Peaking units are units that generate electricity during periods of peak demand. During the summer, a peaking unit operates on the hottest days, when air quality is poorest, to provide electricity for air-conditioning. During the winter, a peaking unit operates on the coldest days to provide electricity for heating. Peaking units, because they generate electricity when demand is highest, are generally paid a premium for the electricity they generate.
Nothing precludes the operation of peaking units as base-load plants.
Peaking units affect air quality. Across a year, peaking units do not emit high amounts of air pollution because they do not operate much. However, peaking units emit air pollution at higher than normal rates. Peaking units have the potential to emit high amounts of air pollution because no environmental limit prevents these units from operating at higher utilization rates. If peaking units operate more, they will become an even more significant source of air pollution.