I have recently read an article about the use of an array of parabolic mirrors to focus sunlight to a single point, this heat then powers a Sterling engine to generate electricity for your home. It's called Helios, but I can't find a good link.
I don't know if this would work or not, but after seeing how reflective compact disks are I couldn't help but wonder if CD's could be held suspended by their outer rim and heated from underneath at the exact temperature needed to melt the plastic for a specific amount of time to create identical, (cheap) parabolic mirrors for use in the Helios array.
The parabolic mirrors need to track the sun across the sky and I figure that the hole in the CD's center would be as good a spot as any to place the sensor.

A quick question for those who understand optics; if a parabolic mirror reflects sunlight to a single point, would a ring of magnifying glasses focusing light onto a parabolic mirror generate more heat at the focal point than the mirror alone?
-- 2 fries shy of a happy meal, Dec 14 2003

how CD's are made and work http://www.mmsdirec...roducts/cd_how.html
[FarmerJohn, Oct 05 2004, last modified Oct 21 2004]

I’ve recently heated CD’s in a microwave and an oven for use in art projects. In an oven at around 200 degrees Celsius the disc gets soft, a little wrinkled and stinks up the kitchen, but also 1 mm bubbles develop in the CD ruining the mirror effect. A microwave within 3 seconds causes sparks to crack the mirror surface of the disc into a miniature lightning pattern.
-- FarmerJohn, Dec 14 2003


They run the risk of snapping. Rather violently, I must say.
-- Overpanic, Dec 14 2003


For a focal point distant from the CD, the amount of curvature needed would be minimal.

I'm finding that 1/16 inch deflection gives a focal point 2 foot 3-9/16 inches distant from the CD. Or a 1/32 inch deflection gives a focal point 4 foot 7-1/8 inches distant.
-- Laughs Last, Dec 14 2003


[Farmer John] I wonder if the bubbling you describe is blistering caused by heating from above at the same time as beneath.
I like the idea of pulling them from the center to warp their shape, this would let you fiddle with the focal point. I think I'm going to play around with this.
Worst case scenario, I end up with a butt ugly flashlight.
-- 2 fries shy of a happy meal, Dec 14 2003


As laugh_last said: No curvature needed. A large amount of CDs can be mounted on a structure forming a parabolic concentrator, resulting in the desired effect. The CD reflector material is cheap and readily available. But it is not designed to withstand the sun's UV radiation, which is a problem for all plastics. The costs of the CDs is negligible, but the mounting structure will be somewhat expensive because the CDs are very small for this purpose.

In any case: If I build a prototype, i'll consider your advice. The answer to your "quick question": No. You would loose power while the sun light passes the lenses, and the lenses are more expensive than the mirror (yielding the same concentrator effect).
-- stonux, May 08 2004



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