Solar thermal feed preheating techniques integrated with membrane distillation for seawater desalination applications: Recent advances, retrofitting performance improvement strategies, and future perspectives

Membrane distillation (MD) is a promising technology for seawater desalination, integrating the advantages of both membrane segregation and thermal distillation. High energy consumption is one of the key barriers to the evolution of MD. The concern of utilizing solar thermal heating techniques for feed water heating in MD systems is increasing worldwide for sustainable freshwater production and lowering of energy consumption. In this review, the recent advances and latest developments in solar-powered MD technology have been highlighted. A special focus has been considered for hybridization configurations, energy performance evaluation, and economic analyses of solar MD systems. The combination of different solar thermal units with MD systems; including, solar flat plate collectors, evacuated tube collectors, hybrid photovoltaic/thermal collectors, high concentrating solar collectors, salt-gradient solar ponds, solar distillers, …etc., has been examined. Accordingly, reviewed results and related comparisons for the different solar feed heating techniques are critically discussed and panoramically tabulated. Then the bottlenecks of the system's performance and the literature gap in previous studies are also discussed. Overall, this survey sums up the status of solar-based MD research looking at the perspective strategies to realize the next generation of solar MD systems that can address the future demands of MD and achieve a highly more cost-efficient desalination process.