Parabolic solar cooker?

[ewtikins]

I teach in Golders Green/Brent Cross on Tuesdays, and for the past several weeks I have noticed that there is a discarded satellite dish, apparently free for the taking, in one of the random rubbish piles I walk past.

Satellite receiver dishes, as I understand it, collect waves and focus them at the little sticky-out receiver thing (technical

Comments

[martling]

Shiny foil wouldn't really do much, you need stuff that works as an actual mirror.

(Yes, it's all waves, but the wavelength of light is much shorter (a few hundred nanometres) than that of a satellite TV signal (about 3cm), and as such it's more sensitive to small features of what it's reflecting off. To get a clear reflection with light you need a mirror, but with radio signals any flat bit of metal will do, or even a mesh with holes in it as per the Sky minidish, because the holes are much smaller than the wavelength.)

[siliconshaman]

depending on the size of the dish, you could try coating it those very small mirror tiles.

It wouldn't be terribly efficient, but it might work well enough.

[revdode]

I'm afraid martling is right, with a minidisk you probably wouldn't gather that much light. One of the older large discs would probably work better. Having said that, if it's free it would be worth trying, it won't be much smaller than some of the cardboard + aluminium foil plans. Foil isn't an ideal material but it does work, it would probably be more of a curiosity that a practical cooker but it's a first step.

[ex_phelyan]

We actually built one once, at university.

What we used were sheets of tinplate, like they use to make cans for soft drinks. 7 in total, which we scrounged from somewhere. They can be polished, chocolate and aluminium foil work quite well for polishing them.

We had 6 primary mirrors, which were individual wooden frames with the 1x1m sheets on the front bent slightly horizontally. They were then focussed onto the secondary mirror which sat on another wooden frame and focussed the light from the 6 other mirrors onto a black stone plate. It worked incredibly well, although you did need a relatively large area to set up the 7 frames.

Dish solar cooker

[solarcooker]

Mirror tiles would work fine, the smaller the better. One inch square would be about right. Use high temperature silicone for the glue. Any automotive
shop will have it. As for the cooking vessel, you might take a canning jar and spay paint the lid black with grill paint. Place the jar upside down at the focus. Find a way to secure the jar at the focus. Copper tubing or coat
hangers or even rubber tubing for automotive use should help in that regard.
Put a smaller cooking vessel inside of the jar. Good luck.