Improvement of performance of solar still

Abstract

Limited availability of safe drinking water is a major problem, particularly in rural areas of Uganda. Most modern water treatment technologies are costly hence unaffordable for use by the local people. Additionally, the commonest method used; boiling with firewood is expensive, time-consuming, and environmentally unfriendly. Solar distillation is a promising technology for the supply of drinking water on a small-scale level. However, the major challenge with this technology is that it presents a low productivity which has made the technology less popular for use. This study was centered on determining the influence of incorporating both an external passive condenser and a parabolic solar concentrator on a conventional solar still as a way of increasing its distillate yield. Four different configurations of a single slope double glazed solar still were designed using ArchiCAD and then fabricated using the arc welding method. The materials used were; raw water samples from a well, galvanized steel sheets, black food-safe paint, and clear glass. The different still configurations are; a conventional solar still, a condenser coupled solar still, solar still coupled to a parabolic concentrator, and a solar still coupled with both condenser and parabolic solar concentrator. All solar still configurations were simultaneously tested at Entebbe airport weather station. The readings of solar still temperatures, solar radiation, and wind speed were measured and recorded hourly from 8:00 am till 6:00 pm each day of experimentation using a digital thermometer, pyronometer, and cup anemometer respectively. At the same time, the hourly distilled yields were collected, measured using graduated jars, and analyzed to ascertain the most productive solar still configuration. The results of the study indicated that incorporating both condenser and solar concentrator provided the best distillate yield. It enhanced solar still productivity by 149% (from 976 ml/m2 to 2,426 ml/m2 ), with a distilled water cost of 67.5 shillings/liter compared to 111 shillings/liter for the conventional still. The obtained distillate water quality results indicated that Escherichia coli was reduced from 25 to 0 CFL/100 ml which conforms with the Uganda National standards for treated potable water, hence safe for drinking. However, the distilled output of this still (2,426 ml/m2) is insufficient for supplying a family of four. Therefore, further improvements have to be made to the current still design to increase the distillate yield.