Combined cycle technology allows a power plant to generate 50 percent more electricity from its fuel than it could with a single-cycle power system. Here’s how it works:
In a two-on-one combined cycle system, two combustion turbine generators work in conjunction with two heat-recovery steam generators and a steam turbine generator. In the first cycle, natural gas or diesel gas is burned to directly power two gas turbine generators that produce electricity. TVA also has one-on-one combined cycle units where there is a single heat-recovery steam generator and a single steam turbine generator.
The hot exhaust normally lost during this process is captured for the second cycle, where it used to boil water into steam in the heat recovery steam generators. The steam spins an additional turbine generator to produce more electricity. The steam is then condensed back to water and recycled.