A new design for a passive atmospheric multiple effect solar distillation unit is proposed. Inclined glass surfaces with a 40 slope and placed one over the other in an isolated box are used. The cold salty water is fed only in the upper stage and flows along each surface, falling from one stage to the next by gravity and reaching finally a heated tray at the bottom. Vapour condenses below each surface and produces the water evaporation in the upper side of the same surface. For heating the bottom of the still a simple 1.3 m{sup}2 solar collector with a fresnel type concentrator is used. The collector is separated from the still and heat is transported from one unit to the other using a 4 kg aluminium slab, which is placed in the absorber and it is heated at a temperature about 350 C. The slab is then placed below the tray in an isolated box. Four slabs are used and they are changed periodically when the slab temperature drops below approximately 180 C. Several slabs can be used for heat storage if several collectors are built, allowing the use of the still during some hours at night, improving its daily productivity. Experiments have been performed with a prototype and the results are discussed and compared with the values obtained with another electrically heated prototype.
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