The 2024–2025 Coordinated System Plan (CSP) study by MISO and SPP identifies significant economic and reliability needs along the MISO South–SPP South seam, evaluating potential interregional solutions to address these needs. While the study represents progress, it faces four key issues:
- Limited Evaluation of Transmission Benefits: The study primarily focuses on adjusted production cost (APC) savings, neglecting reliability and extreme-weather benefits, which are explicitly included in the Joint Operating Agreement (JOA) and regional planning frameworks. This narrow approach risks underestimating the value of interregional projects and prematurely eliminating promising solutions.
- Understated Production Cost Savings: The current production cost modeling does not fully capture the value of additional transfer capability during challenging market conditions, such as extreme weather, generation and transmission outages, fuel-price volatility, and real-time uncertainty. Historical data shows that a disproportionate share of transmission value occurs during a small number of high-value hours, which are not adequately reflected in normalized production cost simulations.
- Cost Allocation Based on Production Cost Savings: The proposed cost allocation method relies solely on APC savings, potentially leading to an unbalanced distribution of project costs between MISO and SPP. This approach may over-allocate costs to SPP, especially if supplemental analyses reveal significant reliability or extreme-weather benefits in MISO.
- Undersizing Solutions for Future Needs: The proposed solutions may not be appropriately sized for the transmission system that both RTOs are already planning to develop, potentially leaving the seam dependent on lower-voltage facilities between higher-voltage networks on either side. This could increase costs and challenges in future expansion.
To address these concerns, the following recommendations are proposed:
For the 2024–2025 CSP:
- Extend the supplemental benefits analysis to all five candidate solutions.
- Evaluate each solution based on its total quantified benefits, not just APC savings.
- Incorporate supplemental benefits into the RTO-to-RTO cost allocation.
- Assess whether cost-effective solutions should be designed to be 765 kV-ready.
For the 2026 CSP:
- Expand the benefits framework to reflect the metrics used in regional planning, including reliability, resource adequacy and capacity, transmission losses, and performance under stressed system conditions.
- Validate production cost modeling against historical congestion and price separation to ensure it reasonably reproduces the value observed under actual system conditions.
Addressing these issues would strengthen the basis for project selection, cost allocation, and ensure that investments reflect the full value of interregional transmission between MISO and SPP.
