Solar stills

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[edit] Solar still basics

Fresh Water with 3D Printed Water Distiller

Solar stills are a type of appropriate technology used to distill water using the power of the sun. From most sophisticated to least so, their three basic configurations are:

  • box-like
  • cone-shaped
  • pit type

In any solar still, the basic layout is a collection device to capture rainwater. In most cases the collector is covered by a sheet of glass or transparent plastic, which allows solar radiation to pass through but not to escape. Water evaporated by the radiant solar heat then condenses on the cooler cover material. The condensed water is free from impurities, such as salts and heavy metals, as well as microbiological organisms, that might have been present in the intake water. The end result is a supply of fresh, clean water.

[edit] Background

Solar stills have been used for hundreds of years. The earliest known examples date to 1551 when Arab alchemists used such stills. In 1882 Charles Wilson invented the first modern conventional still — a massive solar still plant which was used to supply fresh water to a mining community in northern Chile. Today hundreds of solar still plants and thousands of individual solar stills have been built around the world.

Solar stills can efficiently produce drinking water from ditch water or cistern water, especially high-efficiency multiple effect humidification designs, which separate the evaporator(s) and condenser(s).

[edit] Applications

Schematic of a box-type solar still

Generally, solar stills are used in areas where piped or well water is impractical to obtain. Such areas include remote locations or locations where frequent power outages make pumps undependable. In such areas, solar stills can provide an alternate source of clean water. A major use of small solar stills is in developing countries where the technology to effectively distill large quantities of water on a commercial scale has not yet arrived. The drawback is that each individual still produces a relatively small amount of clean water.

Another application for solar stills is for outdoors back-country survival. Simple solar stills can be created by making use of basic camping gear and materials available in the natural environment. Stills for survival purposes would generally be of the relatively unsophisticated pit type, since they are the simplest to produce. One can extract moisture from the ground, but locally available moisture can be supplemented with water added inside or along the edges of the still. Where no water sources are readily available, urine or shredded vegetation can be used inside the pit. Whilst makeshift solar stills often do not provide enough water for long-term survival, they can prevent dehydration for short periods of time.

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