Researchers from UC Santa Barbara have made a groundbreaking advancement that could eliminate the need for large battery systems and dependence on the electrical grid. In a study published in the journal Science, Associate Professor Grace Han and her team introduce a novel material capable of absorbing sunlight, storing it in chemical bonds, and releasing it as heat when required. This innovative material is derived from a modified organic molecule known as pyrimidone, marking a significant leap in Molecular Solar Thermal (MOST) energy storage technology.
"The concept is reusable and recyclable," stated Han Nguyen, a doctoral student in the Han Group and the lead author of the study.
Nguyen elaborated, "Consider photochromic sunglasses. When indoors, they appear clear, but when exposed to sunlight, they darken automatically. Once back inside, they revert to clear. This reversible change is our focus. Instead of merely changing color, we aim to store energy and release it as needed, enabling repeated use of the material."
Inspired by DNA for Solar Energy Storage
The design of the molecule drew inspiration from an unexpected source: DNA. The structure of pyrimidone mimics a component in DNA that can reversibly alter its shape when exposed to ultraviolet light.
Using a synthetic variant of this structure, the researchers developed a molecule capable of repeatedly storing and releasing energy. To understand why this molecule maintains stability while storing energy over extended periods, they collaborated with Ken Houk, a distinguished research professor at UCLA. Computational modeling provided insights into how the material can retain stored energy for years without significant degradation.
"We focused on creating a lightweight, compact molecule," Nguyen noted. "For this project, we eliminated all unnecessary components to ensure the molecule was as streamlined as possible."
A Rechargeable "Sun Battery"
Unlike traditional solar panels that convert sunlight directly into electricity, this innovative system stores energy chemically. The molecule behaves like a compressed spring; after absorbing sunlight, it transitions into a high-energy state and remains there until triggered.
When subjected to a small amount of heat or a catalyst, the molecule reverts to its original form, releasing the stored energy as heat.
"We often refer to it as a rechargeable solar battery," Nguyen explained. "It captures sunlight and can be recharged."
The molecule boasts impressive energy density, storing over 1.6 megajoules of energy per kilogram, significantly outperforming conventional lithium-ion batteries, which hold about 0.9 MJ/kg. It also surpasses earlier generations of optical energy-storage switches.
Transforming Stored Sunlight into Usable Heat
A pivotal achievement for the team was demonstrating the molecule's capacity for practical applications. In experiments, they successfully showed that the material could generate enough heat to boil water under ambient conditions, a challenging feat in this research area.
"Boiling water requires substantial energy," Nguyen commented. "Achieving this under ambient conditions is a major milestone."
This technology may pave the way for diverse real-world applications, including off-grid heating solutions for camping or home water heating systems. Since the material dissolves in water, it could circulate through rooftop solar collectors during the day and be stored in tanks to release heat at night.
"With solar panels, an additional battery system is necessary for energy storage," co-author Benjamin Baker, a doctoral student in the Han Lab, pointed out. "However, molecular solar thermal energy storage allows the material itself to store sunlight energy."
This project has received backing from the Moore Inventor Fellowship, awarded to Han in 2025, to further develop these innovative "rechargeable sun batteries."
