In the U.S., growing concerns about grid reliability as a result of data center forecasts have largely been focused on PJM and ERCOT. However, the North American Electric Reliability Corporation’s (NERC) 2025 Long-Term Reliability Assessment found that MISO, in addition to PJM and ERCOT, classifies as “High Risk” at some point in the forecast. While ERCOT and PJM are expected to enter the “High Risk” category by 2029, MISO is projected to reach “High Risk” by 2028. MISO’s reliability over the next five years will likely depend on the pace of resource retirements, effective management of transmission expansion, and the success of their expedited program for bringing new generation sources online.
MISO’s Reliability Risk
In NERC’s Long-Term Reliability Assessment, there is a consistent trend of ISOs’ reserve margins decreasing over time. However, the most concerning of these belong to PJM and MISO, as NERC projects both ISOs’ reserve margins will decrease to about half of the Reference Margin Level (RML) by 2030. Specifically, NERC predicts MISO’s RML to fall to just 4.3% by 2030, indicating the risk of insufficient power to meet demand across both regions.
Thermal Capacity Changes
MISO’s planned retirement of over 25 GW of thermal capacity is one of the key contributors to its reduced reserve margin projection, particularly the retirement of over 20 GW of coal-fired generation facilities from its grid. Some of these retirements could be delayed either through emergency orders issued by the Department of Energy or through MISO designating the plants as “System Support Resources” if their retirement were to threaten grid reliability. Ultimately though, MISO will most likely need new generation sources to maintain higher reserve margins. New gas capacity is expected to offset some of these retirements, but MISO is also exploring the addition of more nuclear generation to the region.
All three of the nuclear facilities in MISO that have retired since 2013 have announced plans to begin supplying power to the grid again, either through restarting or adding new reactors on site. In addition, Wisconsin Governor Tony Evers recently announced in his State of the State address that the Public Service Commission (PSC) will be working with the University of Wisconsin–Madison to identify potential sites for new nuclear facilities, indicating a continued shift in sentiment regarding the fuel source.
Transmission and Expedited Interconnection
Besides bringing nuclear facilities back into the generation stack and potentially delaying thermal retirements, another way for MISO to stave off reliability concerns is the implementation of its Expedited Resource Addition Study. The initiative aims to fast-track projects that are positioned to bring power to the grid in an area facing resource adequacy challenges within the next three years. NERC omitted these projects from its 2026 Long-Term Reliability Assessment but noted that the successful implementation of this plan would resolve its concerns and eliminate the reserve margin shortfall. Additionally, MISO has indicated that its planned Tranche 1 and Tranche 2.1 transmission plans have been approved. These plans are set to bring over 5,000 miles of high-voltage transmission to northern MISO and should enter service over the next eight years, providing increased efficiency to the ISO.
Conclusion
As power demand continues to grow, ISOs face mounting pressure to expand their generation resources. The path forward depends on ISOs' ability to coordinate transmission buildouts, expedite new project approvals, and maximize the potential of their existing assets.
For even more insight into the state of transmission across the U.S., be sure to register for our upcoming webinar, Bridging the Gap: New Transmission’s Role Amid U.S. Electricity Market Expansion, scheduled for March 11th.
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