The goal of this work was to perform a detailed, sub-hourly analysis of very high penetration scenarios for a single interconnection (the Western Interconnection). The scenarios analyzed for this study included a variety of generation infrastructure buildouts and power system operational assumptions, with three different portfolios of renewable generators. The High scenario had approximately 82% renewable generation after curtailment, which included 41% of its generation coming from variable generation (VG) sources like wind and solar photovoltaics (PV). The remaining renewable generation came from hydropower, geothermal, and concentrating solar power (CSP). The Higher Baseload scenario adds CSP and geothermal to the High scenario to make 88% renewable generation. This study also included a Higher VG scenario with added wind and solar PV generation to get to 86% renewable generation. Both Higher scenarios added the same amount of possible generation, but the Higher VG scenario showed more curtailment from the incremental generation, leading to lower penetration levels after curtailment. The primary conclusion of this study is that sub-hourly operation of the grid is possible with renewable generation levels between 80% and 90%. Dynamic studies will need to be done to understand any impacts on reliability during contingencies and transient events. 

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