By Robert Mullin

Arizona Public Service and Puget Sound Energy began transacting in the Western Energy Imbalance Market on Oct. 1, bringing the region’s only real-time market up to five members — including market operator CAISO.

The utilities’ full entry into the EIM follows on two months of testing in which they operated in the market under real conditions without their transactions becoming financially binding. (See Arizona Public Service, Puget Sound Energy Enter EIM Testing Phase.)

The two utilities follow in the footsteps of NV Energy, which entered the market last December, and PacifiCorp, which helped launch the effort in November 2014.

“Participation by Arizona Public Service and Puget Sound Energy in the EIM will strengthen the market and yield substantial benefits in the form of access to low-cost energy for them and for all EIM participants,” CAISO CEO Steve Berberich said in a statement.

The EIM has produced $80 million in economic benefits for its members during the past two years, according to CAISO. Those benefits stem from more efficient inter- and intraregional dispatch in the 15-minute and real-time markets, lower curtailment of renewable energy and reduced need for market participants in all balancing areas to carry flexibility reserves.

Studies commissioned by the utilities indicate that APS could save $7 million to $18 million a year through EIM participation, while PSE could save between $18 million and $30 million.

“Participating in a market that enables APS to buy and sell power closer to when electricity is consumed will result in meaningful economic savings to customers through lower production costs and better integration of renewable resources like solar,” said Tammy McLeod, vice president of resource management at APS, which has transmission connections into both the CAISO and PacifiCorp-East balancing authority areas (BAAs).

PSE’s sole point of connection with the market is via a 300-MW long-term firm transmission reservation on the Bonneville Power Administration system that connects the utility with the PacifiCorp-West balancing authority area.

FERC last week authorized PSE to transact in the EIM at market-based rates, ruling that the company provided sufficient evidence that its limited link would not become constrained frequently enough to create an EIM submarket requiring measures to mitigate market power (ER10-2374).

The commission also directed APS to revise its proposed rules related to how resources external to the EIM can use dynamic scheduling to participate in the market through the utility’s transmission network. (See APS Ordered Again to Revise EIM Dynamic Scheduling Rules.)

Portland General Electric is scheduled to enter the EIM in October 2017, with Idaho Power slated to follow in April 2018.