BOSTON (AP) - Offshore wind farm developers are preparing to submit proposals for large-scale operations off Massachusetts.

The state set Wednesday as the deadline for companies seeking to supply at least 400 megawatts of offshore wind power to Massachusetts' utilities. A decision is expected next year.

Deepwater Wind, Bay State Wind and Vineyard Wind are vying for the lucrative contracts. Each has secured federal development rights to pursue their projects.

The wind farms are envisioned for federal waters about 30 miles from the mainland and about 15 miles from Martha's Vineyard.

The state is requiring power companies Eversource, National Grid and Unitil to purchase 1,600 megawatts of power from offshore wind by 2027, roughly enough to power up to 1 million homes.

The first U.S. offshore wind farm opened a year ago off Block Island, Rhode Island.

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