Synergistic enhancement of thermal energy conversion in twin wedge solar stills using graphene nano-coated absorber and nano-composite PCM

Improving the thermal energy conversion efficiency of solar stills is still a key challenge to accelerating clean and sustainable desalination technologies to combat worldwide water scarcity. In this paper, an innovative Twin Wedge Solar Still (TWSS) design is experimentally investigated with two new modifications: (i) a graphene nanoplatelet (GNP)-coated absorber plate to increase solar absorption, and (ii) a mixed nano-composite phase change material (nPCM) based on aluminium oxide (Al₂O₃) and graphene oxide (GO) for enhanced thermal energy storage. This coupled combination has not been used previously for TWSS applications. The new system exhibits improved performance by enhancing solar absorptivity, thermal conductivity, and storage capacity, resulting in a cumulative productivity of 6.133 L/m²/day. The developed modified system shows 139.4 %, 153.2 %, and 230.7 % greater productivity, energy efficiency, and exergy efficiency compared to the existing TWSS. The evaporative heat transfer rate becomes almost double (235.89 W/m²K compared to 99.15 W/m²K), and the economic cost of distilled water decreases to $0.012/L from $0.024/L for the traditional system. The outcomes verify that the integration of the proposed GNP-coated absorber and GO-Al₂O₃-based nPCM provides a new and economical path to enhance solar desalination performance, making it a promising strategy for sustainable freshwater production.