The vertical shaft windmills are well proven technology, having been used in the Middle East for thousands of years. There are some wooden ones still operational in Iran.
While harnessing the thermal driving mass of water (thermal convective flow) is doable, the engineering required is a bugger and fraught with pitfalls. These pitfalls can be avoided, but the engineering is expensive.
You may find it beneficial to altetnately look into a "trompe" for harnessing water power.
Awesome, @torquewrench1969! I'm so happy to get a comment from someone who seems to know something about this. Just to make sure we didn't misunderstand each other: what I want to harness is the thermal covective flow of AIR, that has been heated up in the greenhouse, to pump the water up into the tank. As for generating electricity, I want to use the water coming down for running a micro-hydro turbine. The latter is pretty straight forward. The former part is the one I'm not so sure about.
Now I understand what you're wanting to do!
It could be done with rising hot air, but the greenhouse would need to be pretty big and the water flow rate would be pretty low.
I'll think about this a bit and get back to you
yes get back to him....and untold thousands of us dreaming and waiting for proof of concept ;p
Or maybe just 'me too' ;p