There are several technologies out there that harvest the sun’s boundless energy. Solar panels soak up solar energy and convert it to electricity, while solar thermal systems use mirror-like contraptions to collect sunshine to heat water or living spaces. But there aren’t any efficient ways to store solar heat for days or weeks.
Now, researchers at the University of California Santa Barbara have come up with a way to do that. They have created a new engineered molecule that traps sunlight, stores the energy in its chemical bonds, and then releases it on demand. The team reported this rechargeable solar heat battery in a paper published in the journal Science.
“Think of photochromic sunglasses,” said Han Nguyen, a PhD student and the paper’s lead author in a press release. “When you’re inside, they’re just clear lenses. You walk out into the sun, and they darken on their own. Come back inside, and the lenses become clear again. That kind of reversible change is what we’re interested in. Only instead of changing color, we want to use the same idea to store energy, release it when we need it, and then reuse the material over and over.”
The new material, called a pyrimidone, can store more than 1.6 megajoules per kilogram. That is almost double the energy density of a conventional lithium-ion battery, which is about 0.9 MJ/kg. Just like a lithium-ion battery can store electricity for days, the new liquid battery could store sunshine for days to provide hot water or heat when needed.
Scientists have tried to make such molecular solar thermal (MOST) energy storage systems before. But the materials designed so far either don’t store enough energy, degrade much too quickly, or need complex designs or solvents that made them impractical.
To make their MOST molecule, the California team turned to DNA for inspiration. The pyrimidone structure they have made resembles a component found in DNA that can reversibly change its form when exposed to UV light.
The new engineered pyrimidone molecule acts like a spring. When sunlight falls on it, it twists into a strained, high-energy state. It stays locked in that shape until a small amount of heat or a catalyst triggers it to release its stored energy as heat and revert to its relaxed state.
The molecule, which is soluble in water, releases enough heat to boil water in just a few minutes. The researchers suggest that it could find use in residential water heating: charge in rooftop tanks during the day and provide hot water at night, even days and weeks later.
Source: Han P. Q. Nguyen. Molecular solar thermal energy storage in Dewar pyrimidone beyond 1.6 MJ/kg. Science, 2026.
Image: ©Anthropocene Magazine