2.1. Traditional Desalination Methods

Traditional desalination methods have been employed for centuries to address water scarcity by removing salts and other impurities from saline or brackish water sources [27, 42, 43]. These methods, while effective to a certain extent, come with inherent limitations that impact their efficiency, cost-effectiveness, and environmental sustainability. One of the oldest and most widely used traditional desalination methods is distillation. Distillation involves heating saline water to produce steam, which is then condensed to yield freshwater. While distillation is relatively simple and can be implemented using basic equipment, it is energy-intensive and requires significant amounts of heat to operate efficiently [44, 45]. Additionally, distillation plants are typically large-scale facilities, making them costly to construct and maintain. Another traditional desalination method is RO, which utilizes semipermeable membranes to separate salt ions from water molecules under pressure. While RO is more energy-efficient than distillation, it still requires electricity to power the pumps and membranes, contributing to operational costs. Moreover, RO membranes are prone to fouling and degradation over time, necessitating regular maintenance and replacement [46–49]. Other traditional desalination methods include ED, which relies on ion-selective membranes and an electric field to separate ions from water, and freezing desalination, which involves freezing saline water and then separating the ice crystals from the remaining liquid [49–51].

However, these methods have their own set of limitations, including high energy consumption. Overall, traditional desalination methods face several challenges that limit their widespread adoption and effectiveness in addressing water scarcity. These challenges include high energy requirements, operational costs, environmental impacts (such as greenhouse gas emissions and brine disposal), and limited freshwater production capacity [52, 53].

In recent years, there has been growing interest in developing and deploying more innovative and sustainable desalination technologies to overcome these limitations. These technologies include solar-powered desalination, membrane distillation, forward osmosis, and capacitive deionization, among others. By harnessing renewable energy sources, improving membrane materials and processes, and optimizing system designs, these innovative desalination technologies offer the potential to enhance water security, reduce environmental impact, and lower costs compared to traditional methods.

2.2. Solar Energy Technologies for Desalination

Solar desalination technologies vary in efficiency, scalability, and economic feasibility. The most widely used methods include solar stills, solar-powered RO, ED, MED, and MSF distillation. In recent years, solar-powered desalination has emerged as a promising and sustainable alternative to traditional desalination methods, offering a solution to address water scarcity challenges while minimizing environmental impact. Unlike conventional desalination methods that rely on fossil fuels or grid electricity, solar-powered desalination harnesses the abundant and renewable energy of the sun to drive the desalination process [54–56]. Solar distillation units use sun energy to evaporate salty water, which is collected as freshwater in a condensate trough. The water vapor condenses on a transparent glass or plastic covering, transmitting radiant energy and allowing water vapor to condense (Figure 3). Proper disposal is necessary for the brine solution formed in the still basin, which contains salt and un-evaporated water [58].

There are several ways in which solar energy can be integrated into desalination processes, including photovoltaic (PV) systems, concentrated solar power (CSP) systems, and hybrid solar desalination systems.

3.1. PV Systems

PV systems harness sunlight directly to generate electricity through the PV effect. This effect occurs when photons from sunlight strike the semiconductor material within PV cells, causing electrons to be released and creating an electric current. This electricity can then be used to power various electrical devices, including desalination equipment [69–71]. PV systems are well-suited for powering desalination processes, particularly those that require electricity, such as solar energy RO and ED. In RO desalination, for example, PV-generated electricity can be used to drive pumps that pressurize seawater and force it through semipermeable membranes to remove salt ions [72, 73]. Similarly, in ED, PV electricity can facilitate the separation of ions from water using ion-selective membranes and an electric field. PV desalination systems offer flexibility and scalability, making them suitable for a wide range of applications and locations [74, 75].

PV systems offer several advantages for desalination applications. They are modular and can be easily integrated into existing desalination plants or deployed in remote areas with limited infrastructure. Additionally, PV systems have minimal environmental impact and produce no greenhouse gas emissions during operation, making them environmentally friendly alternatives to fossil fuel-based electricity generation [76, 77]. However, PV systems also have limitations that must be considered. One limitation is their dependence on sunlight, which can vary depending on factors such as time of day, weather conditions, and geographic location. As a result, PV systems may require energy storage solutions, such as batteries, to ensure continuous operation during periods of low sunlight. Additionally, the upfront capital costs of PV systems can be significant, although ongoing advancements in PV technology and economies of scale are driving down costs over time [78, 79].

3.1.1. RO Desalination

Solar-powered RO desalination is a membrane-based process that utilizes semipermeable membranes to remove salt ions and other impurities from water. In RO desalination, seawater or brackish water is pressurized and forced through a membrane, which selectively allows water molecules to pass through while rejecting salt ions and other contaminants (Figure 5). The purified water, or permeate, is collected on one side of the membrane, while the concentrated brine, or reject, is discharged on the other side [46–49]. Subsequently, the fundamental equation that describes the process of RO desalination is the osmotic pressure equation, the van’t Hoff equation (Equation (1)), which governs the flow of water through the semipermeable membrane. This equation is given by the following:

$$ (1)

where Π is the osmotic pressure (in pascals, Pa), n is the number of moles of solute particles, R is the ideal gas constant (8.314 J/(mol · K)), T is the temperature in Kelvin (K), V is the volume of the solution (in cubic meters, m³). Equation (1) is used to describe the pressure required to overcome the osmotic pressure and drive water through the semipermeable membrane. The osmotic pressure represents the pressure required to prevent the flow of water across the membrane due to the concentration gradient between the feedwater (containing dissolved salts) and the freshwater side.

RO desalination is widely used for both seawater and brackish water desalination applications due to its high efficiency, relatively low energy consumption, and compact footprint. It is employed in various sectors, including municipal water supply, industrial processes, agriculture, and small-scale decentralized systems for remote communities or off-grid locations [81–83]. The efficiency of an RO desalination system can be evaluated using the energy consumption per unit of water produced. Hence, the specific energy consumption (SEC) is given by Equation (2):

$$ (2)

RO desalination can be integrated with solar energy systems to reduce reliance on grid electricity and fossil fuels, making the process more sustainable and environmentally friendly. Solar energy can be used to power the pumps, motors, and other electrical components of the RO system, either directly through PV panels or indirectly through grid-connected solar power systems. In standalone solar-powered RO systems, PV panels generate electricity to power the RO process, while excess energy can be stored in batteries for use during periods of low sunlight or high energy demand. In grid-connected systems, solar energy supplements grid electricity, reducing overall energy consumption and operating costs. Additionally, solar thermal energy can be utilized to preheat the feedwater before entering the RO membrane, thereby reducing the energy required for membrane pressurization and increasing overall system efficiency.

3.1.2. ED

Solar-powered ED uses an electric field to drive salt ions through ion-exchange membranes, separating fresh and saline water. Energy consumption E_ED is given by the following:

$$ (3)

where E_ED represents energy consumption (kWh/m³), I is the current (A), V is the voltage (V), t is the time (h), and Q is the volume of water processed (m³). ED is particularly suitable for brackish water desalination but requires significantly higher energy input when applied to seawater desalination due to the increased salinity and osmotic pressure. In ED (Figure 6), a feed solution, typically saline water, is passed between alternating cation-selective and anion-selective membranes. When an electric field is applied across the stack of membranes, ions in the feed solution are driven through the membranes, migrating toward electrodes of opposite charge. As a result, cations are transported through the cation-selective membranes toward the cathode, while anions are transported through the anion-selective membranes toward the anode. This selective ion transport leads to the generation of two streams: a desalinated product stream containing mostly water molecules and a concentrated brine stream containing the rejected ions [49–51]. The principle of ion transport in ED can be described by the Nernst–Planck equation, which governs the flux of ions through the ion exchange membranes. This is given by Equation (4):

$$ (4)

where J (molm⁻²s⁻¹) is the ion flux term representing the rate of ion movement through the membrane. It indicates the quantity of ions passing through a unit area of the membrane per unit time. The flux is influenced by factors such as the concentration gradient $$ and the electric field E (Vm⁻¹), C (molm⁻³) is the concentration of ions, and x(m) is the distance across the membrane. The diffusion term accounts for the diffusion of ions through the membrane due to concentration gradients. It describes the movement of ions from regions of higher concentration to lower concentration within the membrane, where D(m²s⁻¹) is the diffusion coefficient of ions. The migration term represents the migration of ions under the influence of the electric field. It depends on the valence of the ions (z), the electric field strength, and the concentration of ions, where F(Cmol⁻¹) is the Faraday’s constant. This term describes how the electric field drives ions toward the electrodes of opposite charge. Equation (7) includes the gas constant (R) and the temperature (T), indicating that the ion flux is influenced by temperature changes. Higher temperatures generally increase the mobility of ions, leading to higher flux rates.

The feasibility of solar integration in ED depends on various factors, including the energy requirements of the ED process, the availability of solar resources, and solar technologies. While ED itself does not directly utilize heat or electricity for desalination, solar energy can be integrated into ED systems to provide the electricity needed to power pumps, control systems, and other auxiliary equipment. Solar PV panels can be used to generate electricity for powering ED systems, either in standalone configurations or in grid-connected systems. PV systems can be designed to match the energy demand of the ED process, ensuring reliable and sustainable operation. Additionally, excess solar energy can be stored in batteries or used for other applications, further enhancing energy efficiency and system resilience.

Generally, the integration of solar energy reduces operating costs, enhances environmental sustainability, and promotes energy independence, reinforcing resilience in water supply infrastructure and contributing to global water security. However, successful implementation hinges on careful consideration of site-specific factors, technology, regulatory frameworks, and economic viability, emphasizing the importance of ongoing research, innovation, and collaboration in realizing the full potential of solar-powered desalination.

3.2. CSP Systems

CSP systems concentrate sunlight using mirrors or lenses onto a small area, typically a receiver or solar collector (Figure 7). The concentrated sunlight heats a working fluid, such as molten salt or synthetic oil, to high temperatures. This thermal energy is then used to generate steam, drive turbines, and produce electricity through a conventional steam turbine generator or other thermal processes, which is then used to drive the desalination process, typically through distillation or evaporation [86–88]. A distinctive feature of CSP lies in its ability to store the generated heat, enabling continuous operation, even in the absence of sunlight, during early morning or late evening hours.

CSP systems can be integrated with desalination processes in several ways. One approach is to use the thermal energy generated by CSP systems to directly power thermal desalination processes such as MSF distillation or MED. In these processes, the high-temperature steam produced by CSP systems is used to evaporate seawater and separate freshwater from salt [89–93]. Another approach is to use the electricity generated by CSP systems to power electrical desalination processes such as RO or ED. In this case, CSP-generated electricity can be used to drive pumps, membranes, and other electrical components of the desalination plant [49, 50, 81, 82].

CSP systems offer several advantages for desalination applications. They provide a reliable and dispatchable source of renewable energy, as thermal energy storage systems can store excess heat generated during the day for use at night or during periods of low sunlight. Additionally, CSP systems can achieve high temperatures and thermal efficiencies, making them well-suited for thermal desalination processes that require high-temperature steam. Moreover, CSP systems can be deployed in conjunction with desalination plants, providing both electricity and thermal energy to power various desalination processes [94–96]. However, CSP systems also have limitations that must be considered. One limitation is their relatively high upfront capital costs compared to other solar technologies, such as PV systems. CSP systems also require large land areas for the installation of solar collectors and infrastructure, which may be challenging in densely populated or land-constrained areas. Additionally, CSP systems are sensitive to weather conditions and require clear skies and direct sunlight to operate efficiently, which may limit their applicability in certain regions with frequent cloud cover or low solar irradiance.

3.2.1. MSF Distillation

Solar thermal MSF distillation is a thermal desalination process that utilizes the principle of evaporation and condensation to separate freshwater from saline water. In MSF distillation (Figure 8), seawater is heated to high temperatures under reduced pressure, causing it to flash evaporate into vapor. The vapor then condenses on a series of heat exchanger tubes or trays at lower temperatures, producing freshwater. The process consists of multiple stages, each comprising a flash chamber where the seawater is flashed and a condenser where the vapor is condensed. The vapor condenses into freshwater, while the remaining concentrated brine is discharged from the system [89–91, 98, 99].

The working principle of MSF distillation can be described using the heat balance equation, as in Equation (5):

$$ (5)

In MSF distillation, heat is supplied to the seawater to increase its temperature and facilitate evaporation. The heat input Q is equal to the mass flow rate m of seawater multiplied by the difference in enthalpy between the inlet seawater h_in and the outlet brine h_out. This heat input causes the seawater to flash evaporate into vapor, which then condenses to produce freshwater.

MSF distillation has the potential to be integrated with solar energy systems to reduce energy consumption and operating costs. Solar thermal energy can be used to heat the seawater and provide the necessary energy for evaporation. Solar collectors, such as parabolic troughs or flat-plate collectors, can capture sunlight and transfer it to a heat transfer fluid, which is then used to heat the seawater in the MSF distillation system [100–102]. The integration of solar energy can significantly reduce the reliance on fossil fuels or grid electricity, making MSF distillation more sustainable and environmentally friendly.

The potential for solar integration in MSF distillation can be evaluated using the solar fraction (SF), which represents the percentage of total energy input provided by solar energy. The SF is given by Equation (6):

$$ (6)

where Q_solar is the energy input from solar collectors (in kilojoules, kJ) and Q_total is the total energy input (including solar and other sources, in kilojoules, kJ). By increasing the SF, MSF distillation systems can reduce their dependency on nonrenewable energy sources and improve their environmental sustainability.

3.2.2. MED

MED is a thermal desalination process that utilizes multiple stages of evaporation and condensation to produce freshwater from saline water. In MED (Figure 9), seawater is heated to generate steam, which is then passed through a series of evaporator stages, each operating at progressively lower pressures. As the steam passes through each stage, it heats the feedwater in the adjacent stage, causing it to evaporate and produce freshwater vapor. The vapor is then condensed on heat exchanger surfaces, where it transfers its latent heat to the incoming feedwater, thereby preheating it. This preheated feedwater subsequently enters the next stage, where it is further heated and evaporated. The process continues through multiple stages, with each subsequent stage operating at lower temperatures and pressures, resulting in higher energy efficiency and freshwater production [92, 93, 103, 104]. MED is highly suitable for integration with solar energy systems due to its thermal nature and low operating temperatures. Solar thermal energy can be used to provide the heat input required for evaporation, thereby reducing the dependency on conventional energy sources such as fossil fuels or grid electricity.

Solar collectors, such as flat-plate collectors or parabolic troughs, can capture sunlight and transfer it to a heat transfer fluid, which is then used to heat the seawater in the MED system. The energy balance equation for MED is given by Equation (7):

$$ (7)

where Q is the total heat input (kJ), n is the number of stages in the MED system, m_i is the mass flow rate of seawater entering stage, i (in kg/s), h_in,i is the enthalpy of the seawater entering stage (kJkg⁻¹), h_out,i is the enthalpy of the brine leaving stage, i (kJkg⁻¹). Solar thermal energy can be integrated into MED systems by replacing or supplementing the heat input from conventional sources with solar energy. By optimizing the design and operation of the MED system and incorporating solar collectors, it is possible to achieve higher energy efficiency, lower operating costs, and reduced environmental impact.

3.3. Hybrid Solar Desalination Systems

Hybrid solar desalination systems combine the strengths of PV and CSP technologies (Figure 10) to create integrated and efficient solutions for water desalination. These systems leverage the complementary nature of PV and CSP technologies to optimize energy capture, storage, and utilization throughout the day and under varying weather conditions [94, 95].

One of the key synergies of hybrid solar desalination systems is their ability to maximize energy production and utilization. PV systems excel in generating electricity during daylight hours, while CSP systems can provide both electricity and thermal energy, including during periods of low sunlight or at night through thermal energy storage. By integrating PV and CSP technologies, hybrid systems can achieve a continuous and reliable energy supply, ensuring uninterrupted operation of desalination processes [106–108]. Furthermore, hybrid solar desalination systems offer flexibility and resilience in energy management. Excess electricity generated by PV systems during peak sunlight hours can be used to charge thermal energy storage systems or power auxiliary equipment, optimizing energy usage and reducing reliance on the grid [94, 109, 110]. Conversely, CSP systems can provide supplementary thermal energy to meet desalination process requirements, especially during periods of high energy demand or low solar irradiance.

Despite the numerous benefits, hybrid solar desalination systems also face several challenges. One challenge is the system design and integration, as combining PV and CSP technologies requires careful consideration of components, control systems, and operational strategies to maximize efficiency and performance. Additionally, hybrid systems may entail higher upfront capital costs compared to standalone PV or CSP systems, which could pose financial barriers to adoption, particularly in cost-sensitive markets.

4.1. Performance Analysis

These equations, along with considerations of system reliability, environmental impact, and social benefits, provide a comprehensive framework for evaluating the performance of solar desalination systems.

Table 1 provides highlights achieved in recent studies to enhance the efficiency, productivity, and improvement method of solar desalination systems.

For instance, Kaviti et al. [123] demonstrated how integrating nanomaterials like cerium oxide (CeO₂) and multiwalled carbon nanotubes (MWCNTs) can significantly enhance thermal performance while reducing operational and maintenance costs. Similarly, Abdel-Rehim and Lasheen [124] showed a 5%–6% increase in efficiency during peak months through the incorporation of packed layer thermal energy storage, emphasizing the role of optimized thermal management. Innovative designs were explored by Wiener et al. [125], who achieved notable performance improvements using fabric-coated polyurethane rollers, which leveraged capillary action to expand the evaporation surface area. Meanwhile, Narayanan et al. [126] provided a comprehensive review of performance factors, such as solar radiation intensity and ambient temperature, to identify critical areas influencing system efficiency. Lastly, Shoeibi et al. [127] advanced the integration of heat pipes and pulsating heat pipes, significantly improving thermal energy transfer within solar desalination systems.

4.2. Comparative Analysis of Different Technologies

In the performance evaluation for solar desalination, a comparative analysis of the different technologies and configurations plays an important role [128, 129]. This assessment encompasses several key factors, such as energy efficiency, WPC, system reliability, and environmental impact. By scrutinizing these aspects, stakeholders can discern the most suitable technology for a given application [47, 113, 130, 131]. Factors such as energy consumption per unit of freshwater produced, total cost of water production, system uptime, maintenance requirements, and environmental footprint should be evaluated. Additionally, considerations regarding scalability, flexibility, and adaptability to varying water demand are integral to the comparative analysis [77, 131]. Ultimately, this comprehensive assessment aids in making informed decisions regarding technology selection, system design, and implementation strategies, ensuring the optimal balance between energy efficiency, cost-effectiveness, reliability, and environmental sustainability in addressing water scarcity challenges. Table 2 presents a comparative analysis of various solar desalination technologies, highlighting their key features, energy consumption, water production capacity, cost, and environmental impact. Solar stills offer a simple and sustainable method with low emissions, while solar-powered RO systems provide efficient desalination for remote areas, albeit with higher energy consumption.

This table highlights that ED shows promise for desalination and CO₂ capture, reducing emissions significantly. MED improves efficiency with more effects and scales well economically, whereas MSF distillation, though energy-intensive, benefits from integration with power plants to enhance sustainability.

4.3. Challenges in Solar Desalination

In the journey of implementing solar desalination technologies, several challenges have emerged; one significant challenge is the upfront capital cost associated with deploying solar desalination systems, which can hinder widespread adoption, particularly in resource-constrained regions. Addressing this challenge requires innovative financing mechanisms, public–private partnerships, and cost-reduction strategies through technological advancements and economies of scale [19, 137, 138]. Additionally, the intermittent nature of solar energy presents operational challenges, requiring effective energy storage solutions and hybridization with other energy sources to ensure continuous water production [39, 139]. Moreover, site-specific factors such as solar irradiance, water quality, land availability, and regulatory constraints pose hurdles to the deployment of solar desalination projects, highlighting the importance of comprehensive feasibility studies and stakeholder engagement [138, 140, 141]. Thus, there is a need for holistic planning, interdisciplinary collaboration, adaptive management, and knowledge sharing to overcome barriers and unlock the full potential of solar desalination in addressing water scarcity sustainably.

5.1. Cost Analysis of Solar Desalination Systems

Moreover, a comparative cost analysis of solar desalination technologies further highlights the differences in feasibility based on economic factors. Solar stills remain the most cost-effective option, but their scalability is limited. Solar-powered RO systems provide a practical balance between cost and efficiency, making them ideal for medium-scale applications. Meanwhile, MED and MSF systems, despite their high costs, are best suited for industrial and large-scale desalination projects. To improve cost efficiency, future research should focus on hybrid solar desalination systems that integrate multiple technologies to enhance performance while reducing the LCOW.

By conducting cost analysis, stakeholders can determine the LCOW production, compare it with alternative water supply options, and identify strategies to optimize cost-effectiveness and sustainability.

5.2. Factors Affecting Economic Feasibility of Solar Desalination

The factors affecting the economic feasibility of solar desalination systems encompass a range of variables, including technology selection, scale of operation, solar resource availability, energy efficiency, financing and investment options, regulatory environment, water demand and pricing, and lifecycle costs [122, 146, 147]. The choice of desalination technology influences capital costs and ongoing operational expenses, while the scale of the plant impacts economies of scale. Solar resource availability dictates the size and efficiency of solar energy systems, affecting overall costs [143]. Energy efficiency plays an important role in reducing electricity consumption and operating expenses [148, 149]. Access to favorable financing options and investment incentives can improve project economics, as can supportive regulatory frameworks. Water demand and pricing structures directly influence the financial viability of desalination projects [150, 151]. Lastly, consideration of lifecycle costs is essential for accurately assessing economic feasibility [142]. Evaluating these factors comprehensively enables stakeholders to make informed decisions and identify opportunities to enhance cost-effectiveness and sustainability in solar desalination projects.

5.3. Environmental Benefits and Concerns Associated With Solar Desalination

Solar desalination presents several environmental benefits, primarily through its reliance on renewable energy sources, particularly solar power. By harnessing sunlight, solar desalination systems significantly reduce greenhouse gas emissions and mitigate the environmental impacts associated with conventional desalination methods powered by fossil fuels. This shift to renewable energy not only improves air quality but also contributes to long-term environmental sustainability [39, 40, 152]. Furthermore, solar desalination minimizes water stress by tapping into abundant seawater or brackish water resources, thereby alleviating pressure on freshwater sources vulnerable to depletion and contamination [152, 153]. This sustainable water management approach helps conserve sensitive ecosystems, such as rivers, lakes, and groundwater aquifers, by reducing the need for freshwater extraction [31, 154]. Additionally, certain solar desalination technologies, such as membrane-based systems like RO and ED, are inherently energy-efficient, further reducing energy consumption and environmental impact [154–156]. However, environmental concerns persist, including land use and habitat disturbance associated with large-scale facilities, material and resource consumption during production, salinity and brine disposal, ecological impacts of water intake and discharge systems, and the ecological footprint of desalination components [144, 145]. To ensure the sustainable implementation of solar desalination, careful planning, design, and management practices are essential to mitigate these concerns and maximize environmental benefits.

Apart from land use competition, other key concerns include brine disposal, carbon emissions from auxiliary systems, and marine ecosystem disruption (Table 3).

6.1. Africa

In Africa, Morocco is addressing water scarcity through desalination, with RO being the dominant technology. The country has implemented several desalination projects, including plants in Laayoune and Boujdour for seawater treatment and Khénifra for brackish water [164]. The Agadir desalination plant is a significant project in Morocco, utilizing both seawater and brackish water desalination [165]. To reduce energy consumption and environmental impact, researchers are exploring solar-powered desalination systems. A study of six coastal sites in the Middle East and North Africa region found that large-scale central receiver concentrated solar thermal facilities coupled with desalination units could be economically viable, with WPCs varying by location [166]. Similarly, Cape Town’s successful water crisis management during 2017–2018 demonstrated the effectiveness of innovative strategies in reducing urban water consumption. The city achieved an unprecedented 50% reduction in water usage over 3 years through open data initiatives and public engagement [167]. This experience highlights the potential for significant resource consumption reduction in the face of climate change and population growth. South Africa’s favorable environmental conditions, including higher solar irradiation (4.5–6.5 kWh/m²) and lower seawater salinity (35–35.5 parts per 1000) compared to the Middle East and North Africa region, make it suitable for large-scale solar desalination implementation [141]. Moreso, Egypt faces increasing water scarcity due to population growth, industrialization, and agricultural expansion, particularly in the Sinai and Red Sea regions. Desalination has emerged as a crucial solution to meet water demands in these areas, with solar-powered desalination offering environmental benefits. Egypt’s abundant solar resources, with 9–11 h of daily sunshine and 2000–3200 kWh/m²/year of direct vertical solar radiation, make it ideal for solar desalination projects [168]. Studies have shown that solar-driven thermal desalination can reduce CO₂ emissions by 47% compared to conventional methods, producing 4.32 kg CO₂ eq./m³ of desalted water on average [169]. With Egypt’s water demand increasing by 1.25% annually and a projected deficit of 21 billion m³/year by 2025, integrating desalination into water management strategies is crucial for the country’s economic and social development [170].

6.2. Middle East

In the Middle East, solar-powered desalination has gained traction, particularly through PV RO systems. Solar-powered desalination, particularly using PV technology with RO, has emerged as a promising solution for water scarcity in arid regions like the United Arab Emirates. The Abu Dhabi Solar Desalination Plant exemplifies this approach, integrating PV with RO to reduce fossil fuel dependence. Masdar’s Renewable Energy Water Desalination Program aims to develop energy-efficient, cost-competitive desalination technologies powered by renewable energy. PV-powered RO systems have demonstrated cost-competitiveness, with unit costs as low as 2–3 US$/m³ for small-scale systems in remote areas. In Abu Dhabi, a small-scale solar-powered RO plant with a 5 m³/h capacity and 45 kWh PV system was constructed to assess the feasibility for brackish and saline groundwater desalination [159, 171, 172].

These developments support the United Arab Emirates’s goal of producing 100% of its water from renewable sources by 2050, highlighting the long-term viability of solar desalination. The NEOM region in Saudi Arabia has offered a significant potential for solar-powered desalination, with an average annual solar radiation of 12.54 GJ/m². Solar still desalination is proposed as a cost-effective solution for the region’s water challenges. A case study of a RO plant in Saudi Arabia demonstrated that PV systems could generate between 9.15 and 17.95 MWh of electricity at midday, with the potential to provide 20% of total energy consumption at €0.025/kWh [173, 174]. However, the levelized cost of electricity from solar technologies in Saudi Arabia remains higher than subsidized diesel-based grid electricity, with CdTe PV systems offering the most competitive rates at $0.09–$0.10/kWh for tracking and fixed-tilt systems, respectively [175]. These findings highlight the technical feasibility and economic challenges of implementing solar-powered desalination in the NEOM region. Oman, heavily reliant on desalination, is exploring sustainable alternatives to address these issues. Solar-thermal desalination (STD) has been proposed as a viable solution, with Scheffler dish reflectors and parabolic trough collectors suggested for small-to-medium and large-scale plants, respectively. Integrating solar energy with desalination can reduce environmental impacts and operational costs [160]. An innovative approach combines solar and evaporation ponds to extract valuable minerals from brine, enhancing sustainability and economic viability [176]. These advancements show promise in addressing the environmental concerns associated with traditional desalination processes.

6.3. Asia

In Asia, India has made significant progress in solar desalination, with studies already showing that solar desalination can yield up to 29.43 kg/m²-d of distillate, with energy PPs under 1.5 years and production costs as low as 0.73–0.79 INR/L [177]. Globally, water scarcity affects 40% of the population when considering both quantity and quality issues. Expanding desalination capacity from 2.9 to 13.6 billion m³/month could significantly reduce water scarcity, especially in Asia [178]. In Abu Dhabi, small-scale solar-powered RO plants have been successfully implemented for brackish groundwater desalination, with capacities of 5 m³/h using 45 kWh PV systems [179]. In China, STD is emerging as a promising solution to address water scarcity, particularly in regions where freshwater resources are limited [180]. While STD offers sustainability benefits, its energy efficiency remains a challenge compared to PV RO [181]. A small-scale hybrid humidification-dehumidification/RO unit powered by concentrated PV and thermal technology demonstrated improved productivity (90.8% increase), reduced energy consumption (58.2% decrease), and increased recovery ratio (74.8% increase) under optimal conditions in Sanya, China [182]. In the Maldives, floating PV (FPV) systems offer significant advantages in addressing land scarcity and environmental concerns. FPV systems can increase annual energy yield by 13%–14% compared to ground-mounted systems, with a performance ratio of up to 87.10% and annual energy yield of 8.74 GWh for a 5 MW installation [183]. These systems reduce environmental impacts associated with conventional PV, such as deforestation, erosion, and microclimate changes [184]. In the Maldives, FPV-powered desalination presents a sustainable solution for providing safe drinking water, optimizing both financial and environmental outcomes [185]. A fully renewable energy system incorporating floating offshore technologies is technically feasible for the Maldives by 2030, with costs potentially decreasing to 77.6–92.6 €/MWh by 2050 [186].

These case studies highlight the growing adoption and success of solar desalination across diverse regions, showcasing its efficiency, economic feasibility, and environmental benefits, making solar desalination a viable solution for global water security. With continued research, policy support, and large-scale implementation, solar-powered desalination has the potential to address freshwater shortages sustainably.