The September ISO-NE forecast release includes three scenarios. Alongside the Central Case, Modo Energy has added a High Renewables and a Low Demand scenario to capture different views of how the ISO-NE market could develop.

A four-hour battery in ISO-NE earns $106k/MW-year in the Central Case, averaged across the eight zones and the 2027 to 2049 horizon. High Renewables lifts that figure to $109k/MW-year, widening ISO-NE's TB4 spreads by 7% and more than doubling the battery fleet to 8.0 GW by 2049. Low Demand lowers the figure to $99k/MW-year, compressing TB4 spreads by 6% and holding system-wide capacity prices an average of 24% below Central between 2036 and 2040.

Key takeaways

• ISO-NE's TB4 spreads climb through the 2030s in all three scenarios. On average they rise from about $60k/MW-year in 2027 to a peak of $112k/MW-year between 2038 and 2040, then ease to $88k/MW-year by 2049.
• High Renewables lifts ISO-NE's TB4 spreads by 7% on average and 16% at most in 2034, as pricier gas holds the evening peak up and extra solar pulls the midday trough lower. Its battery fleet reaches 8.0 GW by 2049 against 3.4 GW in Central.
• Low Demand takes 6% off TB4 spreads on average and, at most, 15% in 2032, with the gap closing by 2044 as its battery build stalls. Its capacity prices sit an average of 24% below Central over 2036 to 2040, then end 4% above Central as the scenario builds 4.6 GW less gas.
• Capacity prices rise in winter and hold flat in summer in every scenario. In the Central Case, the winter price climbs from $117/MW-day in 2028 to $579/MW-day by 2041, while summer stays below $190/MW-day throughout.

What the three scenarios assume

The Central Case runs on ISO-NE's published load forecast and Modo's base Henry Hub gas curve. New-build costs for generation track the National Renewable Energy Laboratory's Annual Technology Baseline (ATB) Moderate trajectory, and storage alone sits on the Advanced trajectory.

High Renewables uses the same demand forecast but takes wind and solar capital costs from the ATB Advanced trajectory. It also raises gas and coal prices 10% above Central and trims the annual gas build ceiling by 10% to reflect tighter turbine supply and permitting.