Energy may be stored for use during peak demand by pumping water to a high reservoir when demand is low and then releasing it to drive turbines when needed. Suppose water is pumped to a lake 135m above the turbines at a rate of 1.00 X 105 kg/s for 10.0 h at night.
(a) How much energy (kWh) is needed to do this each night?
(b) If all this energy is released during a 14-h day, at 75% efficiency, what is the average power output?