These Windows Can Generate Electricity And Provide Insulation
By Marlene Cimons
The windows of many cars and buildings often are tinted with a film that shuts out unnecessary sunlight, an energy efficiency measure that helps lower heating and cooling costs. Other types of environmentally friendly windows feature a coating of see-through solar cells that transform the windows into mini generators of electricity. But you probably won't find any windows anywhere that can do both. Not yet anyway.
This could be about to change. Chinese scientists have invented a new material that can both block the sun and produce power. They predict that windows outfitted with this product—or even window curtains that have it—eventually could cut the average household's electric bills by half or more.
"We combine both material innovation and optical thin film design to achieve the goal of combining both solar electricity generation and heat insulation in one single film," said Hin-Lap (Angus) Yip, a professor of materials science and engineering at the South China University of Technology. "Our energy efficiency for the house is kind of double: power generation and power saving."
Tinted car windows block light.Pixabay
Constructing a prototype that could simultaneously make electricity and prevent excessive heat required the scientists—who also included Fei Huang, also of South China University—to perform a balancing act between harvesting light to make electricity and blocking it, mixing and matching from among a variety of materials and chemical compounds to find exactly the right working combination.
Eventually, they designed a product that allowed visible portions of sunlight to pass through, but rejected infrared light, which is "a major heating culprit," Yip said. The researchers then transformed the near-infrared region in-between into an electric current.
"The major material we used for turning the solar light to electricity was a polymer semiconductor," Yip said. "We can design the chemical structure and tune [its] absorption property. This organic material has very unique absorption property, which can selectively absorb the near-infrared light, [but] allow a major portion of visible light to pass through it, making it a perfect material for semitransparent photovoltaic (PV) window application."
Current solar cell technology based on silicon or other inorganic semiconductors is not suitable for photovoltaic window applications "as they are opaque and dull in appearance," he added. "Instead, we can make organic photovoltaics into semi-transparent, lightweight and colorful films that are perfect for turning windows into electricity generators and heat insulators."
A paper describing the research appears in the journal Joule.
Yip said the material was similar to the pigment used in printing newspapers or coating cars, "but more functional," he said.
Actually, we can manufacture the polymer solar cell on flexible substrate using roll-to-roll printing process, just like the way we print our newspaper. If you compare this to the energy intensive process required for the production of silicon solar cells, the production of polymer solar cells consumes less energy, with a lower carbon footprint.
The material has a number of potential applications. Because it's a flexible and roll-able film, Yip thinks it would make a great window curtain. "Nowadays, many curtains are controlled electrically to open and shut, and since our photovoltaic window film will generate electricity, the same electrical circuit can be used to carry out the power, which can be then directly used or stored to power other facilities in the house," he said.
He also sees their value for use in self-powered greenhouses. "It just requires tailoring the optical property of the photovoltaic window film, as plants mainly absorb blue and red light, which is why they are green," he said. "So the design of the photovoltaic window film for greenhouse applications will have to maximize the transmission of blue and red light. This is feasible through new material design and optical engineering."
The scientists estimate that installing windows with dual purpose electricity-generating and heat-insulating properties could reduce the average household's reliance on external electric sources by more than 50 percent, although this figure assumes that every square inch of every window would have panels made of multifunctional solar cells.
Yip pointed out that the researchers didn't even use "the best organic photovoltaics that are out there in this field," for their own research demonstration, he said. "Their efficiency is improving rapidly, and we expect to be able to continuously improve the performance of this unified solar-cell window film. Making heat-insulating multifunctional semitransparent polymer solar cells is just the beginning of exploring new applications of organic photovoltaics."
Yip said it would be easy to scale up the product for widespread use and—although it initially may be more expensive than traditional films—it could pay for itself fairly quickly. "We think that polymer based solar cells will have a much shorter energy payback time compared to inorganic photovoltaics, as they can be manufactured using low energy printing processes," he said.
"In terms of the cost of the film, since it has a very similar structure to current heat insulating film—but with just a few additional layers—I expect it will be slightly higher than current window film," he added. "But since its energy efficiency can be double, we believe the cost payback time will be very short, maybe within three to four years."
He projected that the materials could be in commercial use within five years.
"It's been about 25 years from the discovery of polymer solar cells until now," he said. "We've had some very nice progress improving the efficiency and stability of polymer solar cells. If we can identify the best materials and processes to scale up these photovoltaic technologies in the next few years, maybe we will be able to see them everywhere on their 30th anniversary."
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By Katherine Kornei
Clear-cutting a forest is relatively easy—just pick a tree and start chopping. But there are benefits to more sophisticated forest management. One technique—which involves repeatedly harvesting smaller trees every 30 or so years but leaving an upper story of larger trees for longer periods (60, 90, or 120 years)—ensures a steady supply of both firewood and construction timber.
A Pattern in the Rings<p>The <a href="https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/coppice-standards-0" target="_blank">coppice-with-standards</a> management practice produces a two-story forest, said <a href="https://www.researchgate.net/profile/Bernhard_Muigg" target="_blank">Bernhard Muigg</a>, a dendrochronologist at the University of Freiburg in Germany. "You have an upper story of single trees that are allowed to grow for several understory generations."</p><p>That arrangement imprints a characteristic tree ring pattern in a forest's upper story trees (the "standards"): thick rings indicative of heavy growth, which show up at regular intervals as the surrounding smaller trees are cut down. "The trees are growing faster," said Muigg. "You can really see it with your naked eye."</p><p>Muigg and his collaborators characterized that <a href="https://ltrr.arizona.edu/about/treerings" target="_blank">dendrochronological pattern</a> in 161 oak trees growing in central Germany, one of the few remaining sites in Europe with actively managed coppice-with-standards forests. They found up to nine cycles of heavy growth in the trees, the oldest of which was planted in 1761. The researchers then turned to a historical data set — more than 2,000 oak <a href="https://eos.org/articles/podcast-discovering-europes-history-through-its-timbers" target="_blank" rel="noopener noreferrer">timbers from buildings and archaeological sites</a> in Germany and France dating from between 300 and 2015 — to look for a similar pattern.</p>
A Gap of 500 Years<p>The team found wood with the characteristic coppice-with-standards tree ring pattern dating to as early as the 6th century. That was a surprise, Muigg and his colleagues concluded, because the first mention of this forest management practice in historical documents occurred only roughly 500 years later, in the 13th century.</p><p>It's probable that forest management practices were not well documented prior to the High Middle Ages (1000–1250), the researchers suggested. "Forests are mainly mentioned in the context of royal hunting interests or donations," said Muigg. Dendrochronological studies are particularly important because they can reveal information not captured by a sparse historical record, he added.</p><p>These results were <a href="https://www.nature.com/articles/s41598-020-78933-8" target="_blank">published in December in <em>Scientific Reports</em></a>.</p><p>"It's nice to see the longevity and the history of coppice-with-standards," said <a href="https://www.teagasc.ie/contact/staff-directory/s/ian-short/" target="_blank">Ian Short</a>, a forestry researcher at Teagasc, the Agriculture and Food Development Authority in Ireland, not involved in the research. This technique is valuable because it promotes conservation and habitat biodiversity, Short said. "In the next 10 or 20 years, I think we'll see more coppice-with-standards coming back into production."</p><p>In the future, Muigg and his collaborators hope to analyze a larger sample of historic timbers to trace how the coppice-with-standards practice spread throughout Europe. It will be interesting to understand where this technique originated and how it propagated, said Muigg, and there are plenty of old pieces of wood waiting to be analyzed. "There [are] tons of dendrochronological data."</p><p><em><a href="mailto:firstname.lastname@example.org" target="_blank" rel="noopener noreferrer">Katherine Kornei</a> is a freelance science journalist covering Earth and space science. Her bylines frequently appear in Eos, Science, and The New York Times. Katherine holds a Ph.D. in astronomy from the University of California, Los Angeles.</em></p><p><em>This story originally appeared in <a href="https://eos.org/articles/tree-rings-reveal-how-ancient-forests-were-managed" target="_blank">Eos</a></em> <em>and is republished here as part of Covering Climate Now, a global journalism collaboration strengthening coverage of the climate story.</em></p>
Earth's ice is melting 57 percent faster than in the 1990s and the world has lost more than 28 trillion tons of ice since 1994, research published Monday in The Cryosphere shows.
By Jewel Fraser
Noreen Nunez lives in a middle-class neighborhood that rises up a hillside in Trinidad's Tunapuna-Piarco region.