
This is definitely the wrong newsgroup for this, but never mind.
Any machine powered by heat (motor, steam- or gasturbine, steamengine,  
thermoelement,etc) work the better, the bigger the temperature difference  
between input and output is. Because You never get all thermic energy out of  
the powering medium (steam, burning gaz, etc), You have to eliminate the rest  
of the energy to keep the efficency high. A thermal electric power plant (coal,  
oil or atomic power) works just the same way. You heat water (steam) to power  
the turbine and generators. Because You don't get the whole energy out of the  
steam (efficency is never 100%) You have to cool down this steam again by  
something else. Most power plants use cooling towers for this purpose (some  
type of mega-refrigerator...). Others use water of a river (ecologically not  
unobjectionable). Got it ?

Cheers   Robert  (HB9NBY)