Solar distillation
Practical Action
performed with salty water and a typical requirement for distilled water is 5 litres per person per
day. Therefore 2 m² of still are needed for each person.
Solar stills should normally only be considered for removing dissolved salts from water. 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. If there is no fresh water then the main alternatives are
desalination, transportation and rainwater collection.
Unlike other techniques of desalination, solar stills are more attractive, the smaller the required
output. The initial capital cost of stills is roughly proportional to capacity, whereas other methods
have significant economies of scale. For the individual household, therefore, the solar still is most
economic.
For outputs of 1 m³/day or more, reverse osmosis or electrodialysis should be considered as an
alternative to solar stills. Much will depend on the availability and price of electrical power.
For outputs of 200 m³/day or more, vapour compression or flash evaporation will normally be least
cost. The latter technology can have part of its energy requirement met by solar water heaters.
In many parts of the world, fresh water is transported from another region or location by boat, train,
truck or pipeline. The cost of water transported by vehicles is typically of the same order of
magnitude as that produced by solar stills. A pipeline may be less expensive for very large
quantities.
Rainwater collection is an even simpler technique than solar distillation and is preferable in areas
with 400 mm of rain annually, but requires a greater area and usually a larger storage tank. If
ready-made collection surfaces exist (such as house roofs) these may provide a less expensive
source for obtaining clean water (see the Rainwater Harvesting Technical Brief
http://practicalaction.org/rainwater-harvesting-6).
Which solar still?
The single-basin still is the only design proven in the field. Multi-effect stills have the potential to
be more economic but it would be as well to gain experience first with a single-basin still.
Further information
Factsheets & manuals
Rainawater Harvesting Practical Action Technical Biref http://practicalaction.org/rainwater-
harvesting-answers
How to Construct a Solar Water Distiller, Practical Action South Asia.
http://janathakshan.com/PDFs/SolarwaterDistiller%5Bpdf.pdf
Publications
Malik A S et al, 1982, Solar Distillation Pergamon Press
Bloemer, J. W., Washington D.C., Design of a Basin-Type Solar Still. UNT Digital Library.
http://digital.library.unt.edu/ark:/67531/metadc11661/m1/9/
Solar Distillation Practice For Water Desalination Systems
Dr. G N Tiwari, Professor of Energy Studies, Indian Institute of Technology, Delhi, India
Dr. A K Tiwari, Dept of Mechanical Engineering, National Institute of Technology, Raipur,
India, 2008 Anshan Publishing, ISBN: 978 1905740 888
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