Freshwater and energy are critical components for the growth and progress of societies. The scarcity of freshwater and rapid population growth, especially in remote countries, has led to an urgent need to develop desalination technologies in order to raise its productivity and reduce its energy consumption rates. Membrane distillation is one of the effective methods characterized by its high productivity, but its disadvantage by higher electricity consumption. Also, solar stills are one of the sustainable and economical technologies, but the disadvantage by lower productivity. Accordingly, this manuscript dealt with a comprehensive review and detailed comparison of the most important modifications and innovations that were made to the design of the membrane distillation units, which aim to reduce electricity consumption rates, as well as the design of solar stills, which aims to maximize the productivity and efficiency. This was done by providing a detailed comparison of the most important three axes of modifications and innovations that were addressed by recent previous studies on the design of membrane distillation units and solar stills, and their statement as follows: preheating technology, use of the thermal storage materials, and nanomaterials technology. Finally, based on this review, the authors make some recommendations for future work in the field of solar and membrane desalination.

The present study aims to innovate small hybrid desalination plants suitable for remote regions working with higher productivity and lower cost of the produced fresh water. To achieve this idea, the small RO desalination plant was combined with the solar still, as well as this innovative hybrid desalination system was combined with the photovoltaic/thermal panel and the evacuated tube solar collector as preheating units to heat the water before it entered the proposed innovative small hybrid desalination plant. To illustrate the characterized of the proposed innovative small hybrid desalination plant, the performance of an innovative small hybrid desalination plant was compared to the conventional small RO desalination plant experimentally under the climate conditions of Tanta city, Egypt. The results presented that the annual permeate water that can be produced from the conventional small RO desalination plant without modification reached 173.74 m3/year, but for the proposed innovative small hybrid desalination plant the annual permeate water that can be produced will be increased to 352.59 m3/year, with an improvement of 102.94%. Also, the economic analysis presented that the cost of permeate water produced from the conventional RO plant without modification reached 0.915 $/m3. But the permeate water cost produced from an innovative small hybrid desalination plant will be reduced to 0.8178 $/m3, saving 10.62%.