​Evening ramps in the second half of May, exacerbated by several days of extreme weather, defined May 2026 in MISO.

Real-time prices in the Indiana zone (LRZ6) peaked at $484/MWh during the 6 PM hour on May 27, more than 14 times the monthly Indiana real-time average of $34/MWh. Nine hours cleared above $200/MWh between May 17 and May 27, spread across evening ramps and one unusual midday spike on May 18.

TB4 spreads widened across every northern zone, with Indiana reaching $237/MW-day in real-time. These TB4 spreads were up 65% year over year, while the north-south split held firm.

Key takeaways

• Indiana (LRZ6) led real-time top-bottom spreads at $237/MW-day, up 65% year over year. Northern zones averaged 39% above MISO South for day-ahead TB4 spreads.
• Real-time prices peaked at $484/MWh on May 27, but the month's value spread across a cluster of evenings rather than a single scarcity event.
• Solar generation jumped 55% year over year to average 6.1 GW, peaking at 14.4 GW midday. New solar builds steepened the evening ramp that drove May's elevated evening prices.
• Day-ahead regulation averaged $18/MWh, about seven times day-ahead spinning reserve, keeping it the most bankable ancillary product for MISO storage.

Prices and spreads split north to south in May across MISO

The Indiana (LRZ6) and Lower Michigan (LRZ7) zones led day-ahead energy near $34/MWh, while the south sat lower. Arkansas (LRZ8) cleared at $25/MWh, an $8/MWh discount.

That gap widened in top-bottom spreads. Northern zones averaged $128/MW-day TB4 spreads, 39% above MISO South. Indiana led real-time TB4 spreads at $237/MW-day (up 65%), with Minnesota (LRZ1) at $220/MW-day and Illinois (LRZ4) at $218/MW-day.

MISO South experienced minimal scarcity events across May. Arkansas held relatively at $117/MW-day in real-time, and Mississippi (LRZ10) eased to $124/MW-day.

The Louisiana/Texas zone (LRZ9) fell to $154/MW-day from $463/MW-day in May 2025. A load shedding event in LRZ9, driven by transmission congestion, pulled the zone's May 2025 average more than 300% above other MISO South zones.

The structural gap reflects denser industrial load and limited import paths in the north against surplus Gulf Coast gas capacity in the south. A 100 megawatt, four-hour battery cycling against real-time spreads earned roughly $12,000/day more in Indiana than in Arkansas. Therefore, site selection inside MISO outweighs almost every other revenue lever.

Where did May's value actually land?

Spring shoulder months in MISO rarely produce supply scarcity like winter months, and May 2026 did not break that pattern. Value accumulated across a cluster of evenings in the second half of the month as summer weather came early to MISO.

The highest scarcity hour came at 6 PM on May 27, when Indiana real-time hit $484/MWh. May 19 followed with $452/MWh at 8 PM.

May 18 stood out for a daytime move, with the late-morning hours clearing $325 to $429/MWh as load climbed faster than solar could cover. This was caused by elevated temperatures and severe weather across the Midwest, including thunderstorms and tornadoes.

In total, nine hours cleared above $200/MWh and twenty above $100/MWh, concentrated between May 17 and May 27. The day-ahead market underpriced the sharpest of these. On May 27, day-ahead averaged $58/MWh while real-time reached $85/MWh.

Storage that held inventory into the evening captured the difference, while units already committed left value on the table.

The supply stack shifted further toward gas and solar

Natural gas averaged 21 GW in May, up 8% from a year earlier. That increase filled the space left by aging coal plants, which fell 12% to 17.8 GW.

However, solar expanded the most in proportional terms. Solar generation averaged 6.1 GW against 3.9 GW in May 2025, a 55% jump that reflects a year of utility-scale additions. Wind rose 15% to 11.7 GW.

Solar peaked at 14.4 GW at midday, and that growth steepened the evening ramp. Net load fell to 49 GW mid-morning as solar maxed out, then climbed to 67 GW by 8 PM.

The MISO battery fleet was well-positioned to take advantage of a solar-driven load profile. Average dispatch reached its charging trough of 350 megawatts in the early morning and its discharge peak of 450 megawatts at 7 PM, sitting directly inside the evening ramp window.

MISO May ancillary service revenues were led by regulation

Day-ahead regulation averaged $18/MWh, up 7% year over year, and remained the highest-value ancillary product in MISO.

Real-time regulation cleared $17/MWh, up 3%. However, day-ahead spinning reserve fell 46% to under $3/MWh, and day-ahead supplemental reserve dropped 38% to $0.32/MWh.

Regulation cleared about seven times day-ahead spinning reserve in May. Capacity committed to reserves missed both the regulation premium and the late-May evening ramps.

Summer outlook for BESS in MISO

MISO’s impressive solar growth has steepened the daily net-load curve enough that ordinary shoulder-season evenings now experience stress as solar ramps down. Therefore, the cluster of high-priced evenings between May 17 and May 27 may become the seasonal norm for MISO.

Northern zones continue to outperform MISO South zones. Four-hour real-time spreads in Indiana, Illinois, and Minnesota all sat well above their southern counterparts. The structural drivers behind the gap, transfer constraints and thinner northern reserve margins, are not resolving soon.

For storage operators, May reinforces the value of holding inventory into the evening ramp, site selection and the continued dominance of regulation in the MISO ancillary stack.