Economic Long-Duration Electricity Storage by Using Low-Cost Thermal Energy Storage and High-Efficiency Power Cycle

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Golden, Colorado
Project Term:
04/16/2019 - 09/30/2022

Critical Need:

Stationary electrical energy storage plays several important roles in the U.S. electricity system, and these are expected to grow as the grid continues to evolve. Long-duration energy storage systems address grid needs beyond those covered by daily cycling. Such systems could provide backup power for several days, improving grid resiliency, or allow for the integration of even larger amounts of intermittent renewable sources like wind and solar. In the near term, such systems could help shape the output from individual wind and solar installations, improving the reliability of these resources and thus greatly increasing their value to the grid.

Project Innovation + Advantages:

The National Renewable Energy Laboratory team will develop a high-temperature, low-cost thermal energy storage system using a high-performance heat exchanger and Brayton combined-cycle turbine to generate power. Electric heaters will heat stable, inexpensive solid particles to temperatures greater than 1100°C (2012°F) during charging, which can be stored in insulated silos for several days. To discharge the system, the hot particles will be fed through the fluidized bed heat exchanger, heating a working fluid to drive the gas turbine attached to a generator. The electricity storage system is designed to be deployed economically anywhere in the United States.

Potential Impact:

If successful, DAYS projects will provide new forms of long-duration stationary electricity storage systems that enhance grid resiliency, provide low-cost energy capacity, support grid infrastructure, and enable a greater share of intermittent renewable resources in the generation mix.


Long-duration storage can help prevent blackouts and smooth overall grid operation, improving resilience and enhancing grid security.


New, extended storage options could enable greater integration of intermittent renewable energy sources, greatly reducing emissions from the power sector.


Energy storage technologies could help improve grid efficiency and promote the growth of domestic renewable energy sources.


ARPA-E Program Director:
Dr. Halle Cheeseman
Project Contact:
Dr. Zhiwen Ma
Press and General Inquiries Email:
Project Contact Email:


Colorado School of Mines

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