Pumped storage is a great energy saver

At times of low electrical demand, excess generation capacity is used to pump water into the higher reservoir. When there is higher demand, water is released back into the lower reservoir through a turbine,

http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity

http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity

One advantage of hydroelectial energy

Question 3

http://education.nationalgeographic.com/education/encyclopedia/hydroelectric-energy/?ar_a=1