Get our free book (in Spanish or English) on rainwater now - To Catch the Rain.


Jump to: navigation, search

Solar distillation

2,601 bytes added, 19:03, 9 November 2017
Reverted edits by (talk) to last revision by Lonny
Solar distillation differs from other forms of desalination that are more energy-intensive, such as methods such as [[reverse osmosis]], or simply boiling water due to its use of free energy.<ref> Abu-Arabi, M. (2007). Status and prospects for solar desalination in the MENA region. Solar Desalination for the 21 st Century, 163-178.</ref><ref>
Paton, C., & Davies, P. (2006). The seawater greenhouse cooling, fresh water and fresh produce from seawater. In The 2nd International Conference on Water Resources in Arid Environments, Riyadh.</ref> A very common and, by far, the largest example of solar distillation is the natural water cycle that the Earth experiences.   
The earliest onset of solar energy use to desalinate water is widely accredited to Aristotle during the fourth century B.C.E.<ref name = "Emmy">
Delyannis, E. (2003). Historic background of desalination and renewable energies. Solar Energy, 75(5), 357-366.</ref><ref>
Tiwari, G. N., Singh, H. N., & Tripathi, R. (2003). Present status of solar distillation. Solar Energy, 75(5), 367-373.</ref><refname = "Velmu">
Velmurugan, V., & Srithar, K. (2011). Performance analysis of solar stills based on various factors affecting the productivity—A review. Renewable and Sustainable Energy Reviews, 15(2), 1294-1304.</ref>
<ref name = "Gordes">
<ref name = "Hirsch">
Hirschmann, J. R. (1975). Solar distillation in Chile. Desalination, 17(1), 31-67.
</ref>This desalination plant,"can be considered to be the first industrial installation for exploitation of solar energy<ref name="Hirsch"/>." The Las Salinas plant was envisioned to take advantage of the nearby saltpeter mining effluent to supply the miners and their families freshwater <ref name="Emmy"/>.The facility was quite large for its time and now:<blockquote>"The plant was constructed of wood and timber framework covered with one sheet of glass. It consisted of 64 bays having a total surface area of 4450 m2 m<sup>2</sup> and a total land surface area of 7896 m2m<sup>2</sup>. It produced 22.70 m3 m<sup>3</sup> of fresh water per day. The plant was in operation for about 40 years until the mines were exhausted<ref name="Emmy"/>."
Interest in solar distillation wavered for some time, until historical events prompted further research and development. World War II was a great catalyst for the Massachusetts Institute of Technology to develop appropriate solar stills for use in more remote areas of the world during emergencies. These small solar stills were made to float on and collect saltwater to desalt as they floated alongside life-boats and rafts<ref name="Emmy"/>. More siginificant significant studies into solar distillation were carried out by the Office of Saline Water, a sector the US government, in 1952. Many experiments were performed on different conceptualizations of the solar still, including multiple-effect basins and the application of condensers<ref name="Emmy"/>. This trend ended near the early 70's with the advent of more lucrative desalination techniques like the aforementioned reverse osmosis or multi-stage flash, a technique that involves a series of stages where evaporation relies on lowering the pressure of each stage to lower the boiling or "flashing" point of the water <ref> El-Dessouky, H. T., Ettouney, H. M., & Al-Roumi, Y. (1999). Multi-stage flash desalination: present and future outlook. Chemical Engineering Journal, 73(2), 173-190. </ref><ref name= "Fath">
Fath, H. E. (1998). Solar distillation: a promising alternative for water provision with free energy, simple technology and a clean environment. Desalination, 116(1), 45-56.
</ref> Today, renewed enthusiasm for solar distillation comes from individuals, communities, and organizations seeking an [[appropriate technology]] that is cheap, simple, and conceivable in rural settings <refname = "Eibling"> Eibling, J. A., Talbert, S. G., & Löf, G. O. G. (1971). Solar stills for community use—digest of technology. Solar energy, 13(2), 263-276. </ref>.    
The immediate abstraction to make is to the Earth's natural system, but as it was aforementioned, this is unjustified but only if one believes that the water cycle on Earth is a non-complex concept. In "Understanding Solar Stills" it is said,<blockquote>
"It takes a lot of energy for water to vaporize. While a certain amount of energy is needed to raise the temperature of a kilogram of water from 0 to 100 Celcius (C), it takes five and one-half times that much to chnage it from water at 100 C 100°C to water vapor at 100 C100°C. Practically all this energy, however, is given back when the water vapor condenses... This is the way we get fresh water in the clouds from the oceans, by solar distillation. All the fresh water on earth has been solar distilled.<ref name = "Gordes"/>"
The journey for a water molecule from the aqueous to gaseous phase is more difficult to acquiesce than the eloquent writing above. As we will see a tremendous factor will be the difference in temperature between the surface water and that of the interface, be it glass or plastic. Some relevant equations include<ref>
Medugu, D. W., & Ndatuwong, L. G. (2009). Theoretical analysis of water distillation using solar still. International Journal of Physical Sciences, 4(11), 705-712.
''Eqn. (1)'' from the above describes the instantaneous thermal efficiency in relation to the evaporative heat transfer rate from the water surface to the glass cover the solar radiation intensity.
''Eqn.(2)'' represents the evaporative heat transfer rate from ''Eqn. (1) '' and its relationship to product of the convective heat transfer coefficient from the water surface to glass difference between the partial vapor pressure of water and gas.
''Eqn.(3)'' is the equation for determining the monthly output of distillate.
''Eqn.(4)'' was developed to describe the pay back period, n<sub>p</sub> as a function of the Unacost, or the uniform end-of-year annual amount with P being the initial cost and i the interest rate.
Many different methods exist to build solar stills, the most rudimentary involves digging a hole and more the more complex coming off of a manufacturing line.
Common Materials List<ref name = "Gordes"/>:
*insulation (usually under the basin)
*piping and valves
*facilities for storage
*a reflector to concentrate sunlight
*structural components
*wicking fabrics
*blackened wood
*black jute
*black polyethylene
Locally available materials would always be preferred but many things, such as the sealants, might be necessary to find from foreign vendors<ref name = "Velmu"/>. A very practical and thorough tutorial on how to build a small-scale solar still is available here:
[ "A Small Homemade Solar Still"]
==Operation and Maintenance==
==Evaluation ==
Since one of the main goals of solar distillation is to provide a clean source of water, proper disinfection after construction is crucial. Some less intensive methods of cleaning could be use of soap or laundry detergent<ref name ="Gordes"/>. A glass cover is more advantageous with respect to maintenance than a plastic cover, due to the electrostatic properties of plastic that can make it a beacon for detritus<ref name=Modifications"Eibling"/>. The brine left over after thorough distillation can be harvested for sea salt, as it is now a valuable commodity in its own right <ref>KOPSCH, O. (2007). SOLAR STILLS: 10 YEARS OF PRACTICAL EXPERIENCE IN COMMERCIALISING SOLAR STILLS WORLDWIDE. Solar Desalination for the 21 st Century, 239-246.</ref>.  ==Real World== In "Social aspects of a solar-powered desalination unit for remote Australian communities" Warner & Schafer argue that many journals, researchers and others like them rely too much on the technical aspects of solar distillation to prove its worth, "inorder to be socially sustainable, such technologies must:*be accepted by the community,*meet their water needs, and*be within their capacity to operate and maintain.<ref>Werner, M., & Schäfer, A. I. (2007). Social aspects of a solar-powered desalination unit for remote Australian communities. Desalination, 203(1), 375-393.</ref>" The situation that exists today has not changed much from even 50 years ago. Energy and cost intensive technologies still champion over desalination in the modern world<ref>Chaibi, M. T. (2000). An overview of solar desalination for domestic and agriculture water needs in remote arid areas. Desalination, 127(2), 119-133.</ref>.  For this reason, many developing countries and communities, on large and small-scale levels resort to the status quo, when more appropriate resorts exist<ref>Bloemer, J. W., Eibling, J. A., Irwin, J. R., & Löf, G. O. (1965). A practical basin-type solar still. Solar Energy, 9(4), 197-200.</ref>.  ==Existing Products==
Single products are not available at the moment![]</blockquote>
'''Cost''': The planned price is below € 20,[]. Solar distillation needs to become much cheaper than this before it can achieve widespread use by the poor. The website states that this works out cheaper than [[bottled water]] at 50c $.50 per liter once it is used for a number of months; however the target market cannot afford to buy bottled water, so this is not a useful comparison. If they do buy water, it is more likely to be from [[water refill stations]] which charge around 3 c $.03 per liter in major cities in Asia. In isolated areas, the costs increase a lot, but they would need to increase far beyond 3c $.03 per liter to justify the investment by a poor person or family - especially when it would be difficult to guard against theft. Thus it looks like they’re only useful where safe water is exceptionally expensive, or simply unavailable. Even then, other options for purifying the water would need to be weighed up. If these things were mass-produced for more like 1 euro or less each, they might be an option for widespread use - and this would be a more reasonable price for mass-produced pieces of molded plastic (even if they are very cleverly designed pieces of molded plastic).
===Watercone external links===
*[ Watercone - An Ingenious Way To Turn Salt Water Into Fresh Water] - ''The Sietch Blog'', August 2007
* [ Watercone] - '''', July 2006,
==Solar distillation in Mexico==
Florence Cassassuce, of La Paz, Mexico, who invented a five-gallon bucket that can purify several days' worth of water in four minutes.
She was one of 18 people listed as one of CNN Heroes finalists in 2007.
This is her site.
== Interwiki links ==

Navigation menu