MARIA TELKES SOLAR COOKER - Capturing heat: Five earth-friendly cooking technologies and how to build them

The solar cooker that is recommended was designed and tested by Dr. Maria Telkes during the 1950's. (Dr. Telkes invented many solar devices. She could very easily qualify as the mother of Appropriate Technology.) This oven easily reaches 300 degrees R and will touch 400 R on hot summer days. It isn't necessary to constantly reorient it, because the stove is powerful enough that it works even when it's not aimed exactly at the sun. We recommend building fairly large scale cookers because solar energy is diffuse. It takes a pretty big reflector and glass top to build up the heat and temperatures necessary for easy cooking. (The cooker in these plans has a glass cover 24" x 26"; we also use one with a glass cover 30" x 30". This particular design is useful in higher latitudes. Directions are given showing how to adapt the design to all latitudes.)

This solar cooker works well because it combines some important design criteria:

�The box is surrounded by reflectors, which direct visible light down into a box through a glass cover. (On a sunny day, each square foot of earth in sunshine receives about 200-300 btu's of energy per hour. One btu is the amount of energy it takes to raise one pound of water one degree R)

�The box is well insulated and relatively airtight.

�The glass is at a 60 degree angle, minimizing shading. Double panes of glass help a great deal as the air space in between the panes helps to insulate the box.

�The box is metal lined and painted completely black so that visible light is efficiently absorbed and changed into infrared or heat energy. The infrared energy is absorbed by the glass and its escape is slowed by the insulation inside the walls, so that heat leaves the box slowly enough that internal temperatures can rise.

�The pot sits on a black metal floor so that heat enters the pot through conduction (metal to metal contact) as well as through convection (air to metal contact.)