Newsletter Archive
13 October 2006
Today, how to avoid using more power than you think you should.
1) Phantom Loads - where's all that power going?
2) Solar Power Design Manual
3) Economics of Solar Power
1. Phantom Loads - where's all that power going?
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If this is an unfamiliar term then read on. A phantom load is any device that uses electricity even when it's switched off. They fall into two basic categories - appliances that have a standby setting such as televisions, and appliances with an external power supply.
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Teach yourself all about Solar Power
http://www.solar-power-answers.co.uk/solardesign.html
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But why do we care? Surely they use hardly any power? Well that's not always the case, and in fact phantom loads can add up to a very significant proportion of the total load, simply because they're off for a large proportion of the day!
Here's an extreme example: The satellite television receiver in my house consumes 70 Watts when switched on. A lot, but not too bad. But it consumes 63 Watts when it's switched off! If you assume that it's on for 4 hours per day (a lot), then its energy consumption is 70 x 4, or 280 Watt-hours. But its consumption for the 20 hours when it's off is 20 x 63, or 1260 Watt-hours. So it uses 4.5 times more energy when it's not in use than when it is. That can't be right.
So what's to be done? Well, with the example above, not much. The receiver supplies power to the heater in the LNB (the bit sticking out of the dish) to stop it getting damp, plus it needs to be on overnight to receive software updates. Until the manufacturers are encouraged into reducing the power consumption it's no Sky TV for solar users.
But the good news is, most things you can either unplug or switch off. Television sets for example, usually have a button on the front that switches them off properly. Use it. The same with most Hi-Fi equipment. If you buy a multi-way extension lead and plug all your little power supplies into it, then you can switch them off when you're not using them.
The most important thing is, if you're buying new appliances for solar power systems, don't just look at the power consumption when on, try to minimise consumption when off.
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Modules, controllers and other system components
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2. Solar Power Design Manual
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The solar power design manual teaches everything you need to know about stand-alone solar power systems. Equally applicable to enthusiasts, engineers and development workers, it covers the design and installation of solar photovoltaic systems from first principles to final commissioning.
Find out more here:
http://www.solar-power-answers.co.uk/solardesign.html
3. Economics of Solar Power
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I'm often asked "how much will it cost for a three bedroom house?" Well, there's no straight answer to that, because you need to work out the energy requirement of the house and its occupiers, and relate that to the insolation. One thing's for certain though - if you're connected to mains electricty then a stand-alone solar power system will never compete on a cost per kilowatt basis.
Now, that's not to say that solar power is always more expensive - not at all. Let me explain. The cost of electricity delivered by a solar power system is not determined by the fuel costs. That is because there are no fuel costs. But it's not free. The system components, particularly the batteries, have a finite lifespan. If you include the cost of replacing them when they're worn out, then the cost of the electricity produced is usually about the same as the cost of mains electricity.
But that assumes that you're competing with an existing grid connection. In fact, that's very rarely the case. What you're more likely to be competing with is either a very expensive new connection or another form of generation. In these cases solar power can be very competitive indeed. The cost of bringing a mains connection even a few kilometers can, in many cases, be tens or even hundreds of thousands of pounds, dollars or euros. You can buy a lot of modules and batteries for that kind of money.
And when you compare solar generated electricity with electricity generated by a diesel genset, then the advantages become even clearer. Even if it's close to the fuel supply, then the cost per kilowatt is much higher, more like three times as much. And that's before you start to look at servicing costs (every 75 hours) or the cost of transporting fuel.
There are other potential reasons that also make good economic sense. For instance, consider the case of roadside monitoring equipment. It may be close to the grid, but if it only consumes milliwatts, then the standing charge is going to far outweigh the cost of the photovoltaic system.
So all in all, it's not just environmentalists that need to consider solar power. And for everybody living in an ordinary house, on the grid, then a grid-connected system may be the way forward. There are no batteries involved and therefore the economics are far more clear-cut. Once the rest of the European Union follows the lead of the Netherlands in making it very easy to connect such a system to the mains, then the way will be paved for the necessary expansion in renewable energy generation capacity. I live in hope.
