​Real-time four-hour top-bottom (TB4) spreads at the ISO-NE Internal Hub fell 37% year over year in June, from $310/MW-day in June 2025 to $197/MW-day. Day-ahead spreads eased to $144/MW-day from $185/MW-day.

Scarcity was absent: June 2026's highest real-time price was $307/MWh, less than a third of the $1,110/MWh spike a year earlier. Prices held a mild evening peak rather than the concentrated scarcity of 2025, so the spreads that batteries capture compressed across every ISO-NE zone.

Key takeaways

• The Internal Hub real-time TB4 spread fell about a third year over year, to $197/MW-day from $310/MW-day in June 2025. The day-ahead spread eased to $144/MW-day from $185/MW-day, down 22%.
• The driver was a calmer price month: June 2026 topped out at $307/MWh, less than a third of June 2025's $1,110/MWh high.
• Maine led all RT TB4 spreads at $209/MW-day, the only zone above $200/MW-day.
• Natural gas set the tone at 6.5 GW average output, with nuclear steady at 3 GW. Solar (0.3 GW) and wind (0.5 GW) stayed minor and oil generation was 25% of June 2025.
• Day-ahead reserves cleared quietly near $9/MW-day across all three products. The only ancillary spike was real-time regulation, a separate product, which hit $81/MWh on June 11.

Real-time TB4 spreads fell about a third as scarcity disappeared in ISO-NE

At the Internal Hub, the real-time TB4 spread averaged $197/MW-day in June 2026, down 37% from $310/MW-day a year earlier. The day-ahead TB4 spread eased to $144/MW-day from $185/MW-day, down 22%. The reason was the absence of a big scarcity hour. Spreads in this market are influenced by internal transmission constraints and a reliance on Canadian hydropower.

June 2025 had a $1,110/MWh real-time hour that stretched that gap wide. June 2026 topped out at $307/MWh, so the top of the spread came down while the overnight floor barely moved. The 2025 base was warmer, too: that $1,110/MWh hour fell in a hotter June, so the year-over-year drop partly reflects a high comparison rather than only softer 2026 conditions.

The mid-June heat event was the month's one clear story

An early-summer East Coast heat event over June 10 to 12 was the only stretch that pushed ISO-NE prices and demand meaningfully higher. Instantaneous system demand peaked at 22 GW (hourly-average load peaked at 17 GW), well below ISO-NE's all-time record of 28 GW (August 2006). Real-time prices rose with demand, peaking on June 11 with an average price at $112/MWh.

Late June brought a second heat event, but it barely registered in ISO-NE. A major heat dome hit the central and eastern US over June 29 to 30, breaking records along the I-95 corridor. ISO-NE sat on its northern edge and saw only a modest price response: those days peaked between $110 and $136/MWh, well below the mid-June high, unlike the sharper moves in PJM and MISO.

ISO-NE averaged an evening peak of $73/MWh for June

Real-time prices carried a gentle daily shape rather than the concentrated spikes of a scarcity month. The mild evening peak is the BESS opportunity in a calm month. Solar fades through the late afternoon while demand holds into the evening, and gas covers the gap. That lifts prices into the 6 PM to 9 PM window.

Without a scarcity hour to stretch the top, that daily swing is the bulk of what a four-hour battery could capture in June. ISO-NE's batteries leaned into that window, pushing out 205 MW at the 6 PM price peak.

Natural gas set the price at 6.5 GW while oil fell 75%

Natural gas supplied 6.5 GW on average across the day and set the marginal price for most hours. Nuclear held steady at 3 GW as the baseload layer beneath it. Hydro added 1.1 GW of flexible, evening-peaking output.

Oil fell to an average of 44 MW across the day, a quarter of the year-earlier level. Oil units run only when the system tightens, so that drop reflects limited grid stress.

Variable renewables stayed minor. Wind averaged 0.5 GW and solar 0.3 GW across the day, with solar concentrated in the midday hours where it widens the price trough. At this penetration, solar shapes the midday bottom but does not drive spreads in ISO-NE.

Day-ahead reserves cleared near $9/MW-day, with one regulation spike in ISO-NE

Ancillary markets were quiet, in line with a stable month. Day-ahead reserves all cleared near $9/MW-day as all three ran below their June 2025 levels of $13 to $14/MW-day.

Regulation is a separate product, and it produced the month's only ancillary spike. Real-time regulation averaged $9/MW-day but hit $81/MWh on June 11, its monthly high, during the mid-June heat window. That was a balancing-market event and it still sat far below June 2025's $198/MWh regulation high.

Outlook

June showed that BESS value in ISO-NE is event-driven. A single scarcity hour, like June 2025's, can carry a month's spread on its own meaning the tail hours, not the typical day, decide the year.

Neither heat event this June produced the kind of scarcity hour that stretches a spread. The mid-month heat lifted prices for three days, and the late-June heat dome that hit PJM and MISO barely reached New England. With no scarcity hour to stretch the top, the mild evening peak was the bulk of what a four-hour battery could capture.