The state Public Utilities Commission approved a three-year extension of the contract Hawaiian Electric Co. has to buy biodiesel to fire a 110-megawatt power plant at Campbell Industrial Park, HECO announced Wednesday.

The contract with Iowa-based Renewable Energy Group is for 3 million to 7 million gallons of biodiesel made from used cooking oil and waste animal fat. HECO did not disclose the price of the biodiesel, but said REG was the low bidder for the contract. The Campbell plant is the nation’s first utility-scale combustion turbine run entirely on biofuel, according to HECO. The new contract takes effect in July when the existing contract expires.

Energy produced at the plant counts toward HECO’s goal of having 40 percent of its electricity it sells generated by renewable sources by 2030.