Reverse osmosis desalination systems powered by solar energy: Preheating techniques and brine disposal challenges – A detailed review

• An intensive review of the recent solar-powered RO desalination systems is conducted. • Brine disposal methods are compared to show the most applicable for inland plants. • Separate and hybrid preheating techniques are classified and discussed. • Different applicability challenges and limitations are highlighted. Globally, reverse osmosis desalination systems are widely utilized as they have the cheapest freshwater production cost. On the contrary, reverse osmosis systems have high specific energy consumption and membrane fouling that requires continuous chemical cleaning. Additionally, the plants' performance and their applicability can be stated via different terms: specific energy consumption, freshwater cost, thermal efficiencies, configurations, water recovery factors, and water quality. Therefore, many investigations have been conducted to enrich these indicators. Accordingly, the current review aimed to comprehensively merge most of these studies to give a complete picture of the recent developments of reverse osmosis plants considering all the aforementioned parameters. On the one hand, the current survey focused on solar-based reverse osmosis plants, which were established to decrease the specific energy consumption using photovoltaic or solar thermal power plants; especially, the organic Rankine cycle. Besides, various preheating techniques and relevant works were presented. The preheating boosts the plants' thermo-economic performance, and yield as the power consumption and productivity proportionally vary with the feedwater temperature. The preheating can be conducted by recovered heat from other systems, such as photovoltaic cooling unit, humidification-dehumidification process, organic Rankine cycle, and hybrid systems. Finally, the brine disposal methods were introduced, discussed, and compared to help in identifying the most appropriate economic technique, especially for the inland desalination plants. It is proposed that this review can help in the research continuity in the desalination field, especially reverse osmosis plants.