American Electric Power Co. Inc. shut down the last 780-MW unit at its Conesville coal plant in Coshocton County, Ohio.

Unit 4 at the Conesville plant stopped operating April 29 but its official retirement is still scheduled for May 31, AEP spokesperson Melissa McHenry confirmed in a May 1 email. It began operating in 1973.

AEP said in October 2018 that it notified employees of plans to shut down the facility by May 31, 2020.

"AEP has been exiting the competitive generation business in Ohio for several years," McHenry said at the time. "AEP unsuccessfully sought a buyer for the Conesville Plant for a number of years, while continuing to maintain the plant. The costs of keeping the plant operational and the outcomes of recent competitive generation auctions resulted in the decision to permanently close the entire plant by 2020."

AEP retired units 5 and 6 at the coal plant at the end of May 2019. The units represented 750 MW of generating capacity in the PJM Interconnection market.

Mines owned by CCU Coal and Construction LLC were the plant's primary sources of coal in 2019 and 2020, with only about 39,000 tons of coal purchased this year, according to S&P Global Market Intelligence data. CCU Coal took the mines over from Westmoreland Coal Co., now Westmoreland Mining LLC, in early 2019.

One of the mines supplying coal to Conesville in 2019 supplied coal to just one other plant, according to U.S. Energy Information Administration data. Other mines supplying Conesville did not deliver coal to any other plant in 2019.

AEP owns the Conesville plant through subsidiary AEP Generation Resources. AES Corp. subsidiary AES Ohio Generation LLC owns a 16.5% interest in unit 4.