Solar energy is clean but hard to save for later use. Researchers have found that a new material, a changed organic molecule named pyrimidone, absorbs sunlight and holds the energy in chemical bonds, which are links between atoms. This is part of molecular solar thermal energy storage, a method that uses light to trap energy in molecules for release as heat. The material is reusable, meaning it can be charged and discharged many times without wearing out. It works like photochromic sunglasses, where lenses darken in sunlight and clear up indoors due to reversible changes. Here, the molecule changes shape to store energy instead of changing color.
The researchers drew ideas from DNA, where a similar part shifts structure under ultraviolet light. They made a synthetic version that stores energy stably for years. Using computer models, they figured out why it holds energy without leaking. The design is simple and light, with extra parts removed for better efficiency.
A rechargeable battery for heat
The molecule acts like a spring: sunlight twists it into a tense, energy-rich form. A small trigger, like mild heat or a catalyst, makes it snap back, releasing stored energy as heat. Its energy density, the amount of energy per kilogram, is over 1.6 megajoules per kilogram, about twice that of common lithium-ion batteries used in phones and cars.
In tests, the released heat boiled water under normal conditions, showing real-world potential. This could mean pumping the water-soluble material through rooftop collectors to charge during the day and store in tanks for nighttime heating. It avoids needing separate batteries, making systems simpler. The work got funding from a fellowship to advance these "rechargeable sun batteries" for uses like camping warmth or home hot water.
The researchers have published the methods and results of this study in a paper published in Science.