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Joint Plant Ownership (Details) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2026 USD ($) MW | Jun. 30, 2025 USD ($) | Jun. 30, 2026 USD ($) MW | Jun. 30, 2025 USD ($) | Dec. 31, 2025 USD ($)
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Property, plant, and equipment, net |  | $ 2,337,481 |  | $ 2,337,481 |  | $ 2,279,899
Allowance for Funds Used During Construction |  |  |  |  |  |
AFUDC |  | 4,700 | $ 500 | $ 7,900 | $ 2,100 |
Public Service Commission of Wisconsin [Member] |  |  |  |  |  |
Allowance for Funds Used During Construction |  |  |  |  |  |
Authorized AFUDC rate - Signficiant projects (100%) |  |  |  | 100.00% |  |
MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Property, plant, and equipment, net |  | 2,337,509 |  | $ 2,337,509 |  | $ 2,279,927
Forward Wind Units [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Projected renewable project costs | [1],[2],[3] | 14,000 |  | 14,000 |  |
Public Utilities, Property, Plant and Equipment, Construction Work in Progress | [1],[2],[3] | $ 5,300 |  | $ 5,300 |  |
Forward Wind Units [Member] | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, ownership interest | [2],[3] | 12.80% |  | 12.80% |  |
Forward Wind Units [Member] | Wind | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, plant capacity (in MW) | MW | [2],[3] | 18 |  | 18 |  |
Darien Units [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Projected renewable project costs | [1],[3],[4],[5] | $ 18,000 |  | $ 18,000 |  |
Public Utilities, Property, Plant and Equipment, Construction Work in Progress | [1],[3],[4] | $ 7,400 |  | $ 7,400 |  |
Darien Units [Member] | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, ownership interest | [3],[4] | 10.00% |  | 10.00% |  |
Darien Units [Member] | Battery storage | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, plant capacity (in MW) | MW | [3],[4] | 7.5 |  | 7.5 |  |
Koshkonong Units [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Projected renewable project costs | [1],[3],[5],[6] | $ 93,000 |  | $ 93,000 |  |
Public Utilities, Property, Plant and Equipment, Construction Work in Progress | [1],[3],[6] | $ 68,700 |  | $ 68,700 |  |
Koshkonong Units [Member] | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, ownership interest | [3],[6] | 10.00% |  | 10.00% |  |
Koshkonong Units [Member] | Solar | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, plant capacity (in MW) | MW | [3],[6] | 30 |  | 30 |  |
Koshkonong Units [Member] | Battery storage | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, plant capacity (in MW) | MW | [3],[6] | 16.5 |  | 16.5 |  |
High Noon [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Projected renewable project costs | [1],[3],[7] | $ 99,000 |  | $ 99,000 |  |
Public Utilities, Property, Plant and Equipment, Construction Work in Progress | [1],[3],[7] | $ 63,300 |  | $ 63,300 |  |
High Noon [Member] | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, ownership interest | [3],[7] | 10.00% |  | 10.00% |  |
High Noon [Member] | Solar | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, plant capacity (in MW) | MW | [3],[7] | 30 |  | 30 |  |
High Noon [Member] | Battery storage | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, plant capacity (in MW) | MW | [3],[7] | 16.5 |  | 16.5 |  |
Columbia Energy Dome [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Projected renewable project costs | [1],[3],[5],[7],[8] | $ 22,000 |  | $ 22,000 |  |
Public Utilities, Property, Plant and Equipment, Construction Work in Progress | [1],[3],[7] | 6,900 |  | 6,900 |  |
Columbia Energy Dome Remaining Cost |  | 16,000 |  | 16,000 |  |
DOE Reimbursement |  | $ 4,300 |  | $ 4,300 |  |
Columbia Energy Dome [Member] | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, ownership interest | [3],[7] | 19.00% |  | 19.00% |  |
Columbia Energy Dome [Member] | Storage | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, plant capacity (in MW) | MW | [3],[7] | 3 |  | 3 |  |
Badger Hollow [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Projected renewable project costs | [1],[3],[9] | $ 36,000 |  | $ 36,000 |  |
Public Utilities, Property, Plant and Equipment, Construction Work in Progress | [1],[3],[9] | $ 6,900 |  | $ 6,900 |  |
Badger Hollow [Member] | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, ownership interest | [3],[9] | 10.00% |  | 10.00% |  |
Badger Hollow [Member] | Wind | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, plant capacity (in MW) | MW | [3],[9] | 11.2 |  | 11.2 |  |
Whitetail [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Projected renewable project costs | [1],[10] | $ 23,000 |  | $ 23,000 |  |
Public Utilities, Property, Plant and Equipment, Construction Work in Progress | [1],[10] | $ 1,200 |  | $ 1,200 |  |
Whitetail [Member] | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, ownership interest | [10] | 10.00% |  | 10.00% |  |
Whitetail [Member] | Wind | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, plant capacity (in MW) | MW | [10] | 6.7 |  | 6.7 |  |
Dawn Harvest [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Projected renewable project costs | [1],[3],[11] | $ 34,000 |  | $ 34,000 |  |
Public Utilities, Property, Plant and Equipment, Construction Work in Progress | [1],[3],[11] | $ 16,400 |  | $ 16,400 |  |
Dawn Harvest [Member] | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, ownership interest | [3],[11] | 10.00% |  | 10.00% |  |
Dawn Harvest [Member] | Solar | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, plant capacity (in MW) | MW | [3],[11] | 15 |  | 15 |  |
Ursa [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Projected renewable project costs | [1],[3],[7] | $ 46,000 |  | $ 46,000 |  |
Public Utilities, Property, Plant and Equipment, Construction Work in Progress | [1],[3],[7] | $ 6,600 |  | $ 6,600 |  |
Ursa [Member] | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, ownership interest | [3],[7] | 10.00% |  | 10.00% |  |
Ursa [Member] | Solar | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, plant capacity (in MW) | MW | [3],[7] | 20 |  | 20 |  |
Saratoga [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Projected renewable project costs | [1],[3],[12] | $ 46,000 |  | $ 46,000 |  |
Public Utilities, Property, Plant and Equipment, Construction Work in Progress | [1],[3],[12] | $ 12,100 |  | $ 12,100 |  |
Saratoga [Member] | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, ownership interest | [3],[12] | 10.00% |  | 10.00% |  |
Saratoga [Member] | Solar | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, plant capacity (in MW) | MW | [3],[12] | 15 |  | 15 |  |
Saratoga [Member] | Battery storage | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, plant capacity (in MW) | MW | [3],[12] | 5 |  | 5 |  |
Good Oak [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Projected renewable project costs | [1],[3],[7] | $ 22,000 |  | $ 22,000 |  |
Public Utilities, Property, Plant and Equipment, Construction Work in Progress | [1],[7] | $ 8,400 |  | $ 8,400 |  |
Good Oak [Member] | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, ownership interest | [3],[7] | 10.00% |  | 10.00% |  |
Good Oak [Member] | Solar | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, plant capacity (in MW) | MW | [3],[7] | 9.8 |  | 9.8 |  |
Gristmill [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Projected renewable project costs | [1],[3],[7] | $ 15,000 |  | $ 15,000 |  |
Public Utilities, Property, Plant and Equipment, Construction Work in Progress | [1],[7] | $ 5,900 |  | $ 5,900 |  |
Gristmill [Member] | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, ownership interest | [3],[7] | 10.00% |  | 10.00% |  |
Gristmill [Member] | Solar | MGE [Member] |  |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |
Jointly owned utility plant, plant capacity (in MW) | MW | [3],[7] | 6.7 |  | 6.7 |  |
[1] | Excluding AFUDC.
[2] | Forward Wind Energy Center is located in Dodge and Fond du Lac Counties, Wisconsin.
[3] | MGE received specific approval to recover 100% AFUDC. During the three and six months ended June 30, 2026, MGE recognized $4.7 million and $7.9 million, respectively, after tax, in AFUDC for these projects compared to $0.5 million and $2.1 million for the comparable periods in 2025.
[4] | Darien Solar Energy Center is located in Walworth and Rock Counties in southern Wisconsin.
[5] | Estimated costs are expected to exceed PSCW previously approved Certificate of Authority (CA) levels. Notifications are provided to the PSCW when costs increase above CA levels. MGE has and will continue to request recovery of the updated costs in its rate case proceedings.
[6] | Koshkonong Solar Energy Center is located in the Towns of Christiana and Deerfield in Dane County, Wisconsin.
[7] | Located in Columbia County, Wisconsin.
[8] | This project was awarded with a grant from the U.S. Department of Energy's Office of Clean Energy Demonstrations. This will reduce the total estimated project expenses. The remaining cost is expected to be approximately $16 million. As of June 30, 2026, MGE received $4.3 million in reimbursements. This is not reflected in the table above.
[9] | Badger Hollow Wind is located in Iowa and Grant Counties, Wisconsin.
[10] | Whitetail Wind is located in Grant County, Wisconsin.
[11] | Dawn Harvest Solar Energy Center is located in Rock County, Wisconsin.
[12] | Saratoga Solar Energy Center is located in Wood County, Wisconsin.

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