Florida Power & Light Co. plans to build the world’s largest solar-powered battery system and have it in service by late 2021. At 409 MW capacity, it will be four times the size of the world’s largest such system in operation and will cover 40 acres, FPL officials say. An existing, co-located FPL solar power plant in Parrish, Fla., will charge the future Manatee Energy Storage Center. Deploying energy from the batteries when there is higher demand for electricity will offset the need to run other power plants. FPL plans to retire two natural-gas combined-cycle units at its Manatee plant.