First Wind on Friday signed an agreement to sell the majority of the electricity it plans to generate at its Hancock Wind project near Ellsworth to an electric utility in Massachusetts.

Boston-based First Wind, which operates five wind farms in Maine, will sell 75 percent of Hancock Wind’s future electricity output to the Massachusetts Municipal Wholesale Electric Co. under a 25-year, fixed-price contract.

The news comes on the heels of a previous deal, announced earlier this month, in which First Wind agreed to sell 25 percent of Hancock Wind’s electricity to Burlington Electric Department in Vermont at a fixed price for 10 years.

The 51-megawatt Hancock Wind project will feature 17 turbines, each with a capacity of 3 megawatts, and be situated near First Wind’s existing Bull Hill wind farm, which began operations in Hancock County in November 2012.

“As a Massachusetts-based company, we’re excited to bring clean wind power to 17 cities and towns in our home state,” Paul Gaynor, CEO of First Wind, said in a statement. “Finalizing this agreement is a major step forward for this project. We look forward to moving toward construction on this project and making a major economic investment in Down East Maine.”

Signing this type of long-term power-purchase agreement with a utility is standard practice for First Wind. The promise of revenue that long-term fixed-price contracts provide allows First Wind to lower the cost of financing wind farm construction. It recently signed similar agreements with utilities in Massachusetts for two wind farms the company is developing in Aroostook and Somerset counties.

The Massachusetts Municipal Wholesale Electric Co. is a nonprofit entity that will resell the power at cost to its 17 member municipal utilities in Boylston, Chicopee, Groton, Holden, Holyoke, Ipswich, Mansfield, Marblehead, Paxton, Peabody, Russell, Shrewsbury, Sterling, Templeton, Wakefield, West Boylston and Westfield.

“This contract brings competitively priced energy from the Hancock Wind project to the MMWEC power portfolio and to the customers of our municipal utilities,” Ronald DeCurzio, CEO of the Massachusetts utility, said in a statement. “It also brings a valuable measure of diversity and price stability to the MMWEC resource mix at a time when the region’s reliance on natural gas is of concern.”