Various kinds of inorganic photochemical reations in aqueous solutions, in solids, and in solidaqueous solution systems have been re-examined from a viewpoint of chemical conversion and storage of light energy. Certain kinds of photochemical reactions which give rise to metals on the solid surface are light-energy-storage type in nature. We have proposed two types of the photochemical storage battery, in which light energy is stored in situ and therefore, electrical energy is drawn out reversibly whenever it is necessary. In the one-compartment battery based on the photolysis of either AgCl-Fe²⁺ or TiO₂-Ag⁺ system, the deposited Ag on the electrode surface and the oxidized species in a solution were stored for later electrochemical discharge but the cell performance proved to be not so good. We have made up the two-compartment battery having either n -TiO₂ or n -GaP photoelectrode. Light energy could be stored as the oxidized species in a solution at the first compartment and the deposited metal on the electrode surface at the second compartment of the battery. The two-compartment battery has shown may remarkable features in comparison with the onecompartment one. Photochemical metal deposition seems to be interesting for the applications to the light-energy storage system as well as the photographic imaging system.