The potential energy of each kg of water, before it falls, is
(M G H) = (1kg) (9.8 m/s²) x (30 m) = 294 joules
The potential energy lost by 60 kg of water pouring through is
(60 x 294) = 17,640 joules
The power output of the plant is
(17,640 joules/sec) x (85%) = 14,994 watts
= almost but not quite 15 kW.
(If you used 10 for gravity, it would come out to 15.3 kW)
