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Cogeneration

Cogeneration is harnessing the waste energy from one process to power another process. For example, a cogeneration system at Massachusetts Institute of Technology burns fuel to create steam to generate electricity, and then uses the waste heat  to heat buildings. A New England Power facility in Rhode Island drives a generator using a gas turbine similar to a get engine; the exhaust gases are hot enough to generate steam for a second turbine, for a combined efficiency of more than 50%.

The principle was first applied in the early 17th century. In the 18th century, waste steam from industrial processes powered steam engines driving other parts of the process.