Capacity Factor – A Measure of Reliability

One way the energy industry measures the reliability of power plants is by regularly calculating capacity factors.

Capacity factor is the measure of how often a power plant runs for a specific period of time. It’s expressed as a percentage and calculated by dividing the actual unit electricity output by the maximum possible output. This ratio is important because it indicates how fully a unit’s capacity is used.

Capacity factors vary considerably by plant and fuel type (see graphic below). As you can tell, nuclear energy’s average capacity factor is above 90, meaning the average nuclear plant remains on line, generating electricity, more than 90 percent of the time.

Source: NEI

Source: NEI

In 2014, the 100 operating nuclear plants in the U.S. had an average capacity factor of 91.8 percent. This is the highest level ever recorded and attributed to the fact that nuclear plants had fewer and shorter refueling and maintenance outages and less unplanned outages. In 2014, the average refueling outage duration was 37.2 days compared to 41 days in 2013 and 46 days in 2012.

Another factor that increased the U.S. nuclear fleet’s 2014 capacity factor was the fleet’s strong performance in December 2014, when the capacity factor was 98.9 percent.

Operating at six sites in the Carolinas, Duke Energy’s 11 reactors set a combined capacity factor record of 93.18 percent in 2014. This marked the 16th straight year the fleet achieved a capacity factor greater than 90 percent. The fleet also had a capacity factor of 97.04 percent for the summer months (June – August).

Source: NEI

Source: NEI

In addition to supplying nearly 20 percent of America’s electricity, nuclear energy is a proven, dependable source, providing on-demand baseload electricity around the clock – whether during record heat or arctic cold.

Celebrating STEM


Student robotics Team 343 poses with members of Duke Energy and iMAGINE Upstate to celebrate the recent partnership between Duke Energy and iMAGINE Upstate.

“Hookshot” wheeled itself across the floor of the Oconee Nuclear Station’s World of Energy education center, picked up a large red ball and launched it at one of its designers. The robot wasn’t being rude. That’s what he was programmed to do – throw things.

Hookshot is an advanced robot built of complex systems and many functions. He’s the center of attention at all kinds of community events – in fact, you could say he’s kind of a show off.

Would you believe that Hookshot was built by kids under the age of 18?

Those kids belong to Metal in Motion FRC Team 343, a robotics team for high schoolers in Oconee County, S.C. The team was established in 1999 as a collaborative project involving local industries and the School District of Oconee County.


Hookshot, a robot, launches a ball at one of its designers

Team 343 showcased Hookshot to kick off the partnership between Duke Energy and iMAGINE Upstate, a science, technology, engineering and mathematics (STEM) festival March 28-April 4 in downtown Greenville, S.C.

The festival is a celebration of all things STEM, including the young minds behind the engineering and design of such complex robots like Hookshot. Not only will it highlight young talent, but it will also showcase the innovation, creativity and entrepreneurial activity of local businesses and organizations in hopes to spark interest among the future workforce.

Through its partnership with iMAGINE Upstate, Duke Energy’s World of Energy at Oconee Nuclear Station in Seneca will host “Energize Your Mind” during the week of March 28-April 2.

“We see how important STEM is in our own company, and we want to foster that creative, innovative spirit by offering fun, interesting STEM programs at the World of Energy,” World of Energy Communications Manager BJ Gatten said.

For more information about “Energize Your Mind,” visit; to learn more about iMAGINE Upstate, click here.

Nuclear Power Plants: Keeping Us Warm During the Winter

When the weather outside is frightful, leading nuclear energy activist says it is nuclear energy that keeps us warm.

In a recent news release, Nuclear Energy Institute (NEI) Vice President Richard Myers said, “During periods of extreme weather, nuclear energy’s importance to the U.S. electric grid and to the nation becomes more apparent than ever. Our nuclear energy facilities reliably generate large amounts of electricity, and they do so without the price volatility that can hammer customers financially.”

One of the attractive qualities of nuclear as an energy source is reliability even in extreme weather. Fossil fuel systems suffer during extreme cold as coal stacks and diesel generators freeze. Gas lines become stressed to keep up with rising demand. Meanwhile, all electricity providers are stressed when demand grows on the grid as it takes more power to keep homes at comfortable temperatures.

Nuclear, however, thrives in cold weather and was widely credited with keeping the lights on during the 2014 “polar vortex.” Following the storm, Forbes proclaimed, “Polar Vortex – Nuclear Saves the Day.” During the 2014 winter storm, the nation’s nuclear fleet performed at 95 percent capacity, far outpacing any other form of generation.

Nuclear performed similarly well during the recent cold weather that gripped the country and shutdown New York. As the Clean And Safe Energy (CASE) coalition explained, “Nuclear energy facilities operated at electric-sector leading levels of reliability in the face of freezing artic temperatures, helping to keep our homes warm and businesses humming. The value of America’s 99 nuclear energy facilities becomes ever clearer when our electric grid is strained.”

This is just one reason why nuclear is such a crucial component of a diverse energy portfolio.