This paper presents high renewable electricity penetration scenarios in the United States using detailed capacity expansion modeling that is designed to properly account for the variability and uncertainty of wind and solar resources. The scenarios focus solely on the electricity system, an important sector within the larger energy sector, and demonstrate long-term visions of a U.S. power system where renewable technologies, including biomass, geothermal, hydropower, solar, and wind, contribute 80% of 2050 annual electricity, including 49-55% from wind and solar photovoltaic generation. We present the integration challenges of achieving this high penetration and characterize the options to increase grid flexibility to manage variability. Four high renewable pathways are modeled and demonstrate the robustness and diversity of renewable options. We estimate 69-82% annual greenhouse gas emission reductions and 3%-30% incremental electricity price increases associated with reaching 80%-by-2050 renewable electricity relative to reference scenarios. This paper affirms and strengthens similar analysis from the Renewable Electricity Futures study by using an improved model and updated data to better reflect investment and dispatch decisions under current outlooks for the U.S. electricity sector. (C) 2013 Elsevier Ltd. All rights reserved.