Variable, low-cost, low-carbon electricity that would otherwise be curtailed may provide a substantial economic opportunity for entities that can flexibly adapt their electricity consumption. We used historical hourly weather data over the contiguous U.S. to model the characteristics of least-cost electricity systems dominated by variable renewable generation that powered firm and flexible electricity demands (loads). Scenarios evaluated included variable wind and solar power, battery storage,

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... nd dispatchable natural gas with carbon capture and storage, with electrolytic hydrogen representing a prototypical flexible load. When flexible loads were small, excess generation capacity was available during most hours, allowing flexible loads to operate at high capacity factors. Expanding the flexible loads allowed the least-cost systems to more fully utilize the generation capacity built to supply firm loads, and thus reduced the average cost of delivered electricity. The macro-scale energy model indicated that variable renewable electricity systems optimized to supply firm loads at current costs could supply ∼25% or more additional flexible load with minimal capacity expansion, while resulting in reduced average electricity costs ( ∼10% or less capacity expansion and ∼10% to 20% reduction in costs in our modeled scenarios). These results indicate that adding flexible loads to electricity systems will likely allow more full utilization of generation assets across a wide range of system architectures, thus providing new energy services with infrastructure that is already needed to supply firm electricity loads. (T.H. Ruggles). supplied by wind and solar generation [11] [12] [13] . Long-duration energy storage technologies, such as power-to-gas-to-power (PGP), pumped hydropower, and compressed air energy storage, are also being explored to provide flexibility by storing excess produced energy for use during later weeks, months, or years [14] [15] [16] . Flexible electricity loads, such as smart home appliances, can alter their operations within constraints to respond to signals from electricity systems [17] . Demand response programs, which can coordinate flexible loads within an electricity system, have been studied and deployed in industrial [18] , commercial [19] , and residential [17, 20] applications. Flexible loads can also be added to electricity systems by electrifying other energy end uses, such as transportation or space heating [21] [22] [23] . Cross-sector couplings through power-to-gas (PtG) technologies can produce fuel (usually hydrogen or methane) for non-grid uses [24] [25] [26] . The economics of wind-powered electrolysis has been assessed for facilities connected to the electric grid [27, 28] . These studies have analyzed system configurations and operations that produced least-cost electrolytic hydrogen, with a decision made at every time step regarding whether the generated wind power should be used for electrolysis or sold to the electric grid.