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Solar Desalination of Seawater

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The only nearly inexhaustible sources of water—the essence of life on Earth—are the seas and oceans, which, however, are of high salinity. It would, thus, be feasible to address the water-shortage problem with seawater desalination. However, the separation of salts from seawater requires large amounts of energy, which when produced from fossil fuels, can cause harm to the environment. Therefore, there is a need to employ environmentally-friendly energy sources in order to desalinate seawater.

Solar powered desalination units produce potable water from saline water through direct or indirect methods. Countries such as Australia, Italy, and very recently Egypt have adopted this system to provide an additional source of water for its growing population. Most of the plants that have been built so far are small scale plants with limited capacity, but yet with an impressive performance that encourages more research and investment.

The most basic form of solar desalination unit is the “solar still”. The basic principle of this technique is simple distillation which replicates the way nature makes rain. The energy of the Sun heats water to the point of evaporation. As the water evaporates, water vapor rises, condensing on a cool surface for collection. This process removes impurities, such as salts and heavy metals, and eliminates microbiological organisms. The end result is water cleaner than the purest rainwater.

Water production by direct method solar distillation is proportional to the area of the solar surface and incidence angle and has an average estimated value of 3-4 L/m3/d. Due to  this proportionality and the relatively high cost of property and material for construction, direct method distillation tends to favor plants with production capacities less than 200 m3/d.

A more sophisticated solar desalination system would employ two separate systems; a solar collection array, consisting of photovoltaic and fluid based thermal collectors, and a separate conventional desalination plant as that used in solar stills. This type of desalination technology has been commercially available and in use since 2009 with an output up to 1600 liters per hour, and 200 liters/day per square meter of solar cell panel.

Solar desalination introduces a philosophy that uses renewable energy to tackle both the energy and water crisis. The technology progressively becomes more and more price-competitive as production increases. The number of solar desalination plants continues to grow rapidly worldwide promising a brighter future full of possibilities.

References

globalwaterintel.com
theguardian.com

 

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