Scientists Store Sunlight in Molecules That Boil Water

Imagine bottling sunshine and using it to boil water months later, long after dark. Scientists at UC Santa Barbara just made that possible with a molecule that works like a rechargeable solar battery.

The team, led by Associate Professor Grace Han, designed a tiny organic molecule called pyrimidone that traps sunlight inside chemical bonds. When triggered by a small amount of heat, it releases that stored energy instantly, no electrical grid required.

"Think of photochromic sunglasses," explained Han Nguyen, the doctoral student who led the study. "They darken in sunlight and clear up inside. We use that same reversible change to store energy and release it whenever we need it."

The molecule stays stable in its high-energy state for years without losing power. It packs more than 1.6 megajoules per kilogram, outperforming lithium-ion batteries at 0.9 MJ/kg while weighing far less.

The team drew inspiration from DNA itself. Pyrimidone resembles a natural DNA component that changes shape under ultraviolet light, so they engineered a synthetic version that could repeatedly store and release energy without degrading.

In lab tests, the molecule released enough heat to boil water at room temperature. That's a major milestone for molecular solar thermal technology, which has struggled to generate practical amounts of usable heat until now.

Unlike traditional solar panels that convert sunlight directly into electricity, this system stores energy chemically. The molecule behaves like a compressed spring, absorbing light and shifting into a strained form where it stays locked until activated.

"With solar panels, you need an additional battery system," said co-author Benjamin Baker. "With molecular solar thermal energy storage, the material itself stores that energy from sunlight."

The technology opens doors to off-grid heating for camping, home water heating, and emergency power. Because the molecule dissolves in water, researchers envision it circulating through rooftop collectors during the day, then stored in tanks that release heat after sunset.

The Ripple Effect

This breakthrough arrives at a crucial moment for renewable energy. Solar power generation has soared worldwide, but storage remains the biggest obstacle to replacing fossil fuels completely. Massive battery farms are expensive, resource-intensive, and still can't store energy for extended periods.

Molecular solar thermal storage sidesteps those limitations entirely. The material requires no rare earth metals, maintains its charge indefinitely, and works anywhere sunlight reaches. A homeowner could charge the system on a sunny summer day and use that stored heat during a winter power outage months later.

The project received funding from the Moore Inventor Fellowship in 2025 specifically to develop these "rechargeable sun batteries." Han's team is already working on scaling the technology for real-world applications.

Humanity just figured out how to bottle sunshine and save it for a rainy day.