I need to come up with an economic report on what kind of power a hydroelectric turbine can generate. The turbine would be the ones used in large to medium size dams where the head is maybe 20 meters or higher. from the P=head*flow*gravity*efficiency formula, what is the standard efficiency ratio for these kind of turbines? I hear it can be close to 90 percent if the head is high enough?! Can I also ask: 1. What is the approximate cost of one of these turbines? I have no idea - 500,00 ? 5 million? 2. What is the largest hydro turbine in the world.. or where is it being used? Three gorges?