Solar Battery Stores Sunlight for Days, Releases Hydrogen

Imagine capturing sunshine in a jar and turning it into fuel whenever you need it, days later, even at midnight.

That's exactly what researchers at Ulm and Jena universities in Germany have achieved. Their new material works like a molecular battery, storing energy from sunlight and releasing it as hydrogen fuel on demand.

"You can think of it as a combination of a solar cell and a battery at the molecular level," explains Professor Sven Rau from Ulm University. The system charges up when exposed to light, then releases hydrogen fuel whenever needed.

Here's what makes it special: the material achieves over 80% charging efficiency and holds that energy for several days. When it's time to retrieve the stored energy, scientists simply add an acid and a catalyst, triggering the release of hydrogen with an impressive 72% efficiency.

The best part? It works in total darkness. Unlike traditional solar panels that need constant sunlight, this system decouples energy capture from energy use.

The technology uses a water-soluble copolymer, a large molecule designed with special chemical properties. During charging, it absorbs light and stores electrons. To discharge it, those stored electrons combine with protons to create hydrogen gas.

Even better, the system resets itself. Scientists can neutralize the solution and recharge it multiple times using a simple pH switch. The process even comes with a visual indicator: the solution turns from violet when charged to yellow when discharged.

The Ripple Effect

This breakthrough could revolutionize industries that desperately need reliable green hydrogen. Steel production, one of the world's biggest carbon emitters, could run on sunshine stored days earlier. Chemical manufacturing could tap into solar energy around the clock, not just during daylight hours.

The researchers believe their method offers new perspectives for cost-effective, scalable solar storage technologies. Unlike many lab discoveries that never leave the research facility, this one was designed with industrial applications in mind from the start.

Professor Ulrich Schubert, who coordinated the study, calls it "an important building block on the way to a sustainable, chemical-based energy economy." The results appear in the peer-reviewed journal Nature Communications.

The project also bridges two chemistry fields that rarely interact: macromolecular polymer chemistry and photocatalysis. That cross-pollination of ideas often leads to unexpected innovations.

Clean hydrogen has long been called a crucial piece of the climate puzzle, but making it and storing it efficiently has remained challenging. This solar battery tackles both problems at once, storing renewable energy and producing fuel exactly when it's needed.