A variety of renewable energy sources are known and are being used in various parts of the world ^[1][2][27,32]. Solar, wind, geothermal, and tidal energy are the principal conventional sources of renewable energy for desalination processes ^[3][4][5][33,34,35]. It is noteworthy that the major contribution of renewable energy comes from wind and solar energy, and to a lesser extent, geothermal energy. Another emission-free energy source is nuclear energy, but because of safety concerns and waste disposal challenges it has not been broadly applied in desalination.

Solar energy is a widely available source of renewable energy throughout the world. It has been extensively studied in regions such as North America and the Middle East, as these areas often have limited freshwater resources and rely heavily on seawater and brackish water. Therefore, these regions are the perfect choice for using solar energy for desalination. Solar energy can be applied directly to heat highly saline water for desalination, or it can be converted into electrical energy for use in desalination processes. The direct application of solar energy in desalination includes methods such as solar chimneys ^[6][36], humidification–dehumidification process ^[7][37], and solar stills ^[8][38]. On the other hand, photoelectric technology is used to convert solar energy into electric power ^[9][39]. A recent study also reported a photovoltaic–membrane distillation process that can be used for both producing clean water and generating electric power ^[10][40]. The main merit of using solar energy in membrane desalination is that it is a renewable and sustainable source of energy, which reduces the dependence on fossil fuels and the associated environmental impacts. Additionally, solar energy is widely available and can be easily integrated into desalination systems, particularly in coastal and arid regions where sunlight is abundant. The main limitation of using solar energy in membrane-based desalination is that the process can be less efficient than traditional processes, particularly on cloudy or overcast days ^[11][41]. Additionally, the cost of solar-powered desalination systems can be high, particularly for larger-scale systems.

Wind energy is a significant source of renewable energy in many regions worldwide. Desalination processes powered by wind energy are widely available in hilly areas, coastal regions, and islands. Wind resources are found in nearly every part of the world, and as a result the wind energy sector has seen significant growth in the past two decades. Wind turbines are widely used in several countries, and the power generated by these systems can be used mechanically or electrically in desalination units. The development and upgradation of existing wind power stations are limited by various factors such as visual effect, public acceptance, noise, land requirements, telecom interference, and potential effects on wildlife and natural habitat ^[12][13][42,43]. The air pollution caused by wind turbines is widely studied by researchers and is categorized as aerodynamic and mechanical noise. When the wind moves through the turbine blades, aerodynamic noise is generated. It increases in direct proportion to the rotor’s speed and is affected by several other attributes, such as the direction and speed of the wind and atmospheric turbulence, which can produce a “whooshing” sound ^[14][44]. This type of noise can be decreased by altering the design of the turbine blades. Mechanical noise is generated by the moving components of the turbine, such as the bearings, generator, and gearbox. This type of wind turbine noise can be reduced by insulating the nacelle, applying vibration suppression, and using sound-absorbing materials ^[15][45]. Wind energy can be harnessed in coastal and offshore areas where wind speeds are high, making it well-suited for desalination systems located in these regions. The main limitation of applying wind energy in membrane-based desalination is that the system efficiency can be reduced in areas with low wind speeds. Another limitation is that wind energy is not constant and can be affected by weather conditions, which can cause fluctuations in the energy supply for the desalination process.

Wave energy, also known as wave power, is a type of renewable energy that is captured from the wave motion in the sea and oceans. Several techniques or wave energy devices are known to capture the energy generated by the waves of the ocean. The estimated net theoretical ocean power potential is 29.5 PWh/yr ^[16][46]. If there are adequate waves along the coast, it is possible to directly apply wave power to pressurize seawater to yield fresh water. According to this concept, a number of desalination plants have been constructed, where the converter absorbs wave energy and then transfers it directly to the RO setups ^[17][47]. The transformation of wave energy is more efficient than the transformation of other kinds of renewable energy. Although wave energy is seldom used in comparison with wind and solar energies, the theoretical conversion efficiency for solar energy, for instance, does not cross 87% and is based on best arrangements. One limitation of using wave energy for membrane-based desalination is that it can be less reliable and consistent compared with other forms of renewable energy, such as solar or wind. The amount of energy that can be generated from waves can vary depending on weather conditions and the location of the system. Additionally, wave energy systems can be costly to install and maintain, and the technology is in the early stages of development.

Geothermal energy is another renewable energy that is stored in the form of heat under the surface of the Earth. It is recognized as a high-potential energy source that can provide power and heat while emitting minimal greenhouse gases. The nature of geothermal resources varies by region, depending on factors such as basic rock composition, the efficacy of geothermal wells, the temperature of geothermal fluid, and the availability of geothermal fluid ^[18][48]. It is a sound approach for the production of heated water from underground reservoirs. The temperature of geothermal sources ranges from 70 to 80 °C, which makes them appropriate for low-temperature multi-effect distillation (MED) processes ^[19][49]. One limitation of applying geothermal energy for membrane-based desalination is that it is only available in certain geographic locations where there is suitable geothermal activity. Moreover, there may be environmental impacts associated with extracting geothermal fluids ^[20][50].

Since the last 30 years, a significant rise has been observed in the production of electricity from nuclear energy, ranging from 14% of the net electricity production in 2009 to almost 19% in 2016 ^[21][51]. According to recent publications, the capacity of global nuclear power will increase to 511 GW(e) in 2030 from a capacity of about 370 GW(e) in 2009 ^[21][51]. Nuclear energy is mainly produced by the nuclear fission process. This process produces heat to generate steam that is used to power turbine generators for electricity production. It is also considered free of greenhouse gas emissions because it does not involve the burning of fossil fuels. However, this technology is conditioned by operational safety challenges and the appropriate disposal of radioactive waste. The utilization of nuclear energy in desalination processes introduced the term “nuclear desalination”. Nuclear desalination is defined as the use of nuclear power plants’ heat and electricity to remove minerals and salts from brackish water and seawater. A range of membrane-based desalination processes has been observed to be efficaciously integrated with various kinds of nuclear power plants to generate electricity and water at different levels ^[21][51].

Blue energy, also known as salinity gradient energy, is also an emerging sustainable and renewable energy that originates from the salinity difference between seawater and freshwater. Where the river meets the sea, an irreversible and spontaneous mixing of seawater and freshwater happens, thus enhancing the entropy of a system. This change in entropy can be employed to convert a portion of the fluid’s thermal energy into electrical energy ^[22][52]. The total global energy extraction potential from this resource is estimated at about 2.4–2.6 TW, close to the global utilization of electricity ^[23][53]. Pressure-retarded osmosis ^[24][54] and reverse electrodialysis ^[25][55] are two widely known membrane-based technologies for harvesting blue energy.