Role of Long-Duration Energy Storage in Variable Renewable Electricity Systems

Reliable and affordable electricity systems based on variable energy sources, such as wind and solar may depend on the ability to store large quantities of low-cost energy over long timescales. Here, we use 39 years of hourly U.S. weather data, and a macro-scale energy model to evaluate capacities and dispatch in least cost, 100% reliable electricity systems with wind and solar generation supported by long-duration storage (LDS; 10 h or greater) and battery storage. We find that the introduction of LDS lowers total system costs relative to wind-solar-battery systems, and that system costs are twice as sensitive to reductions in LDS costs as to reductions in battery costs. In least-cost systems, batteries are used primarily for intra-day storage and LDS is used primarily for inter-season and multi-year storage. Moreover, dependence on LDS increases when the system is optimized over more years. LDS technologies could improve the affordability of renewable electricity.