A team at UC Santa Barbara has developed a molecule capable of capturing sun energy and storing it for later use as heat. The system is described as a “rechargeable” solar battery. Unlike conventional solar technologies that generate electricity, this approach stores energy directly within a chemical structure. Solar power remains limited by its dependence on daylight. Storing that energy efficiently has long been a central challenge in expanding renewable energy use, especially for heating applications.
The system explored here belongs to molecular solar thermal (MOST) storage, a field focused on trapping solar energy in molecules. While the concept is not new, achieving both strong performance and stability has remained difficult, as reported in Science.
A Molecule That Captures And Releases Sun Energy
The researchers designed a compound called pyrimidone that changes structure when exposed to sunlight. This shift places the molecule in a high-energy state, allowing it to store solar energy internally. According to lead author Nguyen Han , the molecule behaves like a compressed spring: it absorbs energy when activated by light and releases it later as heat when triggered. She described the system as “reusable and recyclable,” emphasizing its ability to undergo repeated cycles without degradation, as detailed in Science.
“That kind of reversible change is what we’re interested in. Only instead of changing color, we want to use the same idea to store energy, release it when we need it, and then reuse the material over and over,” she said.
Where DNA Meets Everyday Materials in Design
To create this molecule, the team drew inspiration from DNA structures and photochromic materials such as transition lenses. These systems can reversibly change form under light, a property the researchers adapted for energy storage.
The pyrimidone structure mimics components found in DNA that respond to UV light. With computational support from K. N. Houk at UCLA, the team refined the molecule to ensure it could remain stable while holding energy over time.
Nguyen said the design process focused on simplicity, with unnecessary elements removed to create a compact and efficient molecule capable of storing sun energy, as explained in the study.
Energy Density High Enough To Boil Water
The material achieves an energy density exceeding 1.6 MJ/kg, which is higher than typical lithium-ion batteries at around 0.9 MJ/kg. This level of performance marks a significant step for MOST systems.
“Boiling water is an energy-intensive process,” Nguyen stated in the university statement. “The fact that we can boil water under ambient conditions is a big achievement.” This represents a demanding benchmark, as boiling water requires substantial energy input.
The molecule’s solubility also suggests practical applications. It could circulate through solar collectors, store energy during the day, and release heat later. As co-author Benjamin Baker noted:
“With solar panels, you need an additional battery system to store the energy. With molecular solar thermal energy storage, the material itself is able to store that energy from sunlight.”