The 800MW Double Black Diamond Solar project was developed by Swift Current Energy in Illinois, US.
Construction works for the project commenced in March 2023 with an investment of $779m, and the project began operations in April 2025.
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The project is the largest solar farm operating within the Midcontinent Independent System Operator (MISO).
The annual power generation from the plant is enough to support 100,000 homes and offset regional CO₂ emissions by approximately one million tonnes a year.
The project generated employment for approximately 500 craft workers during its construction phase by aligning with the Illinois Clean and Equitable Jobs Act’s (CEJA) labour and hiring standards for renewable energy development.
During its operational life, the project is expected to generate $100m in tax revenue for Sangamon and Morgan counties in central Illinois. Additionally, the City of Chicago, Sangamon Growth Alliance, Cook County, and the Auburn School District will receive $10m in community benefits funds from Swift Current.
Double Black Diamond Solar project location and details
The Double Black Diamond Solar project is located within Sangamon and Morgan counties. The site is approximately 30 miles (48.2km) west of Springfield, Illinois.
The project involved the installation of 1.6 million solar panels mounted on solar trackers that rotate to follow the sun’s movement and maximise output by up to 30% compared to fixed tilt panels. Approximately 100 inverters were installed at the project site.
A substation, comprising three main power transformers, was also developed on the site and connected to a switch yard operated by Ameren Transmission.
Power purchase agreements
Constellation, a power distributor based in Baltimore, Maryland, signed a long-term power purchase agreement (PPA) with Swift Current Energy to purchase 24MW of renewable energy from the Double Black Diamond Solar project.
In partnership with Constellation, the City of Chicago is sourcing 70% of clean energy from the project to partially power Chicago O’Hare and Midway international airports, including other large facilities.
Insurance company State Farm is procuring approximately 11.7MW of energy and renewable energy certificates (RECs) annually through Constellation.
TransUnion is also purchasing 8.5MW of energy and RECs from the project through a 12-year partnership with Constellation starting in April 2025.
Other offtakers through Constellation include Cook County, Illinois, CVS Health, Loyola University of Chicago, PPG, and TransUnion.
Retail company Lowe’s will purchase 250MW of clean energy per year from the project for 12 years.
Financing details of the Double Black Diamond Solar project
Swift Current Energy announced the closure of financing for the Double Black Diamond Solar project in August 2023.
The project financing included construction and tax equity bridge loans amounting to $695m and an $84m letter of credit facility, making it one of the largest US solar project financings.
Coordinating lead arrangers of the project financing included Mitsubishi UFJ Financial (MUFG), Société Générale and Truist. MUFG and Societe Generale acted as joint bookrunners.
ING served as the green loan structuring agent while Wilmington Trust served as the collateral and depositary agent.
Law businesses Vinson & Elkins and Husch Blackwell represented Swift Energy Current in the financial transaction. Paul Hastings acted as the lenders’ adviser.
Google also provided a tax equity investment for the project.
Contractors involved
Missouri-based construction company McCarthy provided engineering, procurement and construction (EPC) services for the project.
US-based solar PV manufacturer and services provider First Solar supplied solar modules for the project.
Intelligent solar tracker solutions provider Nextracker supplied the smart solar trackers for the project.
Castle, a heavy civil construction services provider, was contracted for earthworks, including designing and installing various roads, laydown yards, and project entrances, as well as performing mass grading.
