solar funnel cooker

Excerpts from Jim Conrad's
Naturalist Newsletter

from the July 5, 2009 Newsletter, issued from the Siskiyou Mountains west of Grants Pass, Oregon:
MY NEWEST SOLAR OVEN
Wednesday, July 1, was the official beginning of the fire-hazard season here, so I had to give up my morning campfires. In their place I've constructed my newest solar oven, seen above.

That's a solar funnel cooker, the detailed, illustrated, building instructions apearing at http://solarcooking.org/plans/funnel.htm.

The instructions call for a sheet of cardboard measuring 2 x 4 feet but I used a 3 x 6 sheet for more power. They advised gluing the aluminum foil in place but I stapled mine with a simple office stapler. Their design calls for painting a canning jar black and putting it inside a plastic bag, then cooking what's in the black jar. Anita provided me with a clear-glass pan and top large enough to enclose a small skillet with its handle removed, and I used that. The top of an old pot just happened to fit the skillet. The skillet and pan top both were blackened with soot from woodsmoke. You can see a view inside the cooker below:

The secret here is having the loosely sealed, black cooking container inside a loosely sealed, clear-glass one. Concentrated sunlight is absorbed by the black skillet and lid, they radiate heat, and the clear- glass enclosure keeps the heat from escaping, causing the heat to build to a very high temperature because of the greenhouse effect.

This was a pretty cheap creation and took only two hours to put together, yet it bakes my cornbread, fries eggs, simmers stews -- covers all the basics. A skillet-sized pone of cornbread or a really big biscuit made of whole-wheat flour takes about an hour to bake to perfection, and in an hour a couple of eggs get more than hard-fried. I'd worried that this far north such a design wouldn't function but so far it does as well as the manufactured kit I used in central Mexico a couple of years ago.

Each time I construct a solar cooker I'm reminded how we grossly underestimate the potentials of solar energy. The good part of that is that "going solar" will be much more productive than most of us think. The bad part is that as we screw up the Earth's weather with greenhouse-effect gasses and by releasing solar energy stored in fossil fuels over millions of years, the consequences can be much worse than we imagine.

from the July 12, 2009 Newsletter, issued from the Siskiyou Mountains west of Grants Pass, Oregon:
SOLAR COOKER UPDATE
The Solar Funnel Cooker introduced last week works much better than hoped. This week I spray-painted a quart jar black, set it inside the cooker atop the upside-down lid of a wide-mouthed gallon jar, positioned the upside-down gallon jar over the quart jar atop its upside-down lid (black container inside clear glass container) and was amazed when soon water in the quart jar began boiling.

This is a neat trick to keep in mind for that pending day when the infrastructure cracks a bit more or a global-warming storm takes out the local water supply, for this simple system can sterilize water! At least, when the sun is shining.