Leaving regional grid would raise costs for New Hampshire ratepayers, report finds

A path exists for New Hampshire to electrically isolate itself from the rest of New England, according to a study released this month. But such a move, the authors said, would likely come at a significant cost for ratepayers.

The July 15 report is the outcome of a monthslong investigation into the feasibility of New Hampshire leaving ISO New England, the nonprofit that oversees electric grid operation and the wholesale electricity market in the six New England states. The $230,000 report was compiled by Boston-based consultant London Economics International at the request of the New Hampshire Department of Energy, after a bill passed in 2025 directed the department to examine the feasibility of detaching from the regional system.

Ultimately, the report found, the “unprecedented” move of leaving ISO-NE would herald significant changes for the New Hampshire electric ecosystem. While it would accomplish certain hypothetical goals legislators had outlined, like securing more autonomy over how electricity is bought and sold in the state, it would also sacrifice the efficiency gained by operating within the ISO. New Hampshire would also be forced to take on a wide range of regulatory duties, for which officials would answer to federal oversight. The scope of those tasks, the report found, would make the departure costly for the state.

Ultimately, the study projected that leaving the regional grid would raise total costs for ratepayers by about $148 million, or roughly 14%, with additional, harder-to-estimate costs of implementing the separation also likely to be unavoidable. Ratepayers in New Hampshire already pay some of the highest costs for electricity in the U.S., with state rates often ranking in the top ten nationally. Other New England states rank similarly high. 

The report found that instead of detaching, New Hampshire could push for reforms within the structure of the ISO that would grant more autonomy and benefits, a conclusion like those reached by Maine and Connecticut when they asked similar questions in 2008 and 2020, respectively.

Degrees of separation: What would an exit from the regional grid entail?

Transmission owners, not states, are members of the ISO. Therefore, in order to separate, New Hampshire would have to mandate through statute that transmission owners themselves withdraw.

The major transmission owning entity in New Hampshire is Eversource Energy. Other transmission owners include Unitil Energy Systems, National Grid, the New Hampshire Electric Cooperative, and New Hampshire Transmission, LLC, according to the report.

The consultants analyzed various ways New Hampshire might attempt to leave the ISO, from a complete physical disconnection from the grid to a more moderate distancing.

The complete physical disconnection and withdrawal from the New England grid would not be feasible, they concluded.

Such a move would, as intended, island New Hampshire — but also inadvertently island Maine, which relies on electric transmission lines running through New Hampshire to engage with the rest of New England. Disconnecting from the regional grid would also remove the means through which generators within New Hampshire convey the electricity they sell to entities outside the state.

Affected generators would include the NextEra-owned Seabrook Station nuclear power plant, which sells electricity beyond state lines.

Taking away the ability for those privately owned generators to trade with existing buyers could be seen as a regulatory taking, potentially resulting in “expensive legal ramifications,” the report warns. 

The exit scenario the consultants deemed most likely, though still potentially problematic, would involve New Hampshire leaving the ISO-NE regulatory umbrella while keeping physical transmission connections intact. This would not necessarily shut down trading with outside entities, but it would introduce new financial pressures to keep electricity within the state.

In this case, New Hampshire would still need to take on regulatory roles currently shouldered by the ISO, the report states, at significant cost. The report also outlines other potential effects of such a move, such as possible unwillingness among investors to construct new generation in the relatively isolated market New Hampshire would become. 

Cost and emissions impacts

While overall costs would increase, the cost of wholesale energy for customers in New Hampshire would likely decrease if the state were to separate from the rest of New England, the report found. This is in part because New Hampshire’s generation fleet is lower-cost overall than those of neighbors, the report stated, and because isolating the state’s grid would “trap” low-cost energy in the local market.

But other costs would rise to such an extent that they would negate those savings, the report states. And those costs would ultimately affect ratepayers. 

New costs for the state include the price of maintaining the physical grid, transmission fees, planning for reserves and adequate generation capacity, and more. Upon exiting, New Hampshire would need to develop the capacity to carry out an array of regulatory functions currently undertaken by the ISO in order to stay compliant with the requirements of the Federal Energy Regulatory Commission and prevent grid malfunctions that could result in blackouts.

Other costs the state would face upon leaving could include millions in legal expenses to implement the separation; the price of administering local wholesale energy markets; possible ISO exit fees; and more, according to the report.

Furthermore, New Hampshire’s identity as part of the ISO is baked into the state’s statues. Leaving the grid would require updating many laws — and the changes required would be more complicated than simply swapping out terms, as the laws are framed around and depend upon certain assumptions about the regional grid, the report states.

The nature of the energy mix generated within New Hampshire would also shift if the state were to reduce trading with neighbors, according to the report. With a reduction in energy exports, the amount of electricity generated in-state — including at major gas-fired generators — would decline, the report found. 

Under the status quo, New Hampshire often, but not always, generates more electricity than is needed within the state. Therefore, under a potential exit scenario, if New Hampshire were to reduce generation to meet only in-state demand, some gas generation could cease and “most of the energy consumed by New Hampshire ratepayers would be generated from zero-emission resources including nuclear, hydro, wind and solar,” the report concluded. 

The result would be an approximate 90% reduction in emissions by 2030, according to the report. But increases to other costs associated with leaving the ISO make this scenario unlikely, it concludes.

ISO-NE links New Hampshire to states with greener policies

The report was mandated by a bill, passed in 2025, from prime sponsor and Newton Republican Rep. James Summers. The bill directed the New Hampshire Department of Energy to conduct an investigation into the state’s potential withdrawal from ISO-NE. 

Summers did not respond to a request for comment.

The bill was rooted in questions about whether other New England states’ policies targeting greenhouse gas emissions had raised the cost of energy for New Hampshire consumers, he told the Bulletin in February. Among the questions the entirely Republican-sponsored bill directed the study to address: Does New Hampshire pay extra for electricity by virtue of sharing a grid with our neighbors?

Ultimately, the report concluded, regardless of participating states’ ideological alignment, being a part of the ISO saves money for the state and ratepayers by spreading the burden of grid oversight.

The benefits of ISO membership are not distributed equally among member states, nor are they required to be, the report states, but participation is still a net financial positive. 

“Even though a state in ISO-NE may feel that it is not receiving its fair share of benefits relative to other states, it does not mean being part of an RTO (short for regional transmission organization, describing the ISO) is net negative,” the report states. “It may just mean the benefit is not proportional to the load share of the state.”