Khalifa University researchers wanted better ways to store heat in solar-energy systems. Their solution? Tiny capsules containing a phase-change material, or PCM, mixed with water.

These PCMs can absorb and store large amounts of heat when they change from solid to liquid. This heat-storing solar fluid is surrounded by extremely thin shells made from gold, silver, copper or aluminum, which interact strongly with sunlight, helping the capsules absorb even more energy. Think of it as a two-for-one effect.

The new fluids generally performed much better than conventional nanofluids, in which metal nanoparticles are simply mixed into water, the researchers say.

The KU team published a paper about the work in Energy Conversion and Management.

More isn’t always better, though, which the KU researchers discovered. They found that when capsules were larger, they tended to cluster and reduce heat transfer. Increasing the PCM concentration from 8 to 16 percent generally reduced the temperature increase because the thicker mixture lowered thermal conductivity.

The researchers are looking for a sweet spot with enough PCMs to provide sustainable heat storage but not so much that the liquid loses its effectiveness.

They also need to look more closely at such issues as cost, environmental impact and manufacturing at scale.

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