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When you flip on a light switch, odds are you're burning coal. But as the fracking boom unlocks huge quantities of natural gas, the nation's electric grid is changing. Power plants are increasingly turning to natural gas, a low-cost, cleaner-burning fossil fuel. That shift is driven by economics and also regulations. Marie Cusick of member station WITF reports.
MARIE CUSICK, BYLINE: Decked out in a hard hat and safety goggles, Bill Pentak stands in the middle of a construction site. He's looking up at his company's latest project towering overhead, a new natural gas power plant.
BILL PENTAK: This plant was sited precisely where it is because of its access to the abundant, high-quality natural gas that's found a mile to two miles beneath our feet.
CUSICK: He's referring to the Marcellus Shale underfoot. In recent years, this part of north-central Pennsylvania has become one of the most productive gas fields in the world. Pentak works for Panda Power Funds, a Dallas, Texas-based company that has two more gas plants planned for Pennsylvania. The projects are part of a bigger story. The electric grid is shifting away from coal toward gas.
PENTAK: What's taking place here is taking place across the United States.
CUSICK: It's a trend Gary Helm is watching. He studies emerging markets for the PJM Interconnection. That's the regional grid organization for the mid-Atlantic U.S. and Midwest. It's sort of like an air traffic controller for the power system, helping keep the lights on for 61 million people.
GARY HELM: We see, down the road, definitely a lot of gas coming online.
CUSICK: That's because the fracking boom freed up a lot more cheap gas. Up until the mid-2000s, about half the electricity in the U.S. was produced by burning coal, 20 percent or less came from gas. Tyler Hodge is an analyst with the U.S. Energy Information Administration. He says these days, coal has dropped to about 40 percent of the nation's power while gas now accounts for nearly a third.
TYLER HODGE: Definitely the mid-Atlantic and Pennsylvania regions especially are showing some significant shifts towards natural gas.
CUSICK: Coal plants are also retiring as the Obama administration pushes its climate change action plan, which would require the country to cut carbon emissions by 30 percent from 2005 levels by the year 2030. Back at the construction site, Bill Pentak stands next to the plant's generator and points out that gas has an advantage in all this. As more renewables come online, gas plants can ramp up and down quickly. So when the sun isn't shining or the wind isn't blowing, he says gas can fill in the gaps.
PENTAK: You have to have something that can be quickly dispatched to make up for that lost power, or it threatens the reliability of the grid.
CUSICK: That's not to say using more gas doesn't pose some problems. Although gas produces about half the carbon emissions that coal does when you burn it, there's still uncertainty within the scientific community about its overall climate impact. Christina Simeone is with the Kleinman Center for Energy Policy at the University of Pennsylvania. She says drilling and transporting gas leads to the leakage of methane, a potent greenhouse gas.
CHRISTINA SIMEONE: When you look at gas production, you look at coal production, you know, these are imperfect resources that do have impacts just like all of these resources are imperfect and they all have impacts.
CUSICK: The U.S. Energy Information Administration is projecting that gas power generation will become increasingly common under the Obama administration's climate plan. The agency expects the regulations would cause more coal plants to shut down, and gas will begin to take its place, followed by more renewable energy. For NPR News, I'm Marie Cusick.
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