Commitments and Contingencies	3 Months Ended
Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies. a.Environmental - MGE Energy and MGE. 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 by the end of 2023 and Unit 2 by the end of 2024. Final timing and retirement dates for Units 1 and 2 are subject to PSCW and regional regulatory reviews, including identification and approval of energy and capacity resources to replace Columbia. Effects of environmental compliance requirements discussed below will depend upon the final retirement dates approved and compliance requirement 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 which focus on the reduction of metals and other pollutants in wastewater from new and existing power plants. The standards were finalized in August 2020. In February 2021, MGE and the other owners of Columbia filed a Certificate of Authority (CA) application with the PSCW. The CA application commits to close Columbia's wet pond system to comply with the Coal Combustions Residuals (CCR) Rule as described in further detail in the CCR section below. By committing to close the wet pond system, Columbia will be in compliance with ELG requirements. The Elm Road Units must satisfy the rule's requirements no later than December 31, 2023, as determined by the permitting authority. The operator of the Elm Road Units has been evaluating the rule impacts and has conducted an analysis of compliance obligations, pollution prevention technologies, and their associated costs. In February 2021, MGE and its co-owner filed a CA application with the PSCW. If approved, MGE's share of the estimated costs to comply with the rule is estimated to be approximately $4 million. Subject to approval from the PSCW, construction is expected to begin in 2022. •The EPA's cooling water intake rules require 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's Wisconsin Pollution Discharge Elimination System permit assumes that the plant meets BTA for the duration of the permit, which expires in 2023. However, MGE must conduct studies of its Blount plant by the end of 2021 to help regulators determine BTA. Columbia's river intakes are subject to this rule. BTA improvements may not be required given that Columbia could be fully retired before the issuance of the next permit, which is expected to be issued in 2023 or later. MGE will continue to work with Columbia's operator to evaluate all regulatory requirements applicable to the planned retirements. MGE does not expect this rule to have a material effect on its existing plants. •Greenhouse Gas (GHG) reduction guidelines and approval criteria 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 January 2021, the U.S. Court of Appeals for the District of Columbia Circuit (D.C. Circuit) vacated and remanded to the EPA the Affordable Clean Energy Rule (ACE Rule) and the repeal of the predecessor Clean Power Plan Rule (CPP Rule), both of which regulated greenhouse gas emissions from existing electric generation units pursuant to Section 111(d) of the Clean Air Act. As a result of these legal proceedings, neither the CPP nor ACE rules are currently in effect. MGE will continue to evaluate the rule development and monitor ongoing and potential legal proceedings. •The EPA's rule to regulate ambient levels of ozone through the 2015 Ozone National Ambient Air Quality Standards (NAAQS). In May 2018, the EPA issued a final rule that designated the northeast portion of Milwaukee County as being in nonattainment with Ozone NAAQS. The Elm Road Units are located in Milwaukee County, outside the designated nonattainment area. In August 2018, several environmental groups, the City of Chicago, and the State of Illinois filed federal lawsuits challenging several of the EPA's attainment designation decisions, including the partial Milwaukee County designation as being too narrow and not sufficiently protective. In July 2020, the U.S. District Court of the District of Columbia remanded the partial Milwaukee County attainment designation back to the EPA for further explanation. MGE is monitoring the outcome of the EPA's remand analysis and how it may affect the Elm Road Units in Milwaukee County. At this time, MGE does not expect that the 2015 Ozone NAAQS will have a material effect on its existing plants based on final designations. •Rules regulating nitrogen oxide (NO_x) and sulfur dioxide (SO₂) emissions, including the Cross State Air Pollution Rule (CSAPR) and Clean Air Visibility Rule (CAVR). The EPA's CSAPR and its progeny are a suite of interstate air pollution transport rules designed to reduce ozone and fine particulate (PM2.5) air levels in areas that the EPA has determined as being significantly impacted by pollution from upwind states. In September 2019, the D.C. Circuit remanded the rule to the EPA holding that the rule improperly provided only a partial remedy for addressing interstate transport of pollutants from upwind to downwind states. In March 2021, the EPA addressed the remand by finalizing its revised CSAPR Update Rule. The revised rule does not require further emission reductions from Wisconsin stationary sources beyond those under the original CSAPR. MGE has met its current CSAPR obligations through a combination of reduced emissions through pollution control (e.g., SCR installation at Columbia), as well as owned, received, and purchased allowances. MGE expects to meet ongoing CSAPR obligations for the foreseeable future. MGE will continue to monitor legal developments and any future updates to this rule. •The EPA's Coal Combustion Residuals Rule (CCR), which regulates coal ash from burning coal for the purpose of generating electricity as a solid waste 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. In August 2020, the EPA revised the CCR rule to require owners or operators of coal-fired power plants to stop transporting CCR and non-CCR wastewater to unlined surface impoundments. In addition, regulated entities must initiate impoundment closure as soon as feasible and in no event later than April 2021, unless the EPA grants an extension. Columbia requested an extension to comply by October 2022. The EPA will address the remaining issues on remand in a subsequent action. Review of the Elm Road Units has indicated that the costs to comply with this rule are not expected to be significant. Columbia's operator has completed a review of its system and has developed a compliance plan. In February 2021, a CA application was filed with the PSCW for approval to install technology required to cease bottom ash transport water discharges rather than extend the longevity of the ash ponds. If approved, MGE's share of the estimated costs of the project would be approximately $4 million. Construction is expected to be completed by the end of 2022. b.Legal Matters - MGE Energy and MGE. 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. In January 2021, certain environmental groups filed a petition against the PSCW regarding MGE's 2021 rate settlement. MGE has intervened in the petition in cooperation with the PSCW. See Footnote 9.a. for more information regarding this matter.

Commitments and Contingencies

3 Months Ended

Mar. 31, 2021

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies.

a.Environmental - MGE Energy and MGE.

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 by the end of 2023 and Unit 2 by the end of 2024. Final timing and retirement dates for Units 1 and 2 are subject to PSCW and regional regulatory reviews, including identification and approval of energy and capacity resources to replace Columbia. Effects of environmental compliance requirements discussed below will depend upon the final retirement dates approved and compliance requirement 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 which focus on the reduction of metals and other pollutants in wastewater from new and existing power plants. The standards were finalized in August 2020.

In February 2021, MGE and the other owners of Columbia filed a Certificate of Authority (CA) application with the PSCW. The CA application commits to close Columbia's wet pond system to comply with the Coal Combustions Residuals (CCR) Rule as described in further detail in the CCR section below. By committing to close the wet pond system, Columbia will be in compliance with ELG requirements.

The Elm Road Units must satisfy the rule's requirements no later than December 31, 2023, as determined by the permitting authority. The operator of the Elm Road Units has been evaluating the rule impacts and has conducted an analysis of compliance obligations, pollution prevention technologies, and their associated costs. In February 2021, MGE and its co-owner filed a CA application with the PSCW. If approved, MGE's share of the estimated costs to comply with the rule is estimated to be approximately $4 million. Subject to approval from the PSCW, construction is expected to begin in 2022.

•The EPA's cooling water intake rules require 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's Wisconsin Pollution Discharge Elimination System permit assumes that the plant meets BTA for the duration of the permit, which expires in 2023. However, MGE must conduct studies of its Blount plant by the end of 2021 to help regulators determine BTA.

Columbia's river intakes are subject to this rule. BTA improvements may not be required given that Columbia could be fully retired before the issuance of the next permit, which is expected to be issued in 2023 or later. MGE will continue to work with Columbia's operator to evaluate all regulatory requirements applicable to the planned retirements. MGE does not expect this rule to have a material effect on its existing plants.

•Greenhouse Gas (GHG) reduction guidelines and approval criteria 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 January 2021, the U.S. Court of Appeals for the District of Columbia Circuit (D.C. Circuit) vacated and remanded to the EPA the Affordable Clean Energy Rule (ACE Rule) and the repeal of the predecessor Clean Power Plan Rule (CPP Rule), both of which regulated greenhouse gas emissions from existing electric generation units pursuant to Section 111(d) of the Clean Air Act. As a result of these legal proceedings, neither the CPP nor ACE rules are currently in effect. MGE will continue to evaluate the rule development and monitor ongoing and potential legal proceedings.

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

In May 2018, the EPA issued a final rule that designated the northeast portion of Milwaukee County as being in nonattainment with Ozone NAAQS. The Elm Road Units are located in Milwaukee County, outside the designated nonattainment area. In August 2018, several environmental groups, the City of Chicago, and the State of Illinois filed federal lawsuits challenging several of the EPA's attainment designation decisions, including the partial Milwaukee County designation as being too narrow and not sufficiently protective. In July 2020, the U.S. District Court of the District of Columbia remanded the partial Milwaukee County attainment designation back to the EPA for further explanation. MGE is monitoring

the outcome of the EPA's remand analysis and how it may affect the Elm Road Units in Milwaukee County. At this time, MGE does not expect that the 2015 Ozone NAAQS will have a material effect on its existing plants based on final designations.

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

The EPA's CSAPR and its progeny are a suite of interstate air pollution transport rules designed to reduce ozone and fine particulate (PM2.5) air levels in areas that the EPA has determined as being significantly impacted by pollution from upwind states. In September 2019, the D.C. Circuit remanded the rule to the EPA holding that the rule improperly provided only a partial remedy for addressing interstate transport of pollutants from upwind to downwind states. In March 2021, the EPA addressed the remand by finalizing its revised CSAPR Update Rule. The revised rule does not require further emission reductions from Wisconsin stationary sources beyond those under the original CSAPR. MGE has met its current CSAPR obligations through a combination of reduced emissions through pollution control (e.g., SCR installation at Columbia), as well as owned, received, and purchased allowances. MGE expects to meet ongoing CSAPR obligations for the foreseeable future. MGE will continue to monitor legal developments and any future updates to this rule.

•The EPA's Coal Combustion Residuals Rule (CCR), which regulates coal ash from burning coal for the purpose of generating electricity as a solid waste 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. In August 2020, the EPA revised the CCR rule to require owners or operators of coal-fired power plants to stop transporting CCR and non-CCR wastewater to unlined surface impoundments. In addition, regulated entities must initiate impoundment closure as soon as feasible and in no event later than April 2021, unless the EPA grants an extension. Columbia requested an extension to comply by October 2022. The EPA will address the remaining issues on remand in a subsequent action.

Review of the Elm Road Units has indicated that the costs to comply with this rule are not expected to be significant. Columbia's operator has completed a review of its system and has developed a compliance plan. In February 2021, a CA application was filed with the PSCW for approval to install technology required to cease bottom ash transport water discharges rather than extend the longevity of the ash ponds. If approved, MGE's share of the estimated costs of the project would be approximately $4 million. Construction is expected to be completed by the end of 2022.

b.Legal Matters - MGE Energy and MGE.

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.

In January 2021, certain environmental groups filed a petition against the PSCW regarding MGE's 2021 rate settlement. MGE has intervened in the petition in cooperation with the PSCW. See Footnote 9.a. for more information regarding this matter.