ISO New England’s Grid Planning Report Forecasts Behind-the-Meter Batteries for the First Time

ISO New England’s 2026 Forecast Report of Capacity, Energy, Loads, and Transmission, published May 1, contains a line item that has never appeared in the document before: a forecast for behind-the-meter battery storage. The grid operator projects 173 MW of customer-sited battery additions across its six-state footprint over the next decade, concentrated in Massachusetts.

For a planning document that has tracked distributed rooftop solar for years, the addition is procedural. Its consequences are not.

What the CELT report does. The CELT report is the spreadsheet the New England grid is built against. It sets the load and resource assumptions that drive transmission planning, capacity procurement, and reliability studies. A resource that is not in the CELT report is, for planning purposes, invisible. Transmission gets sized as if it does not exist. Capacity gets procured as if it will not respond.

Distributed solar crossed that threshold years ago. ISO-NE began forecasting behind-the-meter photovoltaics, modeling it as a load-modifying resource that suppresses daytime demand. Once the solar forecast existed, the operator could plan around the duck curve instead of being surprised by it.

Behind-the-meter batteries have now reached the same status. They are counted.

Why the count is small, and why that matters. The 173 MW figure looks modest against a regional peak demand near 24,000 MW. Part of that is genuine: customer-sited storage in New England is early. Part of it is definitional.

ISO-NE defines the new category narrowly. It forecasts batteries under 1 MW that are co-located with rooftop solar. A battery paired with a panel array on a warehouse roof is in the forecast. A standalone battery installed at a commercial building purely to shave a demand charge, with no solar attached, is not.

That definition tracks the residential and small-commercial solar-plus-storage segment well. It systematically misses the pure demand-management installation, which is the fastest-moving commercial use case in high-demand-charge territory. New England has plenty of that territory. Eversource and National Grid commercial customers in Massachusetts face some of the steepest demand charges in the country, and Boston’s BERDO carbon-intensity penalties give building owners a second reason to manage peak load. A battery sized to cut a monthly demand spike does not need a solar panel to pencil out.

The result is a forecast that is real but incomplete. The 173 MW is a floor on behind-the-meter battery deployment, not an estimate of it.

The heat pump problem underneath. The same CELT report flags a load-shape issue that the battery forecast quietly addresses. New England is electrifying heating. As heat pumps replace oil and gas furnaces through 2035, the regional peak migrates further into winter, when cold mornings drive simultaneous heating load across millions of buildings. A summer-peaking grid is becoming a winter-peaking one.

Winter peaks are harder. They are weather-driven, they coincide with constrained gas supply, and they were the direct cause of the roughly $6 billion ISO-NE spent keeping the lights on during the cold stretches of early 2026. A behind-the-meter battery does not generate heat, but it can move a building’s electrical draw off the coincident winter peak. Counted at scale, distributed storage is one of the few resources that can blunt the heat-pump peak without building new transmission.

ISO-NE has now put both halves of that equation into the same document: the winter peak that electrification creates, and the distributed batteries that could shave it.

From forecast to market access. Counting a resource is the first administrative step toward compensating it. The sequence is familiar from distributed solar. First the operator forecasts the resource as load modification. Then it studies how the resource behaves under stress. Then, eventually, market rules evolve to let the resource participate and earn.

Behind-the-meter storage in New England is at step one. It is not a capacity resource. It cannot bid into the forward capacity market as an aggregation today. But the CELT inclusion is the data foundation that aggregation pathways are built on. A grid operator does not design a market product around a resource it has never measured.

The contrast with FERC’s recent direction is worth noting. FERC’s May order pushing PJM to open demand response to round-the-clock dispatch, and to lift battery accreditation toward 92%, shows what the mature end of this process looks like: explicit market revenue for distributed flexibility. ISO-NE is several steps behind that, but it is now on the same path, and the CELT forecast is the milepost.

What the number understates. For commercial building owners in Massachusetts, the practical takeaway is not the 173 MW. It is that a grid operator has formally acknowledged the resource class while drawing its definition too tightly to capture the demand-charge installation. A developer or lender financing a standalone commercial battery in Eversource territory can now point to an ISO-NE planning document that confirms the category is real, and simultaneously argue that the official forecast undercounts it, because the operator only counts the solar-paired version.

That is a useful position. The forecast is conservative by construction, which means deployment has room to run ahead of it without contradicting the grid operator’s own numbers.

The deeper signal is that New England’s grid planning has started to treat customer-sited batteries as infrastructure rather than noise. The 173 MW will be revised. The definition will widen as standalone commercial storage becomes too large to fold into a solar-paired category. The first forecast is rarely the accurate one. It is the one that makes every forecast after it possible.

Sources