New thermal energy storage technology uses sand as medium
By Mary Villareal // Sep 03, 2021

Energy storage is becoming a critical component of the economy. Renewable energy sources such as solar and wind power are changing how our buildings, industries and grids operate. However, they remain intermittent, and as such, energy storage remains critical.


To meet the energy storage problem, researchers at the National Renewable Energy Laboratory (NREL) are developing a game-changing thermal energy storage technology that uses inexpensive silica sand as a storage medium.

The technology is a reliable, cost-effective and scalable solution that can be deployed anywhere.

Called Economic Long-Duration Electricity Storage by Using Low-Cost Thermal Energy Storage and High-Efficiency Power Cycle (ENDURING), it uses electricity from surplus solar or wind to heat silica sand. Particles are fed through electric resistive heating elements to heat them to 1,200 degrees Celsius, and then gravity-feed them into insulated concrete silos for thermal energy storage.

This baseline system is designed to store up to 26,000 MWh of thermal energy. Its modular design and storage capacity can also be scaled up or down with ease.

When energy is needed, the hot particles are fed through a heat exchanger, which then heats and pressurizes a working gas inside to drive the machinery and spin the generators to create electricity for the grid. The system then discharges when there is limited solar photovoltaic or wind power available, such as in the early morning or evening. Once discharged, the spent particles of silica sand are once again fed into the insulated silos for storage until conditions are appropriate for charging.

This proposed storage technology can be deployed at $2 to $4 per kWh and can provide a continuous source of heat for industrial and chemical processes. The prototype heaters and heat exchangers for the system are also currently being tested.

Silica sand revolutionizes energy decarbonization

ENDURING systems have no siting constraints and can be situated anywhere in the country. It can also use existing infrastructures, for instance, from retired coal and gas-fired power plants. Its technology can support the expansion of renewable energy generation across the United States.

Building cost-effective particle thermal energy storage systems could help utilities continue using solar and wind power without running the risk of destabilizing the grid or curtailing the generation of renewable energy. Particle thermal energy storage provides energy reserves so that communities can better navigate through extended weather events, from week-long cold fronts to summer heatwaves.

Zhiwen Ma, the principal investigator of the ENDURING project, sees its important role in particle thermal energy storage. "While decarbonization of electricity has a clear path, decarbonization of the whole economy -- which includes things like building heat and industrial processes -- is more challenging because natural gas is very cheap, making it hard to displace." (Related: Soaring metal prices may delay ongoing transition to clean energy.)

Converting renewable energy into heat can help decarbonize industrial processes and Ma sees this as an opportunity for particle thermal energy storage to play a role in cost-effectively supplanting natural gas. By using a heat pump, one unit of electricity can be transformed into two to three units of heat that can be stored in the particle thermal energy storage system. It can then later be delivered to the end-user. The technology can be used to replace coal or natural gas.

ENDURING also offers a steady source of heat for industrial and chemical processes that are otherwise incompatible with solar and wind power. Economic environment, decarbonization goals, and technology have all aligned for particle thermal energy storage. Sand and concrete silos with refractory insulation are inexpensive and can lead to low-cost energy storage.

There is a lot of promise to ENDURING. Clean energy technology firm Babcock & Wilcox has an exclusive intellectual property option agreement to license its thermal energy storage technology and has contributed to the project.

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