This month, the Department of Energy (DOE) released its National Transmission Planning (NTP) study), a much-anticipated follow-up to its 2023 National Transmission Needs study. While the 2023 study primarily identified transmission needs through the year 2040 using already existing data, the NTP Study takes a more comprehensive approach, introducing new models to forecast longer-term transmission growth under 96 unique scenarios. This solution-focused report emphasizes the cornerstones of reliability and “least cost planning” principles, as stated by the DOE. The study concludes that, regardless of climate policy, anticipated load growth will require additional transmission capacity to ensure the future reliability of the U.S. power grid.
Reliability and cost-benefit-ratio highlights
The study examines potential grid expansion under both conservative and aggressive decarbonization scenarios. Even when factoring in existing decarbonization policies, it is evident that the U.S. transmission system requires significant upgrades to meet projected demand at affordable costs.
The NTP study specifically indicates that, under current policies, the transmission system will need to at least double in size by 2050 to accommodate power demand. If policies achieve a 90 percent reduction in power-sector greenhouse gasses by 2035 (with full decarbonization by 2050), transmission capacity requirements could expand up to three and a half times the current system size. Notably, grid expansion in this clean-energy scenario is projected to yield up to $1.80 in savings for every dollar invested, by enabling access to affordable and readily transferable energy. Crucially, the study concludes that under all tested grid expansion scenarios, electricity supply remained reliable, even with very high levels of renewable energy integration.
High opportunity transmission identified
Three long-term planning scenarios were evaluated against the “limited” transmission baseline case to determine potential buildout pathways. The first scenario allowed for alternating current lines within interconnections, the second scenario permitted interconnectivity to be achieved across the interconnections with HVDC point-to-point transmission, and the third builds on this principle by also allowing multiterminal HVDC lines to be integrated into the system.
All three scenarios identified what the DOE refers to as “high opportunity transmission (HOT) interfaces,” which represent suggested new transmission routes that appear in at least 75 percent of the sensitivity tests conducted under the high renewable energy penetration scenario (See Figure ES-11 in NTP study Executive Summary). Modeling results indicate that much of the needed transfer capacity is concentrated in the Midwestern and Southern regions of the U.S. The Niskanen Center’s analysis confirms that these regions currently have minimal transfer capacity, increasing the risk of power outages for customers in these areas. Despite this, the Americans for a Clean Energy Grid’s 2023 Transmission Projects Ready To Go report reveals that only one of the ten high-voltage transmission projects that have started construction in the contiguous U.S. since 2021 is located in the Midwest, with none in the Southeast region.
The case for interregional transmission
Calls to increase regional and interregional electricity transfer capacity are central to many transmission studies. The DOE’s Transmission Impact Analysis, released alongside the NTP Study, highlights that “deficiencies in planning, siting, and cost allocation processes have hampered the buildout of otherwise valuable infrastructure.” A recent Niskanen Center report addresses the challenges posed by our current permitting frameworks, which tend to “favor incremental transmission expansion at the expense of building grid-beneficial large projects.” Legislation such as the BIG WIRES Act aims to enhance interregional transfer capacity to improve overall system reliability, and the newly-introduced Energy Permitting Reform Act proposes improvements to the siting and permitting processes for power lines. However, entrenched compartmentalized planning structures continue to obstruct meaningful interregional transmission development across the U.S. power grid.
The new NTP study highlights this reality. While the extensive data produced by the DOE is undoubtedly valuable, the study authors emphasize that data availability is not the only hurdle in planning the future grid. To realize the reliability and cost benefits highlighted in the report, the existing patchwork of planning processes must be reformed.