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.

Landfill Methane

Methane, a combustible gas, is a primary component of the gas generated by landfills. It is a greenhouse gas with 20 times the greenhouse potential of carbon dioxide; thus, burning methane for heat or electric power has a roughly 20:1 greenhouse savings potential.

There are about 510 operational methane-to-electricity projects in the U.S., generating about 156 megawatts annually, enough to power 920,000 homes. Direct use of methane — burning it to create heat, replacing natural gas or coal — uses about 304 million cubic feet a year, enough to heat 715,000 homes.

In Durham, NH, the University of New Hampshire’s ECOLine project was cited as one of the Environmental Protection Agency’s Projects of the Year in 2010. The plant, which went online in 2009, draws methane from Waste Management of New Hampshire’s Rochester landfill and burns it in cogeneration plants to provide up to 85% of the electricity and heating needs for the 5 million square feet campus.

UNH is also selling the Renewable Energy Certificates it has earned from the project to finance the project, and to invest in additional energy efficiencies.