Cambridge’s new solar VPPA is the largest ever by any US city

Cambridge, Massachusetts, has signed the largest-ever virtual power purchase agreement (VPPA) by a US city to help build a utility-scale solar farm in Illinois.

The 135 megawatt (MW) project on 800 acres in Champaign County, called Prairie Solar, will add clean energy to the grid, and Cambridge will earn renewable energy certificates (RECs) for making it possible.

These credits will benefit residents and businesses enrolled in Cambridge’s Community Electricity Program, which already offers stable and competitive electricity rates. This marks Cambridge’s second major renewable energy deal, following last year’s VPPA for a wind farm in North Dakota. Together, these projects are accelerating the city’s efforts to cut carbon emissions more effectively than waiting for the Massachusetts grid to go fully renewable by 2050.

Dennis Carlberg, chief sustainability officer at Boston University, said, “Since the New England Grid is one of the cleanest in the country, and these projects are in grids slower to transition, they should reduce nearly twice the global greenhouse gas emissions than if the same projects were located in the greening New England grid. This is truly remarkable work that I hope others will replicate.”

Why solar in Illinois?

The Prairie Solar project, expected to come online in summer 2026, will be built near a former coal mine. Illinois residents will benefit from new jobs, local investment, and improved air quality on top of the clean electricity the project will generate.

Julie Wormser, Cambridge’s chief climate officer, put it this way: “Preventing carbon emissions in Cambridge or Illinois has the exact same impact on the global climate. It will allow us to make a bigger difference more quickly and cheaply than, say, pursuing smaller rooftop solar within city limits while providing local benefits to people in Illinois.”

This approach also helps Cambridge reach its sustainability goals without being limited by its small size and dense urban footprint. With 120,000 people in just 6.5 square miles, there isn’t enough space for the city to generate all its own power locally. That’s where strategies like VPPAs come into play.

Ellen Katz from Cambridge’s Department of Public Works explained the logic: “Renewable projects, like this VPPA, make the most difference because they replace more carbon-intensive fuel sources, like coal, compared to Massachusetts, where most of the electricity is fueled by natural gas.”

How Cambridge’s VPPA works

Cambridge’s 50 MW virtual power purchase agreement doesn’t send electricity directly to the city. Instead, it commits to purchasing renewable energy certificates from the project, which helps the developer secure financing to build the solar farm. The Prairie Solar project will be owned and operated by renewable company MN8 Energy, while Sustainability Roundtable Inc. facilitated the deal through their Net Zero Consortium for Buyers.

When Prairie Solar comes online, more than half (55%) of the power in the Standard Green option in Cambridge’s Community Electricity Program will come from renewable energy. Residents can already opt to buy 100% renewable power at a slightly higher rate.

Cambridge’s clean energy strategy

Cambridge isn’t stopping at VPPAs. The city continues to invest in its own backyard with energy-efficient buildings, geothermal systems, and solar installations. Local programs are also helping residents and businesses phase out fossil fuel use.

The city has committed to reaching net-zero emissions by 2050, and a big chunk of its carbon pollution comes from buildings and transportation. While the Massachusetts grid is on track to be 100% renewable by 2050, Cambridge is speeding up the transition by supporting new solar and wind projects where they’re needed most.

Cambridge City Manager Yi-An Huang summed up: “We’re increasing the amount of renewable energy getting built – whether it’s here in Cambridge or other parts of the country.”

What do you think about Cambridge’s big VPPA? Let us know in the comments below.

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