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6 September 2006

After a rather longer delay than I was expecting, I'm back at my desk. We had a sudden overwhelming urge to convert the attic. Oh well, I've got a nice new office now.

1) Absorption Fridges - why they're a bad idea
2) New product range
3) 24 Volt Wiring

1. Absorption Fridges - why they're a bad idea
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I was going through my emails just now and found a couple that I had forgotten to answer - sorry - and which raised important points. The first was from a guy wanting to run a fridge freezer which consumes 3.2 kWh per day. I guess this is a caravan type absorption fridge, but it might just be an enormous compression fridge. Anyway, let's assume it's the former.

If you're not familiar with the terminology an absorption fridge, rather than push the refigerant around with a mechanical compressor, uses a second fluid which absorbs the refrigerant at key points in the cycle. This is then circulated by applying heat at the right point.

This is an old, but excellent technology. I remember my family having an Electrolux fridge when I was a child, which was silent and amazingly effective at freezing the milk. I've also seen them operating in developing countries keeping vaccines cool on a dribble of kerosene. Most people will know them, however, from the tiny caravan fridges that run on gas or the car battery. I've got one in my barn at the moment in fact. But they're inefficient.

I've just had a look at some numbers. From the Dometic website, the electricity consumption of a 142 litre absorption fridge with a small freezer compartment is 3.2 kWh / 24 h. Roughly the same sized 12 Volt compressor fridge from Shoreline Refrigeration (143 litres) consumes 345 Wh in the same period. That's over 9 times less! So you can see that it would pay for itself in no time. Dometic fridges are very good, but run them on gas!

Shoreline Refrigeration: http://www.boatfridge.com
Dometic: http://www.dometic.com/

Or you can use an inverter to run a mains fridge. The only small inverter that I know that will do that is the Steca Solarix Sinus range. Find out more here:

http://www.solar-power-answers.co.uk/products.html

2. New product range
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You might have guessed from the link above - I've introduced a range of solar power products. There is everything you'll need to build a solar power system; panels, controllers, batteries, lights and inverters. Plus you've got an expert (me) on hand if you need advice.

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Buy securely on line for shipping Europe-wide

http://www.solar-power-answers.co.uk/products.html
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I'm particularly pleased with the solar LED torch - it's much nicer than the others I've seen - £19.95 or 29.95 Euros. I must like it; I've got two myself. They're great for putting the bins out - it's pitch black here in the winter. Have a look, I think you'll like it.

3. 24 Volt Wiring
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I've been asked a few times what the yellow wire is for in the wiring diagram at http://www.solar-power-answers.co.uk/inverter_system.html so here's the reply I gave to the last person who asked:

"The reason it's like that is that it's a 24 Volt system diagram. Panels are 12V nominal output, so they need to be wired in series/parallel, but it can't be done like the batteries, because it's necessary to keep the junction boxes sealed.

So, the way it's usually done is to split the array in half, and wire each half in parallel. Then the positive of one half is connected to the negative of the other, hence the yellow wire, giving a 24 Volt nominal output on the other positive and negative connections.

In fact, it's normal to use a two core cble where the yellow wire is, so that the output cable can be connected in just one junction box. Some panels have an extra unconnected terminal to facilitate this."

I think I'd better put that on the page so that everybody understands.

A quick word on 24 Volt systems might be appropriate. It used to be that 24 Volt was the only option for inverter based systems. That was because there were no decent inverters available in 12 Volt versions, and those that were were expensive. That's not true any more, and in fact, for systems of 1 kW peak or less, you may well be better sticking to 12 Volts.

You'll still need shorter or fatter cables mind you, so if it's a long way from the array to the battery then 24 Volts will still be better. It's just not essential any longer.

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