The challenges of achieving a 100% renewable electricity system in the United States

Summary Understanding the technical and economic challenges of achieving 100% renewable energy (RE) electric power systems is critical, given the increasing number of United States regional and state commitments toward this goal. Although no detailed study of a major utility of large interconnection under 100% RE system has been published, considerable literature explores the potential to greatly increase RE penetration. This literature, combined with real-world experience with increased RE deployment, points to two main challenges associated with achieving 100% RE across all timescales: (1) economically maintaining a balance of supply and demand and (2) designing technically reliable grids using largely inverter-based resources. The first challenge results in a highly nonlinear increase in costs as the system approaches 100% RE, in large part because of seasonal mismatches. The second challenge might require new inverter designs, depending on the mix of RE technologies. Analysis and experience to date point to no fundamental technical reasons why a 100% RE electric power system cannot be achieved, but the economic challenges indicate the need for advancements in several technologies and careful consideration of the suite of options that could be used to achieve equivalent carbon-reduction goals. Previous work also points to the need for analytic tool development, and techno-economic feasibility analysis must also consider the host of regulatory, market, and policy issues that might limit the ability to deploy mixes of resources that are suggested by least-cost modeling exercises.