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6 June 2007

This time, a few thoughts about how to expand your solar power system. Hope you find them interesting.

1) System Expansion
2) Solar Garden Lights

Solar Power Design Manual - Teach yourself Solar Power

1. System Expansion

So, you've installed a solar power system, or you've inherited one with a house you've bought. But it doesn't provide sufficient power. How can you expand it? There are a number of possibilities:

- Add more modules and / or batteries. That's the obvious way, but there are limitations. What if the controller can't handle the extra current? Well, you can change it for a larger one, so that's not a great problem. But it's best if the modules and batteries you add are of the same type as the existing ones. This may pose a problem if they are no longer available. And there is a limit to the number of batteries you can put in parallel. And, if the existing batteries are nearing the end of their life, then it would be more sensible to replace them altogether.

Practically, it depends on the nature of the system. If you have a system with two 70 Watt modules and one 100 Ah vented battery, then adding one more module and one more battery of the same type, if not the same exact model, will work fine. If the system already has four batteries in parallel, then you might add one, but certainly not another four. You have to use your judgement and common sense.

- Double the voltage. If the system is a 12 Volt one, you can double the voltage to 24 Volts. If the controller is a self-selecting one, such as the Morningstar Prostar, then you only have to rewire the system, and you can double the number of modules and batteries without increasing the current. The downside? It won't work if you've got 12 Volt lamps and you'll have to change the inverter. But you'd probably want to do that anyway.

- Add another autonomous system. This may be a good solution if you have a completely separate power requirement, for example a new building on the same site. I wouldn't recommend having two or more separate systems in the same place though, apart from special applications such as medical refrigeration which require complete autonomy.

- Add new modules and controller, but use the same battery. This may be an option if you have two different sized arrays. But, check with the controller maufacturer first - there may be an interaction between the controllers.

- Throw it all away (or sell it on ebay ;o)) and start again. If it's a big increase in capacity you need, this may turn out to be cheaper. Anyway, it's best to cost it out and check.

The lesson here is; if at all possible, avoid the situation arising in the first place. Make sure you've taken all the loads into account whan you design the system, allow some reserve capacity and leave room for expansion if you might need it.

To do the calculations you'll need a guide, and I know the very thing:
The Solar Power Design Manual.

And if you subscribe to the list on the download page, you'll get updated versions for no extra charge, as soon as they're uploaded.

2. Solar Garden Lights

I really like the little cheap solar garden lights which can be bought in supermarkets. In fact, our garden is rapidly filling up with them. When I look out of the window in the evening there are loads of little white and orange pools of light, and it's really pretty.

But there's another reason I like them, apart from the way they look. When people come to see us, they remark on them, and ask how they work. I think they're a great advertisement for solar power - they perform a function, and they are silent and completely reliable. I think they really help in persuading people that solar power is a genuine alternative, and not just in hot countries.

So I thoroughly recommend them if you're lucky enough, like me, to live in a country where the cost of little gadgets is inconsequential. If you don't then I hope that the advances in technology and decrease in cost represented by these lamps soon bring you greater comfort and prosperity.

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