it's going to cost a little bit more, and be a bit more awkward to set up, but nothing impossible, depending on what you want to do and how much you want to spend.

There's 3 basic components you'll be needing now:
  • big solar panel
  • charge controller
  • leisure/deep cycle battery

Solar Panel
How big a solar panel you choose is up to you. You need ask 3 questions:
  • how much power do I actually need
  • how much space have I got
  • how much money have I got
Remembering the "current = watts divided by volts" rule, on a 12v system you're going to be something like:

Watts Amps
12 1.0
16 1.3
32 2.7
64 5.3

but do remember, this is the manufacturer's rating of the panel, not what you're actually going to see. For my van, I started with a 32 watt Unisolar FLX-32

as the manufacturer intended, or how it looks actually lashed to the top of the van:
These panels are great. They're flexible - designed for yachts, being lashed to booms, sat on by hairy old sea-dogs, everything that the cruel sea can throw at them. Ideal too then for the naturally keen but clumsy. Here's the data-sheet for this series of panels

Rated Power

Rated Voltage

Rated Current


Open Circuit

Voltage (Voc)

Short Circuit

Current (Isc)

USF-5 516.50.3023.80.3721.80” x 9.71”
USF-11 10.316.50.6223.80.7821.80”x 16.70”
USF-32 3216.51.9423.82.4056.27” x16.70”

I've highlighted the USF-32 output- 1.94 amps! More than enough to charge the phone. Unbreakable, manageable size, decent output - just one snag. Unisolar don't make them anymore ...

But there are plenty of other options, but bear in mind the size of the panel and how you're going to fix it to the roof. The guys at Solar Energy Alliance are a great place to start, but other outlets are available ... there's a lot more to say about panels, but I personally feel that 32w is the minimum you need for a van.

Charge Controller
These little rascals sit between the panel and the battery. They stop the battery being overcharged (you should be so lucky) and also stop the electricity flowing back out of the panel at night. The one I've used for years is the ICP 7 amp controller - as the manufacturer intended:
As you can see, it has 2 wires going in and out - red for positive, black for negative. The input from the panel has bare-wire, the output to the battery are rings to attach to the terminals. It's down to you to work out the best way of connecting everything together, I'll cover the way I've done it later.

If you've got power coming in from your panel, then the yellow light on the left lights up, in the eventuality you actually manage to fully charge your battery, the green on one the left comes on (it will also do this if connected to an active panel, but not a battery - check your connections).

Again, other controllers are available, but I've used this for years, it's nice and tidy, doesn't get in the way, and is reasonable value.

You'll need a charge controller if your panels are anything above 5w, but check the capacity of the controller, remembering the watts/volts rule. The 32w unisolar panel can produce about 2 amps, so the 7amp total for this controller is fine. My current full solar array can get up to about 5/6amps on a good day, and I have noticed the charge controller kicking in to slow things down. I haven't quite got to the bottom of that yet, but be careful to match your controller input to the total power of the solar panels.

The workhorse of your system. When the sun goes down, who's there for you? Not your solar panel, that's for sure. If it wasn't for the charge controller, the turncoat would be letting all your hard generated power leak out into the night.

Your battery is the foundation of your renewable energy system. Sun (and wind) are too variable to rely on at any particularly moment, and solar just isn't there when you need it at night, when you're rummaging around in the van trying to find the brandy (for example).

The type of battery you need is a leisure/deep cycle battery. These look like normal car batteries, are rated just the same at 12volts, but are specially designed to withstand repeated charge and more importantly, discharge. If you run a normal car battery flat more than a few times, then you'll kill it, and running down a battery flat can happen quite a lot.

I've used a 110 amp hour Elecsol battery successfully for several years now:

They come in all shapes and sizes, but expect to pay about £100. There's lots of rules and things to remember, but all you need to know for now is don't buy second-hand. You don't know where it's been, or what it's been through. Get yourself a nice leisure battery if you haven't got one in the van already - put it where the existing one is, it works just the same, plug in your panel and charge controller/diode and that's it!

I ran a 32watt solar panel, 7amp charge controller and 110 amp/hour battery for years - it sometimes went flat if things got left on for too long, but if the panel was left to charge the battery for a few hours without anything on the battery, it always charged enough to start the engine and get us off site

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