Benefits of SPP RTO West participation highlighted in filing with Colorado PUC

• Tri-State requests Colorado Public Utilities Commission finding that SPP RTO is a statutory Organized Wholesale Market and Tri-State’s expanded participation in SPP RTO is in the public interest.
• Expanded participation in SPP RTO promotes reliability, affordability and environmental responsibility.

(June 17, 2025, Westminster, Colo.) Following years of collaboration with other regional utilities, transmission providers and stakeholders, Tri-State has filed an application to the Colorado Public Utilities Commission (CoPUC) as the cooperative power supplier plans to expand its participation in the Southwest Power Pool Regional Transmission Organization (SPP RTO) in the West.

Tri-State’s application outlines the significant benefits of joining the SPP RTO, under a Federal Energy Regulatory Commission (FERC) approved tariff, as Tri-State and six other Western utilities prepare for full market integration in April 2026. Tri-State’s filing marks another milestone in a multi-year effort to expand its market participation to bring increased reliability, affordability, efficiency and responsibility to the region’s power grid.

“Grid reliability and resiliency is bolstered with the western expansion of the SPP RTO, as Tri-State serves growing member loads, diversifies our resource portfolio and reduces emissions,” said Duane Highley, Tri-State’s Chief Executive Officer.

SPP RTO West to deliver market benefits for Tri-State members

The SPP RTO provides Tri-State and its members greater access to:

• Economic benefits: An estimated $20 million in annual net benefits for Tri-State alone, as part of more than $200 million in potential annual regional benefits.
• Efficient dispatch: Optimized use of regional generation and transmission, and more efficient resource integration, including intermittent renewable energy resources.
• Transmission system optimization: Coordinated regional use of transmission assets to meet growing energy demand.
• Environmental performance: Ability to meet greenhouse gas reduction requirements more cost-effectively, with robust tracking and reporting mechanisms.
• Improved generator interconnection: New interconnection procedures and queue reforms to make integrating new resources more efficient.

“The expansion of the SPP RTO is the most cost-effective pathway to organized market benefit for Tri-State’s members,” said Highley. “Our participation will support our members’ goals for reliability, affordability, and a cleaner energy future, with cost savings shared by all members.”

The SPP RTO West would include a cohort of utilities and transmission providers currently participating in the SPP Western Energy Imbalance Service (WEIS) market—including Basin Electric Power Cooperative, Colorado Springs Utilities, Deseret Power Electric Cooperative, the Municipal Energy Agency of Nebraska, Platte River Power Authority, and the Western Area Power Administration (WAPA).

Significant Tri-State resources, loads to participate, as regional market reduces seams

FERC approved SPP’s amended tariff in March 2025, enabling SPP to become the first RTO to operate across both the Eastern and Western Interconnections, improving operational flexibility and resiliency across regions.

Tri-State’s owned and contracted resources, transmission and loads in portions of Tri-State’s Colorado, Nebraska and Wyoming Western Interconnection system in the WAPA “WACM” balancing area (BA), which are currently participating in the SPP WEIS market, would transition to the SPP RTO West, including:

• Resources: More than 20 generating units, renewable purchase power and contracted resources.
• Transmission: More than 3,100 miles of high voltage transmission and more than 200 substations and switching stations.
• Member Load: Portions of 23 of Tri-State’s members’ loads, representing 67% percent of gross load across the Tri-State system.

The transition to the SPP RTO West will reduce the number of transmission provider-related seams between transmission providers in Colorado, Wyoming, Montana and Nebraska through the consolidation of seven transmission providers’ tariffs into a SPP RTO common tariff, also reducing the costly “pancaking” of transmission rates. In addition, two BAs will combine to form the SPP West BA. In Colorado, the seam currently between the WACM BA (which becomes part of the SPP West BA) and the Public Service Company of Colorado (Xcel Energy) BA will still exist.

“SPP has successfully shown that it can optimize operations and develop seam agreements between other markets and balancing areas, ” said Highley. “These conversations are already underway for the SPP RTO West.”

Participation in SPP RTO West years in the making

Tri-State has played a foundational role in bringing organized markets to the West, working collaboratively with peer utilities and transmission providers to explore and develop organized market participation frameworks tailored to the needs of Western utilities.

“We greatly value the full benefits of the SPP RTO, including day-ahead, real-time and ancillary services markets, efficient regional transmission planning, reliability coordination, a common transmission tariff and a participatory governance model that help us reduce costs and advance clean energy goals,” said Highley.

In 2015, Tri-State became a member of SPP and placed its Eastern Interconnection transmission facilities under SPP’s tariff. In the Western Interconnection, Tri-State was a founding member of SPP’s WEIS market in 2021. Tri-State has participated in the California Independent System Operator’s Western Energy Imbalance Market in a portion of Wyoming since its inception in 2014, expanding participation into New Mexico in 2021.

In 2020, Tri-State first announced its interest in the western expansion of the SPP RTO, with subsequent resource plan filings and stakeholder engagement processes, maintaining transparency concerning Tri-State’s progress in considering its SPP RTO West participation.

“This effort by our staff, SPP, western utilities, and stakeholders, reflects years of collaboration and commitment to shared goals,” said Highley. “We look forward to further demonstrating the benefits of the market to Colorado regulators and stakeholders.”

Tri-State’s filing seeks a CoPUC finding that participation in SPP RTO is in the public interest and SPP RTO meets the Colorado statutory definition of an Organized Wholesale Market. Colorado regulations signed into law in 2021 require transmission utilities, including Tri-State, to join an organized wholesale market by 2030.

About Tri-State

Tri-State is a power supply cooperative, operating on a not-for-profit basis, serving electric distribution cooperatives and public power district member-owners in four states. Together with our members, we deliver reliable, affordable and responsible power to more than a million electricity consumers across nearly 200,000 square miles of the rural West. Visit www.tristate.coop.

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Contact:

Lee Boughey, VP Strategic Communications, 720-670-6696, lee.boughey@tristategt.org

Mark Stutz, 303-254-3183, mark.stutz@tristategt.org

Certain information contained in this press statement are forward-looking statements including statements concerning Tri-State’s plans, future events, and other information that is not historical information. These forward-looking statements are subject to a number of risks, uncertainties and assumptions, including those described from time to time in Tri-State’s filings with the Securities and Exchange Commission. Tri-State’s expectations and beliefs are expressed in good faith, and Tri-State believes there is a reasonable basis for them. However, Tri-State cannot assure you that management’s expectations and beliefs will be achieved. There are a number of risks, uncertainties and other important factors that could cause actual results to differ materially from the forward-looking statements contained herein.