​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, 12 GW above September's average daily peak. 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

• 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