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Seams refer to the interfaces between adjacent wholesale electric systems – such as balancing authorities, reliability coordinators, transmission service providers, and electricity markets – where neighboring entities perform essentially the same function on either side of a jurisdictional boundary within a shared network.
A CAISO perspective on seams
Seams issues arise at these interfaces, impacting the ability of neighboring entities to carry out their responsibilities efficiently and effectively.
Market-to-market seams refer to the interfaces between centrally cleared, structured electricity markets – such as the interface between CAISO’s Western Energy Imbalance Market (WEIM) and SPP’s western regional transmission operator (RTO) expansion.
Market-to-market seams issues arise when separate markets – with different configuration, designs, and protocols – optimize interdependent portions of a shared transmission network with limited or imperfect representation of neighboring systems. The resulting issues can include barriers to trade, inefficient congestion management, and suboptimal dispatch.
Boundary changes are not a one-time event in the West. EDAM is designed to offer the same incremental participation framework that facilitated the WEIM footprint expansion. The CAISO launched EDAM in May 2026 with PacifiCorp as its first participant and Portland General Electric scheduled to join in the fall of 2026.
EDAM and seams
PacifiCorp's participation in EDAM and SPP's RTO expansion in the Western Interconnection will introduce day-ahead market interfaces in 2026. Additional day-ahead interfaces will be introduced as entities begin participating in Markets+ starting in 2027.
Real-time market interfaces will undergo change as well. The WEIM continues to add new participants, while some entities plan to leave the WEIM footprint to join Markets+.
To address multi-stage, evolutionary market changes in the west, seams arrangements will need to be flexible, adaptive, and replicable.