Subject: Solar Stills 2 of 2

From: [email-masked] (Don Kulha)
Date: 7 Jul 94 03:28:50 GMT

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.

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