A pump storage facility takes water from a river at night when demand is low and pumps it to a hilltop reservoir 500 ft above the river. The water is returned through turbines in the daytime to help meet peak demand. 

(a) For two 30-inch pipes, each 2,500 ft long and carrying 20,000 gal/min, what pumping power is needed if the pump efficiency is 85 percent? The friction loss is estimated to be 15 ft of water.

(b) How much power can be generated by the turbines using the same total flow rate?

(c) What is the overall efficiency of this installation as an energy storage system?