When we first ran across the Primrose cooker we were fascinated with it.  The first impression was that it probably works only for a limited range of sun elevation angles.  The simulation proved this first impression to be false, and shows that the cooker can operate over a range of sun elevation angles.

 

The simulation was done in MathCad.  To make the math easier, the parabola was fixed, and everything else rotates about it. The pivot point is on the front leg of the supporting stand.  In the simulation, the green line represents the ground and the dark brown lines represent the support structure.  The pot is represented by the circle.  The upper end of the parabola was not trimmed to length because we decided to keep the whole parabola for reference.  The actual parabola ends about where the upper ray hits it.

 

The dimensions we used were obtained from

 

The only inconsistency that we found was that the update to the parabola brochure lists the focal length as 75 cm, and we had to make it 54 cm to get the parabola to fit in the support structure.  The brown lines that represent the stand were located at the center of the legs.

 

To vew the simulation click the link below.