CHICAGO — The Sears Tower, that bronze-black monument that forms the 110-story peak of the skyline here and stands as the tallest office building in the Western Hemisphere, will soon have another unique feature: wind turbines sprouting from its recessed rooftops high in the sky.

The building's owners, leasing agents and architects said Wednesday that they are literally taking environmental sustainability to new heights with a $350 million retrofit of the 1970s-era modernist building — and the turbines are only the tip of the transformation. The plan, to begin immediately, aims to reduce electricity use in the tower by 80 percent over five years through upgrades in the glass exterior, internal lighting, heating, cooling and elevator systems — and its own green power generation.

In such a huge tower, with 4.5 million square feet of office and retail space, 16,000 windows and 104 elevators, the project is bound to be one of the most substantial green renovations ever tried on one site, planners said. The Sears Tower is significantly larger than the 102-story, 2.6-million-square-foot Empire State Building, for instance, which is also undergoing renovation to reduce energy consumption.

“If we can take care of one building that size, it has a huge impact on society,” said Adrian Smith, an architect whose firm designed the Sears Tower renovation. “It is a village in and of itself.”

Buildings are among the world's largest contributors of greenhouse gas emissions. After the retrofit, energy savings at the Sears Tower, which is to be renamed the Willis Tower this summer, would be equal to 150,000 barrels of oil a year, officials said. The savings are expected to help redeem some of the project's cost, which is to be financed through private equity investment, grants, debt financing and government funds.

The Sears Tower plans to open a first-floor center to educate the public about the redesign, and hopes to serve as a model for other aging skyscrapers around the world, officials said.