4.72 Figure P4.72 shows a

pumped-hydro energy storage

system delivering water at

steady state from a lower

reservoir to an upper reservoir

using off-peak electricity (see

Sec. 4.8.3). Water is delivered to

the upper reservoir at a

volumetric flow rate of 150 m³/s

with an increase in elevation of

20 m. There is no significant

change in temperature,

pressure, or kinetic energy from

inlet to exit. Heat transfer from

the pump to its surroundings

occurs at a rate of 0.6 MW and g

= 9.81 m/s². Determine the

pump power required, in MW.

Assuming the same volumetric

flow rate when the system

generates on-peak electricity

using this water, will the power

be greater, less, or the same as

the pump power? Explain.