Passive solar stills coupled with Fresnel lens and phase change material for sustainable solar desalination in the tropics

Abstract

Passive solar still is one of the solutions to mitigate water scarcity for its simple design and its least demand on electrical energy. However, the production from passive still is limited due to low efficiency. In this study, a refraction-based concentration of solar irradiation is introduced to improve the performance of conventional passive solar stills used for desalination in tropical weather of Malaysia. Performance evaluation in terms of efficiency and productivity is conducted on two passive double slope single basin solar stills coupled with Fresnel lens (FRL) and Phase Change Material (PCM). Both prototypes showed a similar trend in the augmentation of efficiency and productivity. The experimental values of daily water yield show a good match with the theoretical values. The highest water yield recorded from a prototype coupled with FRL was 3.19 L/m2/d. With FRL, the efficiency has reached 37% from 28% compared to conventional design. An increase in productivity (g/kJ) by 60% compared to the conventional still was also observed. Further studies were conducted to observe the effect of PCM energy storage. PCM alone stabilized the process with enhanced productivity. FRL coupled PCM system was able to reach an efficiency of 32% compared to conventional still. The collected freshwater from the 35,000-ppm saline solution produced by the prototypes was very high quality and complied well with World Health Organization (WHO) standard.