Duke Energy Corp (NYSE: DUK ) and Exelon Corporation (NYSE: EXC ), two of the nation's largest electric generators, have been investing heavily in alternative energies to help allay the high costs of coal-fired plants and, in Exelon's case, the high cost of nuclear energy generation. Duke Energy Corp (NYSE:DUK) is required by the North Carolina energy commission to meet a minimum of 12.5% electric generation from renewable energies by 2021, while Exelon Corporation (NYSE:EXC) owns 44 wind projects located in 10 states throughout the U.S. that's capable of producing nearly 1,300 MW of electricity. While impressive, no company can hold a candle to NextEra Energy's renewable energy capacity, which is second-to-none. The company is an industry giant with nearly 43,000 MW in electrical capacity and recently commissioned a 400 MW project in Colorado that'll put it over the 10,000 MW generation mark in wind capacity!