​Real-Time TB4 spreads in PJM averaged $897/MW-day in September 2026, up 244% year-on-year. That narrowly beats the 2026 record of $895/MW-day, set in July. September 16 and 17 alone made up half of September's cumulative spread. Without them, the month would have averaged $494/MW-day.

On September 16, load peaked at 128 GW, only the month's eighth-highest. But that load, combined with scheduled maintenance taking 19 GW of generation offline, left PJM short of reserves from 5:45pm to 8:10pm.

Despite the spike, Modo Energy's virtual BESS (vBESS) benchmarks put a 100 MW, 4-hour battery at $14/kW-month to $20/kW-month across ComEd, Dominion, and Penelec. That is 9% to 17% below September 2025. The modeled batteries missed most of the spike, because they sell their cycle in Day-Ahead first and the shortage only showed up in Real-Time. Day-Ahead energy revenue still rose $3/kW-month to $5/kW-month year-on-year. But regulation revenue halved, from about $11.40/kW-month to between $5.38/kW-month and $5.92/kW-month, a drop those energy gains could not cover.

Key takeaways

• Modeled batteries in ComEd, Dominion, and Penelec earned $17/kW-month, $20/kW-month, and $14/kW-month. Day-Ahead energy made up 47% to 60% of each stack, the highest share in nearly two years of vBESS data.
• Real-Time TB4 spreads averaged $897/MW-day, up 244% year-on-year. Day-Ahead spreads reached $448/MW-day, up 139%.
• On September 16, Real-Time prices hit $3,479/MWh at 7pm. Day-Ahead priced that hour at $353/MWh.
• Synchronized reserve prices averaged $12.47/MWh, three times September 2025. On September 16 alone, they averaged $177/MWh.

vBESS benchmarks show a battery could have earned $14/kW-month to $20/kW-month

Day-Ahead energy led every vBESS revenue stack: $8.35/kW-month in ComEd, $11.91/kW-month in Dominion, and $6.72/kW-month in Penelec. That is 47% to 60% of each stack, against 21% to 32% a year earlier.

Regulation followed at $5.38/kW-month to $5.92/kW-month, about half its September 2025 level, even though the regulation price more than doubled. That implies reduced regulation throughput, as the modeled dispatch opted for energy arbitrage instead.

Day-Ahead synchronized reserve added $1.65/kW-month on average, within the $1/kW-month to $4/kW-month range of 10 of the past 12 months.

The September 16 reserve spike barely affected revenue. It cleared in Real-Time, where reserves added under $0.10/kW-month across September. Day-Ahead reserves caught the 17th instead, paying $0.33/kW that day, nearly a quarter of their monthly total.

An evening reserve shortage sent Real-Time spreads to $8,252/MW-day on September 16

Real-Time TB4 spreads averaged $897/MW-day, while Day-Ahead averaged $448/MW-day, half of Real-Time.

September 16 cleared a daily Real-Time TB4 of $8,252/MW-day, nine times the monthly average. That single day made up 34% of the month's cumulative Real-Time spread.

Day-Ahead cleared September 16 at $945/MW-day, about 11% of Real-Time. In the 7pm hour, Real-Time prices reached $3,479/MWh against $353/MWh in Day-Ahead.

September 17 followed at $3,617/MW-day in Real-Time, taking the two days to half the month's cumulative spread. Day-Ahead prices were elevated by then and set the month's highest spread, $1,456/MW-day. The virtual batteries earned more as a result. The vBESS benchmarks made 10% to 12% of their September revenue that day, against 3% to 6% on the 16th.

Scheduled maintenance and the evening ramp left PJM short of reserves