New tools are giving ISO New England greater insight into solar power and battery systems that reduce demand for electricity from the regional power grid, it said on May 27.
For several years, the ISO has been tracking the growth of behind-the-meter photovoltaics (BTM PV), including rooftop solar installations, that are connected to local distribution systems instead of the regional grid. The ISO continuously refines its methods, developing sophisticated modeling techniques to project how BTM PV will reduce grid demand in the future, it said.
To further these efforts, the ISO in 2024 implemented Planning Procedure No. 12, which requires distribution companies to provide information about BTM PV and any other equipment connected to their systems that generates or stores electricity -- distributed energy resources. One of several inputs to the ISO’s long-term demand forecast, the new DER data "increases confidence in the forecast’s accuracy and enhances the ISO’s ability to respond to evolving system conditions," it said.
The ISO’s latest BTM PV projections are included in the 2025 Forecast Report of Capacity, Energy, Loads, and Transmission (CELT Report) and related materials. Battery projections will be incorporated in a future edition of the CELT as data collection and refinement continue.
At the end of 2024, the region had 4,542 megawatts of installed BTM PV nameplate capacity. That is expected to more than double over the next 20 years, rising to 11,156 MW in 2045.
BTM PV already reduces the amount of grid electricity the region consumes each year, with greater reductions expected as more installations come on line.
"While BTM PV increasingly reduces energy consumption on an annual basis, its effect on peak demand—the times of greatest use of grid electricity—is reaching saturation. That’s because the peak hour is typically in the early evening while solar production is usually at its strongest at midday."
In summer 2024, BTM PV reduced the peak by an estimated 1,520 MW, or about 6%. The forecast summer peak reduction from BTM PV remains roughly at that level for the next 10 years, declining slightly thereafter, as the anticipated effects of electrified vehicles pushes summer peaks to nighttime.
The winter 2024/2025 peak saw no impact from BTM PV. However, BTM PV is expected to have a modest impact as winter peaks shift toward morning in the 2030s.
