Software for designing solar cookers and reflectors for solar panels Answered
Parabolic dishes are favoured because they are "perfect". Unfortunately they are only perfect if they are kept constantly pointed at the sun. In practice this is very hard to do. A better shape would maintain good reflection of the sunlight for a long time without moving the dish.
I think I have found useful easy software to help with this design work. It is called art of illusion and you can see my first results and a downloadable scene file to help you get started on step 12 of this instructable