Steven E. Jones, a BYU Physics professor, invented a homemade solar cooker that actually works, as compared to all the box-style cookers for which we've seen patterns over the years. This solar cooker was tested by the Benson Institute. Some problems with other homemade versions were overcome by the BYU Solar Oven.
It looks easy to make, with cardboard and aluminum foil. Here is a link to the article on FourWinds10.com, including great photos like the one at left : How to Make and Use The BYU Solar Cooker/Cooler
I love how this professor set out to conquer a problem that made the lives, especially of women, so much easier in developing countries (many women use much of their day gathering fuel to cook their family meal). I also love that he and BYU did not attempt to make money, but instead did their best to give this information free of charge.
I think the BYU solar oven would be a great emergency item to have on hand. Even if you don't need to cook food, pasteurizing water alone would be worth having this oven. Moreover, this same funnel,used a bit differently, works to cool foods during the night.
March 2013 Update: updated information and modifications on this funnel are found at The Save-Heat Cooker and Update on the BYU Solar Funnel Cooker/Cooler Having lived in high-altitude Bolivia, where I DID try to cook dry beans without a pressure cooker (never got done), this modification sounds great. Most of the Bolivians I knew used pressure cookers when cooking dry beans. My two bits: perhaps a smaller version of a Wonder Oven thermal cooker would work instead of the drilled polystyrene box -- after all, how many of us average folk know how to "mold" our own polystyrene box to fit our jars? The concept is the same, but I don't know if the Wonder Oven would hold the heat quite as well.
Here are two Youtube videos with Dr. Jones showing how to make his solar funnel:
Last, here is a paper from one of Dr. Jones' former students, with all the graphs you could want to show how this works. (Note: this is a downloadable file, so don't think you're being spammed.)
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