By the Numbers: "Cogen" plants do double duty to save energy

6.2 megawatts

Amount of electricity to be produced by a natural-gas generator, enough to provide up to half the power for the 57-story New York City skyscraper where its located. The steam the generator will be produced won't go to waste—it will be used to heat and cool the building, according to this recent story in The New York Times. This generator, known as a cogeneration plant, or cogen, can reduce energy costs.

Con Edison, the main juice provider for the Big Apple, is a fan of cogens. "We're encouraging demand-side energy management. Rather than our supplying it, they manage the supply and we back them up and deliver as needed," says Chris Olert, a Con Ed spokesman. "It takes the stress off the system. At the same time, somewhere someone is using less fossil fuel so there's less carbon in the air. Cogens are good for the environment." (The photo shows a 236-megawatt Con Ed cogen plant in New Jersey.)

Essential information: Use our Energy-Saving Guide to learn how to reduce save your own energy consumption.