Fuel a City.

Cremating a body uses up a lot of energy - and a lot of nonrenewable resources. So how do you give Grandma the send-off she wanted and protect the planet at the same time? Multitask. Some European crematoriums have figured out a way to replace conventional boilers by harnessing the heat produced in their fires, which can reach temperatures in excess of 1,832 degrees F. In Fact, starting in 1997, the Swedish city of Helsingborg used local crematoriums to supply 10 percent of the heat for its homes.

A less morbid way to look at it is the functionality of a hybrid vehicle. The energy being used when the brakes are applied is captured to recharge the electric battery, thus providing the car with better fuel efficiency in the city as opposed to driving on the highway.