A civil engineering student is working to apply the energy of the sun to a major social problem that doesn’t have to do with electricity production: the production of clean water in developing countries. Deshawn Henry, a sophomore at the University of Buffalo, performed a study to determine how to most cheaply and efficiently build a water purifying lens. His creation, a six-foot tall structure built from plywood and plastic sheeting, was successful at heating a liter of water enough in one hour to kill 99.9% of pathogens and bacteria.
The idea of using solar power to purify unclean water is not a new one. In fact, solar water disinfection encompasses a range of technologies. One way to use solar energy in this way is by electric means. In this method, electricity generated from photovoltaic panels or stored solar energy from a battery is used to purify contaminated water. Another technique uses temperature, and is called solar thermal water disinfection (Henry’s project falls under this category). Finally, high energy ultraviolet light from the sun can be used to produce clean water works by disrupting structure and metabolism of bacteria in the water.
Some of these technologies can be quite expensive, so in developing countries, the cheapest and simplest way to disinfect water is called the SODIS method, an acronym for “Solar Water Disinfection.” In this method, plastic or glass bottles are filled with untreated water and left in the sun for at least six hours. The combination of heat and ultraviolet light provided by solar radiation deactivates illness-causing organisms in the water. The World Health Organization (WHO) recommends the SODIS method for safe, at-home water treatment.
Taking into account the alternatives for solar disinfection, the advantages of Deshawn Henry’s solar water lens are twofold. First, the materials to build such a lens are cost-efficient: his lens consists of plastic sheeting on top of a plywood frame, with water poured on top of the sheeting to serve as a lens. The water lens acts to focus sunlight on the container of water to be treated (exactly the way a concentrated solar power system focuses the sun to produce electricity). In addition, the speed at which water can be purified (1 hour per liter of water) vastly improves upon the six-hour wait with the SODIS method. Part of Henry’s project examined optimal thickness of the plastic sheeting and size of the water lens. He found that the most efficient arrangement was a plastic sheet 0.7 millimeters thick supporting 8 liters of water. Going forward, Henry and his research advisor, Dr. James Jensen, hope to use what they have learned to build a larger solar water lens, allowing a larger volume of water to be purified at one time. This innovative young man’s simple technology has the potential to be a real solution to the problem of waterborne diseases that occur too frequently in many parts of the world.