Cutting sheet material to make a parabolic dish is a massive undertaking!
I have made a first prototype and it works.
It is"tweaked" to provide 2 hours of cooking time at pretty much full power. So you can set it and leave it. A parabolic dish on the other hand needs to be adjusted every half hour.
The trough arises from a solar software project I did.
I have uploaded the most recent scene file here thirdcombined troughblabla.aoi If you download it, it might change the file extension to .temp. Just change it back to .aoi and it will work just fine when you open it in art of illusion
The file just happens to contain a parabolic dish, winston curve dish, and various others too. And all in 11kbytes!
Art of illusion software certainly helped me come up with this design.
http://www.youtube.com/watch?v=qXVfGFQpYD8 shows my first prototype Kyoto trough.
Step 1: Concentrating sunlight with 2 troughs (why it works)
Here is one of his videos of how it works.
I want to solar cook so I do not want a point of light. Instead I want the light to focus on the place where my cooking pot will be for 2 hours. How can I do it? First thing is to make a compound trough. This is easy. You just make a parabolic trough and twist its sides inwards. If you twist both sides inwards by 15 degrees each, you have a 30 degree "acceptance angle" . If you allign it with the suns path, and let the sun shine over it, for 2 hours, all the light from both sides will fall at or below the focus of the dish.
So there is some concentration!
So put your pot here. But the trough is wider than your pot! so the next stage is to concentrate that light a bit more. This is where the wings come in. They are parabolas too and they have a focus on the front of the pot and a focus on the back of the pot.
As long of their angle of rotation is at right angles to the angle of rotation to the first trough, they will not affect that rule "at or below the focal line" when the light arrives under it but it will concentrate the light towards the center of the trough! (I give these parabolas a little twist inwards too to do the at or below thing and spread the light over the pot a bit more).