Five years ago Mitchell Posin and Clarissa Allen had a vision: of sheep grazing under a windmill that powered their Chilmark farm. It was a vision of a working farm functioning with clean energy, from the grass the sheep ate to the compost tea they helped produce to the wind that spun the turbine.

On Monday morning that vision became reality when a 149-foot turbine was installed at the farm, the largest turbine to date on the Island.

Once it is fully operational, the windmill will produce 125,000 kilowatt hours per year.

The following letter was sent to the Edgartown selectmen:

The Martha’s Vineyard Agricultural Society, founded in 1859, has had as its mission these many years to improve breeds, promote agriculture and educate in the “mechanic and domestic arts.” We currently have over 1,200 dues-paying members, many of whom are Edgartown citizens, and our affairs are administered by a 16-member board of trustees. At our meeting on Jan. 12 the board unanimously voted to instruct me to send this letter to you.

The Island’s largest wind turbine to date went up this past week at Morning Glory Farm in Edgartown. The 50-kilowatt wind turbine sits atop a 120-foot galvanized steel tower.

The project began as an idea three years ago, and on Thursday it took a single day to bring the huge pieces together and assemble it. The turbine now appears high above the landscape to drivers headed out of Edgartown on the Edgartown-West Tisbury Road.