Chicago, Illinois is kicking off the New Year with clean energy. As of Jan. 1, all of Chicago’s 411 municipal buildings, such as its international airports, fire stations, libraries and City Hall, are now powered entirely by renewable energy.

The feat has been made possible through a 5-year power purchase agreement (PPA) with Constellation signed in August 2022, the Chicago Tribune reported.

“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,” Angela Tovar, chief sustainability officer for Chicago, told the Chicago Tribune.

Most (70%) of the municipal buildings’ 900,000 MWh of annual power demand is now met through a new, 4,100-acre solar farm called Double Black Diamond, which was established in Sangamon and Morgan counties, about 30 miles from Springfield, Illinois. Double Black Diamond, developed and operated by Swift Current Energy, is the largest solar farm east of the Mississippi.

As explained by the U.S. Department of Energy, a PPA is when one party purchases power supply from a third-party, which handles the development and operation of the power source. This allows the power source owner and operator to reap tax benefits and generate income by selling energy, while the customer who is buying the power can access clean energy without the cost of installing the infrastructure.

Through this plan, all of Chicago’s municipal buildings now run on clean energy, which the city buys from Constellation and is supplied by renewable energy sources, including the Double Black Diamond solar farm. 

“It’s a plan that gets the city to take action on climate and also leverages our buying power to generate new opportunities for Chicagoans and the state,” Tovar said, as reported by Grist. “There’s opportunities everywhere.”

Constellation will provide the remaining 30% of clean energy for Chicago’s city buildings through renewable energy credits (RECs), where funding from the Chicago’s energy bills is put toward clean energy projects around the U.S., Chicago Tribune reported.

While the move to power Chicago’s municipal buildings entirely with renewable power is expected to reduce the city’s carbon emissions by around 290,000 metric tons — or around the same effect of taking 62,000 vehicles off the roads, Grist reported — some people have concerns over the inclusion of RECs in the plan. 

As the Chicago Tribune reported, critics have argued that these credits are a type of greenwashing that don’t necessarily contribute to local clean energy generation.

However, the city addressed concerns over RECs, noting that the plan could still encourage more renewable energy development locally. 

“That’s really a feature and not a bug of our plan,” Deputy Chief Sustainability Officer Jared Policicchio told Grist. “Our goal over the next several years is that we reach a point where we’re not buying renewable energy credits.” 

Additionally, Tovar told Chicago Tribune that securing the 30% energy from RECs will give the city the time to explore solar installation on local buildings.

The city has also collaborated with Constellation and Swift Current Energy on a $400,000 annual deal for clean energy job training, American Cities Climate Challenge reported. Chicago further set a goal to power all buildings in the city, not just municipal buildings, through renewables by 2035. If it achieves the goal, Chicago would be the largest U.S. city to power all buildings entirely with clean energy, the Sierra Club reported.

Chicago joins around 700 other municipalities in the U.S. that have committed to PPAs, totaling over 18,372 MW worth of renewable energy, or enough clean energy to power about 4 million homes per year, as of 2021, the World Resources Institute reported.