I now think that "compound" parabolic dishes have numerous advantages. (A compound parabolic solar cooker can also be made with the mathematician and I can add instructions later.)
Use hardiplank, cardboard, plaster concrete or cob to make any size or shape parabolic reflector with this device! Solar cookers can be made from waste cardboard boxes covered with kitchen foil. Mostly people use math to figure out the parabola or use a template. Lots of mcguyver types are not into math and waste cardboard comes in all shapes and sizes with cuts all over the place so templates are not always suitable..
This method of making a solar cooker is suitable for a one off or assembly line and will work with ANY cardboard Box. Please try one and spread the word about this way of making parabolic cookers.
I cook in dark glass containers and use an oven bag to reduce thermal heat loss.
Currently, I use My cob solar cooker to steralize soil. At 5 pm when i come home, my soil is still at about 60 C (after cooling down for about 3 hours!) And suitable for growing seedlings.
I feel that this method of making solar cookers will prove very adaptable, very affordable and find use all across the world.
Step 1: Introducing the mechanical mathematician!
Parabola's are hard to make unless you have some fairly fancy math skills.
But there is another way! The mechanical mathematician!
This little genius solves the parabola for all points on the curve! Using some string to help him. The string is attached at the focus of the parabola and goes through a point on the parabola (on a piece of metal for hanging curtains) and ends up tied at the pipe joiner.
There are many ways to make the mechanical mathematician, and the other one was used to make a cob solar cooker. Which works good.
It was made from old metal chairs and junk!