Naked Science Forum

General Science => General Science => Topic started by: katieHaylor on 20/04/2018 13:49:21

Title: How efficiently can one power Christmas lights using flat PV panels?
Post by: katieHaylor on 20/04/2018 13:49:21

Paul says:

My son bought some solar powered Christmas lights last Xmas, but the panels are only about 6"x6" and they are flat. Why don't manufacturers build them curved or cylindrical so they catch the sun throughout the day?

I suppose it is just cheaper to produce flat panels but if you point them towards the rising sun you miss out on the afternoon and evening sun.

What do you think?

Title: Re: How efficiently can one power Christmas lights using flat PV panels?
Post by: chris on 20/04/2018 16:00:31

Flat is a good compromise between ease of manufacture, transport / retail, and installation, and efficiency of solar collection performance. If you made a curved sheet how would it perform optimally all day long? Some parts of the panel would still be off-axis.

Title: Re: How efficiently can one power Christmas lights using flat PV panels?
Post by: alancalverd on 20/04/2018 23:04:26

A curved panel will absorb less solar radiation than a flat one since at any position of the sun, only an infinitesimal portion will be perpendicular to the sun's rays. Placing a flat panel perpendicular to the noon sun will maximise energy output for a simple, fixed  installation. The alternatives are to rotate the panel to keep it pointing at the sun, or to use a curved mirror, considerably larger than the PV panel, to concentrate solar radiation on a small PV generator.

I assume the question came from the southern hemisphere. Sunshine hours are minimal-to-zero at Christmas  in the north.

Title: Re: How efficiently can one power Christmas lights using flat PV panels?
Post by: chris on 21/04/2018 10:50:31

Quote from: alancalverd on 20/04/2018 23:04:26

I assume the question came from the southern hemisphere. Sunshine hours are minimal-to-zero at Christmas  in the north.

Oh, I don't know. Next-door neighbour has got some solar-powered fairylights on an arbour in his garden. They worked throughout the winter, admittedly not for as long as in summer, but they did work! LEDs use so little energy compared with old-fashioned incandescents that solar-powered nightlights are actually a viable phenomenon in Britain these days!