The cost and performance of wind and solar technologies have been changing rapidly in recent years, but uncertainty about future progress creates questions about the extent of renewables deployment moving forward. This analysis compares projections of wind and solar costs across published studies and then uses EPRI’s U.S. Economy, Greenhouse Gas, and Energy (REGEN) model to evaluate how technological change for renewables and energy storage could translate into electric sector planning decisions and costs, especially as deep decarbonization targets are pursued. The analysis indicates that wind and solar costs from different organizations span a wide range both for current estimates, driven by differences in technology, location, plant size, and financing assumptions, and for future projections, which vary in scenario assumptions and approach. Results using REGEN indicate that assumptions about policy targets, policy timeframes, and technological costs alter electric sector planning—including renewables deployment—and costs. Renewables are the largest generation resource for many scenarios and regions, but shares depend on policy and technology assumptions.