'the fifth fuel' - The elusive negawatt(2008)

IN WONKISH circles, energy efficiency used to be known as “the fifth fuel”: it can help to satisfy growing demand for energy just as surely as coal, gas, oil or uranium can. But in these environmentally conscious times it has been climbing the rankings. Whereas the burning of fossil fuels releases greenhouse gases, which contribute to global warming, and nuclear plants generate life-threatening waste, the only by-product of energy efficiency is wealth, in the form of lower fuel bills and less spending on power stations, pipelines and so forth. No wonder that wonks now tend to prefer “negawatts” to megawatts as the best method of slaking the world's growing thirst for energy.

-  The elusive negawatt (The Economist, May 8th 2008)