Real-Time, four-hour, top-bottom (TB4) spreads at Indiana Hub averaged $1,021/MW-day in September, up 235% year over year (YoY). Day-Ahead spreads in MISO averaged $422/MW-day, up 142% YoY.

A BESS in MISO North could have earned $495/MW-day and one in MISO South $488/MW-day. The two came within 1% of each other, smaller than the 3% gap in August and 90% in July.

However, the regions converged despite differing dispatch strategies. Day-Ahead energy arbitrage paid MISO North $21/MW-day more than MISO South, a wider margin than August's $9/MW-day. Regulation lifted both regions, as it clears market-wide. Day-Ahead regulation cleared at $23/MWh, 28% above September 2025 and 35% above August.

​Two evenings carried the month’s revenue stack. September 2 and 17 together paid $1,692/MW in MISO North, 12% of September's revenue from 7% of its days.

Key takeaways

• MISO North and South converged to within 1% of each other, at $495/MW-day and $488/MW-day.
• Day-Ahead energy arbitrage revenue widened the regional gap by $12/MW-day month over month, while regulation and Real-Time energy closed it by $16/MW-day.
• Real-Time TB4 spreads averaged $1,021/MW-day against Day-Ahead's $422/MW-day, up 235% and 142% YoY. But, Real-Time paid less than Day-Ahead on 16 of the 28 days.
• Prices spent 35 minutes at MISO's $10,000/MWh cap on September 17 and 25 minutes on September 2. For an operating BESS, those two evenings anchored the month’s revenue.

What a vBESS in MISO earned in September

Modo Energy's virtual BESS (vBESS) benchmarks model the revenue a battery could have earned dispatching against market prices. The MISO North benchmark sits at Indiana Hub and MISO South at Arkansas Hub.

Day-Ahead regulation paid $318/MW-day in MISO North and $330/MW-day in MISO South. Both rose month over month, by $82/MW-day and $93/MW-day.

Day-Ahead energy arbitrage added $176/MW-day in MISO North against $155/MW-day in MISO South. Real-Time energy paid under $3/MW-day in both regions.

What TB spreads looked like in MISO for September

Day-Ahead TB4 spreads at Indiana Hub averaged $422/MW-day across 29 days, up 142% year over year. Real-Time TB4 spreads averaged $1,021/MW-day across 28 days, up 235% YoY.

However, the Real-Time average is weighted towards two outlier days, Sept 2 and 17. Real-Time paid less than Day-Ahead on 16 of the 28 days covered by the benchmark, underscoring the uplift impact of those two days.

Alongside those spreads, Indiana Hub Real-Time prices averaged $84/MWh, up 90% from $44/MWh a year earlier. Day-Ahead cleared $60/MWh against Arkansas Hub's $47/MWh.

What prices in MISO looked like on the two scarcity days

September 2 set the month's demand record at 123 GW. Five-minute prices held MISO's $10,000/MWh Value of Lost Load cap for 25 minutes that evening, covered in Modo Energy's extreme weather analysis.

September 17 produced the larger spread on typical demand. Prices spent 35 minutes at the cap, between 5:55 and 6:40 PM, when load peaked at 103 GW.

Consequently the spreads diverged. September 17's Real-Time TB4 spread reached $11,828/MW-day against September 2's $5,924/MW-day.

Arkansas Hub capped in the same intervals as Indiana Hub on both evenings. The scarcity priced across the footprint rather than at one hub, which is why MISO South captured it too.

How did the supply stack look for September and what caused the spike on the 17th?

Across September, demand averaged 86 GW, up 12% year over year. Solar averaged 5.5 GW, down from 6.6 GW last month. Wind generation increased 26% from August, with average generation of 8.3 GW in September.

On September 17th, MISO’s system had little headroom to begin with. Forced outages ran 15.1 GW, the month's fourth highest, while planned maintenance sat mid-range at 18 GW.

Furthermore, no generation replaced it. Solar fell 8.8 GW between 4 PM and 7 PM. Gas was already running at 44 GW and added just 1.7 GW. Total MISO output fell 4.7 GW across those three hours.

​Wind is typically suppresses prices from spiking during the solar ramp down. But on the 17th, wind averaged 3.9 GW from 4 PM to 9 PM. This was less than half the month's 8.3 GW average and the second lowest evening of September. Therefore the system ran thin through the evening of September 17 and prices cleared at the cap.

How MISO regulation prices responded during September

Day-Ahead regulation anchored the ancillary stack at $23/MWh, up 28% year over year, and is the benchmark's largest revenue stream.

Regulation and energy reprice together because holding capacity back for regulation carries the opportunity cost of not selling that energy. As Day-Ahead energy at Indiana Hub rose 29% from August, regulation followed.

Real-Time regulation averaged $38/MWh, up 68% year over year. It reached $304/MWh on September 17 and $98/MWh on September 2, its two highest days of the month.

What September means for MISO batteries

For an operating BESS, September was two evenings of high earning potential and 27 typical shoulder season days. In addition, regulation prices also spiked with energy during those scarcity events. Those spikes should shrink as more batteries saturate a market with a fixed volume.

As shoulder season leads to maintenance and refueling outages, Real-Time prices may continue to pay well-positioned BESS in MISO.