Building an Experimental Set Up
As we see in the given diagram (click to enlarge), the base or the ground is preferably painted black in color to enhance better absorption of the solar heat. Also, a concrete base is better suited for the purpose as their absorption and sustainability of heat is consistent and better.
A tower (a PVC pipe here) is erected at the center of the ground and is clamped using angles. The bottom open end of the pipe is elevated at a certain particular distance from the ground. This is done to facilitate free updraft of the hot air into the pipe.
A relatively large transparent or translucent plastic cover or canopy is spread and stretched tightly on the ground around the pipe such that the pipe passes through a cutout over the center of the canopy having a diameter exactly matching to that of the pipe. The cut out section of the canopy should snugly fit the pipe and should be sealed to stop the hot air from escaping or leaking. The canopy should maintain a minimum height of at least a foot above the ground, again to facilitate easy cycling of air.
The pipe is painted gradually from black to white, starting from the bottom to the top. This pattern helps in maintaining a constant speed of the rising air and acts as a “fuel." This happens because the darker shades heat up more quickly than the preceding upper lighter shades and therefore the air enclosed within is always pushed in the upward direction at a constant acceleration.
The lower half of the solar tower or the pipe is fitted with a stepper motor equipped with blades that are quite similar to that of your CPU fan. The rising air hits the blades and turns them with a considerable force. The rotation of the blades moves its internal winding which reacts with the fixed magnets and generates electricity. This electricity passes through the motor output wires and can be used to power a light or an appliance or may be simply stored in batteries for later use.
For more information and videos about these solar towers, please visit Green-planet Solar Energy.