Comprehensive experimental assessment of hexagonal solar stills (HSS) using 12E-based performance and sustainability metrics

Freshwater scarcity remains a persistent global issue, particularly in off-grid and arid regions. While solar stills offer a sustainable desalination method, low productivity and efficiency limit widespread adoption. This study addresses this challenge by experimentally evaluating six hexagonal solar still (HSS) configurations using an integrated 12E framework that combines energy, exergy, economic, environmental, and sustainability metrics. The objective is to identify an optimized design that maximizes freshwater yield while minimizing cost and environmental impact. In this experimental investigation, a total of six types of solar still (SS) cases are considered (Case 1: Conventional SS, Case 2: Conventional SS with fins and black sand, Case 3: Conventional SS with fins and granite stone, Case 4: Conventional SS with black sand, granite stone and fins, Case 5: Conventional SS with fins, black sand and HNPCM can, and Case 6: Conventional SS with fins, black sand and metal sponges). Among all cases, Case 5 incorporating hybrid nano-enhanced phase change materials (HNPCM), black sand, and aluminum fins demonstrated superior performance, achieving the highest freshwater productivity (2.9776 L/m²/day), energy efficiency (60.3%), and sustainability index (1.0122), along with the lowest cost per liter ($0.0113) and the highest carbon credit gain ($14.116/year). Case 5 also demonstrates the largest energo-enviroeconomic factor compared to the other HSS configurations. These results highlight the effectiveness of material and structural enhancements in improving HSS performance. Overall, the findings confirm that optimized HSS systems can serve as cost-effective, energy-efficient, and environmentally sustainable solutions for decentralized water purification. This work contributes meaningfully to achieving the UN Sustainable Development Goals (SDGs) 6 (Clean Water), 7 (Clean Energy), and 13 (Climate Action).