Improving and expanding electric transmission infrastructure in the U.S. is critical to ensuring consumers across the country have access to reliable, affordable power when and where they need it and to enable us to integrate new, clean sources of energy generation into the grid. To understand the transformation needed to ensure the U.S. electric transmission system continues to reliably serve the nation’s electricity customers as the power sector evolves and transitions to cleaner resources, the U.S. Department of Energy's Grid Deployment Office led the multiyear National Transmission Planning Study (NTP Study) in partnership with the National Renewable Energy Laboratory (NREL) and the Pacific Northwest National Laboratory (PNNL).
Full Report
Each chapter of the final report for the National Transmission Planning Study is available to download as a separate PDF.
- Executive Summary describes the high-level findings from across all six chapters and next steps for how to build on the analysis.
- Chapter 1: Introduction provides background and context about the technical design of the study and modeling framework, introduces the scenario framework, and acknowledges those who contributed to the study.
- Chapter 2: Long-Term U.S. Transmission Planning Scenarios discusses the methods for capacity expansion and resource adequacy, key findings from the scenario analysis and economic analysis, and High Opportunity Transmission interface analysis.
- Chapter 3: Transmission Portfolios and Operations for 2035 Scenarios summarizes the methods for translating zonal scenarios to nodal-network-level models, network transmission plans for a subset of the scenarios, and key findings from transmission planning and production cost modeling for the contiguous United States.
- Chapter 4: AC Power Flow Analysis for 2035 Scenarios identifies the methods for translating from zonal and nodal production cost models to alternating current (AC) power flow models and describes contingency analysis for a subset of scenarios.
- Chapter 5: Stress Analysis for 2035 Scenarios outlines how the future transmission expansions perform under stress tests.
- Chapter 6: Conclusions describes the high-level findings and study limitations across the six chapters.
Available Tools
The NTP Study led to the utilization, expansion, and creation of new and existing national transmission planning tools. Transmission planners in the U.S. can leverage these tools to support their planning processes.
Publicly available tools include:
- Sienna Modeling Framework – new capabilities developed through the NTP Study
- NREL’s open-source Sienna modeling framework includes a range of capabilities that allow efficient and reproducible data management, programmatic access, and efficient storage and access to support large-scale modeling, validation, and change management.
- For the NTP Study, Sienna was used as the production cost modeling (PCM) tool for transmission planning and operational analysis for future scenarios.
- The NTP study created the largest representation of a power system ever simulated. To execute NTP simulations, Sienna had to create new capabilities for power system data management and assembly, large scale power flow calculations, network analysis, and massive scale grid scheduling simulations (PCM).
- Regional Energy Deployment System (ReEDS) Model - new capabilities developed through the NTP Study
- NREL’s ReEDS is an open-source capacity expansion model for the contiguous U.S. electricity system that has been used in several transmission, grid integration, and policy and scenarios studies over the last several years.
- Thanks to the NTP Study, ReEDS now offers newer capabilities, including transmission modeling, hydrogen modeling, more granular temporal resolution for models, and integration of resource adequacy models.
- Probabilistic Resource Adequacy Suite (PRAS) - new capabilities developed through the NTP Study
- NREL’s PRAS is an open-source software package for studying power system resource adequacy.
- Under the NTP Study, the tool was integrated with the Regional Energy Deployment System (ReEDS) Model.
- GridSight - new tool developed
- NREL made this tool available as open-source software.
- GridSight can help disseminate results, visualize and interpret large-scale and data-intensive results, and aid transmission expansion planning.
Tools available upon request of a free research license include:
- Chronological AC Power Flow Automated Generation Tool (C-PAGE)
- This PNNL tool extracts the time series system dispatch data from a production cost simulation data to create power flow cases that could be run at specific snapshots in time throughout the year.
- Intelligent sampling
- PNNL’s intelligent sampling technique results in a small number of hourly cases for a given year that are statistically representative of the whole year.
National Transmission Planning Study Companion Reports
Frequently Asked Questions
What is the National Transmission Planning Study?
To understand the transformation needed for the U.S. grid and how that future buildout might serve the nation’s electric customers, the U.S. Department of Energy (DOE) Grid Deployment Office (GDO) partnered with the National Renewable Energy Laboratory (NREL) and the Pacific Northwest National Laboratory (PNNL) on the multiyear National Transmission Planning Study (NTP Study). The study sought to:
- develop new national grid-scale planning tools and methods that can be used by industry, especially when planning for interregional transmission capacity needs;
- identify potential transmission solutions that will provide broad-scale benefits to electric customers under a wide range of potential futures;
- inform planning processes for regional and interregional transmission; and
- identify interregional and national strategies to maintain grid reliability as the grid transitions, including to a reliance on low- and zero-carbon energy resources.
The NTP Study results are not intended to replace regional or interregional planning processes or develop plans of service. This study will provide insights for multiple stakeholders about the role that transmission can play in meeting the nation’s electricity needs in the future and provide tools and analysis that can be used in transmission planning processes, while in particular highlighting potential uses of interregional transmission to reduce system cost and improve reliability and resilience as the grid evolves.
What the study does What the study Does not Do Link several long-term and short-term power system models to test multiple transmission buildout scenarios Replace existing regional and utility planning processes Develop and use innovative analytical approaches to evaluate resource adequacy, reliability, economics, and resilience to extreme events Recommend specific locations or approvals for individual transmission lines or address detailed environmental or other land use issues that may be associated with future transmission lines Provide information that can be used in existing planning processes by evaluating the impact to transmission of various scenarios Evaluate specific transmission policies or proposed legislation Test transmission options that may not be considered in current planning processes within utilities or regional planning organizations Develop detailed plans of service or provide results that are as granular as planning done by utilities Assess a range of economic, reliability, and resilience indicators for each transmission scenario considered Evaluate existing proposed transmission projects Provide companion reports describing opportunities and challenges to realizing potential transmission benefits identified by the study Provide a roadmap for developing specific projects What is the purpose of the National Transmission Planning Study?
This study aims to understand the transformation needed to ensure the U.S. electric transmission system continues to reliably serve the nation’s electricity customers as the power sector evolves and transitions to cleaner resources. This study differs from other recent national-level transmission planning studies in that it integrates a comprehensive range of models in its analysis, including both long- and short-time horizons as well as both zonal and nodal spatial granularity. The study also differs in that robust public engagement was foundational to the analysis.
A lot of transmission planning today focuses on near-term needs within a region and individual utility service territories. DOE believes that broader joint transmission planning between regions over a longer time horizon can unlock tremendous value for consumers both locally and nationally. DOE and the National Labs will work closely with planners, other regional stakeholders, and Tribes, so that the NTP Study’s national results can readily inform interregional dialogue and the exploration of new value propositions. The NTP Study won’t replace current planning, but it will test additional transmission options that lie outside current planning. It will also develop and maintain tools that industry planners can use to advance their examination of beneficial interregional transmission options.
How did the NTP Study conduct stakeholder engagement?
The NTP Study’s external engagement efforts leveraged the expertise of a broad set of power system experts and interested parties around the country and provided opportunities for the NTP Study team to receive input on study assumptions, methods, and objectives. External engagement included the following four components:
- Public engagement through public meetings and an online comment form.
- Engagement with existing convener groups such as the Eastern Interconnection Planning Collaborative and Western Electricity Coordinating Council (WECC).
- A laboratory-led Technical Review Committee (TRC) inclusive of three subcommittees: a Modeling Subcommittee, a Government Subcommittee, and an Environmental Exclusion and Land Use Subcommittee.
- Tribal outreach that included broad outreach to Tribes in the United States with assistance from DOE’s Office of Indian Energy and targeted follow-up with interested Tribes.
During the project, DOE conducted three virtual public meetings, and the laboratory team conducted 18 virtual meetings with various subsets of the TRC which included presenting interim results and gathering stakeholder input. More details on these meetings are in Chapter 1. Additionally, TRC members individually provided input about scope and assumptions, shared modeling details about their regions, and helped clarify messaging regarding modeling results to be relevant for industry.
How long did it take to complete the NTP Study? Will there be another one?
The study took roughly 2.5 years to complete. It kicked off with the first public webinar on March 15, 2022, and was published on October 3, 2024. GDO will be focusing on sharing the findings of the NTPS and applying them in regions across the US, before a decision to conduct a second National Transmission Planning Study will be made.
Is it reasonable to expect new transmission lines recommended by the NTP Study be built?
The NTP Study does not make any specific recommendations for transmission line or substation upgrades. Rather, the study identifies certain areas where the researchers believe new interregional transmission lines should be considered because they would provide benefits to consumers under a broad range of future scenarios. These results are meant to help RTOs, ISOs, and utilities achieve transmission development to support a more reliable, affordable, and clean energy system. DOE hopes that by conducting modeling with input data and assumptions that have been discussed with planners, regulators, other key stakeholders, and Tribes, the results and recommendations of the NTP Study will facilitate the building of new transmission that makes the future power grid more economical, reliable, resilient, and net carbon-free.
How was the NTP Study conducted?
The two key principles behind the study design are least-cost planning (i.e., planning for the lowest system cost portfolio from a broad array of options) and power system reliability (i.e., the ability of the power system to continually supply electricity). These principles are applied to a broad range of future power sector scenarios.
The U.S. transmission system has a variety of technical challenges, many unique to each of the thousands of involved utilities, plus expansive geography with regional diversity in resources and planning outlooks. The transmission system is large and complex enough that modeling the true physics of the system at a fine level of detail over time pushes the limits of current computational capacity. To capture this complexity, the study team used several interlinked models—including translating results from zonal models down to nodal resolution—to enable expansive insights about the future of the U.S. electricity system with the level of detail needed for rigorous transmission planning (Figure ES-1).
What is the Study’s geographic scope?
The geographic scope of the study is the contiguous United States (CONUS), and did not include Alaska, Hawaii, U.S. Territories, or neighboring interconnected countries (Canada and Mexico).
What kinds of scenarios were modeled and why? What kind of factors or assumptions were considered in NTP Study scenarios?
Because the role and impact of transmission can vary based on many factors, the study team examined a wide range of demand growth and emissions reduction scenarios across the four transmission frameworks. Altogether, the study team analyzed 96 scenarios and sensitivities. The study includes current policy scenarios—which include state and federal policies enacted by June 2023, excluding the final Clean Air Act section 111 standards—to examine how transmission development might impact future emissions. The study also includes scenarios with a limit on national annual emissions to achieve 90% power sector CO2 emissions reductions (from 2005 levels) by 2035 and full grid decarbonization by 2045. 15 sensitivities were run on these 90% decarbonization scenarios across each of the four transmission frameworks The sensitivity analysis compared how the optimal electricity system—including generation, storage, and transmission—might evolve with different cost and availability constraints of technologies (e.g. high or low electrolyzer cost, high or low carbon transport and storage costs, availability of carbon capture and sequestration, availability of hydrogen combustion turbines, availability of small modular reactors, etc.) The study team made no judgment about the relative likelihood of different scenarios or assumptions; instead, the scenarios are used to evaluate the role of transmission under a wide range of possible future conditions.
What energy resources were analyzed as part of the study?
The NTP Study recognizes that transmission investments are a complementary investment to distributed energy resources and identifies optimal pathways to leverage geographic diversity to minimize costs and ensure reliability. Clean energy resources included in the NTP Study are wind, solar, distributed generation, fossil fuel plants with carbon capture and sequestration capabilities, extension of the existing nuclear fleet, new small modular nuclear reactors, storage, and new clean firm resources such as hydrogen gas powered turbine generators. The NTP Study modeled existing generation fleets as well.
What role does distributed energy resources play in the NTP Study?
Achieving the goal of a decarbonized electric system will require increased flexibility at all levels of the grid – generation, transmission, and distribution. Distributed energy resources (DER) will be part of the future energy mix and there are many benefits to increasing their deployment. Utility-scale generation resources that require transmission for delivery will still be needed, however, to capture their economies of scale and ensure reliable service to customers who do not have the ability to deploy distributed generation to meet their needs.
Furthermore, regional coordination through a robust transmission system will ensure reliable electricity even when drought, cloudy skies, or a lack of wind limits local production. The NTP study recognizes that transmission investments are a complementary investment to distributed energy resources and identified optimal pathways to leverage geographic diversity to minimize costs and ensure reliability.
How were siting and land use factored into the scenario analysis?
The underlying data in the Regional Energy Deployment System (ReEDS) model used in the scenario analysis of this study takes into account siting and land use factors in the cost assumptions and potential capacity amounts for building new transmission lines and generators. Transmission cost estimates account for terrain, land type, and other siting factors included in the NREL Renewable Energy Potential (reV) model. The technical resource potential for wind and solar is affected by the available land that could be developed. Land availability is estimated by considering siting suitability and spatial exclusions from other uses. These siting considerations include terrain (e.g., slope, elevation), airspace and defense (e.g., airports, radar), environmental factors (e.g., endangered species habitat, wetlands, national parks and conservation areas), and siting regulations (e.g., setbacks from existing structures, roads, railroads, transmission lines, and pipelines).
Additionally, the Technical Review Committee had a Land-Use and Environmental Exclusion subcommittee which provided general information on issues affecting the location of transmission and power generators. They reviewed model input as well as high-level results from the NTPS models to better assess the overall feasibility of solutions.
However, the scope of the study has been limited in order to avoid recommendations on specific locations or approvals for individual transmission lines or address detailed environmental or other land use issues that may be associated with future transmission lines.
How is the study incorporating resilience analysis? How is the study analyzing system reliability and does this take into account extreme weather?
The resilience analysis focused on extreme weather events, specifically in the Western Interconnection (e.g. heat and cold waves), and can be found in Chapter 5 of the report. The events were characterized using the best available atmospheric science research to explore future heat/cold events under a changing climate. The study team performed zonal resource adequacy analysis and nodal production cost modeling analysis for the weather events over a period of the event (approximately one week).
How is the NTP Study different from the National Transmission Needs Study?
The Needs Study is published every 3 years and is an assessment of near-term transmission needs (through 2040) using existing power sector data and reports from a wide variety of sources. No new modeling was performed to complete the Needs Study and it does not identify specific solutions for assessed transmission needs. Rather, the Needs Study is an assessment of published studies and data from other publicly available sources.
The National Transmission Planning (NTP) Study, by contrast, utilizes new modeling and analysis that has identified both near- and long-term (through 2050) transmission needs as well as potential transmission solutions. The NTP Study utilizes both national laboratory and industry tools to conduct new modeling and analysis to quantify the transmission needed nation-wide under a wide array of different potential future scenarios of clean energy and demand growth.
Resources
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