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Rate Matters (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
[2]
Dec. 31, 2021
[2]
Fuel Rules [Abstract]          
Deferred fuel rules monitored costs   $ 3.0 [1] $ 7.2 [2] $ (8.8) $ (3.3)
Electric Rate Proceeding [Member] | PSCW [Member] | MGE [Member]          
Rate Proceedings [Abstract]          
Authorized rate increase (decrease), percentage   1.54% [3],[4] 9.01% [5]    
Authorized return on equity, percentage   9.70% 9.80%    
Approved equity capital structure, percentage   56.10% 55.60%    
Fuel Rules [Abstract]          
Fuel rules, bandwidth   2.00% 2.00%    
Electric Rate Proceeding [Member] | PSCW [Member] | Rate Matters For Future Periods [Member] | MGE [Member]          
Rate Proceedings [Abstract]          
Authorized rate increase (decrease), percentage [3],[4],[6] 2.63%        
Authorized return on equity, percentage 9.70%        
Approved equity capital structure, percentage 56.10%        
Gas Rate Proceeding [Member] | PSCW [Member] | MGE [Member]          
Rate Proceedings [Abstract]          
Authorized rate increase (decrease), percentage   2.44% [3],[4] 0.96%    
Authorized return on equity, percentage   9.70% 9.80%    
Approved equity capital structure, percentage   56.10% 55.60%    
Gas Rate Proceeding [Member] | PSCW [Member] | Rate Matters For Future Periods [Member] | MGE [Member]          
Rate Proceedings [Abstract]          
Authorized rate increase (decrease), percentage [3],[4] 1.32%        
Authorized return on equity, percentage 9.70%        
Approved equity capital structure, percentage 56.10%        
[1] These costs will be subject to the PSCW's annual review of 2024 fuel costs, expected to be completed in 2025.
[2] There was no change to the refund or recovery in the fuel rules proceedings from the amount MGE deferred.
[3] The 2024/2025 rate order includes an earnings sharing mechanism, under which, if MGE earns above the authorized Return on Equity (ROE) in the rate order: (i) the utility will retain 100.0% of earnings for the first 15 basis points above the authorized ROE; (ii) 50.0% of the next 60 basis points will be required to be deferred and returned to customers; and (iii) 100.0% of any remaining excess earnings will be required to be refunded to customers. The earnings calculation excludes fuel rules adjustments. See "Fuel Rules" below.
[4] The electric increase was driven by an increase in rate base including MGE's investments made in West Riverside, local solar, continued investment in grid modernization, as well as higher costs for transmission, pension and OPEB, and uncollectible costs (including costs previously deferred from prior years). This increase in electric costs is offset by a decrease in fuel costs and benefit from lower tax expense (including impacts from the Inflation Reduction Act). In addition, the PSCW authorized MGE to defer a recovery of and a return on costs associated for any change in the in service date for Paris and force majeure costs for Badger Hollow II and Paris that were not reflected in this rate filing. The PSCW also approved deferral of any differential in PTC tax credits reflected in rates and actual credits produced. These deferrals will be reflected in MGE's next rate case filing. The gas rate increases were also driven by MGE's investment made in grid modernization and higher pension and OPEB and uncollectible costs (including costs previously deferred from prior years). This increase in gas costs is offset by a tax benefit related to excess deferred taxes. Included in the gas residential rate is a reduction in the customer fixed charge.
[5] The electric rate increase was driven by generation assets including MGE's investments in Badger Hollow II (solar), Paris (solar and battery), Red Barn Wind Farm (wind), and West Riverside (natural gas). In addition, the reopener request included an increase in fuel costs and the recovery of deferred 2021 fuel costs. The reopener also revised the depreciation schedule for Columbia Unit 2 and shared equipment to 2029 to align with the depreciation schedule for Unit 1.
[6] The PSCW approved a 2025 Fuel Cost Plan in December 2024. The plan lowered the 2025 increase in electric rates to 2.63% to reflect lower expected fuel costs.