Commitments and Contingencies	3 Months Ended
Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies - MGE Energy and MGE. a. Environmental. In February 2021, MGE and the other co-owners of Columbia announced plans to retire that facility. The co-owners intend to retire Unit 1 and Unit 2 by June 2026. Final timing and unit retirement dates are subject to change depending on operational, regulatory, and other factors. Effects of the environmental compliance requirements discussed below will depend upon the final Columbia retirement dates approved, applicable regulations at that time, and required compliance dates. MGE Energy and MGE are subject to frequently changing local, state, and federal regulations concerning air quality, water quality, land use, threatened and endangered species, hazardous materials handling, and solid waste disposal. These regulations affect the manner in which operations are conducted, the costs of operations, as well as capital and operating expenditures. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Regulatory initiatives, proposed rules, and court challenges to adopted rules could have a material effect on capital expenditures and operating costs. Management believes compliance costs will be recovered in future rates based on previous treatment of environmental compliance projects. These initiatives, proposed rules, and court challenges include: • The EPA's promulgated water Effluent Limitations Guidelines (ELG) and standards for steam electric power plants focus on the reduction of metals and other pollutants in wastewater from new and existing power plants. With the closure of the wet pond system in 2023 (as described in further detail in the CCR section below), Columbia complies with ELG requirements. With the installation of additional wastewater treatment equipment completed in 2023, the Elm Road Units comply with ELG requirements. In April 2024, the EPA released a pre-publication notice of the final ELG rule that further regulates the wastewater discharges associated with coal-fired power plants. The rule focuses on wastewater discharges from flue gas desulfurization and bottom ash transport water. The rule includes a reduction in requirements for plants that have already installed pollution controls based on previous versions of the rule, and for plants that will be retiring or switching to natural gas by certain dates. The operator of the Elm Road Units believes that pollution prevention installed under previous versions of the rule and the planned fuel switching will qualify the Elm Road Units for the reduced requirements. MGE and the operator of the Elm Road Units currently are evaluating the final rule. • The EPA's cooling water intake rule requires cooling water intake structures at electric power plants to meet best technology available (BTA) standards to reduce the mortality from entrainment (drawing aquatic life into a plant's cooling system) and impingement (trapping aquatic life on screens). Blount received its most recent WPDES permit from the Wisconsin Department of Natural Resources (WDNR) in October 2023. Blount's latest WPDES permit assumes that the plant meets BTA standards for entrainment for the duration of this permit which expires in 2028. The WDNR included a requirement to conduct an impingement study in the latest permit which needs to be completed by the end of 2027. Once the WDNR determines the impingement requirements at Blount, MGE will be able to determine any compliance costs of meeting Blount's permit requirements. Intakes at Columbia are subject to this rule. The Columbia operator's most recent permit required that studies of intake structures be submitted to the WDNR by November 2023 to help determine BTA. Columbia's permit renewal application is due in 2024 and in November 2023 the Columbia operator timely submitted its renewal application to the WDNR. BTA improvements required by the renewal permit will be coordinated with the owners' plan to retire both units by June of 2026. MGE will continue to work with Columbia's operator to evaluate regulatory requirements in light of the planned retirements. MGE does not expect this rule to have a material effect on Columbia. • Greenhouse Gas (GHG) new source performance standards and emission guidelines established under the Clean Air Act for states to use in developing plans to control GHG emissions from fossil fuel-fired electric generating units (EGUs), including existing and proposed regulations governing existing, new, or modified fossil-fuel generating units. In May 2023, the EPA proposed a rule under section 111(b) of the Clean Air Act to establish New Source Performance Standards and emission guidelines to limit GHG emissions from existing fossil fuel-fired steam EGUs and stationary combustion turbines, and new, modified, and/or reconstructed fossil fuel-fired power plants. In April 2024, the EPA released a pre-publication notice of its final performance standards and emission guidelines for carbon dioxide emissions from new combustion turbines and existing fossil-fuel fired boilers used to produce electricity. The final rule grants some emissions flexibility for existing coal-fired units that retire and/or fuel switch by certain dates. For existing natural gas boiler units, the final rule establishes a process under which states must submit plans to the EPA for establishing standards. States will have two years from the publication date of these rules to submit plans to the EPA for review and approval. MGE is evaluating the final version of the rule for impacts to our fossil-fuel fired steam generation units. The EPA is separately developing performance standards and emission guidelines for GHG emissions from existing natural gas-fired combustion turbines. MGE will monitor this rulemaking to assess its impact on our operations. • The EPA's rule to regulate ambient levels of ozone through the 2015 Ozone National Ambient Air Quality Standards (NAAQS). The Elm Road Units are located in Milwaukee County, Wisconsin, a "moderate" nonattainment area for the 2015 Ozone NAAQS. The deadline for moderate classified areas to meet attainment standards is August 2024. At this time, the operator of the Elm Road Units does not expect that the 2015 Ozone NAAQS or the Milwaukee County nonattainment designation will have a material effect on the Units. • The EPA's proposed rule to regulate Fine Particulate Matter (PM2.5). In March 2024, the EPA published a final rule to lower the average annual PM2.5 NAAQS from 12 ug/m3 to 9 ug/m3 effective May 2024. The new annual PM2.5 NAAQS could impact Milwaukee County, where our Elm Road units are located, if the county is determined to be in nonattainment. A nonattainment designation would require the State of Wisconsin to develop a plan to get into attainment, which would likely include additional limitations for new and modified plants in the county. With the planned transition of the Elm Road Units to natural gas there is a low probability for the need of additional emission limitations. However, we will not know the impact of this rule until PM data from 2023 and 2024 is evaluated and released, the EPA determines the attainment status of Wisconsin counties, and the State of Wisconsin develops an attainment implementation plan. MGE will continue to follow the rule's developments. • Rules regulating nitrogen oxide (NOx) and sulfur dioxide (SO2) emissions, including the Cross State Air Pollution Rule (CSAPR) and Clean Air Visibility Rule. The EPA's CSAPR and its progeny are a suite of interstate air pollution transport rules designed to reduce ozone and PM2.5 ambient air levels in areas that the EPA has determined as being significantly impacted by pollution from upwind states. This is accomplished through a reduction in NOx and SO2 from qualifying fossil-fuel fired power plants and industrial boilers in upwind "contributing" states. NOx and SO2 contribute to fine particulate pollution and NOx contributes to ozone formation in downwind areas. Reductions are generally achieved through a cap-and-trade system. Individual plants can meet their caps through reducing emissions and/or buying allowances on the market. In March 2023 (published June 2023), the EPA finalized its Federal Implementation Plan to address state obligations under the Clean Air Act "good neighbor" provisions for the 2015 Ozone NAAQS. The final rule impacts 23 states, including Wisconsin. For Wisconsin, the rule includes revisions to the current obligations for fossil-fuel power generation, which includes Blount, Columbia, the Elm Road Units, WCCF, West Riverside, and West Marinette. The final rule became effective partway through the 2023 ozone season in August 2023. Emissions budgets can be met with planned retirements, fuel switching, and immediately available measures, including consistently operating emissions controls already installed at power plants. MGE expects to meet the emission reductions with immediately available measures. In 2026, additional obligations would go into effect, including a further reduction in emissions budgets. Wisconsin would need to submit a State Implementation Plan to meet its obligations or accept the EPA's Federal Implementation Plan. MGE is reviewing the final rule and is monitoring the multiple lawsuits challenging the final rule. Based on our current evaluation, the 2026 additional emission reductions may impact the Elm Road Units and additional upgrades may be needed to comply, however, we will not know the final impact until evaluations are completed. • The EPA's Coal Combustion Residuals (CCR) Rule. The CCR rule regulates the disposal of solid waste coal ash and defines what ash use activities would be considered generally exempt beneficial reuse of coal ash. The CCR rule also regulates landfills, ash ponds, and other surface impoundments used for coal combustion residuals by regulating their design, location, monitoring, and operation. The CCR rule requires owners and operators of coal-fired power plants to stop transporting CCR and non-CCR wastewater to unlined surface impoundments. With the coal combustion residuals system that replaced the unlined surface impoundment completed in 2023, Columbia complies with this rule. In May 2023, the EPA proposed a CCR Legacy Rule that if finalized as currently written, will apply to previously closed CCR sites. Columbia's operator has evaluated the proposed rule and has determined that parts of the rule would likely apply to Columbia's previously closed site. In April 2024, the EPA released a pre-publication notice of its final rule. MGE is currently evaluating the final rule to determine if there are impacts to Columbia in the final version. b. Legal Matters. MGE is involved in various legal matters that are being defended and handled in the normal course of business. MGE accrues for costs that are probable of being incurred and subject to reasonable estimation. The accrued amount for these matters is not material to the financial statements. MGE does not expect the resolution of these matters to have a material adverse effect on its consolidated results of operations, financial condition, or cash flows. Certain environmental groups filed petitions against the PSCW challenging the fixed customer charge set in MGE's 2022/2023 rate settlement, 2023 electric limited reopener, and 2024/2025 rate order. MGE has intervened in the petitions in cooperation with the PSCW. See Footnote 9.a. for more information regarding this matter.

In February 2021, MGE and the other co-owners of Columbia announced plans to retire that facility. The co-owners intend to retire Unit 1 and Unit 2 by June 2026. Final timing and unit retirement dates are subject to change depending on operational, regulatory, and other factors. Effects of the environmental compliance requirements discussed below will depend upon the final Columbia retirement dates approved, applicable regulations at that time, and required compliance dates.

MGE Energy and MGE are subject to frequently changing local, state, and federal regulations concerning air quality, water quality, land use, threatened and endangered species, hazardous materials handling, and solid waste disposal. These regulations affect the manner in which operations are conducted, the costs of operations, as well as capital and operating expenditures. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Regulatory initiatives, proposed rules, and court challenges to adopted rules could have a material effect on capital expenditures and operating costs. Management believes compliance costs will be recovered in future rates based on previous treatment of environmental compliance projects.

•

The EPA's promulgated water Effluent Limitations Guidelines (ELG) and standards for steam electric power plants focus on the reduction of metals and other pollutants in wastewater from new and existing power plants.

With the closure of the wet pond system in 2023 (as described in further detail in the CCR section below), Columbia complies with ELG requirements. With the installation of additional wastewater treatment equipment completed in 2023, the Elm Road Units comply with ELG requirements.

In April 2024, the EPA released a pre-publication notice of the final ELG rule that further regulates the wastewater discharges associated with coal-fired power plants. The rule focuses on wastewater discharges from flue gas desulfurization and bottom ash transport water. The rule includes a reduction in requirements for plants that have already installed pollution controls based on previous versions of the rule, and for plants that will be retiring or switching to natural gas by certain dates. The operator of the Elm Road Units believes that pollution prevention installed under previous versions of the rule and the planned fuel switching will qualify the Elm Road Units for the reduced requirements. MGE and the operator of the Elm Road Units currently are evaluating the final rule.

•

The EPA's cooling water intake rule requires cooling water intake structures at electric power plants to meet best technology available (BTA) standards to reduce the mortality from entrainment (drawing aquatic life into a plant's cooling system) and impingement (trapping aquatic life on screens).

Blount received its most recent WPDES permit from the Wisconsin Department of Natural Resources (WDNR) in October 2023. Blount's latest WPDES permit assumes that the plant meets BTA standards for entrainment for the duration of this permit which expires in 2028. The WDNR

included a requirement to conduct an impingement study in the latest permit which needs to be completed by the end of 2027. Once the WDNR determines the impingement requirements at Blount, MGE will be able to determine any compliance costs of meeting Blount's permit requirements.

Intakes at Columbia are subject to this rule. The Columbia operator's most recent permit required that studies of intake structures be submitted to the WDNR by November 2023 to help determine BTA. Columbia's permit renewal application is due in 2024 and in November 2023 the Columbia operator timely submitted its renewal application to the WDNR. BTA improvements required by the renewal permit will be coordinated with the owners' plan to retire both units by June of 2026. MGE will continue to work with Columbia's operator to evaluate regulatory requirements in light of the planned retirements. MGE does not expect this rule to have a material effect on Columbia.

•

Greenhouse Gas (GHG) new source performance standards and emission guidelines established under the Clean Air Act for states to use in developing plans to control GHG emissions from fossil fuel-fired electric generating units (EGUs), including existing and proposed regulations governing existing, new, or modified fossil-fuel generating units.

In May 2023, the EPA proposed a rule under section 111(b) of the Clean Air Act to establish New Source Performance Standards and emission guidelines to limit GHG emissions from existing fossil fuel-fired steam EGUs and stationary combustion turbines, and new, modified, and/or reconstructed fossil fuel-fired power plants. In April 2024, the EPA released a pre-publication notice of its final performance standards and emission guidelines for carbon dioxide emissions from new combustion turbines and existing fossil-fuel fired boilers used to produce electricity. The final rule grants some emissions flexibility for existing coal-fired units that retire and/or fuel switch by certain dates. For existing natural gas boiler units, the final rule establishes a process under which states must submit plans to the EPA for establishing standards. States will have two years from the publication date of these rules to submit plans to the EPA for review and approval. MGE is evaluating the final version of the rule for impacts to our fossil-fuel fired steam generation units. The EPA is separately developing performance standards and emission guidelines for GHG emissions from existing natural gas-fired combustion turbines. MGE will monitor this rulemaking to assess its impact on our operations.

•

The EPA's rule to regulate ambient levels of ozone through the 2015 Ozone National Ambient Air Quality Standards (NAAQS).

The Elm Road Units are located in Milwaukee County, Wisconsin, a "moderate" nonattainment area for the 2015 Ozone NAAQS. The deadline for moderate classified areas to meet attainment standards is August 2024. At this time, the operator of the Elm Road Units does not expect that the 2015 Ozone NAAQS or the Milwaukee County nonattainment designation will have a material effect on the Units.

•

The EPA's proposed rule to regulate Fine Particulate Matter (PM2.5).

In March 2024, the EPA published a final rule to lower the average annual PM2.5 NAAQS from 12 ug/m3 to 9 ug/m3 effective May 2024. The new annual PM2.5 NAAQS could impact Milwaukee County, where our Elm Road units are located, if the county is determined to be in nonattainment. A nonattainment designation would require the State of Wisconsin to develop a plan to get into attainment, which would likely include additional limitations for new and modified plants in the county. With the planned transition of the Elm Road Units to natural gas there is a low probability for the need of additional emission limitations. However, we will not know the impact of this rule until PM data from 2023 and 2024 is evaluated and released, the EPA determines the attainment status of Wisconsin counties, and the State of Wisconsin develops an attainment implementation plan. MGE will continue to follow the rule's developments.

•

Rules regulating nitrogen oxide (NOx) and sulfur dioxide (SO2) emissions, including the Cross State Air Pollution Rule (CSAPR) and Clean Air Visibility Rule.

The EPA's CSAPR and its progeny are a suite of interstate air pollution transport rules designed to reduce ozone and PM2.5 ambient air levels in areas that the EPA has determined as being significantly impacted by pollution from upwind states. This is accomplished through a reduction in NOx and SO2 from qualifying fossil-fuel fired power plants and industrial boilers in upwind "contributing" states. NOx and SO2 contribute to fine particulate pollution and NOx contributes to ozone formation in downwind areas. Reductions are generally achieved through a cap-and-trade system. Individual plants can meet their caps through reducing emissions and/or buying allowances on the market.

In March 2023 (published June 2023), the EPA finalized its Federal Implementation Plan to address state obligations under the Clean Air Act "good neighbor" provisions for the 2015 Ozone NAAQS. The final rule impacts 23 states, including Wisconsin. For Wisconsin, the rule includes revisions to the current obligations for fossil-fuel power generation, which includes Blount, Columbia, the Elm Road Units, WCCF, West Riverside, and West Marinette. The final rule became effective partway through the 2023 ozone season in August 2023. Emissions budgets can be met with planned retirements, fuel switching, and immediately available measures, including consistently operating emissions controls already installed at power plants. MGE expects to meet the emission reductions with immediately available measures. In 2026, additional obligations would go into effect, including a further reduction in emissions budgets. Wisconsin would need to submit a State Implementation Plan to meet its obligations or accept the EPA's Federal Implementation Plan. MGE is reviewing the final rule and is monitoring the multiple lawsuits challenging the final rule. Based on our current evaluation, the 2026 additional emission reductions may impact the Elm Road Units and additional upgrades may be needed to comply, however, we will not know the final impact until evaluations are completed.

The CCR rule regulates the disposal of solid waste coal ash and defines what ash use activities would be considered generally exempt beneficial reuse of coal ash. The CCR rule also regulates landfills, ash ponds, and other surface impoundments used for coal combustion residuals by regulating their design, location, monitoring, and operation. The CCR rule requires owners and operators of coal-fired power plants to stop transporting CCR and non-CCR wastewater to unlined surface impoundments. With the coal combustion residuals system that replaced the unlined surface impoundment completed in 2023, Columbia complies with this rule.

In May 2023, the EPA proposed a CCR Legacy Rule that if finalized as currently written, will apply to previously closed CCR sites. Columbia's operator has evaluated the proposed rule and has determined that parts of the rule would likely apply to Columbia's previously closed site. In April 2024, the EPA released a pre-publication notice of its final rule. MGE is currently evaluating the final rule to determine if there are impacts to Columbia in the final version.

MGE is involved in various legal matters that are being defended and handled in the normal course of business. MGE accrues for costs that are probable of being incurred and subject to reasonable estimation. The accrued amount for these matters is not material to the financial statements. MGE does not expect the resolution of these matters to have a material adverse effect on its consolidated results of operations, financial condition, or cash flows.

Certain environmental groups filed petitions against the PSCW challenging the fixed customer charge set in MGE's 2022/2023 rate settlement, 2023 electric limited reopener, and 2024/2025 rate order. MGE has intervened in the petitions in cooperation with the PSCW. See Footnote 9.a. for more information regarding this matter.