Thursday, October 22, 2009

Solar power(less)

Solar powerI've been looking into augmenting my wind generator with solar power.

For me, the bigger panels I need for my 24V system would cost around the one thousand odd pounds mark (US$ 1,600), so some research makes sense.

The concept seems idyllic - slap in a couple of solar panels and job done. Free power for the next twenty odd years with no maintenance other than an occasional clean of the panels.

After looking into it a little more, I must say that I'm somewhat under whelmed by the whole idea.

Green issues aside, solar power looks very expensive for pretty poor returns.

The panel you see is one of two different types I bought for my solar power experiments. This one for my on-board 12V system.

Forty quid that cost me, and it only produced a sorry amount of power over the course of the last few weeks. Not even enough to keep up with my intermittent use of the radio. Oh yes, and the battery is in really good shape as it's quite new.

4.8w output I think is promised on the box, but in reality I think it only does that when it's pointed directly into blazing sunlight. That's not going to happen. Especially here in England in the daylight savings months.

Before we go any further, bear in mind that this panel could not keep up, so I'd have to use a generator to top up the power at some point anyway.

So here's my, very rough, calculations....

Forty quid buys me forty litres of petrol. At .4 litres per hour (1/4 load from here), this gives me 100 hrs (6000 minutes) generator runtime. In reality the generator will use less petrol than that, as the load to charge the 12V battery is not that significant (say 10 amps * 12V = 120W vs 500W for 1/4 load).

I estimate it would take a maximum of 5 minutes generator runtime to produce the same amount of charge that panel did in two weeks.

Based on the above, 2.5 minutes runtime per week, that forty quid on the solar panel buys me the equivalent of (6000/2.5) 2,400 weeks, or 46 years, generator charge time.

End of experiment.


  1. Anonymous1:53 PM

    That's an amorphous silicon panel and they are utter crap. I have nominally 45W of those on the roof of my cottage and it takes a week for them to restore my 80AH battery to full charge.

    You should be able to find 15W panels of this type for about £40 and wiring a couple in series would give you 28V to charge your main batteries. They do not generate a lot of power though, so they are more of a topping charge.

    Proper mono-/poly-crystalline silicon panels will cost a bit, but £600 should get you a pair of 80W panels that would actually do some good.

  2. I understand that the most economic prices for "Photovoltaic cells" is to be found in Portugal?

  3. My brother has done some research on the topic and he just bought a 35W panel not too long ago. For Ohio we figured it out to take about 20 years for the panel to pay for itself. This doesn't include the battery or the charge controller he bought, but of course it also doesn't figure in the change (likely rise) in electricity cost either. Any way you shake it, the reality exist that solar is not really economical yet. However, he is happy with his panel though as it makes more power than his laptop uses during the day.
    Although you probably already know that the most direct angle to the sun is best, but I did notice that you seem to have put your panel almost vertical. Why is that?
    In the end you are essentially right about the economics, however, cost and value (reliability, etc) are two different things.


  4. Anonymous5:58 PM

    Your calculations are for a petrol powered generator. Do it again for diesel and the economics look even worse for the solar panels.

    I think your wind generator is your best bet. I hope you get that sorted soon, and get it back in full operation. Out of curiosity, what's been happening with that?

  5. Hi Anonymous

    £ 600.00 will get me quite a bit of petrol!



  6. Hi Rob

    I'm sure that even in Portugal the PV cells will be relatively expensive compared to using a generator.



  7. Hi Marc

    Good to hear from you again.

    The panel is positioned to get the best of the sun in the mornings.

    I agree it could be a little better angled if I'd spent more time on fixing it in place.



  8. Hi Anonymous

    I have a wind generator post n it's way soon.



  9. ....and if one build a wind-genset
    (24 or 12v)from bits and pieces, wouldn´t it be cheep and glorius
    piece of art ?

    cheers !

  10. We have also discussed the use of solar power to heat the water in the summer and were surprised when we started looking into the cost. You would think that since the technology has been around for a long time now and that everything is being concentrated on 'green energy' that the prices would have dropped enough to make it economical.

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