Performance enhancement of a single-slope solar still using graphene-coated absorber plate and optimized fin geometry

• Solar still performance enhanced using fins and graphene-dispersed black paint. • Graphene coating with cylindrical fins shows the highest productivity in summer. • Maximum daily energy efficiency of 47% achieved in summer. • Economic analysis shows the lowest water cost of $0.034 per liter in summer. The Single Slope Solar Still (SSS) is widely used for desalination purposes due to its simplicity and low manufacturing cost, but it suffers from limited freshwater productivity. The current study focuses on an innovative design to enhance the performance of a still using graphene-dispersed black paint on the absorber plate, along with variances in the shapes of fins, such as rectangular, cylindrical, and combined fins. An overall one-year analysis was carried out for the study under three predominant climatic situations: summer, monsoon, and winter. From the study, it was observed that the graphene-coated SSS equipped with a cylindrical fin performs best irrespective of all climatic conditions. During summer, the average temperatures of condensate water, absorber plate, glass cover, and basin vapor were recorded as 56.1 °C, 57.2 °C, 50.3 °C, and 60.5 °C, respectively, thereby giving a maximum cumulative freshwater productivity of 2322 ml/day, with an overall energy efficiency of 47%. During the monsoon and winter, freshwater productivities of 1963 ml/day and 1776 ml/day, along with overall energy efficiency of 38.4% and 35.8%, respectively, were observed. The optimum system’s average exergy efficiency was seen to be 2.94%, 2.4%, and 2.2% under summer, monsoon, and winter conditions, respectively. Also, the economic analysis showed that the economic cost of distilled water production lies in the range of $0.034–0.038/liter in different seasons. These results prove that the synergistic integration of graphene coating and cylindrical fins significantly enhances the thermal, exergetic, and economic viability of single-slope solar stills under varying climatic conditions