Chimneys do not require perfect insulators otherwise no chimneys would work. The biggest thing they do is prevent air mixing which in turn prevents a lot of energy exchange. This could work.
I am not qualified to evaluate the actual possibility of this device, and there are many points that don't seem plausible to me.
However, the author is not arguing free energy. That would be like arguing wind turbines are "free energy". It's very clearly a solar powered device, with solar energy providing the heat that drives the air movement.
I'm not qualified either but this is an important point, the energy is definitely available and photoelectric semiconductors are merely one way to harness it.
Regarding the practical issues, what happens at night? Does it collapse under its own weight? How do you get it up in the sky in the first place?
This is absolutely not a free energy device. It may be bunk, but it is an attempt at a heat engine. Or rather, an attempt to make an existing heat engine more efficient/ faster/ controlled. There is outside energy and it is already doing work. We want more heat transfer and more controllable weather.
