IISc's solar desalination system to take potable water to remote areas

Researchers at Indian Institute of Science (IISc) have developed a solar-powered desalination system aimed at increasing the availability of clean, potable water. The desalination unit has been proposed as an energy-efficient, cost-effective alternative to the prevalent methods of membrane-based reverse osmosis and thermal desalination.

In thermal desalination systems, saltwater is heated – typically with electricity or combustion of fossil fuels – and the vapour is condensed to obtain freshwater. Solar stills are an environmentally friendlier alternative, using solar energy to evaporate saltwater in large reservoirs and collecting the condensed vapour on transparent roofs. The process, however, leaves the roofs with a thin layer of water and reduces the amount of solar energy that can penetrate the reservoir.

The novel, portable desalination system makes it convenient to be set up in areas with limited access to continuous electricity, Susmita Dash, Assistant Professor in the Department of Mechanical Engineering, said. Dash is the corresponding author of the study, published in Desalination. Dash and her PhD student Nabajit Deka developed the setup. which comprises a saline water reservoir, an evaporator, and a condenser enclosed within an insulating chamber to avoid heat losses.

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Solar thermal energy is used to evaporate a small volume of water imbibed or “wicked” into the evaporator, which has a textured surface. Wicking allows liquids to be drawn into narrow spaces of a porous material, much like water into sponge. The approach avoids heating the entire reservoir and significantly improves energy efficiency, Dash said.

The system is designed to trap the heat lost during condensation and use it to heat up the imbibed saltwater in another evaporator behind the condenser. These evaporator-condenser combinations are connected to form a multi-stage solar desalination system.

“This system, if built in a footprint area of 1 m2, has the capacity to produce one litre of potable water every 30 minutes – at least twice as much as that produced by a traditional solar still of the same size,” IISc said. The system can also work with groundwater containing dissolved salts as well as brackish water.