Molecular solar thermal storage: Sunburn-inspired 1.65 MJ/kg advance

Researchers at the University of California, Santa Barbara (UCSB) with collaborators at UCLA have reported a pyrimidone-based molecular solar thermal (MOST) system that stores sunlight in a strained Dewar photoisomer and reaches an energy density of about 1.65 MJ/kg.

The team designed molecules inspired by DNA photochemistry so that UV excitation near 300 nm converts a relaxed form into a high-energy Dewar isomer; the stored energy can then be released on demand by an acid-catalyzed reaction, demonstrated in the lab as sufficient to boil a small amount of water. The work appears in Science and lists Han P.Q. Nguyen and colleagues among the authors.

Key practical constraints remain: the charge process relies on high-energy UV wavelengths that represent only a small fraction of sunlight, and the laboratory demonstrations used corrosive acid catalysts that would complicate a commercial closed-loop device. Quantum yield and non-radiative decay pathways also limit how quickly and completely the liquid can be charged under natural sunlight.

On the positive side, some pyrimidone derivatives show strong thermal stability with calculated room-temperature half-lives on the order of many months, suggesting the possibility of seasonal storage (charge in summer, discharge in winter) and a genuine long-duration thermal battery. The researchers also engineered liquid-phase variants to avoid dilution by organic solvents, simplifying pumping and heat exchange in prototype setups.

From an energy-systems perspective, MOST technologies like this could contribute to decarbonizing heating—one of the tougher sectors to electrify—by providing on-demand heat without combustion. Nevertheless, until molecules that absorb more of the solar spectrum and benign, practical catalysts are developed, commercialization will be limited and further R&D and scale-up demonstrations are needed.