Duke Energy Learns From Drought: Increasing Water Efficiency in NC

Cowan's Ford Hydro Station created Lake Norman and generates electricity for Duke Energy.
Cowan’s Ford Hydro Station created Lake Norman and generates electricity for Duke Energy. (Photo via Duke Energy)

When you hear about a power outage, what causes spring to mind? Maybe a thunderstorm during the summer, possibly an ice storm in the winter months. In these cases damaged power lines likely prevented electricity from getting to your home. You may not have thought about how a lack of water could prevent your electricity from ever being generated.

Many don’t realize that water plays a vital role in generating electricity. On average, more water is used to generate your home’s electricity than you use to shower, flush the toilet, and do other daily tasks.

As the largest electric power holding company in the U.S., Duke Energy uses billions of gallons of water every year. Below, we’ll learn more about how Duke uses water and how it is working to conserve water in your state.

 

How much water does Duke Energy use every year?

According to Duke Energy spokesperson Randy Wheeless, Duke withdrew 6,250 billion gallons of water in 2015 and consumed 79 billion gallons of that.

Water withdrawn is water taken out of a reservoir. Most of this water, over 98%, is returned to the source. Water consumed is the amount of water removed and not returned due to evaporation. Water consumed decreased from 93 billion gallons in 2014.

What is this water used for?

Most of Duke’s water use comes from cooling its power plants. Duke’s thermal generation plants convert heat energy to electricity. Such systems generate heat during the electricity-making process and must be cooled to remain functional.

What is Duke doing that reduces the amount of water withdrawn?

Duke has recently retired many old coal power plants and replaced them with natural gas plants.

“When they do that, when they switch from these older coal plants to these newer natural gas plants, they are implicitly switching what type of cooling system they use,” says Dr. Jordan Kern, a research assistant professor at UNC who studies energy and water.

Most natural gas plants generate some of their electricity directly from force created by combustion, rather than relying entirely on steam processes like most coal plants. This means that natural gas plants have less need for cooling than coal plants.

Gas fired plants use about 50 percent less water for cooling than a similar coal plant, according to Wheeless. “As we retire coal plants and replace with natural gas, our overall consumption goes down,” Wheeless says.

Why is it important for Duke to be able to function with less water?

At 800,000 people and counting, Charlotte’s 8.4 percent growth rate poses a risk for Duke. With growing municipalities competing for water and demanding more energy, Duke needs to be able to generate electricity with less water available.

Though Duke’s cooling systems return most of the water to the basin, coal and nuclear plants could be at risk because they require so much withdrawn water. Duke has two major nuclear plants near Charlotte in the Catawba River basin.

“If you’re sucking up a lot of water through a straw and then returning 97% of it back downstream, you still have to have it there in the first place in order to operate the power plants,” says Kern.

Kern says that Duke, like many utilities, is increasingly susceptible to water shortages. “Part of that’s climate, part of that’s growth in that part of the state.”

As climate change continues, scientists expect more extreme weather patterns. This includes more severe droughts.

During the 2007 and 2008 drought, Duke had to make major changes to its energy mix. This included reducing hydroelectric generation by 67% at some points during the drought.

Kern says that the drought was a wake-up call for Duke and that since then the utility has improved on collaborating with municipalities to better manage water. “Compared to many water systems and utilities, I think that group has been pretty progressive in terms of accounting for climate change and uncertainty in the availability of water in the future,”he says.