Transmission Planning

What is Electricity Transmission?

Electricity grids are comprised of two components:

A transmission system, which moves large amounts of electricity from power plants over high-voltage lines to major substations; and
A distribution system, which provides local, lower-voltage power from major substations to smaller residential and commercial consumers.

Many transmission lines cross state and national borders, allowing for regional grid interconnection. Most of Maine shares a regional electric grid with New England, which is made possible by a network of transmission lines connecting each of the states. The New England regional grid also facilitates the movement of electricity between Canada and the United States.

Transmission Planning Background

Transmission and distribution utilities conduct grid planning to forecast how much electric demand there will be, whether their current assets and equipment are sufficient to meet that need, and, if not, what investments will be required. Transmission planning has historically been conducted by transmission companies. The transmission system is regulated by the Federal Energy Regulatory Commission, and proposed transmission projects in New England are reviewed by ISO-New England which operates the grid on a daily basis. Distribution system planning is generally conducted by local utilities and regulated by state agencies such as the Maine Public Utilities Commission (PUC). In 2022, the Maine state legislature passed a law requiring utilities to undertake a new grid planning process that includes stakeholder input to identify priority areas for utilities to address in their plans. These grid plans must be filed with the PUC every five years.

In recent years, many states including Maine have recognized the need for enhanced grid planning to meet clean energy goals in an efficient manner. The Maine Energy Plan, published in January of 2025, underscores the need to implement responsible grid infrastructure investments to advance affordable, reliable, and cleaner energy for Maine. These investments will drive economic development and prepare for electric load growth while maximizing benefits to ratepayers. To that end, the Maine Governor's Energy Office (GEO) works in partnership with various state agencies, federal and local officials, industry, nonprofits, and research institutions to conduct regional transmission system planning.

Active Transmission Planning Initiatives

ISO New England Long Term Transmission Planning Initiative Phase I

ISO-New England has long identified Maine as having transmission system challenges, including congestion along the Maine-New Hampshire interface and in Northern Maine. In regions with FERC-approved independent system operators (ISOs), the ISOs do the bulk of transmission planning, and states participate primarily as observers only. Beginning in 2020, however, the six New England states released the New England States’ Energy Vision, a bipartisan effort to proactively address the region’s transmission needs. The result was a successful effort to amend ISO-New England’s traditional planning process to permit unique, proactive long-term transmission planning (LTTP) conducted cooperatively between the states and the grid operator.

The first exercise of this new planning process started when the states, through the New England States Committee on Electricity (NESCOE), asked ISO to identify transmission upgrades needed to meet state energy goals through 2050. This resulted in the ISO-New England 2050 Study which concluded that:

Congestion is identified as early as 2035 during both the summer and winter seasons, impacting system reliability and the export of new clean energy resources from Maine
The Maine-New Hampshire and North-South transmission interfaces are high likelihood concerns due to a variety of thermal overloads

ISO-New England 2050 Phase II Project RFP

As noted above, the ISO identified congestion in Maine as a regional priority. Maine and other states, working through NESCOE, requested ISO-NE to prepare an RFP for projects to resolve these constraints. GEO staff, in partnership with the Maine PUC, and working directly with neighboring states are actively involved with ISO-NE staff in reviewing and preparing the draft RFP. ISO-NE staff will conduct the initial review of project submissions later this year and then GEO, along with other New England energy offices will analyze ISO’s conclusions to determine if the project(s) meet state goals and policies.

In collaboration with the PUC, GEO will conduct a technical analysis of ISO’s recommended solutions, including consideration of potential utilization of existing ROWs, cost control mechanisms, and potential implementation of non-wires alternatives and advanced transmission technologies. These areas of focus will be particularly valuable as projects proposed in New England generally employ conventional technologies and advanced technologies have rarely been considered. Furthermore, there are documented cases of significant cost overruns on transmission projects in the past.

Maine GEO-U.S. DOE Advanced Conductors Study

This initiative is a Maine-focused collaboration between GEO and the U.S. Department of Energy (DOE) with support from Central Maine Power to support the deployment of Advanced Transmission Technologies (ATTs). ATTs include technologies such as line sensors and other devices that allow operators to significantly increase the amount of energy a power line can carry. While ATTs are common in Europe, Asia, and in some places in the U.S., they are not widely used in New England.

Transmission constraints in southern Maine has been a priority concern for the New England grid for many years. Many power lines in southern Maine are of an older steel technology and half are well past their useful life. To address these constraints, GEO sought funding from the U.S. DOE, and DOE, along with the National Renewable Energy Lab (NREL), have designed a study of selected lines in southern Maine that are known to be at risk. Based on work GEO staff are familiar with in other regions, it is likely that twice as much power could flow across these lines simply by reconductoring with lighter and stiffer composites that allow greater power flow. Results are expected in 2025.

Regional Coordination Activities

State Modern Grid Deployment Initiative

In 2024, Maine joined 20 other states to form the State Modern Grid Deployment Initiative. The initiative aims to bring together states and power sector stakeholders to help drive grid adaptation quickly and cost-effectively to meet the challenges and opportunities that the power sector faces in the twenty-first century. The states have committed to prioritizing efforts that support the adoption of modern solutions to expand grid capacity and build modern grid capabilities on both new and existing transmission and distribution lines.

Northeast States Collaborative on Interregional Transmission

In 2023, a group of Northeast states led a request to the U.S. Department of Energy (DOE) to convene and support a multi-state initiative, the Northeast States Collaborative on Interregional Transmission, in a first-in-the-nation effort to explore mutually beneficial opportunities to increase the flow of electricity between three different planning regions in the Northeast and assess offshore wind infrastructure needs and solutions.

In 2024, GEO announced that Maine has joined a total of 10 Northeast states in signing a memorandum of understanding (MOU) for improved regional planning of electricity transmission to create a stronger, more reliable, and more efficient grid and accelerate the clean energy transition. Other states joining the MOU include Connecticut, Delaware, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island, and Vermont. Through this MOU, the Collaborative sets forth its agreement to work together on interregional transmission infrastructure and establishes mechanisms for sharing information. More information about the Collaborative and the MOU is available here.

Regional & National Transmission Studies

North-South Interface Transfer Capacity Pilot Project: The ISO-New England 2050 Study identified the congested south-central Maine transmission system as a major source of concern in meeting regional clean energy goals. This area of congestion, known as the North-South Interface, will need to be upgraded significantly to unlock onshore and offshore wind energy to meet projected system requirements in the coming years. GEO has coordinated with the U.S. DOE’s Grid Deployment Office and will be working together to identify cost-effective ways to maximize transfer capacity of existing grid resources.
U.S. Department of Energy Studies: The U.S. DOE requested that states support several major transmission studies which have already been completed, including the Atlantic Offshore Wind Transmission Study, West Coast Offshore Wind Study, and the National Transmission Planning Study. GEO staff supported this work via DOE’s Technical Review Committee and Advisory Committee and engaged in numerous technical meetings and webinars.

Questions?

If you have questions about GEO’s work on transmission, please email geo@maine.gov.