Turbines from the nation’s first offshore wind farm have been spinning in the waters beyond Block Island since late December, but residents have yet to receive the first electrons from the array, an official said this week.

That is expected to happen in coming months, as Block Island Power Co. finalizes a contract with the regional grid operator, ISO New England, and completes an interconnection to a cable to the mainland that will allow the 12-square-mile island of 1,000 year-round residents to bring its electric system into the 21st century.

Even when that happens, said David Milner, general manager of Block Island Power, electric rates on the island are expected to stay about where they are now, despite a prior pledge of a 40 percent drop on connection. That is because the price of diesel fuel, which has been used for decades to power a fleet of five Block Island electric generators, has declined in the past several years.

Oil prices have “dropped so much, the savings we’d originally looked at has already been accomplished,” said Milner, a 40-year veteran of the power company. “There may be a small decrease, but it’s not going to be a heck of a lot.”

The Block Island experience is getting increased scrutiny now that LIPA has been authorized to enter a contract with Deepwater Wind of Rhode Island to build a larger array in waters between Block Island and Martha’s Vineyard.

While the Block Island project is in state, not federal, waters, officials navigated a delicate course with municipal and state governments, some angry residents and fishing groups, environmental reviews and union approvals.

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Deepwater Wind chief executive Jeff Grybowski on Wednesday confirmed electricity from the Block Island wind farm is “just going to the mainland. Our project is operating and the ball is in the court of the locals” to establish a connection to the cable via National Grid. “We sell all our energy to National Grid,” Grybowski said.

One turbine was damaged before the project’s on-time mid-December production date. Grybowski said repairs could be finished in weeks.

Once the connection to the new cable is made, Block Island will be powered primarily from power generated by the five 6-megawatt turbines spinning three miles off its coast. An existing fuel surcharge on bills will be replaced by a new power purchase charge of around 13 cents.

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The wind array’s 30 megawatts output is considerably higher than Block Island’s tiny winter load of just around 1 megawatt, so all that excess flows over the cable to mainland Rhode Island, where it flows onto the New England grid. The summer load spikes to around 4.5 megawatts, Milner said. Electricity historically has been so expensive that many hotels don’t have air conditioning.

National Grid, the U.K.-based energy company that formerly operated the Long Island grid, owns the cable.

“We love Deepwater wind because they got us our extension cord to the mainland, which we would never have been able to do,” Milner said.

At the time the wind farm and cable were being discussed, power on Block Island cost around 30 cents a kilowatt hour, Milner said. Since then, with oil price declines, the price of power has dropped to around 16 cents a kilowatt hour. That is about the discount that was promised to island residents when the project was first proposed, he said.

“We hope to be hooked up to the cable sometime in March,” Milner said, with power flowing to residents in April.