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Can solar technology generate clean water for developing nations?

Marco Attisani

Watly's new solar-powered technology aims to provide water, energy and internet connectivity to people living in poorer parts of the world. Marco Attisani discusses the application of the technology and how it works.

Watly aims to change the way in which technology is providing for the poorest people across the globe. Its mission is to improve global living standards for the most in-need people in the world by providing water, energy and connectivity in a green, sustainable system. The company believes the Watly model combines clean technologies in an innovative way in order to provide these three ‘pillars’ of modern civilization in one solution. 

The latest, and most advanced of the company’s machines is the Watly 3.0. Standing at 2.4 metres off the ground, the 40 metre-long machine is capable of sanitising 5,000 litres of water per day, enough to provide for a community of 3,000 people. The solar-powered thermodynamic computer is also a powerful communication device that can download and upload data to and from the Internet. All of these functions are powered by the solar park made up of 40 panels on Watly’s roof. 

A single unit will last for 15 years, according to the company, and, because it is emission-free, could save as much as 1,000 tonnes of greenhouse gas emissions (CO2), equivalent to 2,500 barrels of oil, while purifying millions of litres of water and generating 1GWh (1,000 megawatt hours) of free electricity.     

The technology 

Primarily the machine is a large computer, dealing with all the functions that define it as such, such as calculating, broadcasting and collecting information, while sending data to the cloud. However, the machine also incorporates photovoltaic solar technologies to generate electricity off grid. This energy is used to empower the electronics inside the machine itself, as well as for recharging external devices such as portable phones, tablets and laptops. In addition, a Watly machine uses thermal solar technology to sanitise water, removing chemical, bacteriological, or physical contamination. 

The technologies combine to create what Watly claims to be a self-sufficient and efficient system. The dirty water which is fed into Watly flows underneath the solar panels which cover its roof. This water helps to cool the solar panels down, keeping them at an optimum temperature of 25oC. At this temperature, the solar panels, which do not respond well to excessive heat, become between 40-50 per cent more efficient. 

Simultaneously, the machine uses a patented system to transfer heat to the dirty water, warming it up towards boiling point and thereby contributing towards the sanitation process. Watly purifies water from any form of contamination using a technique called vapour compression distillation. This technology involves heating water to temperatures of around 115oC, at which level different forms of contamination are separated from the clean water, which is distilled. 

Once distilled, the purified water flows in a special mineralizer and acid reducer, which regulates water pH and minerals, optimizing the water for drinking. The technology does not use filters or membranes as some other forms of sanitation do, thus eliminating the need for substitution of filters, or for chemicals such as membrane cleaners, scale inhibitors and antiscalants.

In addition to the vapour compression system, Watly also uses a graphene-based technology to separate water from soaps, solvents and hydrocarbons. The 4,000 litre tank applies graphene in a unique way, and is currently under patentability evaluation. 

A key advantage compared to some other purification and desalination methods may be that Watly’s water output does not depend on the type of water input. Any kind of polluted water – from oceans, lakes, rivers, ponds, or even sewage water –  can be fed into Watly, and according to the company, no matter how polluted the water going in, the result is always the same: clean water. The water is delivered to end users through three interactive stations, where a water filling system automatically fills-up specially designed water carriers in 25 seconds.  

The application

This innovative combination of technologies is proven to be effective, having been trialed in a smaller, but otherwise identical, version of Watly on location last year. The trial saw the team take the Watly 2.0 to Abenta village in Ghana, where residents were able to drink clean water from the machine, recharge their phones and other devices, and benefit from the connectivity provided by Watly. The machine had been tested for almost 2 years prior to this so the trial was not designed to test the viability of the technology. By this point, the technology had received a number of accreditations and accolades, but trial tested the human acceptance and social impact of the technology, helping to show that it would be welcomed and well received by the communities it aims to transform. 

Watly’s innovative design is based on the concept of the ‘Energynet’. The idea of the Energynet grasps the transformational potential of combining vital and basic resources into a self-supporting ecosystem. It also refers to a solar-powered smart-grid which can behave like the Internet but also allow information technology to be fused together with the necessary provision of electricity and water. And contrary to the Internet, the Energynet generates the very same power it needs to function.

The sustainable Energynet system, of which Watly can be counted as a prime example, aims to bring the IoT to places where there is no Internet and where there are very few things, thus providing the resources for survival and advancement to some of the most resource-poor places in the world.


Marco Attisani is founder and CEO of Watly.



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Energy efficiency  •  Policy, investment and markets  •  Solar electricity




21 June 2016
Interesting article.
No doubt the method sounds
No doubt the method sounds novel as we have such buzz words like ATM,prepaid card etc. People with western thinking and orientation are ignorant of the realities in rural areas of developing countries. Can this system work? Is it sustainable? Even simple Box Type Solar Cooker could not penetrate in Rural areas which is more than 60 years old. Only 6 lakh units sold(but not all of them used). What is the fate of solar panels at signals? In India the major problem is dust accumulation on the solar panels. Who undertakes regular cleaning? Even regular ATM(Cash) ,there are many cases of theft. Is the WATER ATM Fool Proof? How much quantity it can meet? There is a notion among planners and western educated that, RURAL IS BAD,URBAN IS BETTER AND FOREIGN IS THE BEST. It is not at all valid in many cases in India.

Technology is culture specific. There are many water purification technologies available which are simple and can be readily adoptable in rural areas. One such method designed, demonstrated and disseminated is SOLAR DISINFECTION OF WATER.
Safe Drinking Water for All
Impure water is the root cause for many diseases especially in developing countries.
Millions of people become sick each year from drinking contaminated water. In many
regions of the world, sunshine is abundantly available which can be effectively utilised to
provide safe drinking water to the millions of people. A portable, low-cost, and lowmaintenance
solar disinfection unit to provide potable water has been designed and
tested. The solar disinfection system has been tested with bore water, well as well as
waste water. In 6 hours when the ambient temperature was 30 degrees Celsius, the unit eradicated 3 log 10 (99.99%) of bacteria contained in the water samples. The unit will provide about 6 liters of pure drinking water and larger units can be fabricated for providing safe drinking water at community level in developing countries.
Every 8 seconds, a child dies from water related disease around the globe. 50% of people
in developing countries suffer from one or more water-related diseases. 80% of diseases
in the developing countries are caused by contaminated water. Providing safe drinking
water to the people has been a major challenge for Governments in developing countries.
Conventional technologies used to disinfect water are: ozonation, chlorination and
artificial UV radiation. These technologies require sophisticated equipment, are capital
intensive and require skilled operators (1,17,20). Boiling water requires about 1 kg of
wood/liter of water which results in deforestation in developing countries. Also halazone
or calcium hypochlorite tablets or solutions (sodium hypochlorite at 1 to 2 drops per liter)
are used to disinfect drinking water. These methods are environmentally unsound or
hygienically unsafe when performed by a layperson. Misuse of sodium hypochlorite
solution poses a safety hazard (2,4,11).
Treatment to control waterborne microbial contaminants by exposure to sunlight in clear
vessels that allows the combined germicidal effects of both UV radiation and heat has
been developed and put into practice (5,712,13,14,18,19).The SODIS system(Solar
Disinfection of water) developed by scientists at the Swiss Federal Agency for
Environmental Science and Technology(EAWAG) recommends placing PET bottles
(usually discarded mineral water/beverage bottles) painted black on one side, aerating
(oxygenating) the water by vigorous shaking three fourths water filled bottles and then
filling them full and placing them in sunlight for 6 hours. In this method, the water is
exposed to UV radiation in sunlight, primarily UV-A and it becomes heated; both effects
contribute to the inactivation of water borne microbes. The use of PET bottles requires
periodic replacement because of scratches and they become deformed if temperature
exceeds 650C. Also dust accumulates on these bottles in the groves (provided for
strength). The PET bottle mineral water manufacturers print on the label,ÔÇÖ crush the bottle
after useÔÇÖ in India. Unless cleaned thoroughly everyday, PET bottles turn brown over
usage rendering lesser transmission of sunlight.
Microorganisms are heat sensitive. Table 1 lists up the required temperature to
eliminate microorganisms within 1,6 or 60 minutes. It can be seen that it is not required
to boil the water in order to kill 99.9% of the microorganisms. Heating up water to 50 -
600C for one hour has the same effect (2,21).
The most favorable region for solar disinfection lies between latitudes 150 N/S and 35 0
N/S. These semi-arid regions are characterised by high solar radiation and limited cloud
coverage and rainfall (3000 hours sunshine per year).The second most favorable region
lies between the equator and latitude 15 0 N/S, the scattered radiation in this region is
quite high (2500 hours sunshine per year).
The need for a low-cost, low maintenance and effective disinfection system for providing
safe drinking water is paramount, especially for the developing countries.
Materials And Methods
The innovative solar disinfection system has a wooden frame of length 2 ft,width 1 foot
and depth 6 inches with bottom sinusoidal shaped polished stainless steel (curvature
slightly larger than standard glass wine bottles, about 5 inches diameter) . On the front is
fixed a glass sheet having lifting arrangement with a knob (this glass enclosure will
protect the glass bottles from cooling down due to outside wind). There are screws which
can be used to keep the contents airtight. On the backside a stand is fixed which will help
the unit to be placed according to the latitude of the place for maximum solar insolation.
In this method clear glass bottles (used wine bottles) are utilised instead of PET bottles as
the former are easy to clean, lasts longer and are available at a low cost in India. Solar
disinfection is more efficient in water containing high levels of oxygen; sunlight produces
highly reactive forms of oxygen (oxygen free radicals and hydrogen peroxides) in the
water. These reactive forms of oxygen kill the microorganisms. Aeration of water is
achieved by shaking the 3/4 water filled bottles for about 20 seconds before they are
filled completely.
The unit has an advantage in that the rear reflection stainless steel will pass the light
through the bottles a second time, to both increase exposure and eliminate shadowing.
This reflection system will increase the light intensity minimum 2 times.
It has been widely experimented and established by earlier researchers that at temperature
of 500C, pathogenic microbes are inactivated. The temperatures which cause
approximately a 1-log decrease in viability with 1 min are 550C for protozoan cysts; 600C
for E.coli, enteric bacteria, and rotavirus; and 650C for hepatitis A virus (3,6,8,9,10,16).
Negar Safapour and Robert H.Metcalf (15) in their extensive studies reported
enhancement of solar water pasteurization with reflectors and the crucial role of
temperature above 500C in the elimination of pathogens.
The unit is placed in the south direction (in India) around 10 am with inclination equal to
the latitude of the place. The glass bottles are filled with water three fourths and shaken
for 20 seconds to generate oxygen and then completely filled. The water filled bottles are
fixed with caps and put in the groves of the solar disinfection unit. The glass door is
closed and clipped airtight. Water bottles are removed from the unit at 3 pm and taken to
a cool place and the disinfected water transferred to a clean vessel, covered for later
Suspended particles in the water reduce the penetration of solar radiation into the water
and protect microorganisms from being irradiated. Solar disinfection requires relatively
clear water with a turbidity less than 30 NTU.To remove turbidity traditional methods of
putting the paste from seed of strichnos potatorum (Nirmal seeds) by rubbing the seed on
a rough stone with water is used. The method is effective, turbidity settles down in half of
an hour and the seed are available in plenty in forests in India besides being inexpensive.
Sample Testing
Water samples from the solar disinfection unit were tested with Most Probable Number
(MPN) technique. To estimate the number of aerobic organisms present in water, Pour
Plate Technique has been used.
The test results of various water samples disinfected show 99.99% purity. In the samples from Ambattur Bore Water, Ambattur Well Water, Anna Nagar Bore
Water and Kavaraipettai Bore Water, since they are highly contaminated, further
dilutions were not carried out. The dilution should be done only when the MPN indicates
more than 1100 organisms/100 ml. For these samples only log reductions can be
calculated. As regards R.S.M.Nagar Bore Water and Thathai Manji Well Water, the
percentage of reduction are 85 and 86.95, which indicates that the water is less
contaminated. As MPN index shows less than 3 organisms for 100 ml, after solar
disinfection of water, the samples are free from coli forms. The results of Avadi Waste
Water and Perambur Waste Water show 3 log reduction (99.8%) and 4 log reduction
(99.993%) respectively.
For comparison PET and Glass bottles were placed with black background as well as in
the innovative device I developed. It can be readily seen that is complete with my device compared to open.
Eradication of coli forms from well water, bore water and waste water has been reported
from test results. The results confirm that there is 4-log 10 reduction of coli forms in the
waste water after solar disinfection. The experiments were conducted at
Kavaraipettai,Tamil Nadu,India.Maximum temperature occurs around 1 pm. Though 6
bottles were used in the system(each of 1 liter capacity),larger units with up to 100 bottles
can be designed. The unit destroyed 99.99% of bacterial coli forms both in well water
and waste water samples in 5 hours.
The innovative solar disinfection system has the advantages like:
1.The unit is portable,
2.It is cost-effective. It can be fabricated in South India for US$ 20.The unit incorporates
the principle of reflection to increase solar intensity and has protection from wind which
results in temperature rise inside the unit,
3.Larger units can be manufactured,
4. Used glass bottles withstand higher temperatures and are available in plenty each for 2
US cents in South India ,
5. Since all the materials are available locally, the unit can be manufactured locally with
local people. Temperatures above 300c occur in south India for more than 10 months in a
year and as such this innovative solar disinfection unit will be a boon in this region.
The project is financially supported by Science and Society Division, Department of
Science and Technology, Government of India.
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The method and device has been widely disseminated. Any technology especially for rural areas should be:
Appropriate Technology
Affordable Technology
Alternative Technology
Accessible Technology
Acceptable Technology
Water is the elixir of life - Leonardo da Vinci
Dr.A.Jagadeesh Nellore(AP),India
E-mail: anumakonda.jagadeesh Nellore(AP),India

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