JUDITH GAP, Mont. (AP) - The No. 1 complaint when the skyscraping turbines at the Judith Gap wind farm were erected was, ironically, the wind, said John Bacon, operations manager for Chicago-based Invenergy, which owns the central Montana site.

"They said, 'Man, this is one of the windiest spots we ever put up wind turbines,'" recalled Bacon of the workers who installed the General Electric turbines for Invenergy.

As the state's first large commercial wind farm nears its one-year anniversary, Invenergy officials aren't complaining about the 25 to 35 mph winds that routinely blow through here this time of year. The wind-powered electric-generating facility is on track to easily meet its energy production budget in its inaugural year thanks to that relentless wind.

As a result of the successful debut, Invenergy is considering a big expansion, possibly as soon as next year. And construction of a second wind farm north of Great Falls, which would be even bigger than the Judith Gap complex, is being discussed as well.

"Of all the turbines General Electric has sold for wind farms throughout North America, this particular wind farm has been the most productive, energy wise," said Mark Jacobson, Invenergy's Milwaukee-based senior development manager.

Nobody's ever doubted Montana's wind power. Jokes about it abound and the state is even ranked No. 4 in the nation by the American Wind Energy Association for wind-energy potential.

But at the Judith Gap wind farm, the state's greatest natural resource is no longer just potential, or a pain in the neck. It's being turned into electricity.

The Invenergy wind farm six miles south of here is the state's first, on a grand scale, to prove wind can be economically transformed into clean electricity to power thousands of homes in Montana.

The 135-megawatt farm, officially called the Judith Gap Energy Center, is located about 125 miles southeast of Great Falls. About 11 employees working out of a small substation maintain it, sometimes making 15-minute climbs up to the tower rotors to make repairs or do maintenance.

The farm features 90, 260-foot tall towers with blades that make whale flippers look small. The blades pitch like an airplane wing to capture the area's mighty west and north winds, which in turn begins the process of generating electricity.

The big steel turbines are strategically situated on 8,300 acres of private farm, pasture and Conservation Reserve Program and School Trust land. Twenty-six miles of gravel road connects them. Landowners continue to use the land for grazing and crops, leasing property to Invenergy for a royalty based on gross production of each individual turbine on their land. The payments range from $2,000 up to $4,000 to $5,000 a year, Bacon said.

"When the wind blows, we produce power," he said simply.

The $180 million complex opened for business in January, prepared to supply power to NorthWestern Energy. A Montana-based company, Wind Park Solutions-Arcadia, laid the groundwork for the farm, then sold 100 percent of its interest to Invenergy.

There's already talk of expansion. Invenergy was, in fact, planning on the possibility of getting bigger from the start.

Enough transmission capacity exists on the existing line to produce an additional 53 megawatts at the 135-megawatt farm.

Invenergy has submitted a bid to a utility for a renewable energy power-purchase agreement. It won't say with whom. But if the company gets the contract, another 35 to 36 turbines would be added to the 90 existing towers at Judith Gap Energy Center, Bacon said. If the bid is accepted, construction could begin next year.

Company officials caution that, in the power generation business, everything depends on the power-purchase agreement.

"You need to be able to sell the power and take that to the lenders," Jacobson said. "We have bids out there right now and continue to work on it. We hope that it's sooner rather than later. We think it's a good project. We sized the interconnection to handle a larger project."

Invenergy already is selling power to NorthWestern Energy - the electricity and natural gas utility that serves much of Montana. The two signed a purchase agreement in which the Judith Gap wind farm would supply electricity to the utility for the next 20 years.

During the life of the contract, Wheatland County will reap $1.2 million annually from a wind-assessment tax, money that will be earmarked specifically for economic development projects.

NorthWestern had small contracts with wind generators before, but the contract with Invenergy is the first deal of any substance with a wind-based power generator, said John Hines, Butte-based NorthWestern's director of energy supply planning.

It's estimated that, on a yearly basis, the farm will produce about 450,000 megawatt hours, which is enough to supply electricity to 7 to 8 percent of NorthWestern's base customers. That's a larger-than-usual percentage for wind in a utility's portfolio of electricity-generating sources, Hines and Invenergy officials said. The rest of NorthWestern's supply comes from plants fired by coal, water-powered turbines and natural gas.

Wind is appealing because the price is stable, Hines said. The drawback is it's intermittent - so when the wind isn't blowing, NorthWestern has to quickly act to replace the lost supply.

"We're quite pleased with this project," Hines said. "We believe this is a very good one in terms of both price and production."

Bacon, who worked for three years at a large wind farm in Minnesota, said the Judith Gap facility has a high wind "capacity factor," even for a wind farm.

Each of the turbines can produce enough energy in a year to power 300 homes, and the 90 towers combined can supply electricity to some 30,000 houses a year.

The farm's maximum production is 135 megawatts a day. The maximum can be reached when winds are blowing between 25 mph and 35 mph.

"We're pretty close to that today," Bacon said Thursday, when winds were so stiff it was difficult to hold the door open at the base of one of the towers, where a computer system inside runs the turbine.

Winds like that typically blow in the late fall, winter and spring, dropping off in the summer. The turbines automatically shut down when winds hit 55 mph - and some did stop one day earlier this week when winds hit that mark. The turbines have been known to sway four to five feet, but they're rated for a Level III hurricane, which is 111 mph to 130 mph.

Invenergy purchased its turbines from GE at $1.5 million a pop. GE monitors all of its turbines for two years, until the warranty expires, and the Judith Gap farm topped all other farms with GE turbines in energy production for the first three months of the year, according to Invenergy officials.

"They basically called us up and told us, for the first quarter anyway, we were the leading producer for the turbines they were monitoring," Bacon said.

"Well, we were happy," he continued. "When you put this much investment (in), you want it to be good and pay off, so that was very good news to hear."

Invenergy expects a return on its investment in 10 years, he said.