Methods
In the direct method, a solar collector is coupled with a distilling mechanism and the process is carried out in one simple cycle. Solar stills of this type are described in survival guides, provided in marine survival kits, and employed in many small desalination and distillation plants. 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 3-4L/m2/d.. Because of 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 200m3/d.
Indirect solar desalination employs two separate systems; a solar collection array, consisting of either photovoltaic or fluid based collectors, and a separate conventional desalination plant. Production by indirect method is dependent on the thermal efficiency of the plant and the cost per unit produced is generally reduced by an increase in scale. Many different plant arrangements have been theoretically analyzed, experimentally tested and in some cases installed. They include but are not limited to Multiple Effect Humidification (MEH), Multiple Stage Flash Distillation (MSF), Multiple Effect Distillation (MED), Multiple Effect Boiling (MEB), Humidification Dehumidification (HDH), Reverse Osmosis (RO), and Freeze effect distillation.
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