Efficiency improvement of vertical solar stills - A review

Freshwater scarcity has become a significant problem for people around the world nowadays. Different desalination methods such as RO, MED and MSF have been used for producing fresh and healthy water. Solar still is one of the easiest and least expensive methods to produce freshwater by solar energy. In general, the efficiency of conventional solar still is low, and for this purpose, different types of solar stills have been designed and built to overcome this drawback, one of which is the vertical solar still (VSS). This type of solar still has a high production capacity. The maximum amount of production obtained with this type of device in recent years is between 4.88 ( Kg/m(2)day) for single effect and 5.78 Lm(-2)h(-1)for multi-effect solar still. In this paper, methods used in the literature to improve vertical solar still efficiency are reviewed. The improvement methods are categorized based on the four major sections in vertical solar still: absorption, evaporation, condensation, and latent heat recovery. Novel modifications examined in each section are analyzed and their effect on the efficiency of the device is discussed, such as using materials with high absorption coefficient and optimizing the dimensions of the device, and finding the most suitable dimensions for different radiation fluxes.