Solar Sell
So, you want a lot of power and don’t like the nuclear option. Here’s an easy answer: why not use the Sun?
It’s been going for nearly five billion years and will probably burn for about as long again. It rises every day and delivers nearly 200 petawatts (200 thousand trillion watts) of power to the Earth. A swimming pool full of 235U could power a city for a century—the Sun delivers that much energy direct to the surface of the Earth in less than twenty minutes.
But don’t rush out, vote for the Green Party and cover your roof in solar panels just yet. There are a few little problems with this sunny utopia powered by photovoltaic cells:
- The Earth is very big, which means all those petawatts of sunlight are rather spread out. The actual insolation (the climate physicists’ name for sunlight power per unit area) at our present distance from the Sun is a mere 1400Wm−2—so a square metre of solar cells delivers about 1400W, meaning that you need a 2 × 1 metre solar panel to power a kettle. Just one kettle.
- Things get in the way of the sunlight. By the time you consider the atmosphere absorbing incoming rays, clouds reflecting them back and the Earth getting in the way (an obtuse way of referring to ‘night time’), the average insolation drops to more like 250Wm−2. So you need a 4 × 3 metre panel to power a kettle. Just one kettle.
- Solar cells are by no means 100% efficient. Some of the best are ‘monocrystalline’ silicon cells (so named because they are made from a single perfect crystal), which convert some 24% of incoming light power into electrical power when made carefully in the lab. However, these cells are so expensive and difficult to produce that they actually use more energy being made than they could conceivably generate in their lifetime. As such, cheaper ‘amorphous’ silicon (basically sand) is used, giving an efficiency of some 5–7% in production models. So you need a 15 × 16 metre panel to power a kettle. Just one kettle. 15 × 16 metres. That’s huge.
I wouldn’t use this as an all-encompassing argument against solar power, but it’s pretty compelling evidence that it can’t form too huge a part of our power portfolio.
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Victor says
07:20:44 15/09/2006
Maybe weather doesn’t permit in the U.K., but in many places, promoting solar can no longer be called “knee jerk environmentalism.” One need not be a Green Party member to appreciate the economics and effectiveness. Today’s solar panels can generate substantial amounts of electricity. For example, right now in California, homes and businesses, including those where kettles are used regularly, generate more power than they use through solar power. The power generated by buildings with solar is then put back in the power grid and used by other buildings.
Admittedly, installing solar is expensive, but, as often occurs with technology, the price will drop with increased demand and production. In addition, installing solar pays for itself through decreased power bills and through tax incentives in some areas.
While lack of sun hinders solar power effectiveness, many places are constantly sunny. Even less sunny areas benefit by using the solar power generated through limited sunny periods.
Tom F says
04:54:33 11/04/2007
I've got a great idea to fix the area issue. Use mulitple layers of solar cells - they're not so thick, so you could probably fit about a hundred layers on top of your house without fear of collapse. That's at least 50 kettles you could power at once.
*cough*
I could work for the BBC News website with common sense like that. Looking forward to your analysis of nuclear power. I'm yet to work out why most Green-leaning people fear we're going to start glowing that colour if we even think the word 'reactor'.
Statto says
12:32:20 11/04/2007
There is, in fact, some research into that area, but not precisely to that end.
Layers of solar cells would be exactly the same as just having a thicker single cell; all the light that can be absorbed will be absorbed and the intensity dies off as a function of distance into the cell. They're probably optimised to catch as much light for as little thickness as possible.
What they are trying is sandwiching together semiconductors with different band gaps (the energy required to make a stationary electron into a current-carrying one); each layer, because of the different band gap, is sensitive to a different wavelength of light, so more use is made of the broad spectrum of light emitted from the Sun. Current single-semiconductor cells only use a fraction of the solar spectrum, so this could be a way to make them a good few times more efficient.