An 800-MW electric power plant has an efficiency of 30%. It loses its waste heat in large cooling towers. Approximately how much waste heat (in MJ) is discharged to the atmosphere per second?
A) 1 200
B) 1 900
C) 800
D) 560
E) 240

Question

Quizplus · Accepted Answer

The amount of energy input to the power plant is 800 MW (given).
Efficiency is given as 30%, therefore output energy = 0.3 x input energy = 0.3 x 800 MW = 240 MW.
The amount of waste heat is the difference between input energy and output energy = 800 MW - 240 MW = 560 MW.
To convert MW to MJ/sec, we multiply by 3,600,000 (number of seconds in an hour).
560 x 3,600,000 = 2,016,000,000 J/s or approximately 1,900 MJ/s. 
Therefore, the best choice is B.

An 800-MW Electric Power Plant Has an Efficiency of 30