"SOLAR STILL"
Contents:
INTRODUCTION,
How does the Solar Still work?,
Costs of the device,
reference
INTRODUCTION
Solar still is a device that purifies water by distillation. It may be used not only for removing of microbiological contamination but also for removing salts. Solar Still was certified for arsenic removal by National Sanitation Foundation (NSF) international [1]. First Solar Stills were used for desalination purpose - to produce salt rather than drinking water.
The first large-scale Solar Still plant for drinking water production was built in 1872 in the mining community in northern Chile. This plant was in operation for 40 years and on a typical summer day it could produce more than 23000 liters of pure water per day [2].
How does the Solar Still work?
To obtain high temperatures that allow water to be distilled simple features of absorption and the greenhouse effects are used.
Solar Still is a basin with a top cover made of glass. The interior of a basin must be waterproof, and should be painted in black for better absorption of the solar energy. The greenhouse effect is obtained due to the glass cover that traps in solar energy.
Solar still operates on the principles of rainwater evaporation and condensation. Water poured into the still is heated by radiation, evaporates and condenses on the glass. The glass is sloped to the south and the condensed water trickles down to the collection through and then is stored outside in a container.
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"Principle of Solar Still work", source:
The Institute for Appropriate Technology
"Solar Still with reflector", source:
The Institute for Appropriate Technology
When water evaporates leaves all contaminants behind that is why condensed water is safe drinking water. All pathogens are destroyed due to high temperatures obtained in a solar still.
Operation is very simple and requires only facing the basin toward the sun. The device should be filled each morning or evening. Distilled water in this device is produced even after sundown as the water is still hot. For best operation feedwater should exceed the distillate production to flush of the basin. This provides cleaning of the basin from contaminants left behind during the evaporation[3].
There are many variations of solar stills. Efficiency may be improved by adding a reflector, or by combining several basins together.
"Solar Still combined in array" source:
The Institute for Appropriate Technology
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Cost of this device depends on the materials chosen for its construction. EPSEA (El Paso Solar Energy Association) organization states that costs of materials to build a single still should be less than USD 300 [4]. ITDG (Intermediate Technology Development Group) organization gives the price of GBP 50-70/m2.
According to ITDG this device is best for purification of the brackish water and "if there is a choice between brackish ground water or polluted surface water, it will usually be cheaper to use a slow sand filter or other treatment device" [5].
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[1] SolAqua: "Distillation Purification Capabilities"
[2] SolAqua: "Solar Still Background"
[3] SolAqua: "Still Operation"
[4] EPSEA: "Solar Water Distillation - Stills"
[5] ITDG: Technical brief: "Solar Distilation"
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