The solar design t-square and a Method for designing reflectors for unattended solar cooking

Step 11 Tradeoff time. Sine rules and bounces.

Tradeoffs are important. For a 2 hour solar cooker, you would line it up with the path of the sun and put it 1 hour (about 15 degrees)  ahead of the sun. For the next hour the sun moves from 15 degrees off target to directly above and then spends another hour going off target again. The area of sunlight that reflects to the target is related to the sine of the angle.  Directly overhead, the sine is 1, one hundred percent of full power.  15degrees off is 75 degrees and the sine of 75 is about .9659 so (assuming one bounce to the target) your dish at its worst will be 96.6 of the power of the same size parabolic dish!
And its average power over those 2 hours will be 98% or better WITHOUT HAVING TO BE THERE TO ADJUST THE DISH.   But of course, you might have to do 2 bounces in some places.
With a 3 hour dish, the sine goes from .924 to 1 and back to .924 so a lot more loss.  Perhaps you only get 95%  over the 3 hours. And with 4 hour dishes, you go from 86.6% to 1 and back to 86.6%
So you get tradeoffs depending on how unattended you want your dish to be.
At some points your design may have 2 or even 3 bounces of light before you get to the target.
You can assume 10% loss at each bounce. 1 bounce is the same as a normal parabolic dish so first bounce does not count.   2 bounces is 90%  and 3 is 0.9 X 0.9 = 0.81 4 is 0.9 X 0.9 X 0.9 = 0.729
so we get tradeoffs whereever we go! 
Hopefully people will use this idea to design dishes with the right amount of tradeoffs for their own situations.