Innovation That Matters

The solar-powered desalination system uses a confined water layer above floating thermal insulation to create an efficient desalination process. | Photo source MIT / Evelyn Wang

New solar-powered desalination system costs only a few dollars

Sustainability

A group of researchers has come up with a novel way to use solar power for desalination

Spotted: Water scarcity is becoming an increasingly important issue. According to the United Nations, 2.3 billion people live in water-stressed areas, of which 733 million are classed as living in high and critically water-stressed countries. Yet at the same time, many of these regions lack access to the dependable electricity needed for large scale desalination. Efforts to power desalinators using solar power have run into issues with salt build-up and expense. Now, a team of researchers at Massachusetts Institute of Technology (MIT) and in China has come up with a solar desalination system that is both more efficient and less expensive than previous methods.

While many existing systems rely on a wick to draw the saline water through the device, the researchers instead created a layered system, with dark material at the top to absorb the sun’s heat, followed by a thin layer of water, and a perforated layer of material above a reservoir of the salty water.

The holes in the perforated layer are just the right size to create natural convective circulation between the warmer upper layer of water and the cooler reservoir below. That circulation draws the salt from the thin water layer down into the larger body of water below, where it becomes diluted, leaving desalinated water to be drawn off. Best of all, the system can be constructed using low-cost and commonly-available materials.

Researcher Xiangyu Li explains that the system offers, “both the high performance and the reliable operation, especially under extreme conditions, where we can actually work with near-saturation saline water. And that means it’s also very useful for wastewater treatment.” He adds that the key was in understanding how the convective flow could be used to drive an entirely passive system, “People say you always need new materials, expensive ones, or complicated structures or wicking structures to do that. And this is, I believe, the first one that does this without wicking structures.”

Global warming has brought new urgency to the problem of how to cheaply and effectively desalinate brackish groundwater and seawater using alternative energy sources, such as solar. At Springwise, we have seen that there is no shortage of ideas on how to accomplish this. Some recent innovations include a lightweight desalination process that uses coal blocks and solar power and a large-scale desalination plant that uses wave power

Written By: Lisa Magloff

Email: emilygk@mit.edu

Website: mit.edu

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