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Rate Matters (Details) - USD ($)
$ in Millions
9 Months Ended 12 Months Ended
Sep. 30, 2023
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2022
Dec. 31, 2021
[3],[4]
Fuel Rules [Abstract]          
Deferred fuel rules monitored costs $ 4.3 [1]     $ (8.8) [2],[3] $ (3.3)
PSCW [Member] | Rate Matters For Future Periods [Member] | MGE [Member] | Deferred Expenditures [Member]          
Rate Proceedings [Abstract]          
Public Utilities, Requested Rate Increase (Decrease), Amount     $ 9.7    
Electric Rate Proceeding [Member] | PSCW [Member] | MGE [Member]          
Rate Proceedings [Abstract]          
Authorized rate increase (decrease), percentage 9.01% [5]     8.81% [6]  
Authorized return on equity, percentage 9.80%     9.80%  
Approved equity capital structure, percentage 55.60%     55.60%  
Fuel Rules [Abstract]          
Fuel rules, bandwidth 2.00%     1.00%  
Electric Rate Proceeding [Member] | PSCW [Member] | Rate Matters For Future Periods [Member] | MGE [Member]          
Rate Proceedings [Abstract]          
Proposed rate increase (decrease), percentage [7]   3.41% [8] 3.75% [9]    
Proposed return on equity, percentage   9.80% 9.80%    
Proposed equity capital structure, percentage   56.10% 56.10%    
Gas Rate Proceeding [Member] | PSCW [Member] | MGE [Member]          
Rate Proceedings [Abstract]          
Authorized rate increase (decrease), percentage [6] 0.96%     2.15%  
Authorized return on equity, percentage 9.80%     9.80%  
Approved equity capital structure, percentage 55.60%     55.60%  
Gas Rate Proceeding [Member] | PSCW [Member] | Rate Matters For Future Periods [Member] | MGE [Member]          
Rate Proceedings [Abstract]          
Proposed rate increase (decrease), percentage [7]   1.66% [8] 2.56% [9]    
Proposed return on equity, percentage   9.80% 9.80%    
Proposed equity capital structure, percentage   56.10% 56.10%    
[1] These costs will be subject to the PSCW's annual review of 2023 fuel costs, expected to be completed in 2024.
[2] In August 2023, the PSCW issued a final decision in the 2022 fuel rules proceedings for MGE.
[3] There was no change to the recovery in the fuel rules proceedings from the amount MGE deferred.
[4] In August 2022, the PSCW issued a final decision in the 2021 fuel rules proceedings for MGE to include the recovery of these costs as part of the 2023 electric limited reopener.
[5] The electric rate increase was driven by additions to generation assets including our investments in Badger Hollow II (solar), Paris (solar and battery), Red Barn (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 electric and gas rate increases were driven by an increase in rate base including our investments in Badger Hollow I and a new customer information system. Also driving the requested electric increase were higher fuel and purchased power costs as well as the completion in 2021 of the one-time return of the electric excess deferred tax credit related to the 2017 Tax Act not restricted by IRS normalization rules. Included in the electric residential rate is a reduction in the customer fixed charge.
[7] In April 2023, MGE filed a proposed 2-year rate case and PSCW approval is pending. In October 2023, MGE filed an updated 2024 fuel cost forecast with the PSCW which will decease forecasted fuel costs filed in the original rate application and reduce the rates ultimately approved. That reduction is not reflected in the proposed rates in the table above. MGE will file an updated 2025 fuel forecast with the PSCW in 2024 which may impact rates in 2025, depending on any variance between the forecast submitted as a part of the proposed rates and updated forecast. MGE has also requested to update renewable project construction costs to include force majeure claims and changes to in-service dates for projects under construction or to begin construction during 2024 and 2025. These renewable project updates have not been reflected in the proposed rates in the table above. Staff audit is completed, and a PSCW decision is expected in November 2023 with a final order expected before the end of 2023. MGE cannot predict with any certainty the final outcome of the rate proceeding.
[8] The proposed electric and gas rate increases are driven by an increase in rate base for our continued investment in grid modernization projects and an increase in labor costs.
[9] The proposed electric rate increase is driven by an increase in rate base including our investments made in West Riverside, local solar, and continued investment in grid modernization. Also driving the requested electric increase are 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). The proposed gas rate increase is also attributable to our investment made in grid modernization and higher pension and OPEB and uncollectible costs (including costs previously deferred from prior years). The proposed gas increase is offset by a tax benefit related to excess deferred taxes. In total for both electric and gas rates, MGE has requested recovery of $9.7 million of incremental uncollectible costs deferred from the periods 2020 through 2023. Regulated entities are allowed to defer certain costs that would otherwise be charged to expense if the regulated entity believes the recovery of those costs is probable. Recovery of the deferred costs in future rates is subject to the review and approval by the PSCW. Any disallowance of previously deferred costs would be charged to income in the current period.