Western Energy Imbalance Market approaches new milestone
FOLSOM, Calif. – The cumulative economic savings for the Western Energy Imbalance Market (WEIM) participants has increased to $6.99 billion, emphasizing that sharing diverse energy resources can result in significant benefits across the West.
During the first quarter of this year, the WEIM effectively balanced supply and demand by enabling energy transfers among its 22 participants and reducing their combined costs by $369.3 million, according to the latest benefits report produced by the California Independent System Operator (ISO).
The WEIM was designed to enable participants to buy and sell power in real time. The market uses state-of-the-art technology to find and deliver the lowest-cost resources to meet immediate power needs while managing congestion on high-voltage transmission lines to maintain grid reliability.
The 2025 Q1 economic benefits by participant are as follows:
| Participants | (millions $) |
|---|---|
| Arizona Public Service | $ 4.10 |
| AVANGRID Renewables | $ 11.22 |
| Avista | $ 2.50 |
| Balancing Authority of Northern California | $ 28.76 |
| Bonneville Power Administration | $ 8.06 |
| California ISO | $ 21.96 |
| El Paso Electric | $ 3.22 |
| Idaho Power | $ 10.31 |
| Los Angeles Department of Water & Power | $ 17.46 |
| NV Energy | $ 81.71 |
| NorthWestern Energy | $ 13.69 |
| PacifiCorp | $ 50.15 |
| Portland General Electric | $ 11.29 |
| Public Service Company of New Mexico | $ 22.53 |
| Puget Sound Energy | $ 11.26 |
| Powerex | $ 7.90 |
| Seattle City Light | $ 23.22 |
| Salt River Project | $ 11.19 |
| Tacoma Power | $ 3.17 |
| Tucson Electric Power | $ 3.96 |
| Turlock Irrigation District | $ 1.10 |
| WAPA Desert Southwest | $ 20.60 |
| Total | $369.36 |
The latest quarterly report also speaks to the value of the ISO’s Extended Day-Ahead Market (EDAM) that is scheduled to launch next spring and promises to build on the benefits of WEIM for participants in the day-ahead market, where the vast majority of energy trading occurs.
The quarterly benefits report measures cost savings to participants, including market efficiencies and environmental benefits such as displacement of more expensive generation with renewable resources. The WEIM has now helped participants avoid emissions of more than 1.07 million metric tons of CO2 since its launch, roughly equal to emissions from 226,133 passenger cars driven for a year.
Since its launch in 2014, the WEIM has expanded to include 22 balancing authorities across 11 western states and represents 80% of the demand for electricity in the Western interconnection. The California ISO is a balancing authority and not a market participant, with benefits estimated for the California ISO balancing authority area accruing to its market participants and not the California ISO Corporation. The WEIM footprint includes portions of Arizona, California, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, Wyoming, Texas, and extends into British Columbia.
WEIM entities PacifiCorp and Portland General Electric are both participating in onboarding activities to join EDAM in 2026. Two additional entities have signed agreements to join the EDAM in 2027, with several more entities signaling their intention to join or indicating EDAM as their preferred day-ahead market option.
For more information about the Western Energy Imbalance Market and the Extended Day-Ahead market visit the Western Energy Market websites.
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California ISO | 250 Outcropping Way | Folsom, CA 95630 | www.caiso.com
The California Independent System Operator (ISO) is a nonprofit public benefit corporation dedicated, with its partners, to continuous improvement and secure operation of a reliable grid operated for the benefit of consumers. It provides comprehensive grid planning, open and nondiscriminatory access to one of the largest networks of high-voltage transmission power lines in the world, and operates a $9 billion competitive electricity market. Recognizing the importance of the global climate challenge, the ISO is at the forefront of integrating renewable power and advanced technologies that will help provide a sustainable energy future efficiently and cleanly.
The Western Energy Imbalance Market (WEIM) is a real-time wholesale energy trading market that enables participants anywhere in the West to buy and sell energy when needed. The Western Energy Markets Governing Body is the governing authority designed by regional stakeholders and has shared authority with the ISO Board of Governors to resolve rules specific to participation in the WEIM.