This light not only heats the water, but also reaches a photovoltaic panel which provides energy to run the PEM electrolysis cell, which is what actually splits the water into hydrogen and oxygen.

More information: Songbo Ye et al, Hydrogen Binding Energy Is Insufficient for Describing Hydrogen Evolution on Single‐Atom Catalysts, Angewandte Chemie International Edition (2025). DOI: 10. ...