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Solar desalination

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Solar desalination is a technique to desalinate water using solar energy. Solar desalination in the modern era extends back to the early 1950s when simple solar stills were studied for remote desert and coastal communities.[1] However, because of inexpensive water pumps and pipelines and declining energy costs in the 20th century, solar stills have become less of a viable solution for these community-scale projects. This trend is currently reversed again, because all of the fossil resources required for 20th century desalination are becoming scarce. Many desalination plants have begun retrofitting and new sustainable technologies, which can also serve as decentralized utilities are being developed by many specialized companies.

 solar desalination Edit

Solar power can be used directly to desalinate water thermally or it can be converted into electricity. Electrically and mechanically driven systems utilize reverse osmosis.

Towered Desalination Plant Built in PakistanEdit

In 1993 a desalination plant was invented by Akhtar Iqbal Zuberi in Pakistan. Zuberi’s plant produces 40 liters of water per square meter per day. This is at least ten (10) times more productive than a conventional Horizontal Solar desalination plant. Water desalinated from this plant has 16 parts per million (ppm).

The structure is a raised tower made of cement, with a tank at the top. The whole plant is covered with glass of the same shape, but slightly larger, allowing for a gap between the cement tower and the glass.

The tank is filled with saline water and water from an outside tank, drop by drop water enters the inner tank. The excessive water from the inner tank drips out onto the cement walls of the tower, from top to bottom. By solar radiation, the water on the wet surface and in the tank evaporate and condense on the inner surface of the glass cylinder and flow down onto the collecting drain channel. Meanwhile, the concentrated saline water drains out through a saline drain.

In this process fresh saline water is continuously added to the walls from the top of the tower. After evaporation, the remaining saline water falls down and drains out continuously. The movement of water also increases the energy of molecules and increases the evaporation process. The increase in the tower’s height also increases the production.

Whereas in the conventional system water that is filled remains at a standstill for several days, a condenser is provided at the top in an isolated space, allowing cold water is to pass through the condenser. The condensed hot vapors and hot water from the condenser are also thrown on the cement wall.

Different successive plants were constructed during 1960’s.

For this invention a Pak-Patent No. on 133598 was granted to Akhter Iqbal Zuberi in 1993.

This plant’s base is 3.5 by 1.5 feet by 10 foot high, and gives about 12 liters of water per day.

Built horizontally, a structured plant receives solar radiation at noon only. But Zuberi’s plant is a vertical tower and receives solar energy from sunrise till sunset. From early morning, it receives perpendicular radiation on one side of the plant. While at noon its top, gets radiation equivalent to the horizontal plant. From noon till sunset, the other side receives maximum radiation. By increasing the height, the tower plant receives more solar energy and the inner temperature increases as height increases. Ultimately this increases the water yield.

Problems Edit

There are two inherent design problems facing any solar desalination project. Firstly, the system's efficiency is governed by preferably high heat and mass transfer during evaporation and condensation. The surfaces have to be properly designed within the contradictory objectives of heat transfer efficiency, economy and reliability.

Secondly, the heat of condensation is valuable because it takes large amounts of solar energy to evaporate water and generate saturated, vapor-laden hot air. This energy is, by definition, transferred to the condenser's surface during condensation. With most forms of solar stills, this heat of condensation is ejected from the system as waste heat. The challenge still existing in the field today, is to achieve the optimum temperature difference between the solar-generated vapor and the seawater-cooled condenser, maximal reuse of the energy of condensation, and minimizing the asset investment.

Solutions Edit

One solution to the barrier presented by the high level of solar energy required in solar desalination efforts is to reduce the pressure within the reservoir. This can be accomplished using a vacuum pump, and significantly decreases the amount of energy required for desalination. For example, water at a pressure of 0.1 atmospheres boils at 50°C rather than 100°C.[2]

See also Edit

References Edit

  1. E Delyannis, 2003, Historic background of desalination and renewable energies, Solar Energy.
  2. Large scale Solar Desalination using Multi Effect Humidification

External links Edit

  • Autonomous desalination in the Mediterranean: ADIRA
  • European Solar Thermal Technology Platform, ESTTP. ESTTP
  • Network on renewable energy based desalination: Coordination Action - ADU-RES
  • Solar Thermal Desalination SolarSpring
  • SEA Panel — manufacturer of personal solar desalination systems
  • European project supporting the use of renewable energy for powering desalination: ProDes
  • SPX Global manufacturer of solar powered water systems for remote areas

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