From bigblue.oit.unc.edu!concert!news-feed-1.peachnet.edu!news.duke.edu!duke!wolves!psybbs!125-7!Don.Kulha Fri Jul  8 21:46:03 EDT 1994
Article: 132 of alt.energy.renewable
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From: Don.Kulha@125-7.psybbs.durham.nc.us (Don Kulha)
Newsgroups: alt.energy.renewable
Subject: Solar Stills 1 of 2
Message-ID: <042_9407081732@psybbs.durham.nc.us>
Date: 7 Jul 94 03:24:22 GMT
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Clean Water from the Sun
Laurie Stone

+1993 Laurie Stone
Many of us turn on the tap and take the stream of pure water for 
granted. Or we go down to the corner store and buy distilled water 
for our car or renewable energy system+s battery.  Many people throughout 
the world do not have these options. Of the 2.4 billion people in 
developing countries, less than 500 million have access to safe drinking 
water, let alone distilled water. In this country, many people who 
live in remote areas don't have running water, and are far from any 
store selling distilled water. A solar still is the answer to all 
these problems.

A solar still is a simple device that can convert saline, brackish, 
or polluted water into distilled water. Principles of solar distillation 
have been around for centuries. In the fourth century B.C., Aristotle 
suggested a method of evaporating sea water to produce potable water. 
However, the first solar still recorded was not until 1874, when 
J. Harding and C. Wilson built a still in Chile to provide fresh 
water to a nitrate mining community. This 4700 m2 still produced 
6000 gallons of water per day. Currently there are large installations 
in Australia, Greece, Spain and Tunisia, and on Petit St. Vincent 
Island in the Caribbean. Smaller stills are commonly used in other 
countries.

Solar Still Basics
 The most common still in use is the single basin solar still. The 
still consists of an air tight basin that holds the polluted water, 
covered by a sloped sheet of glass or plastic. The bottom of the 
basin is black to help absorb the solar radiation. The cover allows 
the radiation to enter the still and evaporate the water. The water 
then condenses on the under side of the cover, and runs down the 
sloped cover into a trough or tube. The tube is also inclined so 
that the collected water flows out of the still. When the water evaporates, 
the salt, dirt, and bacteria are left in the still. Thus you have 
perfectly clean water.  

Still Construction
While working at the solar department of the Engineering University 
of Nicaragua, we decided to experiment with distilling water by the 
sun. Although some commercial stills are available, we decided to 
construct our own. We built two different types of solar stills. 
The first one had a glass cover sloped to one side, and the second 
one had a plastic cover which was sloped on both sides. Both stills 
were made of wood. We lined the bottom and sides of the interior 
with black plastic. There is an inlet hole near the top for the dirty 
water to enter, and another hole at the end of a condensate trough 
for the clean water to leave.  We used some sawed off plastic tubing 
for the condensate trough.

For the glass still we used 1/4 inch thick glass. The thinner the 
glass the better, because thin glass stays cool on the inner surface 
which helps the water condense faster. The plastic we used for the 
second still is a 0.5 millimeter thick clear mylar. Both glazings 
seemed to work well although the water could more easily run down 
the glass.  The glass still has approximately 0.5 square meters of 
glazing and produced about 0.7 liters of water per day, or 1.36 liters 
per square meter of still. The plastic still has about 0.75 square 
meters of glazing and only produced 0.5 liters of water a day on 
the average. This corresponds to approximately 0.7 liters per square 
meter per day. Of course, the output of the stills depended greatly 
on how much sun there was. On very sunny days we could get over a 
liter of water out of the glass still.

(continued)


From bigblue.oit.unc.edu!concert!news-feed-1.peachnet.edu!news.duke.edu!duke!wolves!psybbs!125-7!Don.Kulha Fri Jul  8 21:46:30 EDT 1994
Article: 133 of alt.energy.renewable
Path: bigblue.oit.unc.edu!concert!news-feed-1.peachnet.edu!news.duke.edu!duke!wolves!psybbs!125-7!Don.Kulha
From: Don.Kulha@125-7.psybbs.durham.nc.us (Don Kulha)
Newsgroups: alt.energy.renewable
Subject: Solar Stills 2 of 2
Message-ID: <043_9407081732@psybbs.durham.nc.us>
Date: 7 Jul 94 03:28:50 GMT
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Lines: 75
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Greater Efficiency
We did not use insulation in either still. If we had built a box 
within a box and put insulation between the two, we could have distilled 
much more water per day. Another way to maximize the output of a 
still is to use a reflector to increase the amount of insolation 
hitting the cover of the still, in the same way a reflector is used 
in a solar oven. However, in places close to the equator, such as 
Nicaragua, we felt the reflector would not make a large enough difference 
to be an economically viable option. One can also run water continuously 
over the cover of the still. This keeps the cover temperature as 
low as possible without interfering with the radiation entering the 
still. The water condenses faster when the glazing is cool. Experiments 
have also been done putting black dye in the water.  The black color 
helps absorb solar radiation, which speeds up the process and distills 
more water. When the water evaporates, the dye is left in the still.

Still Costs
The stills were both inexpensive to build. The glass one cost $25.00 
and the plastic one cost $18.00. If the stills are used for one year, 
they will produce water at approximately 10 cents per liter.

Water Quality
The water may taste a little strange at first because distilled water 
does not have any minerals which most people are accustomed to drinking. 
Although everyone at the University seemed to prefer the tap water, 
the still water was perfectly healthy. The University of Heredia 
in Costa Rica has analyzed water distilled using these same types 
of stills. The results were: (graphic in archive files)

Tests in other countries have shown that the stills eliminated all 
bacteria, and that the incidence of pesticides, fertilizers and solvents 
is reduced 75+99.5%. This is good news for many countries where cholera 
and other water borne diseases are killing people daily.  Since the 
stills constructed are small and only produce a small amount of water 
per day, they will not be used for drinking purposes. There are numerous 
farming cooperatives in Nicaragua that use photovoltaics (PV) for 
their lighting needs. The solar stills will eventually be donated 
to two communities to provide distilled water for the batteries for 
their PV systems. These stills can also be used as prototypes to 
build larger stills that can be used for communities which need potable 
water.

Constructing Your Own
If you are going to build your own still there are a few things to 
keep in mind:  N The tank can be made of cement, adobe, plastic, 
tile, or any other water resistant material.  N If plastic is used 
to line the bottom of the still or for the condensate trough, make 
sure the tank never remains dry. This could melt the plastic (which 
we learned the hard way!).  N The container holding the distilled 
water should be protected from solar radiation to avoid re-evaporation.
N Insulation should be used if possible. Even a small amount will 
greatly increase the efficiency of the still.

Distilled Water for All
Whether you live in a remote area and have no running water, or you 
just don't trust your tap water, solar stills can provide safe, healthy 
drinking water at minimal cost and effort. As long as you have a 
sufficient amount of sun, you can produce distilled water for you, 
your family, or your batteries.

Access
Laurie Stone,
Solar Energy International, POB 715, Carbondale, CO 81623
303-963-8855, FAX 303-963-8866
For more information:
McCracken Solar Stills, 329 W. Carlos, Alturas, CA, 96101
Dr. Shyam S. Nandwani, Universidad Nacional Heredia, Costa Rica.
Brace Research Institute, MacDonald College of McGill University, 
Ste. Anne de Bellevue, Quebec, CANADA, H9X 1C0:
For plans and blueprints on how to make solar stills.

     Article Courtesy of and Copyright by Home Power Magazine
     PO Box 520, Ashland OR 97520, Pub 6x/yr, $15 US, $20 Int.
     Editorial 916.475.3179, Subs & Back Issues 916.475.0830
     Note: This article is from an early issue; things change.


