Seams
What are seams?
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.
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.
The ISO's commitment to seams coordination
Changes to market boundaries require adjustments to the way neighbors in different markets interact with each other. Most near-term work on seams involves collaboration amongst balancing authorities, transmission service providers, reliability coordinators, and scheduling coordinators as participants adjust business practices in response to new market configurations. The CAISO actively supports this work in its role as a market operator and reliability coordinator.
Market-to-market seams issues in the Western Interconnection will require coordination between the CAISO and SPP as market operators as well as balancing authorities and transmission service providers in those markets. A diverse set of stakeholders need to engage in scoping procedures, agreements, discussions, and solutions because Western markets are designed to facilitate scheduling-between and cost recovery-by independent balancing authorities and transmission service providers.
Stages of upcoming market configuration changes
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 is currently preparing for the May 2026 launch of EDAM with PacifiCorp as its first participant and Portland General Electric scheduled to join in the fall of 2026.
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.
Lessons from the East's experience with seams
Western markets are distinct, but there are lessons we can learn from the experiences of Eastern energy markets. Recent papers by the Federal Energy Regulatory Commission (FERC), Western Resource Advocates, and Grid Strategies documented these lessons, which ISO intends to draw from thoughtfully. Here are some key takeaways from the East:
- Start with shared principles
- Respect existing investments
- Define responsibilities clearly
- Address barriers to trade
Western arrangements will extend beyond market operators alone. They will involve multiple agreements among transmission owners and operators, balancing authorities, and others. The tapestry of agreements needed to address seams reflects the region's emphasis on local control and autonomy.
Next steps
The CAISO has launched an educational series workshops on seams to explore key issues with industry experts and interested parties from across the West. The workshops will explore the mechanics of each market’s FERC-approved rules to manage imports, exports, and congestion in order to build a shared, technical understanding of the complex design of Western electricity markets and their interaction at seams.
Engage with the market seams workshops - view upcoming meetings and all associated documents.
Market Seams workshop series
The workshops will address principles, problem statements, and technical exploration of market-to-market seams issues. We welcome stakeholders from across the West to join the discussion at these workshops.
Engage with the market seams workshops - view upcoming meetings and all associated documents.