SPP's RTO Expansion (RTOE) is now live, and market participants are beginning to evaluate early impacts across the expanded footprint. In our SPP RTOE retrospective webinar, we discussed early observations, key market developments, and what we're learning from the first months of operation. Here are answers to the most frequently asked questions from that discussion.
Frequently Asked Questions
General
1. SPP has issued several Resource Advisories for SPP West since the RTOE go-live. Can you summarize the specific events and any common themes?
All three Resource Advisories referred to high variability caused by "wind drop events". One of the three advisories also forecasted extreme temperature swings. Managing this type of load uncertainty requires flexible capacity. SPP uses its Uncertainty Reserve product to procure upward flexible capacity to manage net load variation, particularly during the morning and evening ramp periods.
2. How will the Regulation Ancillary Services differ between SPP East and SPP West?
Regulation ancillary services follow the same market rules across the entire RTO footprint. However, the specific requirements, pricing, and certain settlement calculations are managed at the BAA and/or reserve zone level. For more details, see SPP Integrated Marketplace Protocols v118.1 sections 4.1.3, 4.1.5.
3. What changes to general congestion patterns do you anticipate once Markets+ goes live?
When Markets+ goes live, it will operate adjacent to SPP RTO West on different software and tariffs, creating a new market seam structure. There is currently Market-to-Market (M2M) coordination agreements being discussed to prevent/track uncoordinated dispatches and new loop flows, potentially increasing congestion on shared paths. The Interface LMP should reflect the cost of MCC as power is wheeled into our out of the market seem.
LMPs
4. Does the west expansion affect SPP South and SPP North LMPs materially? Is SPP ISO bifurcated, or is the interconnectivity meaningful enough to impact traditional SPP hub prices?
The SPP South and North LMPs have not been significantly impacted by the RTOE. We have seen an increase in congestion volatility in SPP North since the go-live, but that is likely not due to the addition of the SPP West BAA. However, we expect the dual-BAA capability of sharing wind generation and ramp flexibility across the two BAAs will help support more robust pricing signals across the ISO over time.
5. Is SPP using one bus or a collection of weighted buses for the two references buses used to calculate LMP?
SPP distinguishes between the Reference Bus and a Trading Hub. For the reference bus, SPP uses a single imaginary "0 shift factor" point for each respective region. That will calculate the true cost of the marginal energy component (MEC) for each BAA, without any congestion or line loss.
Then the Hub (like the new SWPW Hub) is an aggregate collection of weighted physical buses. The Hub's LMP is calculated by taking the baseline MEC established by the reference bus (above) and adding the weighted average of the localized Marginal Congestion Components (MCC) and Marginal Loss Components (MLC) from all the individual nodes that make up the hub.
Physical Trading
6. How will interchange between SPP West and CAISO's neighboring EDAM BAAs function?
No specific changes have been made to the interchange process between SPP West and EDAM BAs. CAISO has indicated that seams management and coordination is a top priority, but there have not been any changes made to the "market-to-market" coordination process between the regions. In the near term we do not expect EDAM BAs to behave differently than other WECC BAs as a result of SPP's expansion.
7. Is e-tagging no longer allowed across the tie?
Physical e-tagging will no longer occur across the ties and will be scheduled from market optimization.
8. Could you explain the impact of converting DC ties from scheduled interchange to internally dispatched market resources on existing transmission rights and congestion hedges? Specifically, will existing transmission service or existing FTR/TCR/ARR positions and rights tied to these paths be modified or settled differently under RTOE?
Existing legacy transmission rights are preserved and converted to SPP service.
- Miles City: reservations on the tie were already converted in 2015
- Stegall: OATT The Basin
- Sidney: OATT WAPA-RMR
- Miles City (Owned by WAPA-UGP/Basin rights): All legacy reservations were already converted to SPP transmission service when WAPA-UGP joined the Integrated Marketplace in 2015
- Stegall (Owned by Tri-State, 100% Basin capacity): Basin Electric's legacy reservations will convert to SPP OATT network service, unless the respective merchants decide to retain these rights
- Sidney (Owned by WAPA-RMR): All confirmed long-term legacy reservations will be converted to SPP transmission service
For congestion hedging, cross-tie paths will undergo a four-year transition where holders of existing long-term Transmission Service Rights (TSRs) receive automatic congestion payouts in the Day-Ahead market, settled as an option. After four years, these paths enter the standard TCR market and settle in three distinct segments: an AC source obligation, a DC tie option based on the tie's shadow price, and an AC sink obligation.
9. For the DC lines, how does SPP account for the efficiency of converting AC to DC to AC for the ties? Do they use a particular hurdle rate?
Hurdle rates and wheeling charges are no longer relevant on the DC ties, because the market clearing engine directly optimizes the DC lines. To account for AC-DC-AC conversion efficiency, SPP models each tie as a linked withdrawal and injection pair. The modeled injection in the receiving BAA equals the withdrawal in the sending BAA minus the physical losses across the DC tie. When the ties hit capacity, the Marginal Energy Components (MECs) decouple and congestion is settled using the tie's shadow price.
Virtuals Trading
10. What is the impact of SPP RTOE on the virtual market? When can traders place virtual trades on the SPP West nodes?
There are about 299 new tradable virtual nodes for SPP West. These nodes were tradable in the virtual market March 31 for the first operating day April 1. The new tradable nodes for SPP West can be found here.
Congestion Revenue Rights (CRR) Changes
11. If the DC Tie constraints bind at the BAA-level, how will the TCR market hedge against DA congestion for the source-to-sink paths across the DC ties?
There will be a transitional 4-year period after which the paths that span across the DC ties will be tradeable in the TCR Market. Unlike positions across the AC portions of the grid, positions across the DC ties will be settled as options instead of obligations, providing only financial upside to the rights holder. Rather than hedging on the marginal congestion component of the LMP to settle the paths across the seam, the DC tie segments will be settled using the DC tie shadow price. This is a significant departure from traditional congestion hedging. The DC tie shadow price represents the capability of the DC tie to relieve total system production cost. If there is no congestion on the tie, the shadow price will simply be $0/MWh.
12. Real-Time Interchange often leads to uneconomic trades for both SPP East and West. What improvements are being considered in the future, from a market design perspective?
SPP is currently working on implementing Real-Time Dispatchable Transactions (RTDT), which will introduce dynamic scheduling using 5-minute real-time dispatch. Market participants will be able to combine RT LMPs and net actual interchange to submit price-sensitive interchange offers that clear every 5 minutes across the boundaries. This change will create a significant improvement over static hourly schedules, increasing seam transaction efficiency and yielding significant production cost savings.
As the West continues to split into new DA markets (SPP RTO West, Markets+ and EDAM), managing market seams efficiently will require formal seams agreements, or Market-to-Market (M2M) coordination. The first phase of EDAM, along with SPP's RTOE, is critical because future M2M agreements will require accurate pricing data from the interface nodes to manage data sharing, coordinate congestion management, and track transmission rights usage across the interconnected regions.
13. How is the TCR market impacted by SPP RTOE?
The TCR market rules will remain consistent for paths that are contained in each BAA. The nomination cap will be set by SPP West capabilities, sharing the standard business-as-usual procedure for TCRs as SPP East operations. However, the source-to-sink paths that cross the DC Ties will undergo a four-year transition period. During this time, congestion hedging will be based on long-term Transmission Service Rights (TSRs) and settled as an option. The holders of these rights will be automatically awarded. So we will not have offer/bid data for these specific paths that will not reach the TCR market until after the four-year transition period.
14. When was the first TCR auction that will reflect the new RTOE locations?
The SPP West footprint and three internal DC Ties first showed up in the annual ARR allocation process, which opened on April 1, 2026. RTO Expansion-related FTR data first showed up in the Annual TCR/FTR auction (results published May 22, 2026).
Learn More
For a deeper look at the changes introduced by RTOE refer to our previous blog SPP RTO Expansion Frequently Asked Questions.
Have more questions about the expanded market footprint or how to analyze it effectively? Talk with a Yes Energy expert to learn how our data and insights can help you navigate SPP RTOE.
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