Assessing the Effect of Top Cover Material on Productivity of the Solar Distillation Unit

The provision of safe drinking water for all remains a global challenge in spite of astounding developments in science and technology. In the coastal region of Bangladesh, brackish or saline water prevails everywhere and people are always in search of safe drinking water. This work was taken up to design a cost-effective and simple domestic-scale solar water distillation device for use in the coastal villages of Bangladesh where saline-free drinking water is scarce. This study mainly looked at the feasibility of using stretched transparent PVC cover in solar distillation devices in lieu of traditionally used transparent glass sheets. In the present work, two solar-powered small-sized desalination units or ‘solar stills’ were designed and fabricated using locally available low-cost materials. In designing these solar desalination units, the main considerations were the availability of materials, cost, efficiency, ease of construction and ease of maintenance. To increase the total evaporative surface area of the bottom of stills, those were covered with black cotton fabrics with extended fibres. For the same angle of inclination (130) of the transparent cover, the average amount of distilled water produced by the transparent PVC sheet-covered still was about 42% of that collected from a glass sheet-covered still. The reason behind this poor performance could be traced to the increased surface adhesion of condensed water droplets with the PVC cover, which essentially scattered sunrays away from the solar still. So the way to go is to find a suitable plastic sheet material that has reduced surface adhesion to water or to find a coating material that can reduce surface adhesion too. Unless this can be done, traditional glass-covered solar distillation device still remains the cover material of choice. It is concluded that solar distillation could provide a practical solution to the drinking water needs of the people living in the coastal areas of Bangladesh and other low-resource countries where nothing but brackish or saline water is available during most of the year.