The 411 buildings owned by the city of Chicago will run entirely on renewable energy beginning Jan. 1.

The feat will eliminate 290,000 metric tons of carbon dioxide emissions annually, according to Angela Tovar, the city’s chief sustainability officer. That’s equivalent to taking over 67,500 passenger vehicles off the road each year.

“Every Chicagoan interacts with a city-owned building, whether the cultural center, City Hall, Harold Washington Library, O’Hare and Midway (international airports) or your local library. To be able to achieve this milestone on behalf of city residents is exciting,” Tovar said.

Chicago is one of a handful of cities — from Houston to Burlington, Vermont — to transition its municipal buildings to renewable energy.

The switch isn’t as intuitive as plugging a city building into a solar panel or a wind turbine. Electricity generated at a coal- or gas-fired plant is indistinguishable from electricity generated from a renewable source once it’s flowing through the power grid. So the city entered a five-year power purchase agreement with energy supplier Constellation to ensure the local grid will have enough renewable power to meet the city’s demand. The agreement also will keep municipal utility bills stable or potentially drive cost savings, according to Tovar.

This is the largest power purchase agreement Constellation has entered into with a municipality to date, according to company spokeswoman Liz Williamson. The energy supplier operates in six states and Washington, D.C.

Beginning in 2025, 70% of municipal buildings’ electricity will come from Double Black Diamond, a new 4,100-acre solar farm in downstate Sangamon and Morgan counties. Enabled in large part by the city’s demand, it’s the largest solar project east of the Mississippi River.

“Double Black Diamond will serve as a roadmap for us as we continue trailblazing a path for clean energy now,” said Eric Lammers, CEO and co-founder of Double Black Diamond’s constructor and operator, Swift Current Energy.

The remaining 30% of the city’s clean power will come from renewable-energy certificates procured by Constellation on its behalf. They authenticate that a portion of the city’s electricity bill went to funding an accredited solar or wind project somewhere in the country.

Some say the certificates are a form of greenwashing because they don’t ensure renewable energy is generated on the same grid where the certificate receiver is using power. A certificate used in Chicago could, for example, be traced to energy produced at a solar project in Texas or North Carolina.

But Tovar said the city made its decision to use certificates purposefully.

“We want to keep that 30% open because we really want to spend the next year looking at the prospect of starting to put rooftop solar on our own buildings,” she said.

Eventually, such panels could replace the certificates, and Chicagoans can first expect to see them at public buildings like libraries because Tovar wants the whole city to feel the positive impact of the clean-energy transition.

“Really being addictive was of critical importance to us,” she said.

Her team originally wanted to create a solar farm in Cook County, but land was cost-prohibitive. Instead, Constellation and Swift Current Energy have jointly committed to donating $400,000 annually to Chicago nonprofits promoting workforce development in the green economy.

Construction of Double Black Diamond also created about 450 jobs and is expected to bring about $100 million in new tax revenue to Sangamon and Morgan counties.

The city is buying only half the solar farm’s power. The other half will contribute to Illinois’ overall clean-energy infrastructure. Cook County and Loyola University Chicago have already agreed to purchase some for their operations.

“We will continue to explore and find opportunities to leverage our buying power to drive community benefits like the ones we have here,” Tovar said.

City Hall has already committed to powering all buildings, not just municipal buildings, with renewable energy by 2035.