Design and Experimental Evaluation of passive Solar Still under hottest and driest climate condition of Ethiopia: A case of lake-Afdera saline water

Abstract

Access to potable water remains a critical challenge globally, particularly in arid regions such as Ethiopia's Afar Region, where groundwater is often limited or contaminated with high levels of fluoride and salinity. This study investigates the design and performance of passive solar stills for desalinating saline water from Lake Afdera under extreme climatic conditions. The objective was to enhance the productivity of conventional single-slope, single-basin solar stills by incorporating black volcanic rocks as thermal energy-absorbing materials. Two solar still configurations a conventional design and a modified design with black volcanic rocks were constructed and experimentally evaluated over two days in Afdera. Parameters such as ambient temperature, water temperature, and hourly yield were recorded. To validate the results, the modified still was later tested under different environmental conditions at Mekelle University using thermocouples, PicoLog software, a pyranometer, and measuring jars for precise data collection. Results showed that the modified solar still significantly outperformed the conventional still in water yield, producing 3,482 ml and 3,800 ml over two days compared to 1,920 ml and 1,780 ml, respectively. It also demonstrated improved night-time performance, yielding 890 ml versus 340ml, due to better heat retention from the black rocks. Correlation analysis from the Mekelle validation indicated strong relationships between water yield and solar radiation (r = 0.60), rock temperature (r = 0.96), internal temperature (r = 0.85), and ambient temperature (r = 0.83). The modified system achieved 32.87% higher efficiency in Afdera than in Mekelle, highlighting the role of environmental conditions. The findings confirm that integrating black volcanic rocks into solar still design enhances efficiency and output, offering a cost-effective and sustainable desalination solution for arid, high radiation regions like Afar.