Scientists developed a new liquid solar battery that can capture sunlight, store it for long periods, and release it as heat when needed.
The breakthrough by scientists at the University of California, Santa Barbara (UCSB) could help to store solar power after sunset.
The research, published in the journal Science, introduced a new material based on a modified organic molecule called pyrimidone.
The technology belongs to a growing field known as Molecular Solar Thermal (MOST) energy storage.
Solar panels stop generating electricity when the sun goes down. This limits their usefulness without expensive battery systems or large grid infrastructure.
To overcome this problem, Associate Professor Grace Han and her research team at UCSB created a molecule that stores solar energy directly inside chemical bonds. When exposed to sunlight, the molecule changes its structure and locks energy into a high-energy state. The stored energy can later be released as heat when triggered.
“The concept is reusable and recyclable,” said Han Nguyen, a doctoral student in the Han Group and the study’s lead author.
“Think 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 become clear again,” Nguyen said. “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.”
The project was led by Grace Han, an associate professor of chemistry at UCSB. The research team also collaborated with Professor Ken Houk from UCLA, who helped analyze the molecule using advanced computational modeling.
Bio-inspired Design
The pyrimidone molecule resembles a structure found in DNA that can undergo reversible changes when exposed to ultraviolet light. By engineering a synthetic version, the team created a compact molecule capable of storing large amounts of energy for years without losing stability.
“We prioritized a lightweight, compact molecule design,” Nguyen said. “For this project, we cut everything we didn’t need. Anything that was unnecessary, we removed to make the molecule as compact as possible.”
The research received support from the Moore Inventor Fellowship, awarded to Han in 2025 to advance the development of these “rechargeable sun batteries.”
The new liquid solar battery has a high energy density of more than 1.6 megajoules per kilogram. That is nearly double the energy density of standard lithium-ion batteries, which average about 0.9 megajoules per kilogram.
Rechargeable Battery for Heat
While traditional batteries store electricity, this system stores solar energy directly as heat. The molecule behaves like a compressed spring. Sunlight twists it into a high-energy form, and a small trigger, such as heat or a catalyst, snaps it back to its original shape, releasing stored energy.
“We typically describe it as a rechargeable solar battery,” Nguyen said. “It stores sunlight, and it can be recharged.”
In laboratory tests, the stored energy was strong enough to boil water under normal conditions. This marks a major achievement in MOST technology.
“Boiling water is an energy-intensive process,” Nguyen said. “The fact that we can boil water under ambient conditions is a big achievement.”
The material is also soluble in water, making it practical for real-world use. It could be pumped through rooftop solar collectors during the day, stored in tanks, and used to provide heating at night.
“With solar panels, you need an additional battery system to store the energy,” said co-author 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 development could lead to off-grid heating solutions, residential water heating systems, and more efficient renewable energy storage methods.
As countries push for cleaner energy systems, technologies that safely and efficiently store solar power will be essential. The UCSB team’s liquid solar battery offers a promising new path to capture the sun’s energy and keep it available long after sunset.
