SPP has secured two new commitments for its day-ahead Markets+, as Grant County Public Utility District and Tacoma Power in Washington state announced their intent to join.

The utilities are slated to begin participating in Markets+ and SPP’s real-time market on Oct. 1, 2028, joining at least seven other entities that have signed agreements, the RTO announced Feb. 27.

“The addition of Grant County PUD and Tacoma Power reflects the continued growth and momentum of Markets+ across the Pacific Northwest,” said Carrie Simpson, SPP vice president of markets. “These utilities recognize the value of a market built on strong governance, reliability and cost savings for their customers. We look forward to our continued partnerships building a market that works for the entire Western Interconnection.”

The two utilities are both parties to a $150 million funding agreement SPP signed in April 2025 with eight Western entities to develop Markets+. However, neither utility had announced when it would join, according to SPP’s announcement. (See SPP Launches Markets+ Phase 2 With $150M Secured.)

Arizona Public Service, Powerex, Public Service Company of Colorado, Salt River Project and Tucson Electric have said they will begin participating in Markets+ when it goes live in October 2027. Grant County PUD and Tacoma Power, together with Puget Sound Energy and Chelan County PUD, are set to join in 2028.

The Bonneville Power Administration announced in May 2025 its intention to pursue participation in Markets+ over CAISO’s Extended Day-Ahead Market, but a group of nonprofits has challenged BPA’s decision in the 9th U.S. Circuit Court of Appeals. (See related story, Nonprofits Tell 9th Circuit BPA’s DAM Decision Poses ‘Imminent’ Harm.)

Grant County PUD serves approximately 56,000 customer meters in Central Washington and operates more than 2,100 MW of hydroelectric generation, according to SPP’s announcement.

Tacoma Power, meanwhile, serves 186,975 customers in Pierce County.

“Grant PUD’s mission is to deliver reliable and affordable energy to our growing customer base,” John Mertlich, the utility’s CEO, said in a statement. “Joining SPP’s Markets+ is a strategic step that strengthens our ability to do so. Additionally, joining Markets+ aligns us with a growing coalition of utilities across the West who are working toward a more reliable, interconnected and economically integrated regional power grid.”