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SOLAR COOKING

  We wanted to build a solar cooker as high-tech as the house, so we decided on a paraboloid shape that uses mirrors to concentrate the sunlight onto a cast iron cauldron. The mirror assembly rotates smoothly on azimuth and altitude axes. Azimuth position is held by friction, altitude by an adjustable metal strap. In operation, the aim needs to be tweaked every 5-10 minutes to keep things cooking. Auto tracking would be nice, but way too complicated. It works fine as is, and can cook a hotdog in slightly more time than a microwave oven (once the cauldron is heated up).

For you scientists out there, here are the cooker's technical specifications:

Maximum Temperature = 100°C = 212°F
Parabolic Geometry: Y = 1.25X2
Focal Length = 1/4k = 0.20 m
Aperture = 0.51 m x 1.17 m = 0.60 m2
Equivalent Focal Ratio = f 0.33
Solar Insolation Equivalent = 18 suns

     
  By using a cast iron cauldron we take advantage of thermal mass. The iron holds enough heat to maintain the temperature while the lid is removed and replaced. Cooking in water increases this effect, and that's what we usually use. If you like your hotdogs charred and crispy, this cooker is not for you. But if you like your hotdogs steamed and juicy, it works great. We've cooked meatloaf and pot pies without water, and warmed many a muffin for breakfast. The acrylic lid helps hold the heat in and allows easy monitoring of the contents. Note the condensation on the lid. The water is close to boiling.
     
  Maximum temperature at noon on a clear summer day will just hit 100°C (212°F). That's more than enough to safely prepare most food for human consumption. A lab grade thermometer verifies this claim. I rounded up the reading, since the insertion of the thermometer required the lid to be unsealed during measurement. That cools the system rapidly. And I've seen this cooker boil water. As Heisenberg noted, the act of observing a system will change its state.
     
  This spectacular image shows the precise concentrating action of the paraboloid. I reflected sunlight off a large plane mirror into my darkened shop. One of my assistants and I fired up a couple of fine cigars to fill the room with smoke. The reflected rays of sunlight were thereby made visible by the scattered photons. Note that, with individual plane mirrors approximating a paraboloid, we can't get a perfect focus. However, the focal volume pretty well matches that of the cast iron cauldron, so the cauldron does intercept most of the reflected energy.

The solar cooker was used less and less over the years, but cranked out several hundred hotdogs for visitors during our annual Open House. After I retired from teaching, and after several years of the cooker gathering dust, I decided to donate it to any educational institution that could use it. As of 2012, the new owner of this cooker is [yet to be determined]. If you want it, email me and explain why, but preference will be given to museums, schools, or other educational institutions. And you'll have to pick it up since it's too large to ship.