Dear EarthTalk: What is “cogeneration” as a means of providing heat and power?
-- Jerry Schleup, Andover, MA

Cogeneration—also known as combined heat and power, distributed generation, or recycled energy—is the simultaneous production of two or more forms of energy from a single fuel source. Cogeneration power plants often operate at 50 to 70 percent higher efficiency rates than single-generation facilities.

In practical terms, what cogeneration usually entails is the use of what would otherwise be wasted heat (such as a manufacturing plant’s exhaust) to produce additional energy benefit, such as to provide heat or electricity for the building in which it is operating. Cogeneration is great for the bottom line and also for the environment, as recycling the waste heat saves other pollutant-spewing fossil fuels from being burned.

Most of the thousands of cogeneration plants operating across the United States and Canada are small facilities operated by non-utility companies and by institutions like universities and the military. For small cogeneration plants—those that generate anywhere from one to 20 megawatts of power—biomass or even methane from garbage dumps can be used as a front-end fuel source, but natural gas is far more common as the primary input.

For instance, Sunnyvale, California-based Network Appliance Inc., a computer networking company, relies on a one megawatt natural gas-powered cogeneration system to power the building’s extensive air conditioning needs, and for back-up power for use during peak demand times. The company estimates it saves around $300,000 a year in energy costs thanks to the cogeneration system.

In another example, Illinois-based Epcor USA Ventures operates three mid-sized (25 megawatts and up) cogeneration power plants in San Diego to power U.S. Marine Corps and Navy bases there. All three plants work in the same way: Natural gas turbines drive electrical generators that in turn exhaust hot gases. These are then captured to drive a steam generator hooked into the bases centralized heating and cooling systems. Since the systems generate power to spare, Epcor is talking with area companies about kicking in for a share of the steam to keep their energy bills and carbon footprints in check.

Cogeneration is not limited to stationary power plants. Honda is exploring the use of a specialized automotive cogeneration generator designed to improve the overall efficiency of hybrid vehicles by recapturing waste exhaust heat from the internal combustion engine and converting it to electricity to recharge the battery pack. The idea is still in the research and development phase, it could make its way into new cars within a few years, further improving on the already impressive efficiency of hybrid cars.

CONTACTS: Network Appliance Inc.,; Epcor USA Ventures,; Honda Motor Company,

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