Solar cookers

[kihon]

Hi all,

Given that a large portion of the energy I use during summer goes into cooking, I am thinking about building a solar cooker.

Ive been looking at making a parabolic reflector, as well as a box oven. I have found a cheap source of reflective mylar to use for mirrors.

Has anyone here had any experience building solar cookers/ovens? I need to be able to boil water for cooking rice, and if possible reach temperatures high enough to safely cook meat as well.

I was thinking about going for a box oven first as it seems the easier of the two to make. Using a plywood box, with black baking trays to line the inside, and one or more reflective flaps around the top to direct sunlight inside. And a sheet of glass to cover the top.

Do you guys have any views on whether the inside surfaces should be dark or reflective? I have seen some saying dark is better, while others say reflective.

Anyway, will update once I have something to show.

[zap]

My cooker is an old musty suitcase, the cover is an old slider basement window.  I lined the sides with Tuff-R, shiny side towards the inside, and put a thick piece of aluminum foil, painted with black BBQ paint, on the bottom.

I put Tuff-R on the inside of the lid to reflect into the cooker.  It works well enough but needs more collection surface and as is, it will reach around 220­°F on a hot day.

I have an upgrade waiting for some more spare time and hope to post about it soon.

[mbeland]

Why wouldn't you recycle an old oven and concentrate the solar energy through the oven door window with a large reflector. If you choose a self cleaning oven, it would be pretty well insulated and would not risk releasing toxic fumes to the food you are cooking.

Just an idea... let me know what you think.

Martin

[spinningmagnets]

Heres a good start for research:

http://solarcooking.wikia.com/wiki/Category:Solar_cooker_designs

Concentrated visible light will heat anything regardless of color, but the color black (or any very dark color) will convert invisible UV energy into heat. So if you use a dark color on the focal target, it will get hotter and get hot faster.

If you've ever gotten sunburn on a cloudy day that had a cool breeze, that was the invisible UV rays that can penetrate clouds.

One of the projects is a pyrex (high-temp) clear glass bowl that has a black cast iron pot inside. Both the pot and bowl have lids.

If you turn on your cars heater full blast on a cold night, but drive with the windows open, it has the same effect of using an open collector and an open pot.

If a poor third-world-village only has an open concentrator and an open pot, its understandable, but if you have it available...

A suprisingly small concentrator will produce very hot and fast cooking if it has a glass cover thats sealed, and the focal point is a black sealed kettle inside a clear glass sealed bowl.

If you're cooking dry beans at a family bar-be-cue as a demonstration, a pressure-cooker will keep the water from boiling away and will cook faster. This is because when water boils away, it carries off heat in a vapor, and the pot never gets above ~220F. Under pressure, the pot can get above 300F. Just some thoughts...

[ghurd]

There are some pretty impressive videos on youtube, with medium-small satellite dishes covered with reflective material.

Boiling pots of water, burning wood, etc.  Looks like most just made a shelf to put the pot at about the focal point.

Home DePot / Lowe's has some shiny aluminum tape.  Pretty cheap in the large rolls.  The kind without the peel-off paper backing is quite stretchable (Home DePot I think) and should be able to follow slight curves pretty well.

I wish I would have grabbed one of those dishes when there were 3 a week out on garbage day.  That size seems a bit rare now.

G-

[zeusmorg]

 Mylar.. look at the potato chip bags you toss out,,

[motoman465]

I found this a couple of days ago while surfing the net.  Looks pretty cool and inexpensive, too.

Todd

http://www.solarcooking.org/plans/windshield-cooker.htm

[hvirtane]

You can use old satellite dishes and cover them with reflective materials. I have done it. But I would not recommend doing that. The focus point is far and it makes it dangerous.

You can find my ideas by following my 'user account' here. I'm now quite convinced that the best method is to cast the mirror base of cement and glue small mirror pieces on the top.

As printed here:

http://web.archive.org/web/20050404022706/www.cc.jyu.fi/~hvirtane/cooker/

------

Chinese are selling nowadays their good reflective material cheaply, 3 usd per square meter. You can find the address of the manufacturer from my latest diary.

http://www.fieldlines.com/story/2009/2/16/154642/606

At present I think that the Chinese cooker is the best one. You might copy their design of the focusing system and make the mirror of cement with glass piece reflectors.

The Indian design by my friend at Tinytech is very easy to make, but it is more cumbersome to use and the power is not as good as with the Chinese cooker.  

I have made as well several box cookers, some of them of old suitcases. With box cookers I was never satisfied with the power. Parabolic reflectors can cook as well as anything, if you make the reflector big.

- hv