One of the largest land-based wind energy developers in the country has acquired a major stake in a wind farm being developed south of the Vineyard.

Avangrid Renewables, a subsidiary of Avangrid Inc., announced last week that it has formed a strategic partnership with Vineyard Wind, acquiring a half-ownership interest in the company that partnered with the Island energy cooperative Vineyard Power in 2011. Formerly known as OffshoreMW, Vineyard Wind is owned by the Danish company Copenhagen Infrastructure Partners.

Most of Avangrid’s common stock is owned by Iberdrola SA, among the largest electric utilities in the world.

In a statement, Vineyard Power president Richard Andre said the Island cooperative now has about 5,000 members.

“This local partnership within our community is one of the reasons that made the project attractive to Avangrid,” he said. Vineyard Wind has a community benefits agreement to keep jobs and services on the Island.

In a separate statement, Lars Thaaning Pedersen, co-chief executive officer of Copenhagen Offshore Partners, CIP’s offshore wind development company, said the new partnership with Avangrid gives Vineyard Wind an edge in the race to build offshore wind off the coast of Massachusetts.

“This partnership allows Vineyard Wind to leverage the financial firepower that both CIP and Avangrid can bring to bear to develop and build this project,” he said.

A state bill last year requiring energy utilities to buy at least 1,600 megawatts of offshore wind energy by 2027 has spurred offshore wind developers in the region.

The utility companies Eversource, National Grid and Unitil recently submitted a draft request for proposals to the state Department of Public Utilities, beginning the process of establishing the long-term energy contracts.

The companies hope to procure 400 megawatts of offshore wind energy generation, according to the draft, dated April 28. But they will consider procuring up to 800 megawatts, if an evaluation team that includes the state Department of Energy Resources finds it superior to other proposals and advantageous for ratepayers.

Pending state approval, the utilities will be responsible for issuing the RFP to wind developers and negotiating contracts.

In addition to the Vineyard partnership, the Danish company Dong Energy is planning to build a wind farm in the Massachusetts wind energy area south of the Vineyard. Two remaining leases in that area are still available.

Thomas Brostrom, Dong Energy’s general manager for North America, welcomed the draft RFP and reiterated his confidence in the future of offshore wind energy in the state.

“We have seen through the development of more than 20 projects around the globe that utility-scale offshore wind drives the greatest economic benefits for local communities and the supply chain,” he said in a statement.

Jeffrey Grybowski, chief executive officer of Deepwater Wind, which plans to build a wind farm in an area of federal waters between Massachusetts and Rhode Island, highlighted a goal of making offshore wind affordable in the state.

“Deepwater Wind is excited about the opportunity to compete to deliver homegrown clean energy to Massachusetts ratepayers at the right scale, and at the right price,” he said.

The draft RFP includes a general time frame for establishing the energy contracts, with the whole process projected to take about 16 months from the issuance of RFPs to the signing of contracts and final approval by the state.