Duke Energy has a diverse, increasingly clean generation portfolio. Over 38 percent of the electricity we generated in 2017 was from carbon-free (nearly zero carbon emissions) sources, including nuclear, wind, hydro and solar. Over 28 percent was from lower-carbon natural gas, which emits about half as much carbon dioxide as coal when used for electric generation. One-third was from higher-carbon coal and oil. Taken together, owned and purchased renewables are equivalent to almost 9 percent of our generation. Duke Energy Renewables sells the electricity and/or Renewable Energy Certificates (RECs) it generates to its customers.
* Excludes pumped-storage hydro.
Since 2008, the use of coal and oil as generation fuels has significantly decreased. These fuels have been replaced primarily by natural gas, mostly because it has become a relatively less expensive fuel and we have added natural gas generation capacity.
Water withdrawn is the total volume removed from a water source, such as a lake or a river.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 generation diversity and efficiency, demand for electricity, weather, fuel availability and prices, and emissions controls deployed. Since 2005, our carbon dioxide (CO2) emissions decreased by 31 percent, sulfur dioxide (SO2) emissions decreased by 96 percent and nitrogen oxides (NOX) emissions decreased by 75 percent. These decreases are primarily due to addition of pollution control equipment, decreased coal generation, increased natural gas 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 is a founding partner of the U.S. EPA’s Natural Gas Star Methane Challenge program, which is aimed at cost-effective technologies and practices that improve operational efficiency and reduce methane emissions.
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 2016 were down 84 percent from 2007, primarily due to the significant investments we’ve made in environmental controls for our power plants, and decreased coal generation. (Data for 2017 will be available in August 2018.)
We met our goal of increasing the percentage of solid waste that is recycled from 69 percent in 2013 to 80 percent in 2018 one year early. (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).
Fines/penalties were relatively large in 2015 because of the May 2015 coal ash enforcement agreement; and in 2016 because of a 2014 oil spill at the Beckjord Station in Ohio, and a 2014 coal ash spill. See the “Legal Cases Resolved” article in the 2015 Sustainability Report.