Petitioners Toray Plastics America and Polytop Corp had sought to overturn the agreement previously ratified by the state, saying that electricity generated from the project would be too expensive — up to three times higher than current rates.
The Supreme Court's decision paves the way for the first offshore wind-farm scheme in the US to go ahead. Block Island, 5km out to sea, could now be in operation by 2013 and would act as a pilot for a larger 350MW project later.
The petition against the scheme had delayed the project for a year. If the objectors seek to appeal the case to the Federal Supreme Court there could be a further delay of a similar period.