Improving the Productivity of a Double Slope Solar Still by Integrating a PMMA Fresnel Lens: Experimental Approach

Abstract

This study investigates the performance enhancement of a Modified Double Slope Solar Still System (MDSSS) through the integration of a polymethyl methacrylate (PMMA) Fresnel lens under the climatic conditions of Chengalpattu, India. The experimental setup evaluates the impact of solar concentration on basin water temperature, glass cover temperature, freshwater yield, and system efficiencies at three different basin water depths (10 mm, 20 mm, and 30 mm). The Fresnel lens was oriented in the north–south direction with tilt angles ranging from 0° to 60° to optimize solar capture. Results show that the incorporation of the Fresnel lens significantly increases basin water temperatures (by 8–10 °C), glass cover temperatures, and cumulative freshwater yield across all tested depths, with a maximum yield of approximately 6.0 L/m² recorded at 10 mm depth. Energy and exergy analyses reveal notable efficiency improvements in the lens-assisted configuration, with energy efficiency reaching up to 87% and exergy efficiency improving by up to 8% compared to the system without the lens. These findings confirm that the use of a Fresnel lens effectively boosts solar distillation performance by enhancing thermal energy concentration, particularly in systems operating with shallow water depths. The proposed enhancement offers a viable solution for increasing freshwater production in passive solar desalination systems.