Hello, I am building a solar tower miniature replica (keeping the same proportions) but a fraction of the scale. Ideally I'd like the chimney to be no more than 20 feet and the diameter of the chimney 1 foot across. The turbine generator would be installed at the base. Now I'm new to this... But I was wondering what kind of turbine generator would be ideal for this say I get about a 8 mph flow of air. Ideally I'd like to charge a 12-Volt battery. It would be nice to have good solid amperage. Should the chimney diameter be smaller for the venturi effect?