On December 5th, ERCOT's new RTC+B market design introduced Ancillary Service (AS) procurement in the Real-Time (RT) Market. Aside from an increase in AS prices on the first evening, the impact on Day-Ahead (DA) AS prices remain small.

Only Non-Spinning Reserves have shown a meaningful shift. Day-Ahead clearing prices for the service averaged $3.8/MW-hour in the last three weeks of December, up from $2.2/MW-hour in the three months leading up to RTC+B.

Despite the muted DA response, the new market design introduces opportunities for top-performing battery operators to trade between AS markets.

Real-Time AS clearing prices have remained near-zero, clearing well under Day-Ahead prices 93% of the time. This creates a structurally positive Day-Ahead to Real-Time (DART) price spread that operators can leverage, though a single Real-Time price spike can undo weeks of gains.

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A structurally positive DART spread has persisted since launch

Real-Time AS clearing prices have remained near-zero, averaging $0.5/MW-hour since December 5th. They have cleared under Day-Ahead prices 93% of the time.

This creates a structurally positive spread between the Day-Ahead and Real-Time AS markets that operators can leverage.