Duke Energy has a diverse, increasingly clean generation portfolio. Over 40 percent of the electricity we generated in 2020 was from carbon-free sources, including nuclear, wind, hydro and solar. Over 37 percent was from lower-carbon natural gas, which emits about half as much carbon dioxide as coal when used for electric generation. And 21 percent was from higher-carbon coal and oil. Taken together, owned and purchased renewables are equivalent to 11 percent of our MWh generation.
Since 2008, the use of coal and oil as generation fuels has significantly decreased. These fuels are being replaced by natural gas and renewables.
Water withdrawn is the total volume removed from a water source, such as a lake or a river. Because of the once-through cooling systems on many of our coal-fired and nuclear plants, almost 99 percent of this water is returned to the source and available for other uses. Water consumed is the amount of water removed for use and not returned to the source.
Many factors influence emissions levels and intensities, including demand for electricity, generation diversity and efficiency, weather, fuel and purchased power prices, and emissions controls deployed. Since 2005, our carbon dioxide (CO2) emissions decreased by over 40 percent, sulfur dioxide (SO2) emissions decreased by over 95 percent and nitrogen oxides (NOX) emissions decreased by over 80 percent. These decreases are primarily due to decreased demand for electricity in 2020 due to the economic downturn caused by the COVID-19 pandemic, the addition of pollution control equipment for SO2 and NOX in previous years, decreased coal generation, increased natural gas and renewables generation and replacement of higher-emitting plants.
Methane (CH4) is the primary component of natural gas, and is a greenhouse gas. We work to minimize methane emissions, but some is released during pipeline operations and maintenance. Duke Energy announced in October 2020 its goal of reducing methane emissions in its natural gas distribution companies to net-zero by 2030.
Sulfur hexafluoride (SF6) is an insulating gas used in high-voltage electric transmission and distribution switchgear equipment, and is a greenhouse gas. We work to minimize SF6 emissions, but some is released during transmission and distribution operations and maintenance.
Duke Energy’s TRI releases for 2019 were down 87 percent from 2007, primarily due to the significant investments we’ve made in environmental controls for our power plants, and decreased coal generation. Variations in releases were largely due to coal ash basins and their closure operations. These releases are expected to decrease significantly as coal ash basins are closed. (Data for 2020 will be available in August 2021.)
Duke Energy met its goal to recycle 80 percent of solid waste. We are working on strategies to continually improve performance on this goal in the future. (This goal excludes Duke Energy Renewables, which has a relatively small waste stream.)
Oil spills include releases of lubricating oil from generating stations, leaks from transformers, or damage caused by weather or by third parties (typically because of auto accidents).
The increase in the number of citations from 2018 to 2019 was due mostly to an increase in water discharge reporting and compliance issues, which have been resolved with regulatory authorities.