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Joint Plant (Tables) | 6 Months Ended
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Jun. 30, 2026
Public Utilities, Property, Plant and Equipment [Abstract] |
Schedule of Jointly Owned Utility Plants | MGE has ownership interests in generation projects with other co-owners, some of which are under construction, as shown in the following table. Incurred costs are reflected in "Property, plant, and equipment, net" or "Construction work in progress" on the consolidated balance sheets.
Project |  | Ownership Interest |  | Source |  | Share of Generation |  | Share of Estimated Costs(a) |  | Costs incurred as of June 30, 2026(a) |  | Estimated Date of Commercial Operation
Darien(b)(c) |  | 10% |  | Battery |  | 7.5 MW |  | $18 million(k) |  | $7.4 million |  | 2027
Koshkonong(b)(d) |  | 10% |  | Solar/Battery |  | 30 MW/16.5 MW |  | $93 million(k) |  | $68.7 million |  | 2026 Solar 2027 Battery
High Noon(b)(e) |  | 10% |  | Solar/Battery |  | 30 MW/16.5 MW |  | $99 million |  | $63.3 million |  | 2027
Columbia Energy Dome(b)(e) |  | 19% |  | Storage |  | 3 MW |  | $22 million(k)(l) |  | $6.9 million |  | 2027
Badger Hollow(b)(f) |  | 10% |  | Wind |  | 11.2 MW |  | $36 million |  | $6.9 million |  | 2027
Whitetail(g) |  | 10% |  | Wind |  | 6.7 MW |  | $23 million |  | $1.2 million |  | 2027
Dawn Harvest(b)(h) |  | 10% |  | Solar |  | 15 MW |  | $34 million |  | $16.4 million |  | 2027
Forward Repower(b)(i) |  | 12.8% |  | Wind |  | 18 MW |  | $14 million |  | $5.3 million |  | 2027
Ursa(b)(e) |  | 10% |  | Solar |  | 20 MW |  | $46 million |  | $6.6 million |  | 2028
Saratoga(b)(j) |  | 10% |  | Solar/Battery |  | 15 MW/5 MW |  | $46 million |  | $12.1 million |  | 2028
Good Oak(b)(e) |  | 10% |  | Solar |  | 9.8 MW |  | $22 million |  | $8.4 million |  | 2028
Gristmill(b)(e) |  | 10% |  | Solar |  | 6.7 MW |  | $15 million |  | $5.9 million |  | 2028
(a) Excluding AFUDC. (b) 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. (c) Darien Solar Energy Center is located in Walworth and Rock Counties in southern Wisconsin. (d) Koshkonong Solar Energy Center is located in the Towns of Christiana and Deerfield in Dane County, Wisconsin. (e) Located in Columbia County, Wisconsin. (f) Badger Hollow Wind is located in Iowa and Grant Counties, Wisconsin. (g) Whitetail Wind is located in Grant County, Wisconsin. (h) Dawn Harvest Solar Energy Center is located in Rock County, Wisconsin. (i) Forward Wind Energy Center is located in Dodge and Fond du Lac Counties, Wisconsin. (j) Saratoga Solar Energy Center is located in Wood County, Wisconsin. (k) 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. (l) 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.

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- Definition Tabular disclosure of proportionate interests in jointly owned utility plants. Includes the amount of plants in service, the accumulated provision for depreciation (if available), the amount of plants under construction, and the proportionate share. The amounts presented may be further subdivided to show amounts applicable to plant subcategories (for example, production, transmission, distribution). Includes statements that the amounts represent the utility's share in each joint plant and that it must provide its own financing. Information concerning two or more generating plants on the same site may be combined. States that the utility's share of direct expenses of the joint plants is included in the corresponding operating expenses on its income statement (for example, fuel, maintenance of plant, other operating expense). If the share of direct expenses is charged to purchased power, then disclose the amount so charged and the proportionate amounts charged to specific operating expenses on the records maintained for the joint plants. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 980 -SubTopic 360 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 10.C) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479070/980-360-S99-1 + Details
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