BLOCK ISLAND, R.I. — The construction phase of the nation’s first offshore wind farm is nearly complete as Deepwater Wind on Monday installed turbine blades on the fourth of five turbines.

The project is being watched, particularly in New York, because Deepwater plans to build a project three times larger in waters off Rhode Island — around 35 miles from Montauk Point — for the Long Island Power Authority.

Deepwater chief executive Jeff Grybowski said the last blade could be bolted in place by Aug. 22 or sooner. After that will follow two months of interconnection work and testing, with production slated to begin Nov. 1.

The five turbines are 589 feet tall to the tip of each blade, and half a mile apart. The project, in Rhode Island state waters three miles from the Block Island coast, has a capacity of 30 megawatts, more than enough to meet the Block Island’s summer peak of around 4 megawatts for about 1,000 residents.

Excess power will be transmitted back to mainland Rhode Island via a new National Grid-owned cable to the New England grid. That cable is a new link to energy-scarce Block Island, where power costs have surpassed 40 cents a kilowatt-hour in recent years, more than double LIPA’s rates.

Deepwater said Block Islanders will get discounted energy from the wind farm, up to 40 percent cheaper, while the old diesel generators that now power the island will be shut down.

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Grybowski and others said opposition to the project was primarily by islanders who didn’t want their water views spoiled. Some fishing groups opposed it, said Meghan Lapp, fisheries liaison for Seafreeze Ltd., a Rhode Island commercial fishing group, citing concerns about the undersea cable’s path through fishing grounds and impacts on trappers and gill netters.

“People who have homes in that area are not happy with it,” said Kathy Szabo, executive director of the island’s Chamber of Commerce.

But most welcome the promise of cheaper energy bills and some are banking on a new tourist trade of hiring boats out to the array, which were added to the chamber’s tourist maps. Discounted power is widely welcomed, Szabo said, because power is now so expensive that many hotels don’t have air conditioners and food prices bear the weight of the high energy costs.

Grybowski said the appearance of the wind farm, which looms large from the southeast coast, was “one of the things I can’t change,” but he said that the benefits, including a high-speed fiber-optic link to the mainland bundled with the power line, could quell concerns.

Weather has been the only big challenge to construction, which Grybowski said will cost around $300 million, including linking the project to the island. The separate cable to the mainland costs another $108 million. Generally undersea cables cost around $2 million a mile, he said.

The 15-turbine LIPA project that Deepwater has proposed has been stalled awaiting a New York State wind energy blueprint. It also needs LIPA board approval and a power contract from LIPA before sea bottom studies can start next year.

“We’re just waiting for the next board action,” Grybowski said, adding that he “welcomed” Gov. Andrew M. Cuomo’s statement in support of the project last month, before a board meeting to approve it was abruptly canceled. The 90-megawatt project will be constrained by the South Fork’s grid, Newsday reported last week, limiting the accepted output to 75 megawatts. A megawatt of wind energy can power 320 homes.

The LIPA project, if approved, is estimated to cost around $700 million to build, including the 36-mile cable.