Duke Energy will close two of its oldest coal-fired power plants, Riverbend west of Charlotte and Buck in Rowan County in April, two years ahead of schedule.Both plants date to the 1920s and had been planned for retirement in 2015. Theyre among a wave of older, smaller coal plants closing down rather than investing in new pollution controls to meet federal environmental regulations.The plants had been little used in recent years as larger, more efficient plants came online and falling natural gas prices shifted generation to gas.Efficiencies in Dukes management of a larger power plant fleet, following its merger last year with Progress Energy, also contributed to the early retirements, the company said.These stations played pivotal roles in the 1920s and 1930s in helping to electrify the industries and homes of the Carolinas, and we honor all those employees who contributed their time and talents over the years to ensure safe, reliable operations, Keith Trent, chief operating officer of Dukes regulated utilities, said in a statement.Riverbend started up in 1929. Its units 1 and 2 retired in 1979, and Unit 3 in 1976. Units 4 through 7, dating to the 1950s, will close in April. Four smaller gas-fired units retired last October.Buck, Dukes first large-scale power plant, began operating in 1926. Its first two units retired in 1979, and units 3 and 4 in 2011. Units 5 and 6 will retire in April. Three gas units were shut down last October.A 620-megawatt gas-fired power plant at Buck began operating in 2011.Duke said it would try to find new positions within the company for the 65 people who work at Riverbend and Buck.Duke plans to retire more than 3,800 megawatts of older coal- and oil-fired generation by the end of 2013, part of overall retirements of up to 6,800 megawatts.