This is a 90 cm * 90cm * 90 cm pyramidic reflector for solar cooking. Inside there is a 1/3 or 120 degrees of a cylinder wich complete the pyramidic reflector. This part of the sicle reflect almost as good as an parabolics and the design is much simpler. The square 90 cm will collect theoretically about 800 W * 0,8 = 640W of energy, wich is plenty to heat your food. The angels of the pyramid are 60 degrees wich also is matching the angel of the sylinder. The reflector is aiming for a sun 30 degrees above the horizon. For more information see www.solarcookers.ning.com here is an animation of this design: http://solarcookers.ning.com/video/pyramidic-solar-cookerThis design
Inside the pyramidic reflector I have inserted a parabolic structure. In this case I have found that 120 degrees of a circle can do as a parabolic reflector. It is not perfect, but comes very close to a focal point with litle spread. The botle to be heated is painted black and lifted off the ground, then tilted 30 degrees backwards. This model is designed for northern countries where the sun can rest at 30 degree above the horizon for some time.