This isn’t Duke Energy’s first foray into using pig poo to make energy. The company announced another deal in March to buy gas from a group of pig farms in eastern North Carolina and turn that into electricity at four power plants in the state.

While the amount of energy that Duke Energy (DUK) produces with pig waste is still very small, the effort shows how power companies are willing to tap unusual sources in an effort to meet state requirements and increasingly embrace clean energy.

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North Carolina has a unique law that requires electric utilities to use hog manure as a fuel source. The state has one of the largest pork industries in the U.S. and has been plagued by dirty waste-filled hog lagoons.

Duke Energy’s new pig waste-to-energy projects will use technology called digesters installed at the pork farms of Smithfield Foods in Kenansville, North Carolina. Digesters hold waste in heated, air tight tanks, which creates ideal growing conditions for bacteria that consume the manure and release methane gas.

The digesters collect the emitted gas and the operators of the digesters bring that gas to a gas power plant, where its burned to produce electricity. Optima KV will construct and operate the digesters for Duke Energy.

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These types of digesters can be used to capture methane gas from other decaying organic materials, like at landfills (rotting garbage) and water treatment plants. The technology has been used for years in the U.S. and Europe, but it’s still expensive to implement and only produces a small amount of electricity.

Duke Energy can only produce enough electricity from these pig waste operations to power 880 homes annually.

Much of Duke Energy’s 50 gigawatts of power production—providing energy for 7.4 million customers in the U.S. South—comes from coal, nuclear, and natural gas. In recent years, Duke Energy has also invested in solar energy.