Duke Energy Corp. said Monday it is expanding its renewable energy from livestock waste, adding poop power to investments the country's largest electric company has made in whirring wind turbines and acres of solar arrays. The Charlotte-based utility said it contracted with Carbon Cycle Energy, which will build and own a North Carolina plant that collects methane from pig and chicken waste, refines the gas and delivers enough for Duke Energy to generate enough electricity to power about 10,000 homes a year.