A regenerative photoelectrochemical (RPEC) device comprising two substrates, wherein: one or both substrates are transparent and are coated with transparent electrical conductor (TEC) layer; one or more layers of porous wide band gap semiconductor is/are applied to selected area of said TEC layer and sensitised with dye; electrolyte is placed between said two substrates; hole(s) made in one or both said substrates to enable external electrical connection(s) to said RPEC device.