solar power

[shyted]

What size solar panel would I need to absorb enough energy during a winter day to run a small lightbulb for 5 to 6 hours?

[Squirrel]

As it happens, just a few weeks ago I bought a few small solar panels from eBay. They were advertised as "6V, 3W" although I found this not to be the case, no doubt due to the awkward way I have positioned them (and the clouds). As for size, mine are each 12" x 6" (about 31cm x 15.5cm) and, with a fair amount of sunlight (e.g. a sunny winter day) each produces a little less power than a Duracell 1.5V (sorry I can't be more specific - I blue the fuse on my multimeter, hence a previous question I asked.) By "small light bulb" I assume you mean an energy-saving one around 12W, and to run that on full power for 5 hours requires about 0.2 million joules. Assuming each of my solar panels is the same efficiency as most others, with an area of 0.048m� and a power output of 1.5W, a 100% efficient battery would require 8 of them running for 5 hours (or one panel measuring 0.44m x 0.88m running for 5 hours.) Unfortunately, there is no such thing as a 100% efficient battery (I don't know the relative efficiencies), but if I guess a few figures, a range of results might become evident.

Running all day (6 hours of light?) with an average power output of 30W per square metre (I estimated these figures so they're probably wrong):

50% efficient battery, about 0.67m� of panelling required
30%, ≅1.1m�
20%, ≅1.7m�
10%, ≅3.3m�
5%, ≅6.7m�
2%, ≅17m�

You can see where I'm going; listed above, even if they are totally wrong, are at least the relative areas of panelling that you will need. Sorry I couldn't give any more specific information, but I'm glad you're looking for an environmentally-friendly way to run your light bulb! P.S. If you see a load of squares (I do) that is meant to be the symbol for 'Approximately equal to.'

[shyted]

Thanks Squirrel ... sounds like it may not work for my purposes ... I was in fact looking for solar powered outdoor Christmas lights. May be a bit far fetched but it would avoid energy loss and stop you leaving a window open for the cable.

[Squirrel]

What a great idea! Well, there's still a long way to go until Christmas, and energy-saving bulbs have really taken off; who knows, a few small panels might be enough to run a string of efficient bulbs or LEDs. You might even be able to point the solar panels at a neighbour's fairy lights when it gets dark, if you can stand the irony.