Investigation of a modified double slope solar still integrated with nanoparticle-mixed phase change materials: Energy, exergy, exergo-economic, environmental, and sustainability analyses

Despite being simpler, cheaper, and less energy-intensive than other desalination processes, solar stills have apparent shortcomings in terms of productivity. Such a limitation has been prompting the researchers to strive in upgrading this renewable-driven technology through innovative add-ons. With a similar goal, the present study looks into the combined effect of unique modifications of internal sidewall reflector (ISR), hollow circular fin (HCF), phase change material (PCM), and nanoparticle mixed PCM (nano-PCM) on the thermodynamic performance of double slope solar stills. One passive (conventional) and one active (modified) double slope stills are constructed to experimentally evaluate and compare selected energy, exergy, exergo-economic, environmental, and sustainability metrics. The results indicate that the cumulative action of ISR, HCF, and PCM (Case II) leads up to 51.8% augmented productivity compared to the conventional case (Case I) where there is an additional increase of 21.5% when PCM is mixed with nanoparticles (Case III). While both the modified cases experience sizeable improvements in energy and exergy effi-ciencies compared to the conventional one, nano-PCM, in particular, boosts these quantities by 20.1% and 25%, respectively. Furthermore, nano-PCM induces around 2% additional cost-saving per unit of water production while mitigating a maximum CO2 emission of 3.65 ton. In addition to these assessments, the exergetic sustainability of the stills is discussed using vital indicators such as waste exergy ratio, improvement potential, sustainability index, etc. For the three experimental cases, the values of improvement potential, environmental effect factor, and sustainability index are attained within the ranges of 1374-1469 kWh/yr, 0.529-1.137, and 1.006-1.016, respectively.