A review of vacuum solar desalination powered by renewable energy: Recent trends

A lack of clean water and energy has become one of the most perilous glitches in some countries face due to a significant increase in world population and a boom in industrial and agricultural activity. United Nations reports mentioned by 2050 about five billion people of the world's population will face at least one month of water shortages. According to the Energy Information Administration (EIA), world energy consumption will increase by almost 50% between 2018 and 2050. A desalination process that involves the use of solar stills (SS) to obtain fresh water has been studied as a possible solution to these problems. It combines the three key processes of evaporation, condensation, and energy supply into one unit. Less than 5 L/m2/d of productivity and 45% efficiency are the downsides of the SS system, which operates under normal atmospheric pressure conditions. Thus, a major objective of this article is to review the performance and productivity improvements in the SS system. A full review of the SS system operating sub-atmospheric pressure conditions powered by renewable energy will be explained. The vacuum SS system was divided into two main sub-systems: natural and forced vacuum SS systems. Natural vacuum SS was classified into single and multi-stage, while forced vacuum SS was categorized into single and multi-effect. Previous studies as well as the most important recent advancements in this field were comprehensively presented. For example, recent developments in one-, two-, three-, four-, five- and multi module-effect forced vacuum systems are discussed. A single-stage natural vacuum SS system has reached a maximum efficiency of 76.96%. While the efficiency of about 86% made to the multi-stage natural vacuum SS. In general, maximum efficiency was achieved in single and multi-effect forced vacuum SS at almost 76.66% and 87%, respectively. The forced vacuum SS system is superior to the natural vacuum SS system because it removes non-condensable gases that hinder the operation process and produces continuously flowing fresh water. Gaps and vulnerabilities in the vacuum SS system were found after reviewing and analysing earlier studies. As a result, a hypothetical scenario for future study into vacuum SS systems was presented.