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Tuesday, August 19, 2014

Solar-powered lens that purifies polluted water

A university student in the US has developed a two-metre tall, self-sustaining magnifying glass that can treat polluted water with nothing but the power of sunlight.
Image: The University of Buffalo
Named a water lens, this device has been designed for communities in developing countries to very easily and quickly treat their water before using it. The device is made from inexpensive and commonly found materials, such as wood and plastic sheeting, and can heat a litre of water to between 54 and 65 degrees Celsius (130 and 150 degrees Fahrenheit) in a little over an hour. During this time, it will destroy 99.9 percent of bacteria and pathogens in the water. 
"The water lens could have a huge impact in developing countries,” said developer Deshawn Henry, a University at Buffalo engineering student, in a press release. "Millions of people die every year from diseases and pathogens found in unclean water, and they can't help it because that's all they have. Either they drink it or they die.”
The lens is constructed by pulling a plastic sheet covered with water over a wooden frame. The frame holds a small container of water underneath the plastic lens, which has been lined up with a focal point created by a concentrated ray of sunlight. Because the Sun moves across the sky throughout the day, the water container needs to be manually shifted to ensure it remains in line with the focal point.
In developing the water lens, Henry had to figure out how altering the thickness of the plastic sheet and the volume of water over the sheet would affect its efficiency. He found that adding more water to the lens made it more efficient, because larger areas of water transmitted more energy from sunlight. But larger areas of water required thicker sheets of plastic, which consumed more energy from from light, therefore lowering the lens' efficiency.
Henry managed to find the happy medium between the two, reporting that, “a 0.7-millimetre sheet could efficiently heat the container while supporting eight litres of water, but any more and the sheet could potentially break".
The next step for the water lens is for Henry to develop an even bigger version. According to, a family of five would need a lens at least three times the size of the current water lens, which has been designed to heat one litre of water at a time.