USA: Western grid enters new era as CAISO launches Extended Day-Ahead Market

The California Independent System Operator (CAISO) launched the Extended Day-Ahead Market (EDAM) today, transitioning the Western grid from simple real-time energy balancing to a coordinated 24-hour look-ahead system.  

The shift allows utilities across the West to lock in electricity deliveries a full day in advance, a process known as unit commitment, which significantly reduces the price volatility common in spot markets. 

For the solar and storage industries, this expanded footprint means excess renewable energy that might have been curtailed in California can now be scheduled for export to neighboring states where demand is high.

EIA said solar accounts for 93% of all curtailment in the California Independent System Operator (CAISO) region. In 2024, CAISO curtailed 3.4 million MWh of utility-scale wind and solar output, a 29% increase from the amount of electricity curtailed in 2023. While solar power curtailment is increasing in total generation, batteries are improving this.

PacifiCorp serves as the inaugural partner, onboarding roughly 12 GW of generation capacity across its six-state territory. A key driver of this launch is the removal of transmission “wheeling” charges between participating areas, which drastically lowers the cost of moving clean power across state lines.

With the onboarding of PacifiCorp, the market now integrates the California ISO footprint with a six-state utility territory:

• California
• Oregon
• Washington
• Utah
• Idaho
• Wyoming

Additionally, the new Day-Ahead Market Enhancements (DAME) introduce “Imbalance Reserves,” a dedicated procurement category that pays flexible resources like batteries to stand ready for the rapid fluctuations in solar output.

Portland General Electric is slated to join this fall, with major utilities like LADWP and Turlock Irrigation District scheduled for 2027.

Developers can now track performance metrics, including regional solar transfers and storage dispatch, through the Daily EDAM Report released by CAISO today.

From pv magazine USA.