Workers have erected nearly half of the 12 massive turbines at Oahu’s first wind farm in the foothills above Kahuku, putting the project on track to begin delivering electricity to the island’s grid by early next year.

The 30-megawatt project developed by Boston-based First Wind LLC will boost the state’s electrical generation from wind by 50 percent as authorities press ahead with an ambitious plan to reduce the state’s dependence on imported oil. The only other wind farms currently operating in the state, two on the Big Island and one on Maui, have a combined generating capacity of 61 megawatts.

Although the Kahuku project will satisfy just a fraction of Oahu’s peak electricity demand of 1,200 megawatts, it is one of several wind farms on the drawing board that will enable Hawaiian Electric Co. to do a better job of tapping Hawaii’s famous tradewinds in the coming years.

First Wind hopes to break ground on a second North Shore wind farm next year that would add another 70 megawatts of capacity to the HECO grid. And there are two major wind projects in the very early planning stages on Molokai and Lanai of 200 megawatts each that would deliver electricity to Oahu via undersea cables.

In addition, First Wind is in the process of adding 21 megawatts of capacity to its Kaheawa wind farm on Maui, while Sempra Generation is aiming to launch a 21-megawatt project on Ulupalakua Ranch in the remote southeastern area of Maui in 2012.

The 12 Kahuku turbines, manufactured by Clipper Windpower in Cedar Rapids, Iowa, will produce enough energy to power 7,700 homes and eliminate the use of 155,000 barrels of oil a year, according to First Wind.

The towering three-blade turbines sit on tubular steel towers 260 feet high, with the turbine blades reaching 460 feet at the peak of their rotation. The turbines are being installed for First Wind by RMT Inc., a Wisconsin-based company that specializes in engineering and construction of renewable energy projects.

Workers are using a Manitowoc lattice boom crawler crane to hoist the turbine components into place, including the 100,000-pound blades and the 205,000-pound nacelles, which house the generators and gearboxes.

Four of the 12 turbines are fully assembled, and crews should complete two more in the next week or two, said John Lamontagne, First Wind’s spokesman.

"Once they’re finished it will take several weeks to test them. We should be online by early next year," Lamontagne said.

First Wind has wind projects in the Northeast, the West and Hawaii with the capacity to generate up to 504 megawatts of power. Including Kahuku Wind, the company has projects in various stages that will add another 230 megawatts to its wind farm portfolio.

"Hawaii has shown a very strong desire for renewable energy. That and its excellent wind resources are major attractions for us," Lamontagne said.

First Wind officials said they don’t expect the Kahuku project to have turbine noise and vibration issues like in some communities on the mainland where residents live in close proximity to wind farms.

The closest of Kahuku Wind’s 12 turbines is about one mile west of the outskirts of Kahuku town.

"We had a few questions about sound from the community. So First Wind did a detailed sound modeling study, which determined that sound from the project was not likely to be above the ambient sound level in the community," said Kekoa Kaluhiwa, First Wind’s director of external affairs in Hawaii.

The prevailing winds blow from the east, so any noise from the turbines should be carried away from Kahuku toward the Koolau Mountains, he said.

Junior Primacio, a member of the Koolauloa Neighborhood Board, said both the board and the Kahuku Community Association supported the project.

"There were no concerns about noise," he said.