Researchers at the University of California have created an organic molecule that captures sunlight and stores that energy in chemical bonds for months or even years before releasing it as heat, representing a major step in molecular solar thermal (MOST) energy storage, tells Ars Technica. Traditional solar energy systems convert light into electricity, but storing that energy as heat with conventional batteries is inefficient and costly. MOST systems offer an alternative by using specially designed molecules that change structure when exposed to light and later revert to their original form, releasing stored energy as heat on demand. A team led by chemists at UC Santa Barbara and collaborators engineered a pyrimidone-based compound inspired by DNA’s photochemistry that achieves record-high energy density, about 1.6 megajoules per kilogram, roughly double that of a typical lithium-ion battery.
The molecule works by absorbing ultraviolet light, which forces it into a high-energy configuration called a Dewar photoisomer. This metastable state holds energy in strained chemical bonds until a trigger, such as an acid or heat, causes the molecule to relax back to its original shape, releasing heat in the process. In laboratory tests, the energy released was enough to boil water, illustrating that the stored solar heat can be both intense and practical.
Unlike conventional fuels that are burned irreversibly, this pyrimidone system functions more like a rechargeable thermal battery that can be cycled repeatedly without degradation. The design is solvent-free and compatible with aqueous environments, making it more sustainable than earlier MOST materials that relied on toxic solvents or suffered rapid degradation. Stability is another key advantage; theoretical calculations suggest the charged molecule could remain in its high-energy state for around 481 days at room temperature, greatly extending storage lifetimes compared with many previous candidates.
The work, published in Science, signals a promising direction for compact, dispatchable solar heat storage that does not depend on bulky batteries or grid infrastructure. Challenges remain, including broadening the spectrum of sunlight the molecule can capture and scaling the technology economically, but this DNA-inspired approach moves MOST closer to real-world application.