By Editors of Power Engineering
A new study by the Energy Information Administration indicates the average annual heat rates of natural gas-fired electrical generators decreased seven percent from 2006 through 2015.
Coal generation had a relatively steady heat rate through the measured time period. As of 2015, the heat rate for natural gas generation was 25 percent lower than that of coal.
Heat rates for coal generation showed a small rise in 2015, which the EIA said may be due to emissions controls. These controls were installed on nearly 205 GW of cal capacity from 2006 to 2015, representing 73 percent of the coal-fired generating fleet that were operating in 2016. Coal emissions controls often require more on-site electrical use.
Though emissions controls were installed on 37.5 GW of gas-fired generators during the same time – nine percent of the total fleet – they did not have a significant influence on average operating efficiency trends.
Additionally, changes in use can affect heat rates, as plants that are cycle on and off more frequently may consume more fuel to produce electricity, especially during ramping periods.
However, the rise in heat rates from many coal plants was partially offset by the addition of 19.5 GW of more-efficient new coal capacity while retiring 43.1 GW of less efficient capacity.
The average heat rate for natural gas plants were pushed down by the addition of 58 GW of combined-cycle capacity, which are more efficient than single-cycle plants, during the studied period. Combined-cycle plants now account for 85 percent of total gas-fired generation in 2015.