LITTLE ROCK, Ark. (October 8, 2026) - The 2024-2025 Coordinated System Plan (CSP) conducted by the Midcontinent Independent System Operator (MISO) and Southwest Power Pool (SPP) understates the value of interregional transmission, by potentially 200% to 300%, leading to premature elimination of promising solutions and increasing costs and risks to ratepayers, a new white paper by The Brattle Group concludes.

The white paper, Enhancing MISO-SPP Interregional Transmission Planning: Recommendations for Coordinated System Planning, was prepared by Brattle on behalf of the Southern Renewable Energy Association (SREA). Brattle’s expert analysis found that the CSP considers a narrower range of benefits than both RTOs did in their respective regional planning processes. Further, the analysis found that the production cost modeling does not fully capture the value transmission provides during times of stressed system conditions. 

The white paper recommends MISO and SPP: 

• More fully analyze the benefits for all remaining solutions; 
• Consider the total quantified benefits when selecting projects and allocating costs; 
• Incorporate all quantified benefits into the RTO-to-RTO cost allocation;
• Assess whether cost-effective projects should be designed to accommodate future 765kV operation; and 
• Strengthen the benefits framework and production cost modeling used in future CSP cycles.

Interregional transmission lines are one of the most practical tools grid operators have to help keep energy costs down while maintaining reliable service. The proposed new interregional lines between MISO and SPP are important not only for strengthening reliability and reducing the risk of outages across the region, but also for delivering benefits that matter to residents across the Southeast, including:

• Affordability for consumers: Supporting growing demand by helping move the lowest-cost energy to where it’s needed.  
• Economic opportunity: Enabling commercial and industrial customers to plan and invest in the region, helping strengthen local jobs and economic growth.  
• Resilience in extreme weather: Providing grid operators additional options to keep power flowing during heat waves, storms, and other severe events.

MISO and SPP have already completed much of the foundational work needed to move interregional planning from identifying needs to evaluating actionable investments. The 24–25 CSP is a significant step forward for coordinating interregional transmission planning across the two regions. 

“The most recent interregional work between MISO and SPP is groundbreaking, but we may still be leaving savings behind,” said Simon Mahan, SREA Executive Director. “To help future-proof our grid, we need a full assessment of the benefits of transmission.”

For Brattle, Principals Michael Hagerty and Johannes P. Pfeifenberger, and Energy Associate Charlotte Ross authored the white paper and its addendum. 

“SPP and MISO have made significant progress in advancing their interregional planning capabilities in this study, identifying economic and reliability needs along their market seam,” said Michael Hagerty, Brattle Principal. “Broadening the benefits analysis to reflect the identified needs will result in more cost-effective transmission upgrades that reduces costs and risks to ratepayers in both markets.”

Download the report to review the findings and recommendations for interregional transmission planning - an important input for policy decisions focused on reliability, affordability, and resilience in the Southeast. 

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About The Brattle Group: The Brattle Group answers complex economic, finance, and regulatory questions for corporations, law firms, and governments around the world. We are distinguished by the clarity of our insights and the credibility of our experts, which include leading international academics and industry specialists. Brattle has 500 talented professionals across three continents. Our Electricity Practice serves utilities, grid operators, power producers, customers, regulators, developers, investors, law firms, and policymakers. For more than three decades, our experts have been recognized as trusted advisors and thought leaders in the planning, regulation, litigation, and operation of electricity grids and markets. Our clients collectively serve more than 90% of North American electricity customers, and our experts have testified before courts and regulatory agencies worldwide. For more information, please visit www.brattle.com.

For more than a decade, the Southern Renewable Energy Association (SREA) has been committed to promoting the responsible use and development of wind energy, solar energy, and transmission solutions across seven Southeastern states. Our mission is centered on fostering sustainable practices and driving innovative advancements in renewable energy. As an industry-driven initiative, SREA serves Alabama, Arkansas, Georgia, Kentucky, Louisiana, Mississippi, and Tennessee. Discover more at southernrenewable.org.