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Solar Stills 2 of 2
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.