Progresses in improving the effectiveness of the single basin passive solar still

Single basin solar still is a very simple solar device used for converting available brackish or waste water into potable water. This device can be fabricated easily with locally available materials. The maintenance is also cheap and no skilled labor is required. This device can be a suitable solution to solve drinking water problem. Because of its low productivity it is not popularly used. Numbers of works are undertaken to improve the productivity of the still. In this work progresses in the works done on single basin passive types still to improve its productivity are reviewed. The orientation and inclination are optimized to receive maximum radiation and lower the condensation loss. Different materials are used in the basin along with water to improve the heat capacity, radiation absorption capacity and enhance the evaporation rate. Rubber is the best basin material to improve absorption, storage and evaporation effects. The effect of varying the depth of the basin water is also studied.

From the above review on single basin passive type solar still, the different methods used to improve the productivity are listed below. • The orientation of the glass cover depends on the latitude of the place. For northern latitude south facing and southern latitude north facing stills are used. • For lower latitude places double slope stills are preferred with south–north orientation. • The inclination of the cover is optimized for rate of condensation of water on the bottom surface of the cover and to collect it without the mass accumulated drops fall back into the basin. Hence it depends on the intensity of solar radiation, rate evaporation and condensation, material used for cover and its wetting property. • Glass is most suitable material for cover. It has the properties such as higher transmittance, wetting property with water to have less transmittance loss for solar radiation during condensation, higher thermal conductivity and stable transmittance during continuous exposure to sun radiation for long period. Other plastic material lacks in above properties. • The day-time and night-time productivity greatly depends on depth of water and heat capacity of the basin. • For lower sun radiation intensity places shallow basin still is preferable. • For higher sun radiation intensity places deep basin still is preferable to improve nocturnal production. • To improve the absorption and surface heating effect black dye is most suitable with deep basin still. • Other basin materials like rubber, gravel, glass sand, saw dust and sponge are having the properties of absorbing and storing of solar radiation in different proportions along with increasing the exposed area for evaporation of water. • Rubber is the best basin material to improve absorption, storage and evaporation effects. • Surface heating of water mass along with higher heat storing improves day-time and night-time production. • Mica sheet as suspended absorber is better material for surface heating. • To reflect the solar rays falling on the side walls of the still onto the basin reflecting mirrors are fixed one the side walls. This increases the insulation effect also.