Co-generation is the use of heat or other forms of energy
that is a by-product of some other activity.
The most familiar form of co-generation is the heater in
a common automobile. The heat of the engine, a by-product
of locomotion, is used to heat the passenger compartment.
Co-generation is most commonly used in large factories,
such as those of automobile manufacturers. In some cases,
waste heat from large factories is piped into surrounding
communities and used to heat houses.