SALISBURY, NORTH CAROLINA - Ravens fly over a sprawling, abandoned brick building with tall chimneys that once billowed plumes of smoke day and night.
In its heyday, the coal-fired plant continuously produced 370 megawatts of electricity, with each megawatt able to power a thousand households. But its last coal-fired units were shut down a few years ago. Piles of coal are long gone.
Across the compound here in the center of this mid-Atlantic state, three noisy turbines churn at a new natural gas-fired plant that produces 620 megawatts. The Buck Combined Cycle power station stands at the edge of the Yadkin River—and amid a wave of change in the energy industry.
Both plants are owned by Duke Energy, a company with holdings in the United States and Latin America.
Like other U.S. energy firms, it is responding to growing demand for cleaner energy and tighter restrictions on carbon emissions. American firms are being compelled to reduce their dependence on coal in favor of much cleaner fuel sources.
Bill Wilson, senior engineer at the Buck Combined Station, said Duke has retired about half of its coal-fired facilities in recent years and replaced them with natural gas facilities like this.
"Due to the current price of natural gas, it is much cheaper,” he explained. “So on a megawatt basis, it is cheaper to run natural gas than coal."
It costs between $15.30 and $17.30 per megawatt hour (MWh) for natural gas, while coal costs about $28 per MWh, Duke Energy spokeswoman Tammie McGee said. "So, in today’s markets, our natural gas generation does provide lower costs and savings to our customers," she added.
Duke Energy plans to phase out most of its U.S. coal plants in next few decades.
The shift also is evident in other energy companies across the country.
For decades, coal was the main fuel source for generating power in the United States. Last year, natural gas matched it, with each producing a third of the nation’s electricity, according to U.S. Energy Information Administration figures. The other third came from hydropower, nuclear and renewable energy sources.
The administration had predicted that natural gas would overtake coal as the country's biggest source of electricity this year, though this week it posted a story headlined, "Coal may surpass natural gas as most common electricity generation fuel this winter."
About 200 miles northwest of Salisbury, in mountainous Russell County, Virginia, a couple of trucks and a bulldozer in July removed the last few tons of black coal from a field outside the Clinch River Coal Plant.
The plant’s three coal-fired units once produced up to 705 megawatts of electricity. But early this year, plant owner American Electric Power converted two of the units to gas and retired the third.
The new units are not only cleaner, they are more efficient, plant manager Ricky Chaffin said. Now, the plant can produce 484 megawatts of electricity—averaging 242 megawatts per unit, up from the previous 235 each. And running it requires less labor.
"You don't have to handle the coal," Chaffin said. "You don't have to move the coal from the pile to the plant.”
Also, natural gas is delivered via pipeline. “We have got a lot less equipment,” Chaffin added. “So it's a whole lot less manpower required to run a gas plant."
The shift in energy production has also brought change to the workforce. For instance, when American Electric Power switched from coal to gas, the number of people needed to run the plant dropped from 182 to 46.
But there’s been employment growth in renewable energy. The National Solar Jobs Census reported the solar energy workforce grew by more than 20 percent in 2015.
In North Carolina’s Union County, Duke Energy has hired roughly 500 people to construct a solar field spreading over 156 hectares of farmland that used to grow corn and soybeans. Workers are installing 663,800 solar panels on the solar farm, expected to produce 60 megawatts of electricity when it becomes operational next year.
North Carolina, with more than 1.9 gigawatts worth of installed solar capacity, ranks second among U.S. states, according to the Solar Energy Industries Association.
"We have customers who are demanding renewable energy, and we do have energy policies that we are working toward complying with," said McGee. She said the company has more than 50 solar projects in operation nationwide, and 19 wind-powered projects generating electricity. One more wind site is expected to come online in December.
Renewable energy sources supplied roughly 13 percent of U.S. energy produced last year, according to the Energy Information Administration. Of that, 6 percent was from hydropower, 5 percent wind, 2 percent biomass and 1 percent solar.
While big energy companies are phasing out coal, their environmental challenges are far from over.
Last month, Duke Energy reached an agreement to clean up coal ash from its Buck Steam Station.