An overview of recent experimental and numerical studies on hemispherical solar distillers using internal and external enhancers

The water and energy issues have been given great attention in the Sustainable Development Goals (SDGs), and numerous research efforts have been directed toward exploring solutions for both. Accordingly, solar desalination systems have been innovated and developed. The desalination cost is a third issue that has also been considered, and cost-effective systems have been given priority. Hemispherical Solar Still (HSS) has been focused on as a promising solution, due to simplicity, low cost, and dependence on renewable energy. However, HSSs face limitations, for example, low production capacity, limited operation periods, and material degradation. Hence, multiple studies have been conducted to develop HSSs’ performance. This review paper aims to give a full overview of the HSS topic. This includes presenting the principle, performance indices, bibliometric analysis of the research development and widespreadness, conducted research, and prospects. The modifications are categorized into internal (porous, wick, heat localization, energy storage, fins, and corrugated basins), and external (cover cooling, reflectors, and solar heaters) methods. Both separate and combined additives are discussed. Other innovative designs are also surveyed. Moreover, CFD-based studies are highlighted. Generally, the reviewed studies show that impressive performance developments have been discovered. Using such additives, the daily yield ranged from 4.2 L/m² to 11.4 L/m². In terms of improvement ratios, the yield has been enhanced by up to 207 %, in some cases, compared to conventional HSSs. The energy efficiency ranged from 36 to 88 %. Economically, the cost has been remarkably reduced by ratios up to 70 %. From the environmental aspects, many studies show that HSSs can mitigate CO₂ emissions at considerable values.