How do combined-cycle power plants use both gas turbines and steam turbines?

Combined-cycle power plants improve energy efficiency by utilizing both gas and steam turbines in a sequential process. In these systems, a gas turbine burns fuel to generate power, and its high-temperature exhaust gases—which would otherwise be wasted—are directed into a steam generator.12

Within this steam generator, the heat from the gas turbine exhaust is used to produce steam, which then drives a conventional steam turbine to generate additional electricity. Some advanced designs may also burn additional fuel within the steam generator to further increase steam production. By capturing and repurposing the thermal energy from the gas turbine's exhaust, these combined-cycle units can achieve overall thermal efficiencies of nearly 50 percent, making them among the most fuel-efficient power plants currently available.12