The Rhode Island Public Utilities Commission on Wednesday approved a power purchase agreement for a proposed wind farm off the coast of Block Island, ruling over the objection of critics who slammed the arrangement as a sweetheart deal meant to benefit one developer.

Attorney General Patrick Lynch vowed to appeal the decision to the state Supreme Court, saying in a statement that the deal makes ratepayers buy "grossly overpriced electricity."

The agreement between Deepwater Wind LLC, a New Jersey-based developer, and National Grid, the state's dominant utility, involves a proposed eight-turbine pilot project connected by a transmission cable to the mainland.

The 20-year agreement calls for National Grid to buy the energy generated from the wind farm at 24.4 cents per kilowatt hour.

The commission unanimously agreed that wind energy could reap an environmental benefit but split 2-1 on other issues.

Commissioner Mary Bray repeatedly voiced skepticism, siad the agreement would prove a long-term detriment to the economy by hurting ratepayers and small businesses that are already struggling.