Storage Futures Study: The Challenge of Defining Long-Duration Energy Storage

Paul Denholm, Wesley Cole, A. Frazier, Kara Podkaminer, Nate Blair

Research output: NRELTechnical Report


This document explores the definition of "long duration" as applied to energy storage. Given the growing use of this term, a uniform definition could aid in communication and consistency among various stakeholders. There is large and growing use of the ARPA-E definition of greater than 10 hours. However, the term "long-duration energy storage" is often used as shorthand for storage with sufficient duration to provide firm capacity and support grid resource adequacy. The actual duration needed for this application varies significantly from as little as a few hours to potentially multiple days. This leads to the unsatisfying conclusion that there cannot be a simple, uniform, and static definition of long duration storage that captures its ability to provide firm capacity and also aids consistent communication.
Original languageAmerican English
Number of pages23
StatePublished - 2021

NREL Publication Number

  • NREL/TP-6A40-80583


  • distributed storage
  • energy storage
  • long duration
  • U.S. power sector
  • utility-scale storage


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