Anyone with a napkin can elaborate why this is not feasable?
The amount of energy stored in a Tesla is about 100kWh or about 3.6e8J.
You would need 36,660 tonnes suspended by a meter to store an equivalent amount of energy (or 1 tonne suspended 36.7km). https://www.wolframalpha.com/input?i=100kWh+%2F+%281+tonne+*...
> Once all balls are on the bottom, generated electricity is used to rotate the whole thing and start process anew.
If here, you mean part of the electricity generated by the flow, then it can't work because pumping it back up is subject to friction (in fact, generation from when it flows down is also subject to friction) and to mechanical/electrical conversion losses.
On a 100% efficient system with no losses, you would get perpetual motion, but subtracting any energy from the system would make it slow or stop.