EIA: Natural Gas is the Most Common Energy Source for Electricity Generation in the U.S.

Natural gas is the most common energy source for electricity generation in the United States. More than half (280 GW) of the country's 491 GW of gas-fired power generation capacity is a combined cycle system that includes steam turbines and combustion turbines. The main configuration of the combined cycle system consists of two combustion turbines and a steam turbine.

Natural gas power plants utilize simple cycle or combined cycle energy conversion. Simple cycle systems consume natural gas in a single conversion system, such as a combustion turbine, a boiler with a steam turbine, or an internal combustion engine. In these systems, the energy from one conversion of exhaust heat is lost and not sent to another turbine. Combined cycle systems send heat from the combustion turbine to a heat recovery steam generator to pressurize one or more steam turbines that generate additional electricity.

Combined cycle systems tend to be more efficient at converting a unit of natural gas to a unit of electricity. Combined cycle systems typically operate at higher capacity factors than simple cycle systems due to increased efficiency. Therefore, combined cycle systems typically serve the base and intermediate loads of the grid, while simple cycle systems typically serve peak loads.

The EIA's Annual Electricity Survey collects a unit code identifier that groups combined cycle components into power blocks. Power block configurations vary widely, including configurations such as multiple combustion turbines supporting one or more steam turbines. Most combined cycle generator sets have combustion and steam turbine components, each connected to a generator. However, the combined cycle capacity of 13 GW is a single-shaft system in which the combustion and steam turbines drive a utility generator on one shaft.

The largest natural gas combined cycle power plant in the United States in terms of power generation is Florida Power & Light's West County Energy Center. The West County Energy Center consists of three 3x1 generator sets, or a total of 12 combustion and steam turbines. All three generator sets are rated at 1,259 MW, bringing the plant's total installed capacity to 3,777 MW. The Xixian Energy Center will generate 20.3 TW in 2021; by 2021, only 5 nuclear power plants and 1 coal-fired power plant will generate additional power.

The average combined-cycle generator capacity has increased since 2015, when a new type of combustion turbine became more common. These newer combustion turbines allow combined cycle generator sets with greater capacity and higher efficiency. The average capacity of 2x1 generator sets increased from 500 MW built before 2015 to over 700 MW built after 2015.