Commercial Interest Grows for ARPA-E Award-Winning Thermal Energy Storage Technology Utilizing Sand

ARPA-E-Winning Thermal Energy Storage in Sand Attracts Commercial Interest
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In a recent development, a thermal energy storage technology utilizing sand has garnered significant commercial interest. Craig Turchi, manager of the Thermal Energy Science and Technologies Research Group at the National Renewable Energy Laboratory (NREL), stated, “Expanding the amount of energy that can be stored in sand is as simple as adding more sand.”

In 2018, a team from NREL was awarded $2.8 million through the ARPA-E DAYS ENDURING Project to advance long-duration thermal energy storage using sand. This innovative approach has now captured the attention of various industry stakeholders seeking potential applications.

Initially, the project aimed to leverage decommissioned coal plants in the U.S. to facilitate long-duration thermal energy storage. These thermal power plants possess valuable infrastructure that can be repurposed, including access to the grid for energy transmission, existing turbines and generators for converting stored heat back into power, and large coal silos that could store hot sand instead of coal.

Several industry partners, including the New York Power Authority and Homerun Resources—a silica materials company—are exploring the benefits of hot sand storage in conjunction with NREL’s innovation. Notably, Jiri Skopek, a leading green architect and smart city planner, is advocating for the integration of NREL’s Sand Thermal Energy Storage (TES) technology into district heating systems. He believes that utilizing thermal waste from nuclear plants for sand energy storage could enhance the flexibility of baseload power sources, especially as intermittent renewable energy sources are added to the grid.

### The Need for Long-Duration Storage

While batteries are effective for short-term energy storage, their costs escalate significantly when used for longer periods. This reality underscores the importance of developing economical solutions for storing energy over extended durations, a key focus of the ARPA-E DAYS ENDURING initiative.

Thermal energy storage is crucial for stabilizing the grid. Just as the construction of parking lots was essential for the interstate highway system, the increasing reliance on intermittent power sources necessitates locations to “park” surplus electricity. Zhiwen Ma, who leads the thermal energy storage research at NREL, highlighted the importance of this system by stating, “A lot of renewable energy just cannot go up to the grid… it’s just because, with congestion, the energy cannot be uploaded to the grid.”

### Why Sand?

Sand is an attractive medium for thermal energy storage due to its low cost and stability at high temperatures exceeding 1400°C without chemical degradation. Its abundance and non-toxic nature make it an accessible energy storage solution, which can be easily scaled for longer durations. Researchers are examining various types of sand, including silica, bauxite, and desert sands, for their thermal energy storage capabilities. In this process, sand can be heated using electricity during off-peak grid times and then utilized to generate electricity when demand spikes.

### Synergistic Benefits of Silica Calcining

Homerun Resources, based in British Columbia, has collaborated with the NREL team to develop a dual-use case for the thermal energy storage system which also purifies silica sand. The refined silica is utilized in various industries, including ceramics, glassmaking, and silicon chip production. Notably, the cyclical heating of silica sand can enhance its quality, turning it into a higher-value material critical for numerous industrial applications.

Brian Leeners, CEO of Homerun Resources, explained, “When we discovered the NREL system, we contacted Zhiwen with the idea that the thermal energy storage system represented a unique opportunity to integrate our HPQ silica, a high-purity silica sand, into the system for potentially purifying the silica while the system was cycling for energy storage.”

The calcination process requires heating at 1000 °C for ten hours, after which the silica can be cooled and transported. Research indicates that utilizing this silica sand for thermal energy storage could lower costs to under $10 per kWh.

### Competitive Advantages

The process of heating the silica is effectively free since the sand is heated for an additional purpose. However, consistent and predictable temperatures are often necessary for many industrial heat-driven processes. Leeners noted, “The primary market is storage, so the charge and discharge cycles will be variable… The key is that the silica gets held at the 1000°C level until it is calcined and ready for leaching.”

This flexibility allows the silica processing to adapt to any unexpected demands, potentially optimizing the entire process. NREL has been experimenting with various heating conditions to refine silica, supported by Homerun Resources, and has successfully demonstrated that the process is viable.

In conclusion, the integration of thermal energy storage in sand not only presents a sustainable energy solution but also opens avenues for the refinement of silica, creating a dual benefit for industries and the energy market alike.