The Darien Solar Project in Rock County and Walworth County, Wisconsin which came online in March this year is delivering 250 MW of clean energy to the grid—enough to power approximately 75,000 Wisconsin households. The project will soon be paired with 75 MW of battery energy storage, expected to be operational in 2026, which will enhance grid reliability and allow stored solar power to be dispatched during peak demand periods. The solar facility spans roughly 2,000 acres and supplies electricity to multiple Wisconsin utilities.
The developer Invenergy is one of the largest developers of solar energy in the USA.
Ownership of the solar capacity is divided between:
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We Energies and Wisconsin Public Service (subsidiaries of WEC Energy Group) – 225 MW
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Madison Gas & Electric (MGE) – 25 MW
Ownership of the storage will mirror the solar capacity split:
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We Energies and Wisconsin Public Service – 67.5 MW
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MGE – 7.5 MW
Project Development History
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March 2021 – Chicago-based Invenergy announced plans to develop the 250 MW solar farm with a 75 MW / 4-hour battery system. The estimated investment was US$446 million.
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April 2021 – The Wisconsin Public Service Commission held public hearings on the project.
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Mid-2021 – The project received regulatory approval, with construction set to begin later that year.
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Late 2023 – Original target completion date; construction progressed through 2024.
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March 2025 – Project officially completed and began full operations.
Key Facts
| Feature | Details |
|---|---|
| Capacity (Solar) | 250 MW |
| Capacity (Storage) | 75 MW (online in 2026) |
| Location | Rock & Walworth Counties, WI |
| Developer | Invenergy |
| Owners (Solar) | We Energies & WPS – 225 MW; MGE – 25 MW |
| Owners (Storage) | We Energies & WPS – 67.5 MW; MGE – 7.5 MW |
| Acreage | ~2,000 acres |
| Households Powered | ~75,000 |
| Investment | US$446 million |
| Construction Start | Late 2021 |
| Completion | March 2025 |
| Storage Operation Date | Expected 2026 |
Significance for Wisconsin’s Energy Transition
The Darien Solar Project is part of WEC Energy Group’s $2 billion investment plan in renewable energy and battery storage by 2025. The initiative supports the company’s goal of retiring 1,800 MW of fossil fuel capacity and cutting carbon dioxide emissions by 70% before 2030.
This project is also the second major solar-plus-storage collaboration between MGE and WEC, following their joint investment in a 310 MW solar and storage plant in Kenosha County.
Tom Metcalfe, president of We Energies and Wisconsin Public Service, emphasized that these projects maintain reliability, deliver savings, create green jobs, and strengthen Wisconsin’s economy while contributing to a clean energy future.
