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BPA, Tucson Electric Power newest to join CAISO's Western Energy Imbalance Market


WEIM has 19 participants serving 77% of Western load

Columbia River system "vital source of clean energy"

Three entities slated to join CAISO's WEIM in 2023

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Bonneville Power Administration and Tucson Electric Power are the newest participants in the California Independent System Operator's Western Energy Imbalance Market after formally joining May 3.

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WEIM now has 19 participants serving 77% of the demand for electricity in the Western United States, according to a May 3 CAISO statement.

"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," CAISO President and CEO Elliot Mainzer said in the May 3 statement about BPA's participation.

BPA membership

BPA is a nonprofit federal power marketer that sells carbon-free hydropower from 31 federal dams in the Columbia River Basin and 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. It 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.

Joining the WEIM is a monumental and meaningful step in the modernization of BPA operations that unlocks a range of benefits, BPA Administrator and CEO John Hairston said in a statement.

"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," Hairston said.

TEP membership

Tucson Electric Power provides safe, reliable electric service to more than 438,000 customers in Southern Arizona. Joining the WEIM provides opportunities to achieve cost savings and lower carbon emissions for customers, Tucson Electric Power President and CEO Susan Gray said in a statement.

"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," Gray said.

With more variable resources such as solar and wind on the grid, excess clean power would typically be curtailed and go unused to keep the grid from becoming overloaded, but the WEIM enables greater regional coordination so clean power can be moved across a large geographic area to displace other resources, according to CAISO.

With the participation of Tucson Electric Power, CAISO has another highly valued partner in the Desert Southwest, Mainzer said.

"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," Mainzer said.

Extended day-ahead market

As more utilities join the WEIM, CAISO is working with stakeholders to develop an Extended Day-Ahead Market, where the majority of energy transactions occur for participants. While the EDAM stakeholder process started two years ago, CAISO formally launched the stakeholder initiative process in January with three working groups each focused on a market component that is instrumental in building a proposal that will meet the needs of the ISO's partners in the West.

CAISO released the EDAM straw proposal April 28 which seeks to establish the framework for key design elements of the day-ahead market as well as areas requiring additional work and stakeholder input.

The goal is to bring EDAM market design to the CAISO board for a vote before the end of 2022, followed by implementation testing in 2023 and onboarding the first set of EDAM participants in early 2024.

In August, the CAISO Board of Governors and the WEIM Governing Body approved measures that broaden shared governance between the two entities, including joint authority, paving the way for a Western RTO.

WEIM background

CAISO announced Avista Utilities and Tacoma Power membership in March. Avangrid, El Paso Electric and Western Area Power Administration Desert Southwest Region are slated for 2023 participation.

Launched in 2014, the WEIM is the vehicle by which entities outside CAISO's balancing authority area participate in the ISO's real-time market. Utilities participating in the real-time market share resources more cost-effectively across a larger geographic footprint, which lowers the cost of delivering power to customers.

The WEIM uses sophisticated technology to find and deliver the lowest-cost energy to its members, while enhancing reliability and providing significant environmental benefits through the reduction of renewable energy curtailments during periods of oversupply, according to CAISO. Reducing curtailments leads to lower greenhouse gas emissions because the renewable energy can be deployed by other market participants rather than going unused and may also displace power generated using fossil fuels.