The Duration Addition to electricitY Storage (DAYS) program will pursue new long-duration electricity storage (LDES) technologies with discharge durations that range from 10 to approximately 100 hours at rated power. Such “long” durations are beyond the requirements for intra-day (“daily”) energy time shift and many other stationary electricity storage applications common on the grid today. ARPA-E believes durations at rated power of 10 to 100 hours are relevant for needs that go beyond daily cycling but are short of seasonal energy time-shift applications. Long-duration storage applications present new forms of technical challenges associated with exceptionally low lifetime cost requirements (including both capital and operating expenses), particularly for the energy storage media and related components. However, the lower number of cumulative cycles, acceptability of slow ramp rates, and other relaxed performance requirements that are associated with long durations and infrequent cycling provide opportunities for design tradeoffs that may be leveraged to reduce costs and realize economically-viable LDES systems.
The primary objective of the DAYS program is the development of LDES systems that deliver electricity at a levelized cost of storage (LCOS) of 5 cents/kWh-cycle across the full range of storage durations (i.e. 10 to approximately 100 hours). This requirement results in a target lifetime cost that decreases with increasing storage duration, a marked divergence from many existing storage cost targets that focus on a single duration and thus a single cost metric. The LCOS target of 5 cents/kWh-cycle likely requires system round-trip efficiencies greater than 50%.
For this focused program, ARPA-E expects chemical, electrochemical, thermal, and mechanical technical approaches to potentially address this problem statement. The DAYS program requires that all proposed storage systems be charged by electricity alone and produce electricity as the sole output.
If successful, the DAYS program will provide new forms of stationary electricity storage systems that enhance grid resiliency, provide low-cost capacity, support the transmission and distribution infrastructure, enable a greater share of low-cost, intermittent sources of wind and solar in the future generation mix, along with other benefits.
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