Energize Weekly, April 17, 2019
Natural gas-fired combined-cycle generating capacity in the U.S. overtook coal-fired generation as the country’s largest single source of electricity generation in early 2019, according to the federal Energy Information Administration (EIA).
In January 2019, there were 264 gigawatts (GW) of combined-cycle gas-fired plant capacity and 243 GW of coal-fired plant capacity. In 2002, there were about 100 GW of combined-cycle capacity and more than 300 GW of coal capacity.
Since the start of 2015, an estimated 40 GW of coal-fired capacity has retired and no new coal plants have come online, while net natural gas-fired capacity rose 30 GW. Combine-cycle plants are now providing more electricity than coal plants.
“The electricity generation from these NGCC [natural gas combined-cycle] capacity additions, as well as output from new wind and solar generators, has largely offset the lost generation from coal retirements,” the EIA said.
Natural gas generation—of all types—surpassed coal more than 15 years ago, but the combined-cycle technology has become the technology of choice due to its efficiencies.
Coal-fired or oil-fired plants burn fuel to make steam to turn steam turbines to generate electricity. A combined-cycle plant heats up a fuel-air mixture to spin a gas turbine to make electricity, the waste heat is used to make steam for a steam turbine.
Traditional natural gas-fired combustion and steam turbines are less efficient and more expensive to run, so they are usually used only during peak periods of electricity demand.
Almost all coal plants combust coal to generate steam, with little opportunity for efficiency improvements. The one exception is integrated coal-gasification units, which are not widely in use, the EIA said.
By the end of 2018, combined-cycle plants made up about half of the total natural gas-fired generating capacity, but they provided nearly 90 percent of the total natural gas-fired electricity generation.
Capacity factor is a measure of output as a percentage of a plant’s megawatt capacity. For combined-cycle plants and coal plants, the capacity factors are similar—in the 50 to 60 percent range. Natural gas combustion and steam turbines are down around 10 percent, reflecting their limited use during peak periods.
“As more NGCC plants continue to come online and coal plants continue to retire, NGCC-powered electricity generation should consistently rank as the most prevalent source of electricity generation in the United States for the foreseeable future,” the EIA said.
