Researchers 'Bottle the Sun' With a Molecular Battery That Stores Solar Energy for Years
UC Santa Barbara scientists have engineered a molecule that captures sunlight and stores it as chemical energy — releasing heat on demand, even days or years later.
Researchers 'Bottle the Sun' With a Breakthrough Molecular Solar Battery
A team of scientists at the University of California, Santa Barbara has developed a groundbreaking material that functions like a rechargeable solar battery — one that captures sunlight, locks it inside tiny molecules, and releases it as usable heat long after the sun has set. The innovation could reshape how the world thinks about renewable energy storage.
Published in the journal Science, the study was led by Associate Professor Grace Han and her research team, including doctoral student Han Nguyen as lead author. Their work centers on a modified organic molecule called pyrimidone and marks a significant advance in a field known as Molecular Solar Thermal (MOST) energy storage.
The Problem With Solar Power After Dark
Solar panels are highly effective at generating electricity during daylight hours, but they go dark — literally — once the sun disappears. Cloudy days and overnight hours remain persistent challenges for solar energy adoption. Conventional solutions involve large battery systems or dependence on the electrical grid, both of which come with significant cost, infrastructure, and environmental trade-offs.
The UC Santa Barbara team believes their molecular approach sidesteps these limitations entirely.
"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."
How the Molecule Works
The pyrimidone-based molecule behaves much like a compressed spring. When exposed to sunlight, it absorbs that energy and shifts into a strained, high-energy configuration — and stays there, potentially for years, without significant energy loss.
When a trigger is applied — such as a small amount of external heat or a chemical catalyst — the molecule snaps back to its original form, releasing its stored energy as heat on demand.
The inspiration for the molecule's design came from two surprisingly familiar sources: DNA and photochromic sunglasses.
"Think of photochromic sunglasses," said Nguyen. "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. 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 pyrimidone structure itself closely resembles a naturally occurring component of DNA that reversibly changes shape when exposed to ultraviolet light — a biological cue the researchers deliberately mimicked in their synthetic design.
Smarter by Design: A Lean, High-Efficiency Molecule
A key engineering priority for the team was efficiency through simplicity. Rather than building a complex molecule with unnecessary components, the researchers stripped the structure down to its essential elements.
"We prioritized a lightweight, compact molecule design," Nguyen explained. "For this project, we cut everything we didn't need. Anything that was unnecessary, we removed to make the molecule as compact as possible."
To better understand why the molecule remained so stable over long storage periods, the team collaborated with UCLA Distinguished Research Professor Ken Houk. Using advanced computational modeling, Houk's team helped explain the molecular mechanics behind the material's impressive energy retention capabilities.
Outperforming Lithium-Ion Batteries
One of the most striking aspects of this new material is its energy density. The pyrimidone molecule stores more than 1.6 megajoules of energy per kilogram — a figure that significantly exceeds the approximately 0.9 MJ/kg offered by conventional lithium-ion batteries. It also outperformed earlier generations of optical energy-storage switches, setting a new benchmark in the field.
"We typically describe it as a rechargeable solar battery," Nguyen said. "It stores sunlight, and it can be recharged."
The concept is also designed with sustainability in mind. "The concept is reusable and recyclable," Nguyen noted — a critical consideration as the world seeks greener alternatives to traditional battery chemistry.
A Key Milestone: Boiling Water With Stored Sunlight
To validate the material's practical potential, the researchers demonstrated something that has eluded scientists in this field for years: using the stored solar energy to boil water under normal ambient conditions.
"Boiling water is an energy-intensive process," Nguyen said. "The fact that we can boil water under ambient conditions is a big achievement."
This milestone transforms the technology from a theoretical concept into a tangible, real-world application — one that could have broad implications across multiple sectors.
Real-World Applications on the Horizon
Because the material dissolves readily in water, researchers envision a future system where the liquid circulates through rooftop solar collectors during daylight hours, absorbs and stores solar energy chemically, and is then held in insulated tanks that release heat throughout the night or on overcast days.
Potential applications include:
- Off-grid heating solutions for camping and outdoor use
- Residential water heating systems powered entirely by stored sunlight
- Industrial heat applications in remote or energy-limited environments
The research received support from the prestigious Moore Inventor Fellowship, awarded to Professor Han in 2025 specifically to advance the development of these so-called "rechargeable sun batteries."
A New Chapter for Renewable Energy Storage
While the technology is still in its research phase, the results published in Science represent a meaningful leap forward. By storing solar energy directly within a molecule rather than converting it to electricity first, the system eliminates the need for traditional battery infrastructure — offering a cleaner, more flexible path toward round-the-clock renewable energy use.
As the world pushes for faster decarbonization, innovations like this molecular solar battery may prove to be exactly the kind of creative, chemistry-driven solution that bridges the gap between solar generation and consistent, reliable energy access.
