Liquid Sun Battery Stores Summer Heat for Winter Use

Scientists at UCSB and UCLA built a liquid, solvent-free pyrimidone that absorbs sunlight, twists into a high-energy Dewar isomer, and stores energy in chemical bonds for later release as heat. In tests, it achieved an energy density of 1.65 MJ/kg—nearly twice that of typical lithium-ion batteries—and could boil water under ambient conditions, suggesting a potential closed-loop solar-heat system for winter. However, the molecule currently absorbs only UV-A/B (about 5% of solar energy) and has a low quantum yield, requiring extended sun exposure. The heat release relies on an acid catalyst, which would need a neutralization step in real systems. Despite these hurdles, with a projected long storage half-life (up to ~481 days) and no toxic solvent, the approach represents a promising step toward storing summer sunlight for cold months, though practical deployment remains years away.