Efficiency

"It's gone before you even knew it was there: As energy is unlocked from fuels at power plants, two-thirds of the energy consumed to create electricity is lost. The laws of thermodynamics dictate that conversion efficiency will never be 100 percent, because heat is lost at every step of the conversion process. But new technologies may be able to greatly increase conversion efficiency, moving from an overall rate of 36 percent to closer to 50 percent."

http://www.treehugger.com/files/2008/06/efficiency-in-new-york-times.php