Efficiency of natural gas-fired plants improves, coal-fired plants remain stable

Heat rates of natural gas-fired power plants have fallen 7%, and the rates for coal-fired power plants have risen about 1% between 2006 and 2015, according to the U.S. Energy Information Administration. Heat rates are the amount of energy used to generate a unit of electricity, and the lower the rate, the more efficient the plant.

In 2015, the heat rate for natural-gas fired plants was about 25% lower than coal-fired plants, compared to about 18% lower in 2006. “The small rise in the average operating heat rate for coal-fired generation may be attributed to emissions controls,” according to the EIA. “Emissions-control equipment was installed on almost 205 gigawatts (GW) of coal capacity from 2006 to 2015, or about 73% of the coal-fired generator fleet that was operating in 2016.”

Natural gas-fired plants also received emissions controls on about 37.5 gigawatts of natural gas-fired generation or about 9% of generators. But the emissions controls have not had a significant impact on efficiency.

“Changes in usage patterns of coal and natural gas plants could affect their heat rates,” according to the EIA. Plants that are cycled on and off frequently used more fuel to produce electricity.

The rise in the heat rate for coal-fired plants was partially offset by adding 19.5 gigawatts of more efficient coal generators and retiring 43.1 gigawatts of less efficient coal capacity. Plants added between 2006 and 2015 had a heat rate of 9,665 British thermal units per kilowatt-hour, and those retired in the period had a heat rate of 10,343 Btu/kWh.

Since 2006, the majority of natural gas-fired generators that have come online have been more efficient, and most of the retired units have been less efficient.