NOVELTY - The cooling effect is achieved by open evaporation of water from a porous material (3). This takes place on the side of the irradiated surface which is in shadow. The water first wets or washes over the solar cell (2) on the irradiated side and is then led to the evaporation surface (3). Spectral filters keep solar radiation having little or no photovoltaic effect away from the solar cell to reduce the heating effect. By arrangement of a thermotropic protective covering in the beam path, overheating of the solar cells is prevented.    USE - To cool solar collector photovoltaic modules exposed to concentrated sunlight.    ADVANTAGE - Photovoltaic solar cells convert energy largely in the spectral waveband of 300-950 nm. Energy in the wavelengths below 300 nm and above 950 nm, merely heats the cells. The cells are at their most efficient at -20degreesC, and become virtually ineffective (or are eventually damaged) at temperatures above 80degreesC. If the sunlight is concentrated e.g. ten times, damaging temperatures are reached in a few minutes on a clear day. The new method, recognizing these problems, proposes a simple, economically manufactured cooling system to promote efficient solar cell operation. Evaporation cools much more effectively than convection or radiation. The cooling surface area increases proportionately with increase in size of the solar module array. Two stage cooling is employed when a glycol (anti-freeze) circuit must be used. The coolant in either case may contain spectral filtration additives.    DETAILED DESCRIPTION - Cooling water is supplied under pressure. Its container is a self-filling rainwater tank. Cooling is optionally carried out in two stages in which a closed primary cooling circuit is followed by open evaporation. The coolant in the primary circuit is non-aqueous. It has spectral filtration functions. It is monopropylene glycol or tripropylene glycol.    DESCRIPTION OF DRAWING(S) - A perspective view of a solar collector with side concentrators reveals the cross section.    Solar concentrators (1)    Solar cell (2)    Evaporation surface (3)