New England's solar duck curve accelerates, deepens

Continued installations of consumer-sited solar power have poised New England for a new record number of "duck curve" days, or periods when wholesale demand for grid electricity is lower during the middle of the day than during the night. The shift has consequences for the rest of the grid, including on the portfolio of other generating resources needed to meet demand, related emissions, and power pricing.

Historically, consumer demand for electricity has been highest during the day and lowest during the night, based on household, business, and other social patterns of energy use. But as behind-the-meter solar generation was added to the system, midday demand for grid power was reduced. On April 21, 2018 -- a mild sunny day on a spring weekend -- conditions combined to cause grid demand to be lower at midday than at night. Based on graphs showing grid demand reduction in yellow, such as the chart below produced by ISO New England, this phenomenon has become known as the "duck curve".

Since 2018, the duck curve phenomenon has become more frequent, as shown in this chart produced by ISO-NE.

In 2024, the region experienced 107 duck curve days -- a new record. So far in 2025, ISO-NE reports 100 duck days, with a projection to exceed last year's record by the end of December.

The "duck curve" is also reaching new depths of midday load. On April 20, 2025, system demand reached an all-time low of 5,318 megawatts -- which the grid operator projects to be less than half the level of load it would have seen without behind-the-meter solar.

With midday behind-the-meter solar producing power, other grid resources need to ramp down their production to keep supply and demand in balance -- and then need to ramp back up as midday sun fades. This requires the grid operator to ensure a sufficient volume of dispatchable generation capable of responding to these shifts, like natural gas-fired power plants (or large volumes of energy storage which have not yet materialized in the region).

ISO-NE 2022 generation portfolio emissions report

New England's electric power generation fleet emitting slightly less carbon dioxide in 2022 relative to 2021, according to the grid operator's 2022 ISO New England Electric Generator Air Emissions Report.

ISO New England operates the regional transmission grid and the wholesale market for electricity. In support of this role, ISO-NE tracks the portfolio of generation resources used in the region, as well as the resources' emission characteristics.

According to ISO-NE, New England generation emitted 33,382 kilotons of carbon dioxide in 2022, a decline of two-tenths of a percent relative to 2021. The grid operator reports an average 2022 emission rate of 643 pounds of CO2 per megawatt-hour of New England generation. 

Over longer time scales, air emissions from New England's power plants have decreased significantly. "From 2001 through 2022, CO2 emissions fell by 37%, NOx emissions fell by 79%, and SO2 emissions fell by 98%."

While carbon dioxide emissions decreased slightly again this year, sulfur dioxide (SO2) emissions increased to 3.38 kilotons, climbing over 60 percent relative to 2021. The grid operator attributes the sulfur emissions to increased reliance on fuel oil for electric generation:

More electricity came from oil-fired generators in 2022 than in the previous four years combined. At 1,845 GWh, production from these resources in 2022 was eight times higher than in 2021. Oil has a high sulfur content, so SO2 emissions rise when these resources produce more power.

The chart below shows the region's generation portfolio on a monthly basis for 2022; the red and black bars at the top of each month's column represent oil and coal use. The largest blue bars represent natural gas, while the largest orange bars represent nuclear power.

ISO-NE attributes increased use of oil for power generation to "record high natural gas prices associated with the Russia-Ukraine conflict, and thus an increase in regional reliance on oil versus natural gas." The grid operator also says that decreases in coal generation largely offset the increased oil use for purposes of CO2 and NOX emissions.

December 24, 2022 capacity deficiency event in New England

New England's wholesale electricity grid experienced a capacity deficiency on December 24, 2022, according to grid operator ISO New England, Inc., but the system operator says its operating procedures successfully balanced supply and demand on the regional power system during evening peak hours, when unexpected generator outages and reductions and lower-than-expected imports led to a shortfall in operating reserves.

According to ISO-NE:

ISO New England did not call for controlled power outages on Christmas Eve, but did declare a capacity deficiency, meaning the region’s supply of electricity was insufficient to meet required operating reserves in addition to satisfying consumer demand, at 4:30 p.m. This action was taken after approximately 2,150 megawatts (MW) of resources scheduled to contribute power during the evening peak became unavailable. The outages and reductions coincided with net imports being approximately 100 MW less than had been expected based on that day’s Morning Report.

While the capacity deficiency was ongoing, at 4:40 PM, ISO-NE declared a "capacity scarcity condition" under its Forward Capacity Market’s Pay-for-Performance rules. This condition remained in effect until 6:05 p.m. Under the Pay-for-Performance rules, any resource that failed to meet its capacity supply obligation is penalized at a rate of $3,500 per megawatt-hour (MWh) for failing to meet its obligation, while resources that over-performed will receive $3,500/MWh of additional revenue. In total, ISO-NE has estimated penalties for the December 24 event to be approximately $39 million. In addition, any energy resources that cleared in the Day-Ahead Energy Market but failed to provide electricity in real-time are charged the real-time price for the missing energy; Real-Time Energy Market prices averaged approximately $484/MWh over the course of the day, peaking over $2,200/MWh during the 5 p.m. hour while the capacity scarcity condition was ongoing.

On January 12, 2023, ISO-NE provided an update on the December 24, 2022, capacity deficiency, "to help correct any confusion, misinformation, and misunderstanding resulting from various news stories and social media posts." According to that update, the incident was "mainly about timing". After noting that it entered the December 24 operating day with sufficient resource commitments to meet demand and required operating reserves, with a surplus of over 950 megawatts of fast-start resources, ISO-NE explains what happened next:

As the day went on, some generators in the region experienced unanticipated issues that caused them to go offline or reduce their output. These outages were caused by cold temperatures or mechanical problems, and not due to inadequate fuel supplies. Expected imported electricity from Canada was also reduced due to transmission system issues and unexpectedly high consumer demand in Québec. Despite these issues, New England was still expected to meet demand and operating reserves over the evening peak as of 3 p.m.

Around 4 p.m., additional unanticipated outages led to a capacity deficiency in the region. This meant that the 950 MW surplus was depleted and supply was insufficient to meet both demand and required operating reserves. In response, ISO New England system operators implemented procedures for dealing with capacity deficiencies. This included calling upon any resource that could respond quickly enough to be online for the evening peak, which usually falls between 5 and 6 p.m. during the winter months. The ISO dispatched all remaining offline resources that were available to provide electricity or operating reserves during this period.

In its update, ISO-NE described pricing and customer impacts from the incident:

Prices in the Real-Time Energy Market averaged more than $2,000 per megawatt-hour (MWh) during the 2.5-hour capacity deficiency. While high, these prices are unlikely to affect most consumers given how retail rates are set in the region. Though practices vary by state and utility coverage area, the rates paid by most retail customers are set for months-long periods and not subject to volatility within the wholesale marketplace. 

Almost all of New England’s wholesale electricity is bought and sold in the Day-Ahead Energy Market, where prices were unaffected by the capacity deficiency. Average day-ahead prices during that time were roughly $285/MWh.

As ISO-NE noted in its January 4 report, other regions of North America were challenged by extreme weather around the long holiday weekend, prompting varied responses outside New England including controlled power outages.

New England electric fuel security reform filings delayed

Federal electricity regulators have given New England's regional grid operator more time to develop proposed new mechanisms to enhance long-term fuel security, after states and market participants asked for an extension to allow continued stakeholder discussions. At stake are what could be significant reforms to the region's electricity markets, including new opportunities for generators to earn revenue for providing fuel security, as well as the prospect of significant new costs for consumers.

ISO New England Inc. is the regional transmission organization and independent system operator for the electric grid serving nearly all of New England. In this role, it develops and administers markets for electric energy, capacity, and other products. ISO-NE also engages in regional system planning, and manages proposals to retire or close power plants that provide capacity to the region.

In 2018, the owner of the Mystic Generating Station, the largest power station in Massachusetts by nameplate capacity, proposed to retire its units in 2022. But after a study of the remaining electric system, ISO-NE determined that the retirement of Mystic's units 8 and 9 would present "unacceptable fuel security risks" that could lead to rolling blackouts as soon as the winters of 2022 through 2024. In response, ISO-NE asked the Federal Energy Regulatory Commission for waivers to allow the grid operator to retain the Mystic units to meet fuel security needs.

Some stakeholders disagreed that the Mystic units' retirement posed a reliability risk; others argued the costs of retaining them would outweigh any benefits. While the Commission denied ISO-NE's waiver request, it ultimately approved a short-term cost-of-service agreement under which regional ratepayers will pay to keep the Mystic units online. But the Commission also made a preliminary finding that ISO-NE's tariff may be unjust and unreasonable, and directed ISO-NE to file proposed tariff revisions creating a long-term fuel security mechanism by July 1, 2019. At the grid operator's request, the Commission later extended that deadline to November 15, 2019, to allow more time for proposal development and stakeholder discussion.

In the meantime, this spring ISO-NE filed a proposed short-term "inventoried energy program" from December 1 through the end of February during winters 2023/2024 and 2024/2025 as "a bridge to a long-term, market-based solution that more comprehensively addresses the region’s energy security risks" -- but Commission staff identified that filing as "deficient" and requested additional information, which prompted ISO-NE to provide additional information. In the absence of a Commission quorum willing to vote, those revisions became effective by operation of law on August 6, 2019, although parties have sought rehearing regarding the Commission's failure to act.

But even more time may be necessary. On July 31, 2019, the New England States Committee on Electricity (NESCOE) filed a motion requesting an additional six-month extension of time to allow ISO-NE and the region to work through issues related to ISO-NE’s proposed long-term fuel security mechanism. Representing the governors of the six New England states, NESCOE said granting its request would "enable a more complete and holistic filing in response to the directives in the July 2018 Order, allow ISO-NE to address core consumer protection elements that are fundamental to state support, and remove barriers to achieving a greater degree of regional coalescence around a proposal." Several commenters supported the motion.

Ultimately, the Commission granted an extension of time up to and including April 15, 2020 for ISO-NE to file its long-term fuel security mechanism. While New England will soon be forced to address the issue of fuel security for its electric generating portfolio, these short-term and long-term market changes proposed by the grid operator are on hold for now.

Holyoke utility imposes moratorium on new gas service, citing pipeline constraints

The municipal utility serving the town that hosts the headquarters for the operator of the regional electric grid has informed its customers that the utility “is unable to accommodate new natural gas service requests due to the lack of natural gas availability in the region.” Holyoke Gas & Electric adds, “Recent proposals that would increase natural gas capacity in the region have been met with opposition, and the current pipeline constraints are causing significant adverse environmental and economic impacts on the region's ratepayers."

Holyoke Gas & Electric is a consumer-owned municipal utility established in 1902 through the purchase of a gas and electric plant from the Holyoke Water Power Company. According to the utility, the town saw ownership of a municipal utility "as a way to stabilize rates and keep local control over their energy services." As a municipal utility, Holyoke Gas & Electric is operated as a not-for-profit concern, and is owned by the community it serves. The utility cites public power advantages from this structure including operating in the local public interest, with local control over rates and services, local ownership, and reliance on local employees. In 1999, the utility acquired the Holyoke Dam, the city's canal system, and the remainder of the Holyoke Water Power Company's assets. The utility touts its ability to produce over 65% of its electricity needs from these renewable hydropower resources and cites "some of the lowest utility rates in New England."

Holyoke's Gas Division provides natural gas service through about 9,900 meters in Holyoke and Southampton. But on January 28, 2019, the utility gave its customers notice that it had placed a moratorium on most new natural gas service installations. According to that notice, the utility's natural gas customers are served by an interstate pipeline "which has become severely constrained due to a dramatic increase in demand over the last two decades," with "no corresponding increase in pipeline capacity to deliver additional supply to the region." As a result of significant growth in demand for natural gas by Holyoke's customers, HG&E said it is "forced to impose a moratorium on new natural gas connections until the capacity issue is addressed."

The utility further explained, "While inexpensive natural gas has never been more plentiful in the United States, there is insufficient pipeline capacity in our region to deliver additional load. Recent proposals that would increase natural gas capacity in the region have been met with opposition, and the current pipeline constraints are causing significant adverse environmental and economic impacts on the region's ratepayers." In its notice, the utility noted that due to the lack of natural gas during peak demand periods, "more electric generators are forced to switch to oil, while coal generators are called upon to operate, causing significant spikes in greenhouse gas emissions." Regional electric grid operator ISO New England, which is headquartered in Holyoke, reported that during a 15-day cold spell in January 2018, over two million barrels of oil were burned to generate electricity due to the lack of natural gas, more than the total amount of oil burned in 2017.

Beyond increased emissions, the utility also used ISO-NE data to show how "the lack of natural gas has a significant impact on energy costs throughout New England." Citing data from ISO-NE, the utility observed that during the two-week period from December 26, 2017 to January 8, 2018, electricity prices experienced an "approximately $700 million increase in energy costs for New England ratepayers compared to the prior year."

Holyoke Gas & Electric says it is working with gas utility Columbia Gas of Massachusetts to explore a solution involving system upgrades in other communities to "address local capacity issues, which will help reduce regional carbon emissions, improve reliability, and support local economic development." In the meantime, HG&E says its moratorium on new natural gas connections will remain in place "until the capacity issue is addressed."

ISO-NE files info on 2022-2023 capacity market auction

This week the operator of New England's wholesale electricity markets made a series of filings with its federal regulator providing information on its upcoming thirteenth forward capacity auction, through which electric generators may commit to providing electric capacity during the period from June 1, 2022 through May 31, 2023.

ISO New England Inc. is the independent system operator and wholesale market-maker for most of New England's electricity grid. It is a private, not-for-profit entity, which operates pursuant to a tariff on file with the Federal Energy Regulatory Commission. As part of its planning for system operations, ISO-NE operates a forward capacity market through which it conducts annual auctions through which qualified generators and other resources may bid to obtain commitments to provide capacity in a future year, in exchange for which resources will be compensated. The next primary auction for capacity supply obligations will be Forward Capacity Auction 13 (or FCA 13), which will be held beginning on February 4, 2019, and will cover the 2022-2023 capacity commitment period.

In advance of each primary auction, ISO-NE calculates an "Installed Capacity Requirement," which it defines as a measure of the installed resources that are projected to be necessary to meet reliability standards in light of total forecasted load requirements for the New England Control Area and to maintain sufficient reserve capacity to meet reliability standards. In computing the Installed Capacity Requirement, the grid operator considers parameters and assumptions including load forecast, resource capacity ratings, and resource availability. It also considers what relief can be obtained during a capacity deficiency through measures including emergency assistance (tie benefits) from neighboring interconnected regions (New Brunswick, New York, and Quebec), load reduction by reducing system voltage by 5%, and running the system at a minimal level of operating reserve.
 
In its November 6 Installed Capacity Requirement filing, the grid operator told the Commission that it proposed a installed capacity requirement for FCA 13 of 33,750 megawatts, after taking into account 969 megawatts of credits over interconnection with Canadian utility Hydro-Quebec.

In a parallel Informational Filing for qualification in FCA 13, the grid operator noted that 31,432 megawatts of existing generating capacity resources qualified for the 2022-2023 capacity commitment period, as did 80 megawatts of existing import capacity resources, and 3,413 megawatts of existing demand capacity resources, totaling 34,925 megawatts of existing capacity. Some resources submitted bids to retire, and 3,223 megawatts of resources submitted bids to withdraw in part or in whole from the auction if it clears below a defined price. Additionally, ISO-NE qualified 238 new capacity resources, totaling 8,716 megawatts.

ISO-NE will conduct its thirteenth forward capacity auction starting on February 4, 2019.

ISO-NE 2018 CELT projects future energy usage declines

The operator of New England's bulk electric grid projects that both energy usage and peak demand from the utility grid will decline slightly in the region over the 10-year period between 2018 and 2027, primarily due to the deployment of energy efficiency measures and behind-the-meter solar arrays.

ISO New England Inc. is the regional transmission organization responsible for the electric grid and electricity markets across most of New England. On April 30, 2018, ISO-NE published its 2018-2027 Forecast Report of Capacity, Energy, Loads, and Transmission, or CELT Report. The grid operator prepares annual CELT reports which describe the assumptions used in ISO system planning and reliability studies. These assumptions include the total generating capability of in-region resources, as well as a long-term forecast for growth in energy consumption and peak demand.

According to ISO-NE's 2018 CELT Report, overall regional electricity use will grow 0.9% annually over the 10-year period. But when energy efficiency and behind-the-meter generation are taken into account, ISO-NE's forecasts for both regional energy usage and peak demand project slight declines over the 10-year period. The grid operator projects an annual decrease in net energy usage by -0.9% annually, with seasonal peak demands projected to decline by -0.2% to 0.7% annually. ISO cites "continuing robust installation of energy-efficiency measures and behind-the-meter solar arrays throughout the region" as the primary factors driving this decline.