Transmission Transition: modernizing U.S. transmission planning to support decarbonization Alisha Kasam-Griffith 1* , Natasha S. Turkmani 2 , Martin J. Wolf 3 , Nina C. Peluso 4 , and Tomas W. Green 5 Edited by Ruaridh Macdonald and Anthony Tabet HIGHLIGHTS • The aging U.S. electrical grid requires major expansion and upgrades to ensure energy access and support decarbonization trends • Collaboration across regions and types of stakeholders can increase the likelihood of successful modernization of the U.S. energy grid • Federal policy changes may increase adoption of non-transmission alternatives, which can defer or replace the need for new transmission infrastructure Decarbonization and degrading infrastructure present twin challenges to the aging U.S. electrical grid, which is vital to the economy, national security, and public well-being. This article addresses challenges around transmission planning processes and policy options to improve these. Specifically, long-term regional transmission planning is hindered by conflicts over the equitable distribution of costs incurred and the benefits achieved by new development, as well as siting and permitting challenges. Policy changes that require comprehensive estimation of benefits and joint trans-regional evaluation can promote projects that fulfill grid requirements effectively and economically. In addition, increased regulatory direction and consideration for non-transmission alternatives (NTAs) and related distribution technologies could defer or replace the need for new transmission. T he U.S. Energy Transition is already underway, with considerable progress in decarbonizing the electricity sector. Long-term success hinges on the ability of the transmission system to accommodate changes in how 1 Department of Engineering, University of Cambridge, Cambridge, UK 2 Charles River Associates, Washington, DC 3 Yale Center for Environmental Law and Policy, Yale Law School and Yale School of the Environment, New Haven, CT 4 Institute for Data, Systems, and Society, Massachusetts Institute of Technology, Cambridge, MA 5 Center for Energy and Environmental Policy Research, Massachusetts Institute of Technology, Cambridge, MA * Email: aakasam@gmail.com The authors declare no conflict of interest. © 2020 The Author(s) electricity is generated and consumed. With remote renewable generation added to the grid, long-distance transmission infrastructure will be required to transport this clean energy to distribution centers. Difficulties in forecasting variable renewable generation, coupled with the shrinking output from stable fossil fuel generators, will also require modern transmission technology to ensure that supply and demand remain instantaneously balanced. Electrification of heating, transportation, and industrial processes support the shift to a low-carbon economy, but often require that transmission and distribution lines support peak loads beyond their nominal capacity. In addition to supporting the nation’s decarbonization goals, transmission lines present their own security challenges, as the majority of lines are operating decades beyond their original life expectancy; threats include blackouts, wildfire risk, and vulnerability of the grid to cyberattack [1]. Major investments and upgrades are therefore needed to update the nation’s transmission infrastructure, which is critical to preserving national security, economic and technological competitiveness, and energy affordability [2]. This article briefly summarizes the landscape for electric sector organization before addressing the regulatory and socio-economic challenges in transmission planning. Regulation of the Electrical Grid The electrical grid is primarily organized in a top-down manner to transport electricity from generators to users. Transmission lines convey high-voltage electricity from numerous generators, such as power plants and solar farms, to substations. Substations transform electricity to a safer, lower voltage and transfer it to the distribution network for delivery to local customers, who include factories, hospitals, and homeowners. In the continental U.S., the grid consists of multi-state transmission networks, which require planning at the regional level to determine necessary upgrades. Approximately 60% of electrical supply is administered by regional transmission organizations (RTOs), which control the electrical grid and coordinate the expansion of transmission infrastructure, such as cross-border interconnections that deliver hydropower from Canada to homes in Maryland. The remaining 40% is managed by regulated utilities, which are typically responsible for the upkeep of local distribution and transmission lines [3]. MIT Science Policy Review | December 21, 2020 | vol. 1 | pg. 87