Tofu Ingredient Offers a Taste of Cheaper, Safer Solar Energy
British researchers have found a new way to cut the cost of solar cell manufacture, and at the same time make the process less hazardous. Ironically, it is also very old way—using a chemical important in turning soy milk into tofu.
Jonathan Major and colleagues at the University of Liverpool report in Nature journal that magnesium chloride—traditionally added to soy milk as a coagulant to make tofu, but also used in gritting roads in winter time, used as bath salts and sometimes even sold as a health supplement—could replace cadmium chloride as a “doping agent” to increase the efficiency of cadmium telluride solar cells.
Dangerous to Handle
Cadmium chloride is very expensive, costing $0.30 (£0.18) per gram. It is also highly toxic and very dangerous to handle, which adds to the process costs. Naturally-occurring magnesium chloride costs only $0.001 per gram, and is one of the substances that makes the ocean salty. Since the planet is two-thirds ocean, there is no danger of running out of supplies.
Photovoltaic solar cells that convert sunlight directly to electricity are now big business, and getting bigger. They can be made of thin slivers of silicon, but the silicon wafer has to be 99.999 percent pure, and 200 microns thick (0.2 millimetres). So industry has also started using cadmium telluride to make sheets of photovoltaic cells that have a thickness of only two microns (0.002mm)—so thin and flexible they could even be sold by the roll.
The problem with cadmium telluride is that, to make it efficient enough to compete, it must be washed with a doping agent—an impurity added to a pure substance to produce a deliberate change—and, so far, the industry has relied on cadmium chloride. Cadmium is a dangerous metal, toxic if swallowed, fatal if inhaled and linked by some researchers to breast cancer, cardiovascular disease and even gout. It isn’t very good for aquatic life either.
Cadmium telluride is a stable salt and safe to handle, but cadmium chloride separates in solution into cadmium and into chlorine, another toxic substance. So manufacturers have the extra expense of safety during production, and then of safe disposal of waste.
Dr. Major and his team at the university’s Stephenson Institute for Renewable Energy are competitors in a worldwide search for ingenious ways to exploit renewable energy and reduce fossil fuel emissions.
They started this latest research by considering what it was about the cadmium chloride that made it effective, and then whether some other salt might serve the same purpose. They found that magnesium chloride had some of the same important physical properties, and then tested it.
“If renewable energy is going to compete with fossil fuels, then the cost has to come down,” Dr. Major said. “Great strides have been made, but the findings in this paper have the potential to reduce costs further.”
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Size Matters<p>Climates are a bit like woven tapestries. The big picture is important, no question. But so are all the seemingly minor details found inside the larger whole.</p><p><a href="https://research-information.bris.ac.uk/en/persons/tommaso-jucker" target="_blank">Tommaso Jucker</a> is an environmental scientist at the University of Bristol. In an email, Jucker says he'd define the term microclimate as "the suite of climatic conditions (temperature, rainfall, humidity, solar radiation) measured in localized areas, typically near the ground and at spatial scales that are directly relevant to ecological processes."</p><p>We'll talk about that last bit in a minute. But first, there's another criteria to discuss. According to some researchers, a microclimate — by definition — must differ from the larger area that surrounds it.</p><p><a href="https://www.cfc.umt.edu/research/paleoecologylab/publications/Davis_et_al_2019_Ecography.pdf" target="_blank">Forests</a> provide us with some great examples. "The climate near the ground in a tropical rainforest is dramatically different from the climate in the canopy 50 meters [164 feet] above," says University of Montana ecologist <a href="https://www.cfc.umt.edu/personnel/details.php?ID=1110" target="_blank">Solomon Dobrowski</a> in an email. "This vertical gradient among other factors allows for the staggering biodiversity we see in the tropics."</p><p>Likewise, scientists observed that a 2015 partial <a href="https://animals.howstuffworks.com/insects/bees-stopped-buzzing-during-2017-solar-eclipse.htm" target="_blank">solar eclipse</a> caused the air temperature of an Eastern European meadow to <a href="https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/wea.2802" target="_blank">change more dramatically</a> than it did in a nearby forest. That's because trees provide not only shade, but their leaves also reflect solar radiation. At the same time, forests tend to reduce wind speeds.</p><p>All those factors add up. A 2019 review of 98 wooded places — spread out across five continents — found that forests are 7.2 degrees Fahrenheit (4 degrees Celsius) <a href="https://natureecoevocommunity.nature.com/posts/47363-forests-protect-animals-and-plants-against-warming" target="_blank">cooler on average</a> than the areas outside them.</p><p>Now if you hate the cold, don't worry; there's a cozy exception to the rule. According to that same study, forests are usually 1.8 degrees Fahrenheit (1 degree Celsius) warmer than the external environment during the wintertime. Pretty cool.</p>
A Bug's Life<p>When does a microclimate stop being, well, micro? In other words, is there a maximum size we should be aware of when discussing them?</p><p>Depends on who you ask. "In terms of horizontal scale, some have defined 'microclimate' as anything that is less than 100 meters [328 feet] in range," Jucker says. "I'm personally less prescriptive about this."</p><p>Instead, he says the "scale at which we want to measure [a particular] microclimate" ought to be "dictated" by the questions we're trying to answer.</p><p>"If I want to know how temperature affects the photosynthesis of a leaf, I should be measuring temperature at centimeter scale," Jucker explains. "If I want to know if and how temperature affects the habitat preference of a large, mobile mammal, it's probably more relevant to capture temperature variation across [tens to hundreds] of meters."</p><p>For instance, solitary plants have the power to generate itty-bitty microclimates. Just ask <a href="https://www.colorado.edu/geography/peter-blanken-0" target="_blank">Peter Blanken</a>, a geography professor at the University of Colorado, Boulder and the co-author of the 2016 book, "<a href="https://amzn.to/2XN6FT8" target="_blank">Microclimate and Local Climate</a>."</p>
The urban heat island effect is a good example of how microclimates work. NOAA
Microclimates on a Grand Scale<p>It's no secret that our planet is going through some rough times at the macro level. The global temperature is <a href="https://climate.nasa.gov/vital-signs/global-temperature/" target="_blank">climbing</a>; nine out of the <a href="https://www.noaa.gov/news/2019-was-2nd-hottest-year-on-record-for-earth-say-noaa-nasa" target="_blank">10 hottest years on record</a> have occurred since 2005. And by one recent estimate, roughly 1 million species around the world are <a href="https://ipbes.net/sites/default/files/2020-02/ipbes_global_assessment_report_summary_for_policymakers_en.pdf" target="_blank">facing extinction</a> due to human activities.</p><p>"One of the big questions that ecologists and environmental scientists are trying to answer right now is how will individual species and whole ecosystems respond to rapid climate change and habitat loss," says Jucker. "...To me, [microclimates are] a key component of this research — if we don't measure and understand climate at the appropriate scale, then predicting how things will change in the future becomes a lot harder."</p><p>Developers have long understood the impact small-scale climates have on our daily lives. <a href="https://science.howstuffworks.com/environmental/green-science/urban-heat-island.htm#pt0" target="_blank">Urban heat islands</a> are cities that have higher temperatures than neighboring rural areas.</p><p>Plants release vapors that can moderate local climates. But in cities, natural greenery is often scarce. To make matters worse, plenty of our roads and buildings have a bad habit of absorbing or re-emitting heat from the sun. <a href="https://www.google.com/books/edition/Microclimate_and_Local_Climate/LHUZDAAAQBAJ?hl=en&gbpv=1&bsq=urban%20heat%20island" target="_blank">Vehicle emissions</a> don't exactly help the situation.</p><p>Still, it's not like Boston or Beijing are thermal monoliths. Sometimes, the documented temperatures <a href="https://e360.yale.edu/features/can-we-turn-down-the-temperature-on-urban-heat-islands" target="_blank">within a single city</a> vary by 15 to 20 degrees Fahrenheit (8.3 to 11.1 degrees Celsius).</p><p>That's where metro parks and city trees come in. They have nice cooling effects on nearby neighborhoods. "Several cities around the world have developed programs to increase urban green spaces," says Blanken. "Tree planting programs and green roof programs, have been shown to lower surface temperatures, decrease air pollution and decrease surface water runoff (urban flash-flooding) in urban areas."</p>
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By Jessica Corbett
A sheriff in Florida is under fire for deciding Tuesday to ban his deputies from wearing face masks while on the job—ignoring the advice of public health experts about the safety measures that everyone should take during the coronavirus pandemic as well as the rising Covid-19 death toll in his county and state.
<div id="7a571" class="rm-shortcode" data-rm-shortcode-id="aad9dcf60e7385e6553ff23ffc1ae75d"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1293527664389693447" data-partner="rebelmouse"><div style="margin:1em 0">Deaths hit a record in Florida yesterday. This guy's jail system is rife with COVID. And he's banned masks in his s… https://t.co/Cbp2wR32o1</div> — Michael McAuliff (@Michael McAuliff)<a href="https://twitter.com/mmcauliff/statuses/1293527664389693447">1597236002.0</a></blockquote></div>
<div id="79024" class="rm-shortcode" data-rm-shortcode-id="4ac086eab58b9713f2ad777c40938252"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1293578984148606977" data-partner="rebelmouse"><div style="margin:1em 0">This actively puts peoples' lives at risk. https://t.co/GKF0Xgjyex</div> — CAP Action (@CAP Action)<a href="https://twitter.com/CAPAction/statuses/1293578984148606977">1597248238.0</a></blockquote></div>
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