ISONE September 2026 benchmark: top-bottom spreads hit 12-month lows
ISONE September 2026 benchmark: top-bottom spreads hit 12-month lows
Four-hour top-bottom (TB4) spreads at the Internal Hub in ISONE fell 10% year over year to $114/MW-day in September. The Day-Ahead TB4 spread fell 17% to $82/MW-day. Both are the lowest of the past year, compared to a 12-month Real-Time average of $257/MW-day and a Day-Ahead average of $191/MW-day.
The Internal Hub Real-Time price averaged $39/MWh over the month, up 16% year over year. The four cheapest hours of each day rose $4/MWh on average, while the four most expensive rose $1/MWh.
Over four hours, the higher bottom tightens the spread by $17/MW-day and the higher top widens it by $4/MW-day, which nets to the $13/MW-day fall.
Modo Energy's virtual BESS (vBESS) in Boston earned $156/MW-day in September, up 18% from a year earlier. Day-Ahead reserves paid 91% of it, against 63% in September 2025.
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