[gleeaikin]

Regarding an important step left out.

Perhaps these mines are very deep, so the fall between the multiple generators can utilize the energy of gravity to maximize the energy when it hits the generators. What do you think?

[-YYZ-]

See the earlier explanations. It doesn't matter how deep the mine is or how many or what kind of turbines and generators are involved.

[ModelBreaker]

Perhaps these mines are very deep, so the fall between the multiple generators can utilize the energy of gravity to maximize the energy when it hits the generators. What do you think?

I'm not sure if you are being sarcastic. If not, then the deeper the well, the more energy it takes to pump the water back up.

[eraser2005]

You want a good amount of depth to maximize efficiency. But you still cannot produce energy from a system like Bikers4Bush is describing.