Calculating Nonconservative Energy Loss in Pumped-Storage Reservoirs

[BMW25]

new problem!

A pumped-storage reservoir sits 136 m above its generating station and holds 9.0×10^9 kg of water. The power plant generates 346 MW of electric power while draining the reservoir over an 6.9 h period.
What fraction of the initial potential energy is lost to nonconservative forces (i.e., does not emerge as electricity)?

could you please guys help me with that? I gave up with that
I need that in hour guys please please.

 

[learningphysics]

136 m above its generating station and holds 9.0×10^9 kg. so what is the gravitational potential energy?

346 MW over an 6.9 h... what is the energy generated here?

so how much energy is lost?

what is the fraction of this energy to the original gravitational potential energy.