Wildlife groups that want to block construction of a wind power project near the Horicon Marsh and its refuge for migratory birds have found a new and unusual ally: the U.S. Air Force.

The project is caught in a holding pattern because the federal government fears that the rotating blades of the wind turbines could block the ability of a radar system there to track and possibly intercept suspicious airplanes.

As a result, a permit from the Federal Aviation Administration for the wind project is on hold while the Air Force conducts a study of the effects that building as many as 133 turbines could pose for a Brownsville-area radar, an agency official said.

The decision came as a surprise to opponents of the wind farm, who have mobilized because of the project's proximity to the marsh and its potential effect on birds, bats and other wildlife.

"Our main goal has always been and always will be to protect the migratory birds," said Joe Breaden, president of the Horicon Marsh System Advocates, a group opposing the wind farm. "And if the Air Force wants to help out the bird population: Go Air Force."

Lawmakers back wind power

The FAA ruling comes at a pivotal time for wind power projects in Wisconsin. The state Legislature recently enacted a law requiring that 10% of the state's energy be generated by wind power by 2015, up from 4% now. The bill was signed into law by Gov. Jim Doyle on Friday, the same day the FAA applied the brakes at least for now on the project.

Neil Palmer, a spokesman for Invenergy, the Chicago company behind the project, said the firm had hoped to begin construction as soon as next month depending on how the FAA issue and a court challenge filed by HMS Advocates are resolved. A hearing on the court case is scheduled for today in Dodge County Circuit Court.

"This quirk is new to us, and we're still evaluating it," he said.

Invenergy has developed wind farms in Tennessee, Montana and other states and has projects in the works in several others. The company has never encountered this issue, he said.

Bruce Beard of the FAA said the concern has come up with several wind power projects, including another one in Wisconsin and one in Texas.

The second Wisconsin project, a 33-wind turbine project also located near Horicon, was planned to be developed for Milwaukee- based We Energies, but the utility canceled its agreement with the developer of the project last year.

Beard, the national operations manager of obstruction evaluation services at the FAA, said the issue has emerged because of the stepped-up role the U.S. military has taken in the surveillance of U.S. airspace since the Sept. 11 attacks.

Before the attacks, the Air Force and Air National Guard monitored planes flying across U.S. borders into the country. But since the attacks, heightened homeland security concerns have led to monitoring of the nation's entire airspace.

The Air Force uses its own radar equipment as well as FAA radars to track and potentially intercept planes losing radio contact with FAA air traffic controllers, Beard said.

But wind turbines close to a radar site "tend to block the radar signal for a period of many miles, and basically it means that aircraft flying at a lower altitude would not be detected by the radar because the signal would be blocked," Beard said.

Beard, who is based in Fort Worth, Texas, said he couldn't provide details on the exact location of the radar near the wind project. He was unsure whether the agency would release the information because of security concerns.

Breaden said he knows of a radar that's been in use for decades along state Highway 33, roughly seven or eight miles from the Forward project.

Radars, wind farms use hilltops

It turns out that hilltops are ideal spots for radars, and they are the most windy and best suited for wind farms.

"We put these radars on top of hills because that's where we get the best use out of them and we were there first," Beard said. "And now the wind turbines want to come in, and they want to put their wind turbines on top of the same hills because of the wind.

"So right now we're trying to figure out how we're going to commingle with everybody getting most of what they want, without damaging our radar service and without preventing the use of wind turbines being developed," he said.

The Air Force study of the Horicon-area radar is taking place at the same time the Pentagon is preparing a report to Congress on impact of wind turbines on military radar systems. That report is expected to be released in May.

It's possible there will be enough other radars, whether FAA or military, to allow the military to keep detecting low-flying aircraft if the Horicon area radar is blocked by turbines, Beard said. But that analysis hasn't been completed yet.

The $250 million Forward project could meet the electrical needs of 72,000 homes, according to the state Public Service Commission. Invenergy hopes to build up to 133 wind turbines in an area of Fond du Lac and Dodge counties.

Considered by renewable-energy advocates as a symbol of the state's pursuit of clean, sustainable source of generating electricity, the Forward project has been the target of wind-power opponents such as Breaden who are concerned that birds will die by flying into the rotating blades of the wind turbines.

Invenergy says its review of other wind projects, and its analysis of the Forward project near the Horicon Marsh, convince it that there wouldn't be a significant impact on birds. An updated study of the avian issue is being prepared, Palmer said.

In a decision last summer, PSC members said the environmental advantages of the proposal outweigh any potential harm to wildlife.

The other major wind power project announced for the state is an 88-turbine project planned by We Energies in northeast Fond du Lac County, near Lake Winnebago.

That project already has a permit from the FAA, and We Energies hasn't received any notices from the agency raising concerns about the radars, utility spokeswoman Wendy Parks said Wednesday.

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