This Solar Device Converts Seawater to Drinking Water
By Paul Brown
An international team of scientists has developed a cheap way to provide fresh water to thirsty communities by making seawater drinkable without using electricity.
So long as the sun is shining, they say, their device will produce enough high-quality potable water to cover a family's needs, at a cost of around $100.
The scientists, from Massachusetts institute of Technology (MIT), U.S. and Shanghai Jiao Tong University, China, believe their brainwave offers a simple solution to thirsty islands and arid coastal areas which lack a reliable electricity supply but have access to seawater. It could even help to prevent some of the mass migrations expected with climate change.
The researchers report their work in the journal Energy and Environmental Science. Testing their prototype on a roof at the Massachusetts Institute of Technology, they produced more than 1.5 gallons of fresh drinking water every hour for every square meter of solar collecting area.
Their device is cube-shaped, with multiple layers of solar evaporators and condensers piled one on top of another, surmounted with a layer of transparent insulation. Essentially it is a multi-layer solar still, similar to those used for centuries to make strong liquor and used today in many applications.
Diagram illustrates the basic structure of the proposed desalination system. Sunlight passes through a transparent insulating layer at left, to heat up a black heat-absorbing material, which transfers the heat to a layer of wicking material (shown in blue), where it evaporates and then condenses on a surface (gray) and then drips off to be collected as fresh, potable water. Images courtesy of the researchers
A solar still uses flat panels to absorb heat which it then transfers to a layer of water, which begins to evaporate. The vapor condenses on the next panel and the water is collected, while the heat from the vapor condensation is passed to the layer above.
Whenever vapor condenses on a surface, it releases heat; in typical condenser systems, that heat is simply lost to the environment. But in this multi-layer version the released heat flows to the next evaporating layer, recycling the solar heat and boosting overall efficiency.
The efficiency comes from using each of the multiple stages to remove salt from the sea water, with the heat released by the previous stage harnessed instead of wasted. In this way, the team's demonstration device achieved an overall efficiency of 385 percent in converting the energy of sunlight into evaporation.
Evelyn Wang, a co-author, said: "When you condense water, you release energy as heat. If you have more than one stage, you can take advantage of that heat."
Although adding more layers increases the conversion efficiency of the system, each layer also adds cost and bulk. The team settled on a 10-stage system for their proof-of-concept device.
It delivered pure water that exceeded city drinking water standards, at a rate of 5.78 liters per square meter (about 1.52 gallons per 11 square feet) of solar collecting area. This is more than twice as much as the record amount previously produced by any such passive solar-powered desalination system, Professor Wang says.
And a big advantage of the system is that it has a self-flushing mechanism which will clean out the accumulation of salt each night and return it to the sea.
One possible way of using the system would be with floating panels on a body of saltwater. The panels could deliver constant fresh water through pipes to the shore so long as the sun was shining. Other systems could be designed to serve a single household, perhaps using a flat panel on a large shallow tank of seawater.
The team estimates that a system with a roughly one-square-meter solar collecting area could meet the daily drinking water needs of one person. In production, they think a system built to serve the needs of a family might be built for around $100.
The most expensive component of the prototype is the layer of transparent aerogel used as an insulator at the top of the stack, but the team suggests other less expensive insulators could be used instead. (The aerogel itself is made from very cheap silica but requires specialized drying equipment during its manufacture.)
"This new approach is very significant," says Professor Ravi Prasher of Lawrence Berkeley National Laboratory and the University of California at Berkeley, who was not involved in the research.
"One of the challenges in solar still-based desalination has been low efficiency due to the loss of significant energy in condensation.
"By efficiently harvesting the condensation energy, the overall solar to vapour efficiency is dramatically improved … This increased efficiency will have an overall impact on reducing the cost of produced water."
Reposted with permission from Climate News Network.
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The Great Trail in Canada is recognized as the world's longest recreational trail for hiking, biking, and cross-country skiing. Created by the Trans Canada Trail (TCT) and various partners, The Great Trail consists of a series of smaller, interconnected routes that stretch from St. John's to Vancouver and even into the Yukon and Northwest Territories. It took nearly 25 years to connect the 27,000 kilometers of greenway in ways that were safe and accessible to hikers. Now, thanks to a new partnership with the Canadian Paralympic Committee and AccessNow, the TCT is increasing accessibility throughout The Great Trail for people with disabilities.
Trans Canada Trail and AccessNow partnership for AccessOutdoors / Trails for All project. Mapping day at Stanley Park Seawall in Vancouver, British Columbia with Richard Peter. Alexa Fernando<p>This partnership also comes at a time when access to outdoor recreation is more important to Canadian citizens than ever. <a href="https://www150.statcan.gc.ca/n1/daily-quotidien/200527/dq200527b-eng.htm" target="_blank" rel="noopener noreferrer">Studies from the spring of 2020</a> indicate that Canadian's <a href="https://www.bnnbloomberg.ca/moneytalk-mental-health-during-covid-19-1.1567633" target="_blank" rel="noopener noreferrer">mental health has worsened</a> since the onset of social distancing protocols due to COVID-19. </p><p>The <a href="https://www.mayoclinic.org/diseases-conditions/coronavirus/in-depth/safe-activities-during-covid19/art-20489385" target="_blank" rel="noopener noreferrer">Mayo Clinic</a> lists hiking, biking, and skiing as safe activities during COVID-19. Their website explains, "When you're outside, fresh air is constantly moving, dispersing these droplets. So you're less likely to breathe in enough of the respiratory droplets containing the virus that causes COVID-19 to become infected."</p><p>TCT leadership took this into consideration when embarking on the accessibility project. McMahon explains that there has never been a more important time to bring accessibility to the great outdoors: "Canadians have told us that during these difficult times, they value access to natural spaces to stay active, take care of their mental health, and socially connect with others while respecting physical distancing and public health directives. This partnership is incredibly important especially now as trails have become a lifeline for Canadians."</p><p>Together, these organizations are paving the way for better physical and mental health among all Canadians. To learn more about the TCT's mission and initiatives, check out their <a href="https://thegreattrail.ca/stories/" target="_blank">trail stories</a> and <a href="https://thegreattrail.ca/wp-content/uploads/2021/01/TCT_2020-Donor-Impact-Report_EN_8.5x14-web.pdf" target="_blank">2020 Impact Report</a>.</p>
By Kiyoshi Kurokawa and Najmedin Meshkati
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Nuclear power generates about 10% of the world's electricity (TWh = terawatt-hours). About 50 new plants are under construction, but many operating plants are aging. World Nuclear Association / CC BY-ND
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Author Najmedin Meshkati holding an earthquake railing in a Fukushima Daiichi control room during a 2012 site visit. Najmedin Meshkati / CC BY-ND
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"Watch. Connect. Take Action."
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By Kenny Stancil
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<div id="c7fe3" class="rm-shortcode" data-rm-shortcode-id="5664692fdfd187db01eff5ac2787c564"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1367650177436311562" data-partner="rebelmouse"><div style="margin:1em 0">We’re coming together to fight for each other and guarantee #GoodJobsForAll Join us: https://t.co/MoJhmlzoaS https://t.co/IAPa8DeeLR</div> — Sunrise Movement 🌅 (@Sunrise Movement 🌅)<a href="https://twitter.com/sunrisemvmt/statuses/1367650177436311562">1614908186.0</a></blockquote></div>
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