The U.S. Department of Energy has ordered another power plant, this time an oil and gas plant in Pennsylvania, to keep its turbines running through the hottest summer months as a precaution against electricity shortfalls in the 13-state mid-Atlantic grid. The department’s order to the grid operator, PJM Interconnection, regarding the Eddystone power plant just south of Philadelphia on the Delaware River, is the department’s second use of federal power under President Donald Trump to require a power plant to keep operating on the mainland United States. Constellation Energy had planned to shut down Eddystone’s units 3 and 4 on...