They design a totally passive and highly efficient desalination plant: capable of supplying more than 1.5 liters of drinking water per hour for each square meter of solar absorber.

A breakthrough for desalination seawater. A team of international researchers has succeeded in creating a completely passive system with a record efficiency of 385%. A breakthrough thanks to the collaboration between MIT and Jiao Tong University in Shanghai, China. Together, the scientists adapted the design of solar stills, systems that use evaporation to obtain drinking water even in the most arid regions.

This type of solution has never been very effective: in the best case, in the designs so far, it has been possible to achieve a production of about 2 liters of water per day (calculated per square meter solar collection surface).

However, the new design proposed by the Sino-American group succeeded in improving the technology considerably, to the point of being able to provide more than 1.5 liters of drinking water per hour.

© Lenan Zhang, Lin Zhao, Zhenyuan Xu, Evelyn Wang

The key to this record efficiency is how the seawater desalination device uses heat, recycling wasted thermal energy in one step, into the next.

In detail, the system consists of several layers of evaporators and flat condensers, aligned in a vertical module and surmounted by a transparent airgel insulator. The watermaker absorbs thermal energy from the sun through the first panel and transfers it to the water so that it begins to evaporate. The vapor condenses on the next panel: the condensation is collected, while the heat of the vapor passes to the back layer.

In conventional solar stills, this thermal energy is lost; on the contrary, in the new passive desalination device, it flows from layer to layer, increasing the overall efficiency. The researchers found in the first experiments an efficiency of 385% (in the conversion of solar energy into evaporative energy).

Adding more layers increases efficiency, but also adds cost and space to the system. So the team opted for a 10-panel system for their prototype, which was tested on the roof of an MIT building. The system provided pure water that exceeded city consumption standards at a rate of 5.78 liters per square meter of solar collection area. This is more than double the record achieved by passive solar desalination in recent years.

The most interesting aspect is that, unlike some desalination systems, there is no build-up of concentrated salt or brine to be removed, which is particularly difficult for the environment.

The system, the team explains, has yet to be optimized: it is expected to achieve 700-800 percent efficiency. And by replacing some expensive components (eg, airgel) with low-cost alternatives, a family-sized system could be brought to market for just $ 100.

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