A photoelectrochemical system for conducting endoergic chemical processes driven by light energy. This system consists essentially of an illuminated halfcell and a darkened halfcell joined via electrodes and an external circuit to allow for the transport of electrons. Also, the said halfcells are joined by an ion conducting junction so as to allow for the transport of ions. The illuminated halfcell contains a photosensitizer, an electron relay substance and a catalyst, and the darkened halfcell may contain a second electron relay and a catalyst. Illumination with visible light results in the simultaneous and separate generation of oxidation and reduction products.