Solar desalination
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| Water 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. The future of desalination has to rely on the use of solar-energy only. Many desalination plants have begun retrofitting and new sustainable technologies, which can also serve as decentralized utilities are being developed by many specialized companies.
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[edit] Types of solar desalination
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.
[edit] Reverse Osmosis
Reverse osmosis is a pressure-driven process that forces the separation of fresh water from other constituents through a semipermeable membrane. This is the preferred method in large-scale desalination implementations where electricity is cheaply available.
[edit] Solar Humidification-Dehumidification
The solar humidification-dehumidification (HDH) process (also called the multiple-effect humidification-dehumidification process, solar multistage condensation evaporation cycle (SMCEC) or multiple-effect humidification (MEH) [2], is a technique that mimics the natural water cycle on a shorter time frame by evaporating and condensing water to separate it from other substances. The driving force in this process is thermal solar energy to produce water vapor which is later condensed in a separate chamber. In sophisticated systems, waste heat is minimized by collecting the heat from the condensing water vapor and pre-heating the incoming water source. This system is effective for small- to mid- scale desalination systems in remote locations because of the relative inexpensiveness of solar collectors.
[edit] Problems
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.
[edit] Solutions
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.[3]
[edit] See also
- Desalination
- Point Paterson Desalination Plant
- Solar Powered Desalination Unit
- Solar still
- Seawater Greenhouse
[edit] References
- ^ E Delyannis, 2003, Historic background of desalination and renewable energies, Solar Energy. http://dx.doi.org/10.1016/j.solener.2003.08.002
- ^ The MEH-Method (in German with english abstract): Solar Desalination using the MEH method, Diss. Technical University of Munich
- ^ http://www.globalwarmingsolutions.co.uk/large_scale_solar_desalination_using_multi_effect_humidification.htm Large scale Solar Desalination using Multi Effect Humidification
[edit] External links
- Autonomous desalination in the Mediterranean: ADIRA
- European Solar Thermal Technology Platform, ESTTP. ESTTP</
- Optimized solar thermal desalination system
- 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
