transmission lines

FOLSOM, Calif. – The Bonneville Power Administration (BPA) and Tucson Electric Power (TEP) have become the newest participants in the Western Energy Imbalance Market (WEIM), with both utilities formally joining today.

“We are honored to welcome the Bonneville Power Administration and Tucson Electric Power to the Western Energy Imbalance Market,” said California Independent System Operator (ISO) President and CEO Elliot Mainzer. “The Federal Columbia River Power System is a vital source of clean energy that will bring significant resource diversity and transmission capability to the WEIM. And with the participation of Tucson Electric Power, we have another highly valued partner in the Desert Southwest. I am very appreciative of the hard work and focus required to meet this important milestone and look forward to delivering real economic and environmental value to BPA and TEP customers.”

Using diverse and flexible energy resources from WEIM participants, the real-time energy market’s sophisticated technology finds and delivers the lowest-cost energy to its members. Operated by the ISO since late 2014, the WEIM now has 19 participants serving 77% of the demand for electricity in the Western United States.

“Joining the Western EIM is a monumental and meaningful step in the modernization of our operations that unlocks a range of benefits for Bonneville and our customers,” said BPA Administrator and CEO John Hairston. “As we explore additional market-based opportunities to maximize the value of our surplus power and the Northwest’s federal transmission system, we will ensure that they are consistent with our statutory authority and further our ability to deliver affordable, reliable energy to our customers.”

Susan Gray, president and CEO of Tucson Electric Power, said, “We’re proud to join the Western Energy Imbalance Market because it provides opportunities to achieve cost savings and lower carbon emissions for our customers. We’re working toward a dramatic expansion of renewable resources, and participating in the WEIM provides another way to increase our use of wind and solar energy.”

The real-time energy market’s newest members are coming on board a little more than a month after Avista Utilities and Tacoma Public Utilities began participating in April, and on the heels of the WEIM reaching the historic milestone of surpassing $2 billion in total benefits for its participants.

With the addition of these new partners, the WEIM will continue to provide increased reliability and significant environmental gains through the real-time transfer of energy. With more variable resources such as solar and wind on the grid, excess clean power would typically tend to be curtailed and go unused to keep the grid from becoming overloaded. With greater regional coordination enabled by the WEIM, that clean power can be moved across a large geographic area to displace other resources.

As the WEIM continues to grow, the ISO has also been collaborating with its partners to build on that success through development of an Extended Day-Ahead Market (EDAM).  Following three months of intensive stakeholder meetings on a variety of key market issues, the ISO released its EDAM straw proposal on April 28. This initial iteration of the straw proposal (add link to straw proposal), which reflects the concerns and input of the ISO’s stakeholders and customers, seeks to establish the framework for key design elements of the day-ahead market as well as areas requiring additional work and stakeholder input. Current plans call for implementation testing in 2023 and onboarding the first set of EDAM participants in early 2024.

For information about the real-time energy market’s participants, the recent $2 billion milestone, governance, initiatives and upcoming meetings, visit the WEIM website.


About Bonneville Power Administration

The Bonneville Power Administration is a nonprofit federal power marketer that sells carbon-free hydropower from 31 federal dams in the Columbia River Basin. It also markets the output of the region’s only nuclear plant. BPA delivers nearly a third of the power generated in the Northwest to more than 140 electric utilities, serving millions of Northwest consumers and businesses. BPA also owns and operates more than 15,000 circuit miles of high-voltage power lines and 261 substations, and provides transmission service to more than 300 customers. BPA implements a fish and wildlife program that includes working with its partners to make the federal dams safer for fish passage. It also pursues cost-effective energy savings and operational solutions that help maintain safe, affordable, reliable electric power for the Northwest.

About Tucson Electric Power
Tucson Electric Power provides safe, reliable electric service to more than 438,000 customers in Southern Arizona. For more information, visit TEP and its parent company, UNS Energy, are subsidiaries of Fortis Inc. (TSX/NYSE: FTS), which owns utilities that serve more than 3 million customers across Canada and in the United States and the Caribbean. For more information, visit

News Media Contact:Joseph Barrios(520)

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