As of June 16, 2025, January 21 is the highest peak day to date at 19,342 MW from 5-6 pm and well below what we will likely see during the summer months of June through August (and potentially early September). The first day that came close to the date (as of June 16) was June 5 at 19,052 MW from 6-7 pm. 

Trends in Energy Use & the Role of Solar

While annual energy use has gradually declined since 2005, mostly because of an increase in energy efficiency and advanced heating and cooling technologies, peak demand has remained relatively stable but continues to vary from year to year and can spike depending on weather.  Behind-the-meter solar installations will continue to grow and affect both the actual peak and the time of day the peak occurs. (ISO-NE is anticipating a shift to a winter peaking region by 2032) 

During the summer of 2024, Freedom Energy sent seven curtailment notices from June19 through July 17. The National Oceanic and Atmospheric Administration (NOAA) is predicting warmer than normal temperatures for New England this summer. ISO-NE is continually refining and improving demand forecast methods, adding higher resolution and geographic detail.  Given all the variables affecting demand, weather, b-t-m solar installations etc., it is exceedingly difficult to predict the number of curtailment notices to expect this summer. 

ISO-NE’s Summer Expectations: 

• Peak Demand Forecast – Typical Weather – 24,803 MW 

• Peak Demand Forecast – Above Average Weather – 25,886 MW 

• Approximate Available Capacity – 29,000 MW 

• Highest Annual System Peak – 28,130 MW (August 2, 2006) 

2024 was the fourth hottest summer on record for both the US and Canada. NOAA forecasts above average temperatures, again, for much of the northeast and New England.

Background Information

Annual System Peak Voluntary Curtailment Program

The annual system peak is the single hour in the calendar year when electricity demand throughout New England is highest. That hour is most likely to occur during the summer on the hottest and most humid weekday in the late afternoon.  Each year we send curtailment notices during the summer to customers when we think the peak may occur, recommending curtailment between 4-7 pm.

The peak hour establishes each electricity account’s capacity tag based on its load during that hour and becomes effective the following year beginning June 1 for a 12-month period. The annual system peak is essentially the sum of the capacity tags for all accounts combined.  ISO-NE bases its planning on electricity generation to ensure adequate supply during that peak demand hour.  The cost of capacity is established through the Forward Capacity Market auction process.

Every account’s electricity supply cost includes a charge for capacity based on its capacity tag. By curtailing during that peak hour, an account can reduce its capacity tag, and thus the associated cost going forward (depending on the timing and term of their retail supply contract). Additionally, curtailment during that peak hour helps ISO-NE to reduce the need for new, future generation.

Future Annual Peak Changes

As mentioned in prior articles, New England was a Winter-peaking region prior to the early 1990s. Since then, the New England grid has shifted to a summer-peaking system due to the significant increase in air conditioning and reduction in electric heating.

The New England grid is expected to shift back to a Winter-peaking system by 2032 based on ISO-NE’s current studies, largely due to the electrification of heating demand.  Additionally, during the same period solar generation is expected to double from the current 6,000 MW to almost 12,000 MW including behind-the-meter solar, helping to reduce summer demand on the grid.  The shift to a winter peak will occur gradually and add to the complication of estimating when it may occur.