Investigating the performance of periwinkle shell (tympanotonos fuscatus) as energy storage material in a passive solar still

Solar desalination remains a viable technique for addressing the lack of clean water in off-grid and arid locations. Low productivity and over-dependence on the available solar radiation are the main drawbacks of the technology. In this study, the effects of integrating periwinkle shell, an abundant marine bio-waste, as a sensible heat storage material and porous absorber, on the performance of a single-slope passive solar still were experimentally investigated at Nsukka, Nigeria (lat. 6.87°N and long. 7.38°E). Two solar stills, a conventional solar still and a periwinkle shell-assisted solar still, were fabricated with identical technical specifications and experimentally evaluated using equal water masses, with the primary objective of enhancing the productivity of the conventional solar still. The shells were sourced, cleaned, painted black, and evenly spaced in the periwinkle shell-assisted solar basin to improve thermal energy retention and yield. On an hourly basis, the distillate yields and temperatures of the major components were recorded to assess their performance. The results showed a 13.38% increase in daily freshwater yield. The energy and exergy efficiencies of the periwinkle shell-assisted solar still and the conventional solar still were 48.92% and 2.25%, and 41.77% and 1.53%, respectively. These improvements were attributed to the thermophysical properties of the periwinkle shell, thereby demonstrating the potential of marine bio-waste as a robust, sustainable, cost-effective alternative to sensible heat storage materials for low-temperature thermal systems such as solar stills and crop dryers. The findings underscore the viability of the shell in supporting the waste-to-energy nexus, offering economic benefits with minimal environmental impact.