Long-Duration Electricity Storage Applications, Economics, and Technologies

The United States electricity grid is undergoing rapid changes in response to the sustained low price of natural gas, the falling cost of electricity from variable renewable resources (which are increasingly being paired with Li-ion storage with durations up to ∼4 h at rated power), and state and local decarbonization policies. Although the majority of recent electricity storage system installations have a duration at rated power of up to ∼4 h, several trends and potential applications are identified that require electricity storage with longer durations of 10 to ∼100 h. Such a duration range lies between daily needs that can be satisfied with technologies with the cost structure of lithium-ion batteries and seasonal storage utilizing chemical storage in underground reservoirs. The economics of long-duration storage applications are considered, including contributions for both energy time shift and capacity payments and are shown to differ from the cost structure of applications well served by lithium-ion batteries. In particular, the capital cost for the energy subsystem must be substantially reduced to ∼3 $/kWh (for a duration of ∼100 h), ∼7 $/kWh (for a duration of ∼50 h), or ∼40 $/kWh (for a duration of ∼10 h) on a fully installed basis. Recent developments in major technology classes that may approach the targets of the long-duration electricity storage (LDES) cost framework, including electrochemical, thermal, and mechanical, are briefly reviewed. This perspective, which illustrates the importance of low-cost and high-energy-density storage media, motivates new concepts and approaches for how LDES systems could be economical and provide value to the electricity grid.