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Climate change mitigation requires developing zero-carbon, highly renewable energy systems, which require technologies to capture excess renewable electricity such as energy storage. Endeavoring to capture all available excess renewable electricity, however, may require large energy storage capacities and costs. This study therefore investigates how much curtailment is cost-optimal to allow in developing fully decarbonized electricity systems, using compliance with California's Senate Bill 100 goal as a representative case study. We combine electric grid dispatch modeling with an optimization approach for selecting the composition of energy storage technologies to capture excess renewable electricity to minimize overall system costs. We found that overbuilding cheap wind and solar and allowing the curtailment of excess renewable electricity equivalent to 25–43% of the total annual electric load resulted in the lowest cumulative systemwide cost for a fully decarbonized electricity system of about $1.8 trillion, spent between 2020 and 2045. Allowing no renewable curtailment results in significant battery requirements and a cumulative systemwide cost of $5.2 trillion spent between 2020 and 2045. Therefore, allowing some curtailment reduced the cost of building a fully decarbonized electricity system by a factor of 3 when the portfolio of technologies to capture and manage excess renewable electricity is carefully chosen. • Examined cost-minimal renewable curtailment levels for a zero-carbon grid. • Assessed cost-optimal technology mixes for harnessing excess renewable electricity. • Overbuilding renewable capacity is cheaper than vastly expanding energy storage. • Long duration storage is critical to minimize costs to build a zero-carbon grid. • Power-to-gas is well suited for long duration storage alongside batteries. [ABSTRACT FROM AUTHOR]

Highlights • Zero-emissions transportation fueling is the most cost-effective use of excess renewable energy. • Energy storage provides limited emission reduction benefits on already low-carbon grids. • Renewable gas production provides limited emissions reduction but significant cost benefits. • Load flexibility is critical for maximizing the cost-effectiveness of emissions reduction options. Abstract Preventing the curtailment of excess renewable generation, caused by mismatches between variable renewable electricity generation and the electric load, is a key strategy for maximizing greenhouse gas emissions reductions by integrating renewable resources into the electric grid. Strategies to harness excess renewable generation for useful purposes exist, but it is unclear which of these end uses provides the most effective use of available excess generation to maximize greenhouse gas emissions reductions in a cost-effective manner. This study investigates and compares three end-use strategies for utilizing excess renewable generation – storage in electrical energy storage systems, production of transportation fuel or vehicle charging, or production of renewable gas – and their diverse technology pathways on the bases of their greenhouse gas emissions reduction potential and the impacts of their implementation on the cost of energy services. This is accomplished by modeling the integration of 46 different technology pathways for using excess renewable generation in a 70% renewable and an 80% renewable electric grid configuration during the year 2050 in California using the Holistic Grid Resource Integration and Deployment (HiGRID) platform, which is a temporally-resolved resource dispatch model of the electricity system. Technology and cost characteristics for batteries, hydrogen energy storage systems, vehicle fueling or charging, and renewable gas production technologies are collected from multiple sources and their effect on reducing greenhouse gas emissions and affecting the Levelized Cost of Energy (LCOE) services in the HiGRID platform are examined. It was discovered that using excess renewable generation to produce transportation fuel for hydrogen vehicles or to charge electric vehicles provided the largest total greenhouse gas emissions reductions and lowest per-ton cost of greenhouse gas reduction. Use in grid energy storage and production of renewable gas provided similar but relatively lower total greenhouse gas reductions than transportation, with the latter imposing lower per-ton costs of greenhouse gas reduction. More generally, greenhouse gas reduction potential of these end uses depended on the intensity of the fuel being displaced by renewables, while LCOE effects depended on the temporal flexibility of the technologies associated with this end use. Overall, this study provides insight into a priority order for directing the use of excess renewable generation towards end uses to achieve greenhouse gas reduction goals such as those in California in a cost-minimal manner, and investigates the sensitivities that influence the effectiveness of these end uses. [ABSTRACT FROM AUTHOR]