A New Way to Store Solar Heat

Estimated reading time: 5 minutes

The key is a molecule that can remain stable in either of two different configurations. When exposed to sunlight, the energy of the light kicks the molecules into their “charged” configuration, and they can stay that way for long periods. Then, when triggered by a very specific temperature or other stimulus, the molecules snap back to their original shape, giving off a burst of heat in the process.

Such chemically-based storage materials, known as solar thermal fuels (STF), have been developed before, including in previous work by Grossman and his team. But those earlier efforts “had limited utility in solid-state applications” because they were designed to be used in liquid solutions and not capable of making durable solid-state films, Zhitomirsky says. The new approach is the first based on a solid-state material, in this case a polymer, and the first based on inexpensive materials and widespread manufacturing technology.

“This work presents an exciting avenue for simultaneous energy harvesting and storage within a single material,” says Ted Sargent, university professor at the University of Toronto, who was not involved in this research.

Manufacturing the new material requires just a two-step process that is “very simple and very scalable,” says Cho. The system is based on previous work that was aimed at developing a solar cooker that could store solar heat for cooking after sundown, but “there were challenges with that,” he says. The team realized that if the heat-storing material could be made in the form of a thin film, then it could be “incorporated into many different materials,” he says, including glass or even fabric.

To make the film capable of storing a useful amount of heat, and to ensure that it could be manufactured easily and reliably, the team started with materials called azobenzenes that change their molecular configuration in response to light. The azobenzenes can then can be stimulated by a tiny pulse of heat, to revert to their original configuration and release much more heat in the process. The researchers modified the material’s chemistry to improve its energy density — the amount of energy that can be stored for a given weight — its ability to form smooth, uniform layers, and its responsiveness to the activating heat pulse.

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