Direct Solar Desalination Research Articles

Bidirectional solar water production enabled by a breathable Janus photothermal material

Solar-driven interfacial water evaporation offers a promising solution to the global scarcity of freshwater. Despite advances in increasing evaporation rates, current condensate productivity is limited to 0.3 − 0.5 kg m−2 h−1 due to unidirectional vapor diffusion, which is insufficient to satisfy water demands. This paper introduces a bidirectional solar water production (BSWP) device that utilizes a breathable Janus photothermal material made from recycled cotton fabric. The BSWP device allows vapor to diffuse in both upward and downward directions of the evaporation interface. This design features dual condensers, addressing the limitations of traditional solar stills by reducing vapor concentration and minimizing light loss due to condensation on the top cover receiving light. Under 1 sun illumination, the BSWP device achieves a water yield of 1.06 kg m−2 h−1 with a solar-to-water efficiency of 71%. An 10-hour outdoor experiment demonstrates that the BSWP device can yield a water flux of 9.65 kg m−2, showcasing its potential for efficient water generation in practical environmental conditions. The present work provides a new perspective on the structural design of direct solar desalination configurations, potentially offering a more effective solution to cope with global water scarcity.

Recent advances and potential applications for solar still-based direct solar desalination systems

Recent advances and potential applications for solar still-based direct solar desalination systems

Innovative Approaches to Solar Desalination: A Comprehensive Review of Recent Research

Solar desalination systems are a promising solution to the water scarcity problem since the majority of the earth’s water resources are salty. With the increasing focus on desalination research, many innovative methods are being developed to extract salts from saline water. Energy consumption is a significant concern in desalination, and renewable energy, particularly solar energy, is considered a viable alternative to fossil fuel energy. In this review, we will focus on direct and indirect solar desalination methods, specifically traditional direct solar desalination methods such as solar still and humidification dehumidification (HDH) desalination systems. We will also briefly discuss a recent advancement in the desalination method known as the fogging process, which is a development of the HDH desalination system.

Facile formation of Ag nanoworms based Janus nanofiber composites for efficient solar steam generation

In this work, a flexible Janus composites membrane fabricated by large-scale electrospinning, a rapid plasma etching process, and reproducible surface modification is proposed for stable and efficient solar desalination. The upper hydrophobic plasmonic absorbers are used for effective solar absorption while the bottom hydrophilic polymer layer is for water supply and salt resistant. The heat stability and cycle tests demonstrate their superior performance for steam generation (energy conversion efficiency with 76.06% under 6 sun and stable water output with 7.533 kg m−2 h−1). Such Janus membrane provides an alternative way for direct solar desalination, which is achieved by a scalable and cost-effective process.

Three-dimensional open architecture enabling salt-rejection solar evaporators with boosted water production efficiency

Direct solar desalination exhibits considerable potential for alleviating the global freshwater crisis. However, the prevention of salt accumulation while maintaining high water production remains an important challenge that limits its practical applications because the methods currently employed for achieving rapid salt backflow usually result in considerable heat loss. Herein, we fabricate a solar evaporator featuring vertically aligned mass transfer bridges for water transport and salt backflow. The 3D open architecture constructed using mass transfer bridges enables the evaporator to efficiently utilize the conductive heat that would otherwise be lost, significantly improving the water evaporation efficiency without compromising on salt rejection. The fabricated evaporator can treat salt water with more than 10% salinity. Moreover, it can continuously and steadily work in a real environment under natural sunlight with a practical solar-to-water collection efficiency of >40%. Using the discharged water from reverse osmosis plants and sea water from the Red Sea, the evaporator demonstrates a daily freshwater generation rate of ~5 L/m2, which is sufficient to satisfy individual drinking water requirements. With strong salt rejection, high energy efficiency, and simple scalability, the 3D evaporator has considerable promise for freshwater supply for water-stressed and off-grid communities.

STUDY OF A NEW PASSIVE SOLAR DESALINATION DESIGN WITH A HEAT RECYCLING SYSTEM

This study presents a new and innovative suggestion to design a solar water desalination system by the direct passive method, with the aim of raising productivity by recycling the energy lost during the desalination process and raising the efficiency of condensation. In this study, the innovative design was evaluated to demonstrate its ability to increase the productivity of direct passive solar desalination while maintaining simplicity of installation and ease of operation. A prototype of the design was built to make a detailed study on the efficiency of the design and its ability to raise productivity under several different operational and climatic conditions in the city of Aden - Yemen, where several experiments were made to desalinate seawater taken from the city's coasts and the water of semi-salty wells in the city of Aden to compare the readings different. The results prove that the innovative design can raise productivity up to 80% higher than normal. The effect of pond water depth and salinity on productivity was studied. The results show that the higher the water depth in the evaporation basin, the higher the production capacity, and the higher the water salinity, the lower the production capacity of inactive direct solar desalination systems. This study also provides an assessment of the quality of the water produced by the innovative design by carrying out several chemical tests and making a comparison with the water quality before desalination to ensure that the design is capable of desalinating seawater or semi-salty well water to produce potable water. The results were confirmed for the quality of the produced water, which confirms the ability of the design to produce potable water in accordance with local and international standards, as the amount of total dissolved salts in sea water before desalination was 41340 mg/L and in well water 1300 mg/L, while after desalination by innovative design The total dissolved salts in treated sea water was 210 mg/L and in treated well water was 34 mg/L.

Humidifying solar collector for improving the performance of direct solar desalination systems: A theoretical approach

In this paper, a new type of solar collector named humidifying solar collector, that is, a solar collector with air humidification function, is proposed. The particularity of this system compared to previous systems in the literature is that the quantity of liquid water present in the collector at each instant is equal to the quantity that will evaporate within the following unit time, no longer greater. This minimizes the quantity of liquid water present in the collector at each instant, and consequently allows to reach desired evaporation temperatures in shorter times and even under low solar irradiances, and minimizes the thermal resistance between evaporation surface and absorber caused by water depth. Then, a theoretical and comparative study by simulation using Engineering Equation Solver software between the performance of the humidifying solar collector-based solar still (proposed system) and that of the solar air heater-based humidification dehumidification solar desalination system (conventional system) is conducted. The performance parameters assessed are energy and exergy efficiencies, dry air mass flow rate required and the maximum water mass flow rate that can evaporate in that air. The results reveal that, in general case, the proposed system is fundamentally more efficient than the conventional system. For instance, for the sizes and heat transfer parameters chosen in this study, the performance of the proposed system is 1.3–32.2 times higher than that of the conventional system; its freshwater productivity under incident solar irradiance of 900 W/m2 can reach 2.923 kg/h, and can be further improved by optimizing the design of the humidifying solar collector.

Factors affecting the performance of a solar still and productivity enhancement methods: A review.

Good-quality drinking water is an essential requirement for a healthy and sustainable future. In the current scenario, people living in remote areas of the world are deficient of potable water, especially in developing nations. Desalination technologies available today are energy intensive and aggravate carbon emissions as most energy requirements are fulfilled by using fossil fuels. Solar still is a simple and direct solar desalination device used for water distillation. The major problem associated with a solar still is its low productivity. The main aim of this review paper is to discuss various modifications in a solar still which resulted in productivity enhancement. Different parameters affecting a passive solar still performance and their optimum values for maximum productivity are also thoroughly analysed in this paper. Water depth is an important operating parameter that influences still productivity, and various results showed that maximum productivity is achieved mostly at minimum water depths.

High-Performance Salt-Rejecting and Cost-Effective Superhydrophilic Porous Monolithic Polymer Foam for Solar Steam Generation.

Direct solar desalination with excellent solar photothermal efficiency, lower cost, and extended generator device lifetime is beneficial to increase potable water supplies. To address fundamental challenges in direct solar desalination, herein, we present a new and facile method for the scalable fabrication of the polymer porous foam (VMP) as salt-resistant photothermal materials, which was synthesized through a one-step hydrothermal method using styrene and 1-vinyl-3-ethylimidazolium tetrafluoroborate as monomers and N,N'-methylenebisacrylamide as the cross-linking agent. The as-resulted VMP shows excellent mechanical properties which could have a compression strain of 30%, resulting in its superior processability for practical operation. In addition, by taking advantage of its inherent low density, well-controlled porous structure (porosity is 73.81%), and extremely low thermal conductivity (0.03204 W m-1 K-1), the VMP exhibits an excellent solar evaporation property, and the solar photothermal efficiency can reach more than 88% under 1 kW m-2 irradiation. Moreover, the introduction of ionic liquid moiety (imidazolium tetrafluoroborate) into VMP results in its interesting superhydrophilic wettability, which can accelerate water transportation (wetting in 5s) and resolve the crystalline salt within 1.13 h. In addition, the interconnected macropores of the VMP, as water channels, can replenish the vaporized brine on the surface to prevent salt from adhering. The VMP shows a salt-resistant performance, for example, its solar evaporation efficiency remains nearly unchanged after 6 h duration under 1 sun irradiation. Based on its simple and cost-effective manufacturing process, excellent solar photothermal efficiency, and salt resistance, our VMP may be a promising candidate as photothermal materials for practical desalination from seawater and other wastewater.

Efficient Solar-Thermal Distillation Desalination Device by Light Absorptive Carbon Composite Porous Foam.

Solar‐thermal driven desalination based on porous carbon materials has promise for fresh water production. Exploration of high‐efficiency solar desalination devices has not solved issues for practical application, namely complicated fabrication, cost‐effectiveness, and scalability. Here, direct solar‐thermal carbon distillation (DS‐CD) tubular devices are introduced that have a facile fabrication process, are scalable, and use an inexpensive but efficient microporous graphite foam coated with carbon nanoparticle and superhydrophobic materials. The “black” composite foam serving as a solar light absorber heats up salt water effectively to produce fresh water vapor, and the superhydrophobic surface of the foam traps the liquid feed in the device. Two proof‐of‐principle distillation systems are adopted, i.e., solar still and membrane distillation and the fabricated devices are evaluated for direct solar desalination efficiency. For the solar still, nanoparticle and fluorosilane coatings on the porous surface increase the solar energy absorbance, resulting in a solar‐steam generation efficiency of 64% from simulated seawater at 1 sun. The membrane distillation demonstrates excellent vapor production (≈6.6 kg m‐2 h‐1) with >99.5% salt rejection under simulated 3 sun solar‐thermal irradiation. Unlike traditional solar desalination, the adaptable DS‐CD can easily be scaled up to larger systems such as high‐temperature tubular modules, presenting a promising solution for solar‐energy‐driven desalination.

Water Purification with Direct Solar Desalination for Arid Areas in Ethiopia

The use of solar energy in thermal desalination processes is one of the most promising applications of in water purification. Solar desalination can either be direct; use solar energy to produce distillate directly in the solar collector, or indirect; combining conventional desalination techniques, such as vapor compression (VC) and multistage flash desalination (MSF), with solar collectors for heat generation. This paper describes a pilot study of direct desalination technology. The pilot experiment of desalination system was made up of a single basin (1.5m x 1.8m basin area) and two sided roof with 15 degree to the horizontal and sealed roof of 4 mm thick glasses. The glass cover roof was positioned from East to West orientation and obstruction free area to increase the efficiency of available sunlight utilization. Water quality parameters of the water and treated water were tested at Arba Minch University Water quality Laboratory. The study revealed that, the average yield of the distillate water was 2.6 L/m2/ day, where the average efficiency of the system was 29.5 %.Regression analysis showed that climatic variables such as temperature, wind speed and solar intensity were observed to affect the treatment efficiency of the production of distilled water in this pilot study. Accordingly, the experiment output transposed to Dollo Ado, Somali Regional state and the solar still was predicted to produce 3.4 - 5 L/m2 /day with climate condition of the area. Although the system requires large area with relatively low production, it is still suitable for use in remote and arid with high temperature.

(Invited) Mechanistic Details of Protonic Solar Cells Formed Via Covalent Modification of Passive Ion-Exchange Membranes with Photoacid Dye Molecules

Many electrochemical technologies require ion-conducting polymer electrolytes. These polymers are passive in that electric bias across them drives ion migration in the thermodynamically favored direction.1 Recently, my group engineered two important features into ion-selective polymer membranes to introduce the active function of photovoltaic action and demonstration of an ionic solar cell. These features were covalent bonding of photoacid dyes to the polymers such that absorption of visible light liberated protons, and polymers with charge-selective contacts to facilitate separation and collection of H+ and OH–.2,3 The most effective designs join a monopolar cation-selective polymer to a monopolar anion-selective polymer to form a bipolar membrane whose electrostatics and thermodynamics mimic those of a rectifying semiconductor pn-junction diode. Illumination from either side of a photoacid-modified bipolar membrane resulted in photoinduced deprotonation of photoacids followed by charge separation in a direction dictated by the built-in electrostatic asymmetry in the polymers. Performance optimization is underway to increase the state-of-the-art voltage to beyond 120 mV and state-of-the-art current to beyond 100 μA/cm2. The aim of these efforts is to gain a strong fundamental understanding of dye and material function using a variety of techniques. These include electrochemical impedance spectroscopy to quantify properties of capacitive space-charge regions; pulsed-laser spectroscopy to elucidate light-driven mechanisms of ion transfer and transport; finite-element numerical modeling to understand photoacid dye kinetics and drift–diffusion generation–recombination membrane physics; and optical, electron, and ion microscopies to elucidate materials morphology and function. Collectively, these photo-responsive polymers represent a new class of materials that use light to trigger changes in local pH and/or electrostatic potential. These local changes can be used to affect macroscopic processes such as direct solar desalination of salt water or triggering redox chemistry or chemical catalysis. Acknowledgment: This work is supported by a Moore Inventor Fellowship from the Gordon & Betty Moore Foundation, under Grant #5641.

Flexible and Salt Resistant Janus Absorbers by Electrospinning for Stable and Efficient Solar Desalination

AbstractWith recent progress in interfacial solar steam generation, direct solar desalination is considered a promising technology for providing a clean water solution through a cost effective and environmental‐friendly pathway. As a high and stable water production rate is the key to enable widespread applications, salt deposition becomes a critical issue that needs to be addressed. Herein, the authors demonstrate that a flexible Janus absorber fabricated by sequential electrospinning can enable stable and efficient solar desalination. Taking advantage of the unique structure of Janus, two functions of steam generation, solar absorption and water pumping, are decoupled into different layers, with an upper hydrophobic carbon black nanoparticles (CB) coating polymethylmethacrylate (PMMA) layer for light absorption, and a lower hydrophilic polyacrylonitrile (PAN) layer for pumping water. Therefore, salt can only be deposited in the hydrophilic PAN layer and quickly be dissolved because of continuous water pumping. Janus absorber demonstrates high efficiency (72%) and stable water output (1.3 kg m–2 h–1, over 16 days) under 1‐sun, not achieved in most previous absorbers. With a unique structure design achieved by scalable process, this flexible Janus absorber provides an efficient, stable and portable solar steam generator for direct solar desalination.

Conversion of Visible Light into Ionic Power Using Photoacid-Dye-Sensitized Bipolar Ion-Exchange Membranes

Summary For over half a century, it has been recognized that the classical physics that dictates the behavior of hydrated ion-exchange membranes, such as Nafion, and semiconductors, such as doped silicon, are similar. However, no demonstrations of photovoltaic action from ion-exchange materials existed. We recently reported a synthetic light-driven proton pump derived from an ion-exchange membrane. Absorption of light by covalently bound photoacid molecules resulted in photovoltaic action. This design lacked a second permselective membrane contact, which limited its performance. Here, we report a ∼60-fold increase in the photovoltage through use of a bipolar membrane structure consisting of a cation-exchange membrane affixed to an anion-exchange membrane. The junction between the layers was characterized in detail using electrochemistry, scanning electron microscopy, spectroscopy, and thermal gravimetric analysis. Our results represent considerable progress toward a device that directly converts sunlight into ionic electricity, which has implications for direct solar desalination of salt water.

Analytical investigation of different operational scenarios of a novel greenhouse combined with solar stills

This study is an analytical investigation for the performance of a new stand-alone agriculture Green House (GH) integrated with on-roof Transparent Solar Stills (TSS) to be a self-sufficient of irrigation requirements. This system utilizes the surplus solar energy via direct solar desalination in TSS and Humidification-Dehumidification (HDH) process as two sources for water production. The effect of using the on-roof TSS on the GH performance, the power required for heating and fans operation at different climate conditions is discussed. The paper investigates the effect of the fresh air ratio and the bypass ratio for the condenser of the cooling system on the internal micro-climatic conditions of the GH. For different climatic conditions of Borg-Elarab, Egypt, controlling both the condenser bypass and fresh air ratios can be used to satisfy the required micro-climate conditions and water requirements for plant growth and minimize the power consumption for cooling system. The results show that the daily average temperature inside the GH can be increased during winter. Furthermore, the system can produce a sufficient amount of fresh water during summer. The system can only produce a maximum amount of water of 2.44L/m2⋅day during the coldest day which indicates the need for additional solar stills to be installed if a higher amount of water is required. In general, recovering the extra solar radiation to either produce fresh water via on-roof TSS or reduce the power consumption by cooling, heating and ventilation systems is the main advantage of the new proposed GH system. This work is a good applied example for food, water, energy and climate change Nexus which covers the main elements of Sustainable Development Goals (SDGs).

Solar thermal desalination technologies

The use of solar energy in thermal desalination processes is one of the most promising applications of the renewable energies. Solar desalination can either be direct; use solar energy to produce distillate directly in the solar collector, or indirect; combining conventional desalination techniques, such as multistage flash desalination (MSF), vapor compression (VC), reverse osmosis (RO), membrane distillation (MD) and electrodialysis, with solar collectors for heat generation. Direct solar desalination compared with the indirect technologies requires large land areas and has a relatively low productivity. It is however competitive to the indirect desalination plants in small-scale production due to its relatively low cost and simplicity. This paper describes several desalination technologies in commercial and pilot stages of development. The primary focus is on those technologies suitable for use in remote areas, especially those which could be integrated into solar thermal energy systems.

Perspectives of solar-assisted seawater distillation

The use of solar energy in thermal desalination processes is one of the most promising applications of renewable energies to seawater desalination. A solar distillation system may consist of two separated devices—the solar collector and the distiller—or of one integrated system. The first case is an indirect solar desalination process, and the second one is a direct solar desalination. This paper deals with indirect solar desalination and its perspectives in the future. First, a summary of existing plants was given. Second, different technologies were compared. Finally, the possible improvements of thermal solar and seawater distillation technologies were considered in order to analyze the perspectives of the competitiveness of solar vs. conventional energy in seawater desalination.