TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Cell: The electrodes are in contact along the side of E1 that faces away from the source of light (preferably sunlight), and E2 is evaporated on to the face of E1. Both electrodes are preferably formed as plates. The housing is (a) made of a transparent material, particularly Plexiglas, or (b) is made of a non-transparent material but then has a window, preferably of material transparent to UV light, e.g. quartz glass, Plexiglas, zinc selenide or magnesium fluoride. The gas outlet can be sealed tight with a valve and preferably each compartment of the cell has its own gas outlet. The cell may include a heat exchanger and is supplied with water, preferably containing an antifreeze, as electrolyte. It may contain several electrode pairs, with different materials for each E1, mounted behind each other in the irradiation direction, with progressively smaller band gaps.Preferred Device: This includes, in the reaction cell or in an extra cell connected to it by a gas line, an anode-cathode arrangement, connected together through an external circuit (to which an electrical consumer may be connected). The anode and cathode are arranged so that gases from E1 and E2, respectively, circulate around them. Particularly the anode-cathode arrangement is formed as a fuel cell, especially one that operates at low temperature, and many electrode pairs are used, alternating with many fuel cells. Alternatively, the anode-cathode arrangement is present in a separate unit, functioning as a galvanic cell.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Materials: 16 materials for E1 are specified, e.g. titanium dioxide, germanium, silicon, gallium phosphide, zinc oxide or cadmium selenide, optionally doped (n or p), and most preferably the irradiated surface is formed as the (110) or (100) surface of a titanium dioxide crystal. The surface of E1 may have a dye or platinum clusters adsorbed on it. 16 metals for E2 are specified, e.g. ruthenium, rhodium, silver, gold, chromium, copper or nickel.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Materials: 16 materials for E1 are specified, e.g. titanium dioxide, germanium, silicon, gallium phosphide, zinc oxide or cadmium selenide, optionally doped (n or p), and most preferably the irradiated surface is formed as the (110) or (100) surface of a titanium dioxide crystal. The surface of E1 may have a dye or platinum clusters adsorbed on it. 16 metals for E2 are specified, e.g. ruthenium, rhodium, silver, gold, chromium, copper or nickel.