Southern Co. said its profit for the fourth quarter was depressed by continued cost overruns at its troubled high-tech coal power plant under construction in Mississippi.

The Atlanta utility, which is the parent company of Georgia Power, said its fourth-quarter profit was $271 million, 4.2 percent below its year-earlier profit of $283 million.

The quarter's results included a $113 million charge, after taxes, for higher costs to build its subsidiary Mississippi Power's clean-coal Kemper County plant.

Similar charges also affected the year-earlier quarter and full-year financial results for 2015 and 2014.

Southern said its 2015 profit was $2.4 billion, vs. $2 billion in 2014.

The much-delayed Kemper project was hoped to result in a cleaner-burning alternative to conventional coal-fired plants. But the plant is now expected to cost over $6 billion to complete — triple early cost estimates.

Southern said revenue declined 5 percent in 2015, to $17.5 billion from $18.5 billion in 2014, thanks to lower fuel costs that were passed on to customers.