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| Fig. 1: Projected ratio of human water demand to water availability and the Global Horizontal Irradiance. [2,19] (Courtesy of WRI and the World Bank.) |
Approximately half of the global population currently faces severe water scarcity. [1,2] By 2030, a 40% shortfall in available freshwater resources is projected, which, when combined with population growth from 8 billion today to an estimated 9.7 billion by 2050, could escalate into a major global water crisis, with serious implications for food security, economic growth, and the energy needs of developing nations. [3,4]
Although water scarcity is a growing global challenge, its impacts are uneven across regions. Twenty-five countries home to one-quarter of the worlds population experience extremely high water stress each year. [2] The most severely affected regions include the Middle East and North Africa, where 83% of the population faces extreme water stress, and South Asia, where 74% of the population is similarly affected. [2]
Desalination has become an essential strategy for augmenting conventional freshwater supplies in coastal and arid regions facing acute water scarcity. In broad terms, desalination refers to the removal of salts and dissolved solids from seawater or brackish water to produce water suitable for drinking, agriculture, or industrial applications. Desalination technologies fall into two major categories: thermal and membrane-based processes.
Thermal desalination methods such as multi-stage flash (MSF) and multi-effect Distillation (MED) operate on the principle of distillation. Feedwater is heated to generate vapour, leaving behind salts and other impurities; this vapour is then condensed under controlled pressure to yield purified water. In contrast, membrane desalination techniques force water through a semipermeable membrane under high pressure, allowing water molecules to pass while rejecting salts and contaminants. Reverse osmosis (RO) is the dominant membrane-based approach, and seawater RO (SWRO) is the primary technology deployed at large scale worldwide. [4]
Despite its widespread adoption, SWRO remains relatively energy intensive. Typical energy requirements, including intake, pretreatment, membrane pressurisation, and post- treatment lie in the range of 3.5 to 4.5 kWh/m, depending on feed salinity, system configuration, and the efficiency of energy-recovery devices. [5] Even the theoretical minimum energy for desalinating seawater with a salinity of 35,000 mg/L at 50% recovery is 1.07 kWh/m, which is still an order of magnitude higher than the energy needed for conventional surface-water treatment (0.2 to 0.4 kWh/m). [6,7] Because of this high energy demand, both the cost and carbon footprint of desalinated water are strongly determined by the energy supply, motivating efforts to integrate renewable energy sources into desalination systems. [7]
As shown in Fig. 1, many regions experiencing the most severe water scarcity also benefit from some of the world's highest solar irradiance, creating a natural alignment between desalination demand and solar energy availability. Countries in the Middle East and North Africa, for instance, receive the largest annual global horizontal irradiance (GHI) in the world, frequently surpassing 2,000kWh/m2 while simultaneously experiencing extremely high water stress affecting more than 80% of their population. [2,8] Similar overlaps exist in South Asia, western Australia, and large swathes of Africa, where increasing desalination needs coincide with abundant solar resources. [9] It is therefore unsurprising that these regions also host the largest existing and planned desalination infrastructure. This geographic congruence makes solar-powered desalination particularly attractive for water-scarce, solar-rich regions.
At the same time, the cost of solar-PV electricity has declined rapidly over the past decade. The global weighted-average levelized cost of electricity (LCOE) for utility-scale Solar PV fell from approximately US$0.46/kWh in 2010 to roughly US$0.043/kWh in 2024, representing nearly a 90% reduction. More importantly, the average cost to install 1 kW of photovoltaic capacity decreased from US$5,124 in 2010 to US$876 in 2022, an almost 80% reduction over the decade. [10] These trends position solar PV as a cost-competitive, low-carbon energy source for desalination systems, particularly in regions where conventional grid electricity is inaccessible or prices remain high.
Having established the need and opportunity to incorporate solar energy inputs into desalination, this report will discuss existing plants across the globe that have implemented either solar PV as an electrical input to existing desal processes or solar thermal energy directly for the evaporation step in the thermal desal. Solar-powered desalination has been implemented across a wide range of scales and technological configurations, from small community units to utility-scale seawater RO facilities. These deployments provide concrete evidence of technical feasibility, while also highlighting the operational constraints and trade-offs associated with integrating solar energy into desalination processes.
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| Table 1: Examples of Large-Scale Solar-Powered RO Desalination Plants |
General insights: Industry assessments consistently identify energy as the dominant cost component in desalination systems, accounting for 40 to 50 % of total cost. It has also been noted that renewable energy is already cost-competitive for many remote desalination sites, though feasibility depends strongly on the specific solar technology deployed and the desalination process in use. Recent research indicates that solar-driven RO can achieve up to 75 % reductions in energy use compared with conventional systems. Modern installations increasingly rely on advanced battery-storage systems to buffer excess generation and maintain output during non- sunlight hours. The integration of AI-based control and smart-grid management enables real-time optimisation of energy consumption, improving reliability and lowering operating costs. [13] Despite these advantages, persistent challenges, especially high capital expenditure, system-level complexity, and requirements for supportive grid and storage infrastructure remain key barriers to broader deployment.
Solar-thermal desalination uses solar heat rather than only solar electricity to drive evaporation-based desalination processes(MED or MSF). Concentrated solar power (CSP) systems, which use heliostats to focus sunlight onto a central receiver filled with thermal salts, can deliver high-temperature heat suitable for these processes and can store thermal energy for several hours, enabling operation beyond daylight hours. This storage capability gives CSP an advantage over photovoltaic (PV) systems, which provide cheap electricity but no usable heat, making PV better suited for reverse-osmosis (RO) while CSP heat aligns more naturally with thermal desalination. [13]
Thermal desalination also becomes attractive in regions with very high salinity feedwater, such as the Persian Gulf and Red Sea. In such places, RO requires higher pressures and therefore higher electricity inputs, raising operating costs. Evaporation-based desalination paired with CSP may be preferable in these environments because evaporation energy requirements do not significantly increase with salinity. This makes CSP-MED or CSP-MSF a potentially cost-competitive option in highly saline coastal zones. [13]
Despite these benefits, large-scale solar-thermal desalination remains far less common than PV-RO. CSP infrastructure has higher upfront costs, requires large tracts of land away from corrosive coastal spray, and is complex to maintain. Consequently, most operational solar- powered desalination plants today use PV-RO, while CSP-thermal systems remain limited to pilot- or demonstration-scale deployments. [14]
Thermal solar desalination has recently seen renewed commercial interest, driven by the need for off-grid, low-carbon water supply solutions. In the United States, a solar-thermal treatment system in Californias Central Valley has processed approximately 1.6 billion gallons of saline agricultural drainage, demonstrating the feasibility of solar-driven thermal purification for inland brines. Commercial plug-and-play thermal units have also emerged, including fully containerized, off-grid systems capable of producing potable water using only solar heat, enabling decentralized deployment in remote coastal regions. A prominent example is Desolenator, a Dutch company partnering with the Dubai Electricity and Water Authority (DEWA) to construct what they describe as the worlds first fully sustainable solar-thermal water purification system. Unlike PV-RO, these configurations use photovoltaic-thermal (PVT) collectors or solar-thermal absorbers to supply both heat and electricity to an integrated distillation module, avoiding RO membranes and reducing fouling-related maintenance. While still at pilot or early commercial scale, these projects illustrate how thermal solar desalination is transitioning from experimental prototypes toward modular, field-ready systems designed for operation on 100% renewable energy. [15]
Community-scale solar-powered desalination systems typically producing 50 to 500 m3/day represent some of the most successful real-world demonstrations of off-grid renewable desalination. Unlike large industrial plants that rely on grid-tied solar farms, these installations are often stand-alone PV-RO(SW or brackish) systems designed to serve towns, villages, tourism regions, or remote coastal communities where grid electricity is limited or expensive.
One of the most widely cited examples is the Witsand Solar-Powered RO Plant in Western Cape, South Africa, which supplies roughly 150 m3/day of potable water to local residents, a significant portion of which is produced with only solar energy. [16]
Kenya has emerged as one of the most successful adopters of community-scale solar desalination, with multiple operational systems delivering measurable benefits in off-grid regions. GivePowers flagship solar-powered RO plant in Kiunga produces over 75,000 L/day of drinking water and now serves approximately 25,000 people, using a containerized PV array coupled with a battery- supported microoff-grid system that allows desalination to continue after sunset. Similar successes include Lamus solar desalination unit, which supplies clean water to over 10,000 residents, as well as Kilifi Countys 3,000 m3/day RO plant that serves households and local industries. Smaller solar-RO systems producing 3,500 m3/h have also been deployed in rural coastal communities where residents previously traveled over 5 km to access potable water. Across Mombasa, Likoni, Nairobi, Wajir, Turkana, and Kwale counties, additional installationsincluding Boreal Lights planned rollout of 19 new plants further illustrate Kenyas broad, practical success with solar-powered community desalination. [2,17,18]
However, performance and long-term operational data from these pilots remain limited, making it difficult to assess their reliability and large-scale deployment. These projects demonstrate that small-scale solar desalination can be technically viable and socially impactful, providing a model for broader deployment in rural and water-stressed regions.
Solar-powered desalination is a viable, low-carbon solution for water-scarce, solar-rich regions. Large- and community-scale PV-RO systems demonstrate technical feasibility, while solar-thermal approaches provide options for high-salinity waters. Remaining challenges include high capital costs, integration with storage or grids, and limited long-term operational data.
© Devashish Bhave. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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