MONTPELIER, Vt. — Vermont utility regulators have given the go-ahead for a $150 million wind project that will erect 400-foot windmills on top of a mountain ridge in Lowell.

The state Public Service Board signed off late Tuesday on the Kingdom Community Wind project, a joint venture of Green Mountain Power Corp. and Vermont Electric Cooperative.

Twenty-one of the 400-foot-tall turbines will be placed along 3.2 miles of ridgeline, generating enough electricity to power 20,000 households.

“This is a really important step forward, for the state of Vermont and for our company,” said Mary Powell, president and CEO of Green Mountain Power.

Lowell residents overwhelmingly approved the plan in a Town Meeting vote last year, amid assurances from the project’s developers that the town government would be paid between $410,000 and $535,000 annually by the developers.

Some residents lobbied hard in hopes of persuading the Public Service Board to deny the project a certificate of public good, turning out for testimony before the Public Service Board and protesting at the Statehouse.

Among their complaints: That the towering turbines would ruin the view of the mountains, and that construction of them would hurt the environment.

But regulators concluded the project would promote the general good of the state.

It won’t produce greenhouse gases but it will boost the region’s renewable energy portfolio, the three-member board said in its 170-page order released Wednesday.

“We also find that the proposed project will provide an economic benefit to the State of Vermont in the form of jobs and tax revenues,” the board wrote.

Board members also said the project will generate “a long-term source of stably priced power” for the two utilities.

“These economic benefits, coupled with the fact that the addition of a renewable source of power in the region is consistent with the state’s legislated policy goals, have led us to conclude that we should approve the proposed project,” they wrote.

The approval came contingent on satisfaction of 44 conditions having due with permits, pre-construction surveys, construction damage and dozens of other concerns. Among them: Filing a decommissioning plan with a detail estimate of costs necessary to mothball the wind project.

Brice Simon, a lawyer representing an organization of about 100 opponents called Lowell Mountains Group, said his clients will continue to fight the project.

“We’re going to continue to oppose this project. The Public Service Board’s decision leaves many issues unresolved. The decision fails to adequately address some of the issues raised by the opponents,” he said.

Construction is to begin in August, said Powell, who said Green Mountain Power hopes to have the wind turbines providing electricity in the fall of 2012.