A completely passive solar-powered desalination system developed by researchers at Massachusetts Institute of Technology (MIT) and in China could provide more than 1.5 gallons of fresh drinking water per hour for every square metre of solar collecting area. 

Such systems could potentially serve off-grid arid coastal areas to provide an efficient, low-cost water source, said MIT doctoral students in a paper appearing in the journal ‘Energy and Environmental Science’.

The key to the system’s efficiency lies in the way it uses each of the multiple stages to desalinate the water. At each stage, heat released by the previous stage is harnessed instead of wasted. In this way, the team’s demonstration device can achieve an overall efficiency of 385 percent in converting the energy of sunlight into the energy of water evaporation.