Barriers to implementation of phase change materials within solar desalination units: Exergy, thermal conductivity, economic, and environmental aspects review

The freshwater shortcoming with its soaring cost alerts the public around the globe to seek new technologies in the desalination of saline water agenda. In the past few years, desalination powered by solar energy, the well-known source of clean energy, has attracted more attention than its peer technologies running on fossil fuels. Solar stills have various developments to extend their working period and boost their productivity. Phase change materials (PCMs), as heat storage materials, are the options to enhance solar stills' performance by storing the solar energy during its sunshine period and releasing it during its off-peak period. Solar stills incorporated with PCM face some challenges which limit their full development. In this work, all the attempts to address these barriers, namely exergy destruction, poor thermal conductivity, economic failure, and environmental issues, are reviewed. The literature review revealed that researchers had reached promising results in exergy efficiency via up-cycling the stills using various methods where 221.8 % enhancement compared to a conventional solar still with a tubular configuration was reported. Using some methods to increase the thermal conductivity of PCMs, such as nano-enhanced PCMs by which an increment of up to 71 % in this feature was revealed, and other solutions are explained in this paper. The economic feasibility is another priority for researchers in which since stills with PCM could boost productivity; they can overcome the excess expenses created by implementing PCM and accompaniments within the stills. Apart from exergy, thermal conductivity, and economic monitoring, solar stills with PCM need to be evaluated by environmental analysis, which has not been appropriately considered yet. Also, the exergo-economic, exergo-environmental, enviro-economic, and exergo-enviro-economic analyses are the parameters on which stills with PCMs do not perform well, and the subsequent study should have more focus on them to give full credit to PCM implementation within the solar stills. •Exergy destruction can be solved via operating in cold climates and enhancing conductivity and surface contact of PCM-water.•Introducing nanomaterials is among the practical ways of enhancing PCMs’ poor thermal conductivity within solar stills.•PCMs cause extra cost; however, they can outweigh this rise with lower CPL via increase in water production.•The exergy-based environmental feasibility has yet to be achieved albeit a sat