Compound parabolic dishes have a super advantage over parabolic dishes. You rarely have to reposition them as the sun moves. So you can leave them unattended for long periods!
There are many possible compound parabolic dish configurations and rather than me try to satisfy everyone, I though it would be better to give you a method to make your own petal templates.
Then you can make a 1 hour, 2 hour 3 hour or 4 hour compound parabolic solar cooker.
Whatever you want is within your grasp! You can easily make petal templates for parabolic dishes with this method too.
For 12 petal templates the error in the method (because you are using flat material to make a surface curved in 3 dimensions) is about 1%. I believe that is acceptable.
If you do not want to read the whole instructable, just read the image notes on the first image.
It should suffice for many people.
Step 1: Compound parabolic concentrators, what are they?
The typical compound parabolic concentrator is a fairly old device, They are shaped like a bicycle light or a tulip flower with a hole at the bottom and as long as the sunlight enters within the acceptance angle it gets reflected all the way down the concentrator and gets trapped there at the bottom. They are made by putting the focus for 2 identical parabolas on the curve of the other one. To do this you have to twist each parabola (which gives you the acceptance angle) and the resultant 2 dimensional shape is spun on its axis to get the flower shape of the compound parabola.
Many times the reflectors for box ovens are based loosely on this type of concentration. They are good because if you face the box cooker the right way it stays collecting sunlight well for a long time.
But I wanted something different. I set out to apply the same principle to parabolic dishes.
Parabolic dishes are great because they can focus a lot of energy but they quickly go out of focus and have to be readjusted. There is virtually nothing out there about applying the same principles to parabolic dishes so I had to start from scratch. My first compound parabolic dish was a great success but not many people were interested in copying my construction method. They prefer a template.