(Providence, RI)--The state Public Utilities Commission is approving a twenty-year contract to purchase electricity from a future offshore wind farm.The approval is between power companies Orsted and Eversource, which both own the four-hundred-megawatt Revolution Wind project, and National Grid.It's estimated that Revolution Wind will generate one-quarter of the total electricity used by Rhode Islanders annually.Officials hope to start construction on the wind farm as early as next year.