If we’re going to get better at powering the planet with renewable energy, we need to get better at finding ways of efficiently storing that energy until it’s needed – and scientists have identified a particular material that could give us exactly that.

The material is known as a metal-organic framework (MOF), in which carbon-based molecules form structures by linking metal ions. Crucially, MOFs are porous, so they can form composite materials with other small molecules.

That’s what the team did here, adding molecules of the light-absorbing compound azobenzene. The finished composite material was able to store energy from ultraviolet light for at least four months at room temperature before releasing it again – a big improvement over the days or weeks that most light-responsive materials can manage.