I finally managed to get a paper turbine to turn with version 6. Instead of using a solar tower, I decided to keep the overall temperatures in the solar energy to heat conversion area lower to make construction more feasible. To that end I built a mini screen solar air heater and put it further from the fresnel lens' focal point (see the diagram below.)
To keep the solar air heater at the proper location at all times, I mounted it to the mirror of my fresnel lens and mirror solar cooker setup (see photos below.)
The paper turbine turned fairly rapidly at the hot air inlet as a result of the exiting hot air.
The paper turbine turned, but much more slowly, at the cold air outlet as a result of the entering cold air. This showed that the strength of the incoming cold air is less than that of the exiting hot air.
The PC fan did not turn at all at either the inlet or the outlet. I was able to turn it easily with my finger, so it wasn't being prevented by anything.
Click on the photos for larger versions.
Here's a video I made of the setup, all testing and the construction.