TerraCaps provide a novel method of encapsulating molten salt for increased thermal heat storage. 10- to 15-millimeter capsules provide high heat transfer surface. A void in the capsule accommodates the expansion of salt as it melts. Image from Terrafore

Sometimes great things come in small packages. In the case of developing ways to more efficiently store solar energy, they come in tiny capsules. With support from a SunShot Baseload Concentrating Solar Power (CSP) Generation award, Terrafore has pioneered a new method to improve storage efficiency and reduce the cost of energy delivered from CSP plants.

"SunShot has played a major role in this achievement," says Terrafore CTO Anoop Mathur. "We're a very small company and without SunShot, this could not have been done."

In large CSP installations, the cost of storing the high-temperature thermal energy collected is a significant determining factor for the plant's cost and efficiency. Partnering with the Southwest Research Institute and University of California, Riverside, Terrafore has found a cost-effective way to produce small capsules containing phase change material (PCM) salt in a spherical shell, which provides increased surface area for heat transfer.

The challenge was to find a way to encapsulate the salt in a shell that would not rupture when the salt melts and expands. The solution, called TerraCaps, contain a void within the capsules to provide space for salt expansion without the shell rupturing.

The capsules can contain a variety of PCMs and can be stacked inside the thermal energy storage tank to provide cascaded thermal storage. The TerraCaps cascaded thermal storage (patent filed) improves energy density, allowing the system to store 52% more energy than could be stored in a standard thermal storage material of the same volume. With further investment, the solution is expected to be commercialized in four to five years.

"Our project reduces the total costs and increases the efficiency of CSP plants," Mathur says. "And it is on track to achieve the SunShot cost goal."

This project is funded by the Baseload Concentrating Solar Power Generation program under the U.S. Department of Energy SunShot Initiative.

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