Solar desalination is a technology that uses solar energy to desalinate water in other words, it is a technology for removing salt from the water that employs solar energy to boil saltwater and catch the steam, which is then cooled and condensed into pure fresh water.
In the still, salt and other contaminants are left behind.
This technology may be used to achieve desalination in two main ways: direct and indirect.
Sunlight may produce heat for evaporative desalination procedures, or it can convert to electricity to power a membrane process in some indirect techniques.
Unlike fossil-fuel-powered desalination, solar desalination systems provide free daily energy.
As the energy consumption per unit of water produced increases, the area required for solar collectors also increases, resulting in higher investment costs.
As a result, solar desalination system performance is frequently expressed in terms of the number of liters cleansed every day per unit area of the collector (L/m2-day).
This value alone is insufficient for performance comparisons since available daily solar energy varies by geographic location and time of year.
However, we can separate the impacts of solar incidence and system design by decomposing them.
The desalination technology and the solar energy gathering system are separated in first order using these expressions.
Other parameters, like the top and bottom temperatures of the desalination cycle, will affect the GOR and collector thermal efficiency and these temperatures may change during the day.
Energy storage may be used in both thermal and electrically powered desalination systems to level off daily cycling and extend operation into the night.
Methods of solar desalination
In the direct method
As part of a 2-phase separation, direct techniques employ heat energy to evaporate the salt water.
Because such approaches are simple and take up minimal space, they are commonly utilized on tiny systems.
However, they have a limited output rate because of the low working pressure and temperature.
The procedure is carried out in one straightforward cycle using a solar collector and a distillation mechanism.
This type of solar still is detailed in survival publications, included in sea survival kits and used in a variety of tiny desalination and distillation units.
Direct method solar distillation produces 3–4 liters per square meter (0.074–0.098 US gal/sq. ft.) of water, which is proportional to the area of the sun’s surface and incidence angle.
Distillation by the direct method favors plants with production capacities of less than 200 m3/day (53,000 US gal/day) because of this proportionality and the comparatively high cost of property and material for construction.
Indirect method
A solar collecting array, comprising photovoltaic and/or fluid-based thermal collectors, plus a separate conventional desalination plant are used in indirect solar desalination.
The indirect method of production is depending on the plant’s performance and increasing size reduces the cost per unit produced.
Many various plant arrangements have been studied theoretically, tested practically and placed in certain circumstances.
Multiple-effect humidification (MEH), multi-stage flash distillation (MSF), Multi-effect humidification (MEH), multi-stage flash distillation (MSF), multi-effect distillation (MED), multi-effect boiling (MEB), humidification–dehumidification (HDH), reverse osmosis (RO) and freeze-effect distillation are examples of these processes.
Since 2009, commercially available indirect solar desalination systems have been used using photovoltaic (PV) and reverse osmosis (RO) panels.
By 2013, each system will be capable of producing 1,600 liters (420 US gal) per hour and 200 liters (53 US gal) per day per square meter of PV panel.
Systems at the municipal level are in the works.
Since 2010, the atoll of Utirik in the Pacific Ocean has been replenished with fresh water.
Solar desalination’s advantages
The following are some of the major advantages of solar desalination:
1-It is powered by free solar energy.
2-Solar desalination facilities are low-cost, lightweight and transportable.
3-Onshore or offshore, the plants are simple to put up.
4-Low-cost maintenance.
5-Environment-friendly.
The challenges and solutions of solar desalination
Thermal solar desalination plants confront inherent design issues:
Competing heat and mass transfer rates during evaporation and condensation determine the system’s efficiency.
Condensation heat is vital because evaporating water and producing saturated, vapor-laden hot air requires a lot of solar energy.
Even during condensation, this energy is transmitted to the condenser’s surface by description.
This heat is released as wasted energy throughout most solar stills.
We can solute these problems by
The heat dissipation problem, on the other hand, can be reduced by shielding the condensation chambers from direct sunlight or employing an optical system to elevate the system’s temperature.
The inefficiency of the system in terms of evaporation may be rectified by appropriately constructing the system’s surfaces in terms of heat transfer performance.
Lower the pressure in the reservoir may be done with a vacuum pump, which reduces the amount of thermal energy required greatly.
For example, water at 0.1 atmosphere boils at 50 degrees Celsius (122 degrees Fahrenheit) rather than 100 degrees Celsius (212 degrees Fahrenheit).
Innovative technology
Solar dome
The decentralized system, called the “solar dome,” employs concentrating solar power (CSP) technology to treat seawater.
The procedure includes running saltwater beneath a “glass-enclosed aqueduct system,” which heats the water as it passes inside the dome.
The sun’s energy is concentrated onto the dome by an array of parabolic mirrors, or “heliostats,” which surround the sphere.
This transmits heat to the ocean, resulting in a “cauldron effect” in which the water is superheated. Steam condensate is piped as freshwater to reservoirs and irrigation channels after evaporation.
Nanoparticles
Nanoparticles first appeared in the solar-thermal field around six years ago, when Rice University researchers mixed Some nanoparticles with cold water and were able to generate steam when exposed to sunshine.
Since then, much research in what is now known as photothermal conversion has shifted to the subject of plasmonics, which makes use of the wave of electrons formed when photons impact a metallic surface.
However, creating plasmonic nanostructures is not as simple as dissolving some nanoparticles in water.
Researchers in China have now coupled the ease of adding nanoparticles to water with plasmonics to create a photothermal conversion mechanism that outperforms any previously reported plasmonic or all-dielectric nanoparticles.
By dispersing these nanoparticles in water, the rate of water evaporation under solar radiation is increased by a factor of three.
This allows the water temperature to rise from 29 degrees Celsius to 85 degrees Celsius in 100 seconds.
References
[1] Solar desalination. (online) available at: https://solarshams.com/content/solar-desalination
[2] Solar desalination. (online) available at: http://web.mit.edu/lienhard/www/papers/reviews/Solar_Desalination_AnnRevHeatTransfer-Vol15-2012-4659.pdf
[3] Can Solar Desalination Slake the World’s Thirst? , 21 Sep, (online) available at: https://www.scientificamerican.com/article/can-solar-desalination-slake-the-world-s-thirst/
[4] How Solar Desalination Can Help the Environment, 14 Jan, (online) available at: https://www.azocleantech.com/article.aspx?ArticleID=344
[5] Nanoparticles Take Solar Desalination to New Heights, (online) available at: https://spectrum.ieee.org/nanoparticles-take-solar-desalination-to-new-heights
