Development of Desalination Unit Using Solar still Coupled with Evacuated Tubes for Domestic Use in Rural Areas

Potable water and energy are two main priorities of mankind. The rural communities, especially of developing and under-developed countries are facing acute shortage of both. A sustainable, domestic water desalination process for rural India to meet the demand for potable water is the need of the hour and solar thermal desalination proves to be a promising alternative. In this article, experimental studies of single-slope, single-basin solar still integrated with evacuated tubes in natural mode (coupled system) are carried out for the climatic conditions of Bangalore (12.96°N, 77.56°E), Karnataka, India. For solar still basin area of 0.51 m², the distillate yields obtained from the coupled system for water depths of 0.06, 0.04 and 0.02 m are 3.289, 4.652 and 5.534 kg respectively, from 7:00 h to 19:00 h. The variation of instantaneous energy efficiency for the coupled system is found to be in the range 0.33-73.18% between 9:00 and 17:00 h for water depth of 0.02 m, which decreases with increase in water depth in the solar still. Chemical analysis of inlet water sample and outlet distillate was carried out and compared with Indian drinking water standards, IS-10500:2012. It is observed that the values for chemical composition of distillate are well below the limits of drinking water standards. The total cost of the developed coupled system was estimated to be Rs 6980 (US$ 1 = Rs 60.25 as on 15 April 2014). This eco-friendly system does not depend on any conventional source of energy for its operation and is easy to build and maintain.