Reflections on Solar Cooking - Capturing heat: Five earth-friendly cooking technologies and how to build them

I worked in Mexico for ten years until moving full time to Aprovecho. This experience pointed out a lot of realities, one of which is that no matter how well a device works in theory, if people don't use it, it doesn't really work at all! Solar cookers are a very good example of this principle, because even though solar cooking "works" it has been




almost universally rejected worldwide. All of the cookers that I first built in Mexico were found unused a year later.'

When asked why the initial cookers weren't helpful people listed the following reasons:

1.) Cooking outside in the sun is uncomfortable and unusual.
2.) The cooker worked too slowly and wouldn't cook beans.
3.) The solar cooker was unreliable and more trouble than cooking with wood or gas.

I hoped that we could find a solar cooker that would be more attractive, since it's very sunny in Mexico and solar cooking is the one cooking method that doesn't diminish an earthly resource. One of the ways that Aprovecho addressed this problem was to try to make sure that the solar cooker was more powerful, to work almost as fast as other stoves. We tried to find designs that were pleasant, and even fascinating, to use. Both the Telkes and conical cookers meet these criteria!

Both can perform rapidly and reliably. The conical can make boiling water for coffee or tea very rapidly. But, it can be irritating to use because of the glare. The Telkes has no problem with glare because the light is directed down into the box. But since it is less concentrating it takes a long time to boil water.

Different shapes seem best suited to different solar tasks. A box with a glass top (a flat plate collector) is great at heating water for bathing. With one added reflector (a "Solar Box Cooker") temperatures will rise high enough to do slow cooking. Adding a full array of reflectors (a Telkes cooker) raises the temperatures and amount of btu's to the point where faster cooking can be done. A conical or parabolic can do concentrated tasks, like boiling or frying, as quickly as any other stove. But, as the cooker becomes more concentrated, it needs to be aimed more frequently and can have trouble with glare. Both the cone and parabola concentrate sunlight by focusing it in front of the reflector. The Telkes reflects sunlight downwards into a box, below the reflector.

The Telkes cooker is easy to recommend. It convinced me, a solar sceptic, that solar cooking is a viable possibility. A Telkes cooker with a 24 by 26 inch glass cover will cook food easily and quickly. We've used one now for years. I believe that powerful solar cookers are easier to accept than slower cooking models. But, a large solar cooker is not mobile, it can be expensive to build, and still requires a change in cooking routines. All solar designs should be considered because no one design will be universally "best."

Of course, the solar cooking option that is almost universally accepted is to burn bio-mass. Wood and other plants have stored direct sunlight in a chemical form through the mysterious process of photosynthesis. Direct solar energy is diffuse; wood has a built-in concentrated advantage.