Solar desalination

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 [E Delyannis, 2003, Historic background of desalination and renewable energies, Solar Energy. http://dx.doi.org/10.1016/j.solener.2003.08.002] . 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.

Types of solar desalination

In general, there are two different designs for solar stills: electrically and mechanically driven systems which utilize reverse osmosis and thermally driven systems.

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. Here, solar energy is collected and converted into electrical or mechanical energy to initiate the process.

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) [The MEH-Method (in German with english abstract): [http://mediatum2.ub.tum.de/node?id=601861 Solar Desalination using the MEH method, Diss. Technical University of Munich] ] , 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.

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.

See also

*Point Paterson Desalination Plant
*Solar Powered Desalination Unit
*Solar still

References

External links

* Autonomous desalination in the Mediterranean: [http://www.adira.info/ ADIRA]
* European Solar Thermal Technology Platform, ESTTP. [http://www.esttp.org/ ESTTP] * [http://www.solar-desalination.com/ Optimized solar thermal desalination system]
* Network on renewable energy based desalination: [http://www.adu-res.org/ Coordination Action - ADU-RES]
*Solar Thermal Desalination [http://www.solarspring.de/ SolarSpring]