Design and evaluation of a modified basin-type stepped solar- still under Malaysia climate conditions

Distillation represents one of the earliest methods of treating water, and it remains as such in many parts of the world. A basin-type stepped solar-still remains the simplest desalination technology. It is simple, easy to construct, requires minimal maintenance, and is cost-effective. The objectives of this study were to design, fabricate and evaluate the performance of a modified stepped solar-still. The theoretical analysis was conducted to determine the optimum design of the still. The productivity and solar-still efficiency were obtained by solving the energy balance equations for the absorber plate, saline water, and glass cover, the temperature difference between saline water and the glass cover, and evaporation, convective, and radiative heat transfer coefficients under the climate of Malaysia. The experimental setup was constructed, and experiments were conducted at the Universiti Kebangsaan Malaysia (UKM), Selangor (Latitude 2°56‘22“North and Longitude 101°47’16” East). The basin area of the stepped solar-still was 1.m2 (0.5 m × 2.0 m). The basin of the still was constructed from a black-painted galvanized steel sheet to increase the absorptivity. The cover of the still was made up of glass. The absorber plate of the stepped still consisted of 5 steps (0.1 m × 2 m). The stepped solar-still has been modified to include external and internal reflectors, fins, and an external condenser. The performance of the modified stepped solar-still design has been investigated and compared with the unmodified stepped solar-still. The theoretical results show a significant improvement in the performance of the modified stepped solar-still. The productivity was higher than that for stepped solar-still before modification by approximately 29% under the same climate conditions. The experimental results have shown that the maximum temperature of saline water and glass cover were 62.1°C and 56.2°C, respectively. The maximum distillate water in the still was 6.10 kg/m2. The daily efficiency of the modified stepped solar-still was approximately 52.3%. Based on the experimental and theoretical results, the proposed design significantly enhanced the stepped solar-still thermal performance. A statistical t-test was conducted to establish the significance of the difference in the stepped solar-still experimental. It was found that there was a significant improvement in the stepped solar-still performance after modification. The techno-economic analysis showed that the product cost would be around USD0.07 per liter of distillate.