Solar Point Focus
Concentrating solar power is good idea. But concentrating sunlight can be dangerous and is not as easy as it looks. Idealab and eSolar show a solar array and an energy receiver. The receiver cavity has an opening that’s rectangular. It matches their modular mirrors which are also rectangular. See images.
In many respects it’s a good design. However, the reflected image of the sun is not rectangular. The reflected image is round. And it also gets larger the farther away the image is reflected. It is impossible to concentrate sunlight beyond certain levels. And to concentrate the sun to the theoretical limit requires near perfect optics. The cost of astronomical quality optics is prohibitive.
At the distances shown in the figure the reflected image of the sun takes on the shape of the sun, not the shape of each facet. The size of the image grows as well which means the heat loss from the receiver also grows. Watch the video to see how a rectangular image at a short distance turns into a round, larger image at a distance. (Video)
Figure 1 Rectangular cavity aperture.
Figure 2 Rectangular flat mirrors.