A consortium of electric utilities recently completed the last Minnesota leg of a $2.1 billion transmission mega-project: a 156-mile power line from Dakota County through Rochester and on to La Crosse, Wis.

The CapX2020 project, which has been under construction for about six years, covers four states and includes 725 miles of new high-voltage lines. It's the biggest electricity transmission project in Minnesota since the 1970s, and it's aimed partly at freeing up power line capacity for the Upper Midwest's burgeoning wind energy industry.

"We have made great strides forward for wind," said Teresa Mogensen, senior vice president for transmission for Minneapolis-based Xcel.

Eleven days ago, the final phase of the 345-kilovolt line from Hampton, Minn., to La Crosse was switched on — "energized" in power line lingo. Executives from Xcel and its partners feted the $485 million project Monday at a substation in Hampton, which is about 35 miles southeast of downtown Minneapolis.

The Hampton-Rochester-La Crosse line is jointly owned by Xcel, Southern Minnesota Municipal Power Agency, La Crosse-based Dairyland Power Cooperative, Rochester Public Utilities and Sun Prairie, Wis.-based WPPI Energy. The new line is the fourth of five transmission projects within CapX2020.

One is still under construction, a segment in eastern South Dakota from Brookings to Big Stone. It's due to be completed next year.

CapX2020 developed out of a hallway conversation at a 2004 industry meeting between executives of Minnesota's two largest power companies, Xcel and Maple Grove-based Great River Energy. Nine more utilities would join them for the entire project, which also features lines from Fargo to Monticello, Minn., and Bemidji, Minn., to Grand Rapids, Minn.

The project was opposed by citizens groups who argued that with power demand falling, expensive new transmission lines weren't needed. Costs of transmission lines are passed down to customers through electricity bills.

Indeed, electricity demand has been stagnant since the 2008 economic meltdown. But the strong growth of renewable energy — particularly wind — has challenged the Upper Midwest power grid, heightening the need for more transmission capacity. CapX2020 is providing that capacity, Mogensen said. More transmission lines will eventually be needed as wind power continues to grow, she said.

Last week, Xcel announced it would increase its wind power generation in the Upper Midwest over the next few years by 60 percent, adding eight to 10 wind farms and enough electricity to power about 750,000 homes.

Xcel has been the nation's leading utility for wind generation for more than a decade, and Minnesota ranks seventh among states in wind power production.