Because combined heat and power (CHP) plants optimize energy use, they cut fuel costs and pollution. Even though U.S. power plants have been using CHP for decades, today’s energy experts have a newfound appreciation for its ability to promote sustainable energy use.
Many veteran power professionals are somewhat surprised that combined heat and power (CHP), a well-established approach to the generation of electrical power and thermal energy, especially in Europe (see sidebar), is gaining popularity among energy analysts looking for solutions to America’s growing need for sustainable electrical generation.
CHP, also called cogeneration, is the concurrent production of electricity or mechanical power and useful thermal energy (heating and/or cooling) from a single source of energy. CHP plants may use one of several generation technologies (from gas turbines to Stirling engines), which means that they can use a variety of fuels to generate electricity or power at the point of use, allowing the heat that would normally be lost in the power generation process to be recovered to provide needed heating and/or cooling (Figure 1).
1. Waste not, want not. More than two-thirds of the fuel used to generate power in the U.S. is lost as heat (shown as conversion losses in this diagram). Source: Oak Ridge National Laboratory
CHP is typically a feature of distributed generation, which, unlike central station generation, is located at or near the point of consumption. Instead of purchasing electricity from a local utility and then burning fuel in a furnace or boiler to produce thermal energy, consumers use CHP to provide these energy services in one energy-efficient step (Figure 2). As a result, CHP improves fuel efficiency and reduces greenhouse gas emissions. In addition, newer CHP applications show a trend toward the use of cleaner fuels. For optimal efficiency, CHP systems typically are designed and sized to meet the users’ thermal baseload demand.
2. Increased efficiency results in reduced carbon emissions. An example of the CO2 savings potential of CHP based on a 5-MW gas turbine CHP system with 75% overall efficiency operating 8,500 hours per year providing on-site steam and power compared to a separate heat and power supply consisting of an 80% efficient on-site natural gas boiler and average fossil-fueled electricity with 7% transmission and distribution losses. Source: ICF International
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