Duke Energy today became the first electric utility in the state to include hydroelectric power in its renewables mix under the state's 2007 law requiring alternative energy.

Charlotte-based Duke, the state's biggest power company, registered four small hydroelectric plants, including two in North Carolina, with the N.C. Utilities Commission. Even though the hydro plants are decades old, they count toward Duke's green energy targets under an exception in state law.

The registration will allow Duke to claim renewable credits for the clean electricity generated at those facilities towards meeting the state's renewables mandate. A 2000 state law requires that 12.5 percent of all retail electricity sold by utilities in this state come from renewables, such as solar power, and from energy conservation projects.

Most of the renewable resources tapped in this state have been solar energy farms, but they've also included biomoass such as burning agricultural waste and landfill methane gas to generate power.