‘Rechargeable Sun Battery’ Outperforms Lithium-Ion in Energy Storage

A new molecule, inspired by DNA, captures solar energy and releases it as heat on demand, offering a potentially transformative solution to the challenges of renewable energy storage. Researchers at UC Santa Barbara have developed a material that surpasses the performance of traditional lithium-ion batteries, paving the way for more efficient and sustainable energy solutions.

The Challenge of Intermittent Solar Energy

The intermittency of solar energy – its reliance on sunlight – has long been a hurdle to widespread adoption. While solar panels excel at converting sunlight into electricity, storing that energy for use when the sun isn’t shining has required bulky and expensive battery systems. This new technology aims to overcome this limitation by storing solar energy chemically, rather than electrically.

How the ‘Rechargeable Sun Battery’ Works

The breakthrough centers around a modified organic molecule called pyrimidone, a key component in the field of Molecular Solar Thermal (MOST) energy storage. The molecule functions similarly to photochromic sunglasses, darkening in sunlight and becoming clear indoors. However, instead of changing color, pyrimidone stores energy and releases it as heat when triggered.

“Reckon of photochromic sunglasses. When you’re inside, they’re just clear lenses. You walk out into the sun, and they darken on their own. Come back inside, and the lenses grow clear again,” explains Han Nguyen, a doctoral student in the Han Group at UC Santa Barbara and the paper’s lead author. “That kind of reversible change is what we’re interested in. Only instead of changing color, we desire to use the same idea to store energy, release it when we need it, and then reuse the material over and over.”

The team drew inspiration from DNA, noting the reversible structural changes that occur in a component of DNA when exposed to ultraviolet light. By engineering a synthetic version of this structure, they created a molecule capable of storing and releasing energy reversibly. The molecule, when exposed to sunlight, twists into a high-energy state, effectively “charging” it. This stored energy can then be released as heat when triggered by a catalyst or a small amount of heat.

Superior Energy Density and Performance

The new molecule boasts an energy density of more than 1.6 megajoules per kilogram, exceeding the approximately 0.9 MJ/kg energy density of a standard lithium-ion battery . This represents a significant advancement over previous generations of optical switches.

Researchers demonstrated the material’s ability to release enough heat to boil water under ambient conditions, a feat previously difficult to achieve in this field. “Boiling water is an energy-intensive process,” Nguyen says. “The fact that we can boil water under ambient conditions is a big achievement.”

Potential Applications and Future Outlook

This technology opens doors to a range of practical applications, including off-grid heating for camping and residential water heating. Because the material is soluble in water, it could potentially be integrated into roof-mounted solar collectors, charging during the day and storing heat in tanks for nighttime use.

“With solar panels, you need an additional battery system to store the energy,” says coauthor Benjamin Baker, a doctoral student in the Han Lab. “With molecular solar thermal energy storage, the material itself is able to store that energy from sunlight.”

The research was supported by the Moore Inventor Fellowship, awarded to Associate Professor Grace Han in 2025 to pursue the development of these “rechargeable sun batteries” .