Productivity Enhancement of a Single-Slope Solar Still Using Square Hollow Tubular Fins and Paraffin-Wax Thermal Energy Storage: An Energy, Exergy and Economic Investigation

Abstract

Solar distillation offers a low-cost, decentralised route to potable water for off-grid communities, yet the low productivity of the conventional single-basin single-slope solar still (CSS) remains its principal limitation. This study experimentally investigates the simultaneous use of square hollow tubular fins and latent-heat thermal energy storage (TES) to enhance still productivity. Two geometrically identical 0.5 m² single-slope stills were fabricated and operated side by side at Ahmedabad, India (23°N), one retained as the CSS and the other progressively modified. The work was conducted in two phases. In Phase-1, the basin liner was fitted with 32 square hollow fins (20 mm × 20 mm), and paraffin wax (3 kg) was added beneath the liner as the TES medium. In Phase-2, the fins were extended below the liner into the storage chamber to raise the effective thermal conductivity of the wax. Performance was assessed through daily productivity, energy efficiency and exergy efficiency, supported by a validated thermodynamic model and an economic analysis. The optimum basin water depth was identified as 2 cm. Relative to the CSS, fins alone increased daily yield by 64.3%, while the combined fins-plus-TES configuration almost doubled the yield (+100.7%) and raised daily energy efficiency from 24% to 48%. Nocturnal output of the storage-integrated still reached about 5.3 times that of the CSS, and the exergy efficiency rose markedly during the night-time discharge cycle. Extending the fins into the storage chamber yielded a further 55.7% improvement over the CSS but only 4.8% over the above-liner configuration, indicating limited cost-effectiveness. The payback period fell from 144 days for the CSS to 81 days for the modified still. The results establish hollow-finned latent-heat storage as an effective and economical productivity-enhancement strategy for passive solar stills.