Associate Professor Grace Han and her team at UC Santa Barbara have engineered a solar battery that stores sunlight as chemical energy—not electricity—and can hold that power for months or even years before releasing it on demand as heat. The breakthrough, published in the journal Science, centers on a molecule called pyrimidone, which mimics a structural component of DNA that naturally responds to ultraviolet light.
The technology matters because it sidesteps the limitations of traditional energy storage. As global demand for renewable energy accelerates, so does the hunt for batteries that can bridge the gap between peak solar production and peak energy need. The BESS (battery energy storage systems) market is projected to grow 15-fold this decade, but lithium-ion batteries still dominate—and they come with environmental, supply-chain, and cost concerns. What Han's team has created is fundamentally different: a liquid that absorbs sunlight and converts it into stable chemical potential, avoiding the photovoltaic conversion step altogether.
Here's how the "Coiled Spring" Effect works: when sunlight hits the pyrimidone liquid, the molecules absorb the light and twist into a highly strained, high-energy state called a Dewar isomer. They stay locked in this configuration—stable for months or years—until a small trigger like a catalyst or heat flash is applied. Then they snap back to their relaxed state, instantly releasing the stored energy as pure thermal energy. In the lab, researchers successfully heated the liquid hot enough to rapidly boil water under normal conditions, proving the system can reach temperatures practical for real-world heating applications—a hurdle that Molecular Solar Thermal (MOST) energy storage systems have historically struggled to clear.
The energy density tells the story of why this matters: pyrimidone delivers 1.65 megajoules per kilogram, nearly double the energy density of a standard lithium-ion battery. That means massive energy can be stored in a far more compact form, making the system viable for homes and off-grid applications where space and weight matter.
The molecule's reversibility is another key advantage. Unlike conventional batteries that degrade through physical wear, pyrimidone can be charged and discharged indefinitely without losing capacity. A homeowner could circulate the liquid through rooftop solar collectors during the day to "charge" it, then pump that same liquid into a storage tank overnight, feeding heated water to boilers or heating systems on demand. For off-grid and industrial users, the applications stretch further: emissions-free portable thermal energy for cooking, camping equipment, or defrosting surfaces, all without electrical connections.
Researchers are also exploring hybrid systems, coupling MOST technology with thermoelectric generators to supply both heat and electrical current. That bridge between thermal and electrical output could eventually make the system useful across even more applications. While the science is still maturing—the full article was truncated before discussing scaling or cost timelines—the fundamental breakthrough is clear: Han's team has shown that a DNA-inspired molecule can hold the sun's energy hostage for months, then release it with precision when needed. In a world racing toward renewable energy, that's a gift with long-term possibilities.