Solar basin still consists
of a simple blackened box for storing and heating water. This box
is provided with a glazed top, which serves the purposes of both
insulator and condensing surface. The glazed top is kept at an
angle to allow the condensed water to flow to one side and into
a small gutter. Bottom of the unit is insulated with glass wool
to improve the efficiency. Solar energy is allowed into the collector
to heat the water. When water gets heated to a certain temperature
it evaporates and condenses on the underside of the glass. Rising
of only the water vapor leaves contaminants behind, thus purifying
The gentle slope of the glass directs the condensate to a collection
trough, which in turn delivers the water to the collection bottle.
The still is filled each day with twice as much water as was produced.
The still is also fitted with overflow outlets, which allow the
excess water to flush the still every day. A major advantage of
the basin still is that it does not require a pressurized water
Solar still is a useful devise to get fresh/distilled water that
is required in industries, hospitals and dispensaries, garages
and automobile workshops, telephone exchanges, laboratories and
marshy and costal area.
3.3.4 Solar Disinfection and Purification of Water
There are a few methods commonly advocated for the disinfection
of drinking water at the household level. These include boiling
of water for about 10 minutes or the use of certain chlorine
compounds available in the form of tablets. As each of these procedures
its own drawbacks, their application is extremely limited in
the developing countries, where water-borne diseases are most common,
and the purity of drinking water supplies from external sources
cannot be assured.
Boiling of water and condensation using fuel and use of tablets
or proper solution is neither cost effective nor convenient.
The experiments conducted on solar disinfection of drinking water
the American University of Beirut for two years concluded that
the rate of destruction of bacteria actually depends upon a number
of influencing factors such as:
- intensity of sunlight
at the time of exposure, which in turn depends upon the geographic
and cloud cover, the effective range of wavelengths of
light, and the time of day
- kind of bacteria, the
nature and composition of the medium, and the presence of nutritive
elements capable of
the growth and multiplication of various microorganisms
of the containers/bottles in which the contaminated water is kept
during exposure (e.g. colour, shape, transparency
to sunlight, size, and wall thickness)
of water (i.e. degree of turbidity) and its depth are important
factors that determine the extent of penetration of sunlight, and to
what extent they have the possibility of shielding the microorganisms
from its lethal effects.
Based on the above finding and analysis, it became clear that sunlight
with wavelengths ranging from 315 nm to 400 nm is the most lethal
region, as it accounts for about 70% of the bacterial destruction
The wavelength of this band is known as the near-ultraviolet region
of the light spectrum.
Visible light is characterized by having wavelengths ranging from
400 nm to about 750 nm, and accounts for about 30% of the bacterial
capacity. Accordingly, the most appropriate colours of the containers/bottles
have to be selected that would yield optimum results in terms of
microbial destruction. While violet /blue have better effect as compared
yellow/ orange/ red tinted bottles, the colourless plastic bottles
are the best for the purpose. Very light green containers may also
provided the period of exposure to sunlight is somewhat extended.
Thus, preference should be given to containers that are either colourless
or blue in colour. The brown colour bottles and to a lesser extent
red ones, are recommended for the storage of water. Therefore,
of water by exposing it to the solar rays using appropriate colour
containers/bottles could be one of the most economical way for
the disinfection and purification
of water for drinking purpose by the rural households, especially
the poor peasants living in the remote and far-flung areas/regions
- Container needs to be
exposed to sun for 6 hours if the sky is bright or up to 50% cloudy.
needs to be exposed to the sun for 2 consecutive days if the sky
is 100% cloudy.
- During days of continuous
rainfall, SODIS does not work.
a water temperature of at least 50°C is reached, an exposure
time of 1 hour is sufficient.
3.3.5 Nedap solar powered drinking water UV disinfection
This solar powered drinking water UV disinfection
unit, named as “Nedap,” is
developed by ‘NAIADE’, The Netherlands
developed. The Nedap is capable of producing
2,500 liters/ day, catering to the drinking water
needs of about 800 people per day. The unit is
no maintenance other than cleaning the PV panel.
Spare parts like the UV lamp needs replacement only
after 10,000 hrs of operation. It is reported to
water as per
the WHO standards.
It can be installed within 30 minutes and can be
used at all places since it needs no fossil fuel
Filtration of unsafe water is done by washable bag
filters and disinfection by UV. The unit weighs less
kg and is shipped
packed palletized box.
Daily Av Capacity to Purify
UV Disinfection Lamp
Water Tank storage Cap
2,500 ltrs / 8 hrs of sunlight
Cap 100 litres
54 x 75 x 140 cm (excluding solar panel)
viruses, bacteria, protozoa & worm eggs
The unit has been tested and approved by various leading
water research labs worldwide, such as UNESCO-IHE, Ghanaian Water Research
Institute, Atitra India, KIWA, and many more.