Newsletter Archive
28 March 2004
1) Products page2) What size modules?
3) Design manual
1. Products page
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Thanks to an affiliate agreement there is now a full range of solar power products available from my website. Take a look at the new 'products' page at:
http://www.solar-power-answers.co.uk/products.html
There are all sorts of useful things like solar mobile phone chargers and garden lighting, and more serious stuff with panels of up to 100 Watts.
2. What size modules
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The other week, somebody asked me: "If the calculated array size is 100 Wp, is it best to use two 50 Wp modules, five 20 Wp modules or one 100 Wp module?".
On the face of it of course it doesn't matter, but it's worthy of further discussion.
Let's start with the case of a 12 Volt system. All the modules will be connected in parallel, so the peak wattage is all that's important. So, does it matter if you use lots of little modules or one big one? Electrically no, but you should consider these points:
- Each extra module requires interconnecting cables.
- The cost of smaller modules is likely to be higher.
- Because of the framing, smaller modules take up more space per watt.
However:
- A large number of small modules may be more flexible.
So, generally, the bigger the better except where the particular installation requires greater flexibility. It will take up less space, be easier to install and more reliable and probably cheaper.
However, if you're offered a job lot of small modules, don't turn them down out of hand. Cost in the extra cabling and they may still turn out cheaper.
What about 24 Volts? Because the nominal voltage of your average solar panel is 12 Volts, they have to be in series / parallel. That means that there have to be an even number. In this case, five 20 Wp modules or one 100 Wp module won't work. The only viable option is two 50 Wp modules wired in series.
So it's not always as simple as it seems. The Centre for Alternative Technology used to have a 1 kW solar roof made from 10 Watt thin-film modules. They wouldn't be my (or their) first choice, but they were donated, so suddenly it makes sense. Last time I went there they were dismantling it though, so perhaps it wasn't such a good idea after all...
3) Design manual
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My new book has got a title. It's called the "Solar Power Design Manual". Probably. I haven't finished it yet though. Soon, honestly...
