This is my July 1, 2011, version 4 attempt to generate electricity using a very small scale solar tower. The source of concentrated solar energy is a large fresnel lens from a rear projection TV.
The two main big new features of version 4 were:
Both of the above helped because, as you can see in a photo below, unlike verison 3 where I got only 65C (150C) in the air chamber, this time I got at least 165C (330F).
The problem was that the polystyrene insulation melted, as you can see in the last photo below.
Video for version 4 of the mini solar tower
The following video is of version 4.