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Solar Desalination
 
 
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Solar desalination is a technique to desalinate
Desalination

Desalination, desalinization, or desalinisation refers to any of several processes that remove excess sodium chloride and other minerals from water....
 water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
 using solar energy. Solar desalination in the modern era extends back to the early 1950s when simple solar still
Solar still

A solar still is a very simple way for distillation water, powered by the heat of the sun, especially when distillation equipment is unavailable....
s were studied for remote desert
Désert

?D?sert? is ?milie Simon's debut single, released in October 2002. The song was a huge success both critically and commercially in her homeland....
 and coast
Coast

The coast is defined as that part of the land adjoining or near the ocean or its saltwater arms. A precise line that can be called a coastline cannot be determined due to the process of tides....
al communities. 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.
eneral, there are two different designs for solar stills: electrically and mechanically driven systems which utilize reverse osmosis and thermally driven systems.
rse osmosis is a pressure
Pressure

Pressure is the force per unit area applied to an object in a direction surface normal to the surface. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure....
-driven process that forces the separation of fresh water from other constituents through a semipermeable membrane
Semipermeable membrane

A semipermeable membrane, also termed a selectively-permeable membrane, a partially-permeable membrane or a differentially-permeable membrane, is a membrane that will allow certain molecules or ions to pass through it by diffusion and occasionally specialized "facilitated diffusion." The rate of passage depends on the press...
.






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Solar desalination is a technique to desalinate
Desalination

Desalination, desalinization, or desalinisation refers to any of several processes that remove excess sodium chloride and other minerals from water....
 water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
 using solar energy. Solar desalination in the modern era extends back to the early 1950s when simple solar still
Solar still

A solar still is a very simple way for distillation water, powered by the heat of the sun, especially when distillation equipment is unavailable....
s were studied for remote desert
Désert

?D?sert? is ?milie Simon's debut single, released in October 2002. The song was a huge success both critically and commercially in her homeland....
 and coast
Coast

The coast is defined as that part of the land adjoining or near the ocean or its saltwater arms. A precise line that can be called a coastline cannot be determined due to the process of tides....
al communities. 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
Pressure

Pressure is the force per unit area applied to an object in a direction surface normal to the surface. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure....
-driven process that forces the separation of fresh water from other constituents through a semipermeable membrane
Semipermeable membrane

A semipermeable membrane, also termed a selectively-permeable membrane, a partially-permeable membrane or a differentially-permeable membrane, is a membrane that will allow certain molecules or ions to pass through it by diffusion and occasionally specialized "facilitated diffusion." The rate of passage depends on the press...
. 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) , is a technique that mimics the natural water cycle
Water cycle

The water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth....
 on a shorter time frame by evaporating
Evaporation

Evaporation is the slow vaporization of a liquid and the reverse of condensation. A type of phase transition, it is the process by which molecules in a liquid State of matter spontaneously become gaseous ....
 and condensing
Condensation

Condensation is the change of the physical state of aggregation of matter from gaseous phase into liquid phase. When the transition happens from the gaseous phase into the solid phase directly, bypassing the liquid phase the change is called Deposition , which is the opposite of sublimation....
 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
Waste heat

Waste heat refers to heat produced by machines and industrial processes for which no useful application is found, and is regarded as a waste by-product....
 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 collector
Solar collector

A solar collector is a device for extracting the energy of the sun directly into a more usable or storable form. The energy in sunlight is in the form of electromagnetic radiation from the infrared to the ultraviolet wavelengths....
s.

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
Standard enthalpy change of vaporization

The enthalpy of vaporization, , also known as the heat of vaporization or heat of evaporation, is the energy required to transform a given quantity of a substance into a gas....
 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

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.

See also

  • Point Paterson Desalination Plant
    Point Paterson Desalination Plant

    The Point Paterson Desalination Plant is a planned municipal-scale solar-powered desalination plant with land-based brine disposal just outside Port Augusta, South Australia....
  • Solar Powered Desalination Unit
    Solar Powered Desalination Unit

    A Solar Powered Desalination Unit designed for remote communities has been tested in the Northern Territory of Australia.The Reverse Osmosis Solar Installation uses membrane filtration to provide a reliable and clean drinking water stream from sources such as brackish water groundwater....
  • Solar still
    Solar still

    A solar still is a very simple way for distillation water, powered by the heat of the sun, especially when distillation equipment is unavailable....
  • Seawater Greenhouse
    Seawater Greenhouse

    The Seawater Greenhouse is an established technology with the potential to create surplus fresh water from seawater, using a novel form of greenhouse that also provides suitable food-growing conditions in arid regions....


External links

  • Autonomous desalination in the Mediterranean:
  • European Solar Thermal Technology Platform, ESTTP.
  • Network on renewable energy based desalination:
  • Solar Thermal Desalination