UCSB Creates Liquid Solar Battery That Stores Sun as Heat

Solar panels go dark when the sun sets, but what if sunlight could be bottled up and saved for later? Scientists at UC Santa Barbara just figured out how to do exactly that with a molecule small enough to float in water.

In a study published in Science, Associate Professor Grace Han and her team created a material that captures solar energy, locks it into chemical bonds, and releases it as heat whenever you need it. The innovation stores nearly double the energy per weight of a standard lithium-ion battery, and it can be reused over and over without degrading.

The secret lies in a molecule inspired by DNA. Doctoral student Han Nguyen and the team focused on pyrimidone, a structure similar to components in DNA that change when exposed to ultraviolet light. They stripped away everything unnecessary to create the smallest, most efficient design possible.

"Think of photochromic sunglasses," Nguyen explains. "When you're inside, they're clear. You walk out into the sun, and they darken on their own." The molecule works the same way, except instead of changing color, it stores energy and releases it when triggered by a tiny amount of heat.

The molecule acts like a mechanical spring. Sunlight strikes it, twisting the structure into a high-energy configuration where it stays locked until needed. When triggered, it snaps back and releases the stored energy as heat. The team calls it a rechargeable solar battery.

The numbers tell an impressive story. The molecule achieves an energy density of more than 1.6 megajoules per kilogram compared to 0.9 megajoules per kilogram for lithium-ion batteries. That means it stores nearly twice the energy in a recyclable, reusable liquid format.

To prove it works in the real world, the researchers demonstrated that the stored energy could boil water under normal conditions. Boiling water takes serious energy, and reaching that milestone marks a major achievement in molecular solar thermal energy storage.

The practical applications could transform daily life. Off-grid campers might carry compact systems that store solar heat during the day and release it at night for cooking or warmth. Homes could integrate roof-mounted solar collectors that charge the liquid during daylight hours, then circulate it through water heaters after sunset.

"With solar panels, you need an additional battery system to store the energy," says co-author Benjamin Baker, also 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 Ripple Effect

Heat accounts for a huge share of global energy demand, from hot showers to industrial manufacturing. Most renewable energy breakthroughs focus on electricity storage, but this innovation tackles heat directly. By creating a compact system that captures, stores, and releases heat on demand, the UCSB team offers a new pathway that could reduce our reliance on traditional batteries and heavy infrastructure.

The work received support from the Moore Inventor Fellowship, which Han earned in 2025 to develop what the team calls "rechargeable sun batteries." The sun still sets each evening, but now its warmth can linger long after darkness falls.