Defining long duration energy storage

Abstract

Accelerating the deployment of variable renewable energy is changing the operational characteristics of the electric grid and creating an emerging need for storage technologies with extended energy-duration capabilities to maintain grid reliability. Extended or “long-duration” energy storage scales for supporting future grids are not well defined but can be anticipated to grow by estimating gaps in renewable performance of a decarbonized grid. Variable generation resources create a mismatch between electricity generation and use; as the amount of variable generation on the grid grows, so too do mismatches. This study reviews current uses of energy storage and how those uses are changing in response to emerging grid needs, then assesses how the power generation industry and academia are defining long-duration storage and organizing research efforts to develop commercial technologies. Using an illustrative example of a decarbonized grid, the study identifies the depth and breadth of future energy mismatches and concludes that two classes of long-duration energy storage will be needed in a decarbonized grid; one class lasting up to 20 h to manage daily cycles and one lasting for weeks or months to manage seasonal cycles. This study elucidates the necessity of long-duration energy storage in a decarbonized grid and may inform long-term planning processes. Grid planners can play an important role in the development of long-duration energy storage technologies through granular identification of storage needs that creates a market signal for investment in and development of the necessary technologies to provide a reliable and resilient grid for the future.