Why in news? As a possible solution to increase the availability of clean, potable water, Indian Institute of Science (IISc) researchers have developed a novel thermal desalination system which can work using solar energy.

Highlights:

• The most common methods for desalination are membrane-based reverse osmosis and thermal desalination. However, both consume a lot of energy.

How does it work?

• According to IISc, thermal desalination systems work by heating saltwater and then condensing the resulting vapour to obtain freshwater.But the energy required for evaporation is usually obtained from either electricity or combustion of fossil fuels.
• An environmental-friendly alternative is using solar stills in which solar energy is employed to evaporate saltwater in large reservoirs and the vapour that condenses on a transparent roof is collected.
• However, during condensation, a thin layer of water forms on the roof, reducing the amount of solar energy that can penetrate the reservoir and therefore, the system’s efficiency.

About the novel design of IISc

• “As an alternative to such solar stills, the IISc team has developed a novel design for a solar-powered desalination unit that is more energy-efficient, cost-effective and portable, making it convenient to set up in areas with limited access to continuous electricity.
• The setup, comprises a reservoir of saline water, an evaporator, and a condenser enclosed within an insulating chamber to avoid heat losses to the ambient air.
• The system works by using solar thermal energy to evaporate a small volume of water imbibed or “wicked” into the evaporator, which has a textured surface. The wicking of liquid into the evaporator takes advantage of the capillary effect of micro scale textures.
• This effect allows liquids to be drawn into narrow spaces of a porous material, much like water being absorbed by a sponge. Utilising this approach, instead of heating the entire liquid volume in the reservoir, results in a significant improvement in the system’s energy efficiency.

Works for groundwater too

• Apart from seawater, the system can also work with groundwater containing dissolved salts as well as brackish water. It can be adjusted to align with the shifting positions of the sun during the day.