Transmission planning for 100% clean electricity

This paper synthesizes a number of studies that investigate pathways to goals of up to 100% clean electricity to determine the implications for transmission needs and approaches. In particular, it examines the role of a macrogrid, or large-scale inter-regional transmission network, in enabling decarbonization at least cost, and the role of transmission infrastructure in maintaining a secure and reliable system over all timescales. The National Renewable Energy Laboratory's Interconnection Seams Study, Brown and Botterud (MIT study), Vibrant Clean Energy's ZeroByFifty Study, and the Midcontinent Independent System Operator's Renewable Integration Impact Assessment Study, among others, use different assumptions and datasets, employ different types of models, and have diverse goals, but all share some common findings regarding the need for significant transmission expansion. We also examine the competition and complementarity between transmission and other resources such as battery storage, long-duration storage (including hydrogen) and distributed energy resources. Finally, we discuss recommendations for national-scale transmission planning, based on lessons learned from these studies and previous efforts