Tuesday, November 20. 2012
Via MIT Technology Review
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Flexible photovoltaics made of carbon promise low cost and durability, if their performance can be improved.
By Katherine Bourzac on November 15, 2012
Carbon cell: The all-carbon solar cell consists of a photoactive layer between two electrodes.
Using a grab bag of novel nanomaterials, researchers at Stanford University have built the first all-carbon solar cells. Their carbon photovoltaics don’t produce much electricity, but as the technology is perfected, all-carbon cells could be inexpensive, printable, flexible, and tough enough to withstand extreme environments and weather.
The goal is not to replace solar cells made from silicon and other inorganic materials, says Zhenan Bao, professor of chemical engineering at Stanford University, who led the work. Rather, it is to fill new niches. “Carbon is one of the most abundant elements on earth, and it is versatile,” Bao says.
Carbon is remarkably tough—atom-thick graphene and long, thin carbon nanotubes are two of the strongest materials ever tested. So carbon photovoltaics might be sprayed on the sides of buildings, or rolled up and taken into the desert. Various forms of carbon can be printed to make thin, flexible, transparent, and even stretchable electronics.
Thanks to its versatility, carbon in one form or another was used to make each solar-cell component. The three main parts—a nanotube cathode and a graphene anode sandwiching an active layer made of nanotubes and buckyballs—were all made by printing or evaporating from inks.
Making the cathode work was the trickiest part, says Bao—researchers have had a hard time making carbon nanomaterials that collect electrons. The Stanford researchers solved the problem by picking the right flavor of nanotubes and giving them a chemical treatment. This work is described in the journal ACS Nano.
The all-carbon photovoltaics convert less than 1 percent of the energy in light into electricity (by comparison, a silicon solar cell converts around 20 percent of light into electricity). However, Bao says that her group worked mostly with off-the-shelf materials, with just a bit of tuning. She attributes part of the problem to the roughness of the carbon films, which trips up traveling charges, and says it should be possible to smooth them out by working on the processing methods.
Carbon nanomaterials “are still relatively new materials,” says Bao. “There’s a lot of research on how to control their properties and how to use them.”
IBM Yorktown researcher and 2011 MIT Technology Review young innovator Fengnian Xia, who is not involved in the work, agrees, saying that the solar cells need better-quality starting materials and processes. “The idea is great, and this is a good first demonstration, but it’s not ready for realistic applications,” he says.
Other groups are focused on making better carbon materials for the active layers of photovoltaics. According to theoretical calculations by Jeffrey Grossman at MIT, carbon solar cells should be able to reach 13 percent conversion efficiency.
For carbon solar cells to be commercially viable, says Shenqiang Ren, assistant professor of chemistry at the University of Kansas, their efficiency must cross 10 percent. Ren’s lab set the conversion-efficiency record for carbon solar cells (equipped with conventional metal electrodes) at 1.3 percent this September, in work that appeared in ACS Nano. That’s about how well the first polymer solar cells performed, he notes.
Ren is working with computational materials scientists, including Grossman, to design better carbon photovoltaics by picking the right kinds of carbon nanomaterials. With this guidance, Ren says, his lab has already made carbon solar cells that convert 5 percent of light energy into electricity, and he expects to go higher still.
Monday, November 19. 2012
Via Wired
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Personal comment:
Besides the debate about the location of this solar farm (apparently in what should be a natural reserve), impressive pictures of the construction of the plant, in particular the one above. Really impressive structure, yet highly symetrical and centralized. A sort of reverse power panopticon.
Friday, November 16. 2012
Via The New York Times
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WASHINGTON — Climate change is accelerating, and it will place unparalleled strains on American military and intelligence agencies in coming years by causing ever more disruptive events around the globe, the nation’s top scientific research group said in a report issued Friday.
The group, the National Research Council, says in a study commissioned by the C.I.A. and other intelligence agencies that clusters of apparently unrelated events exacerbated by a warming climate will create more frequent but unpredictable crises in water supplies, food markets, energy supply chains and public health systems.
Hurricane Sandy provided a foretaste of what can be expected more often in the near future, the report’s lead author, John D. Steinbruner, said in an interview.
“This is the sort of thing we were talking about,” said Mr. Steinbruner, a longtime authority on national security. “You can debate the specific contribution of global warming to that storm. But we’re saying climate extremes are going to be more frequent, and this was an example of what they could mean. We’re also saying it could get a whole lot worse than that.”
Mr. Steinbruner, the director of the Center for International and Security Studies at the University of Maryland, said that humans are pouring carbon dioxide and other climate-altering gases into the atmosphere at a rate never before seen. “We know there will have to be major climatic adjustments — there’s no uncertainty about that — but we just don’t know the details,” he said. “We do know they will be big.”
The study was released 10 days late: its authors had been scheduled to brief intelligence officials on their findings the day Hurricane Sandy hit the East Coast, but the federal government was shut down because of the storm.
Climate-driven crises could lead to internal instability or international conflict and might force the United States to provide humanitarian assistance or, in some cases, military force to protect vital energy, economic or other interests, the study said.
The Defense Department has already taken major steps to plan for and adapt to climate change and has spent billions of dollars to make ships, aircraft and vehicles more fuel-efficient. Nonetheless, the 206-page study warns in sometimes bureaucratic language, the United States is ill prepared to assess and prepare for the catastrophes that a heated planet will produce.
“It is prudent to expect that over the course of a decade some climate events — including single events, conjunctions of events occurring simultaneously or in sequence in particular locations, and events affecting globally integrated systems that provide for human well-being — will produce consequences that exceed the capacity of the affected societies or global system to manage and that have global security implications serious enough to compel international response,” the report states.
In other words, states will fail, large populations subjected to famine, flood or disease will migrate across international borders, and national and international agencies will not have the resources to cope.
The report cites the simultaneous heat wave in Russia and floods in Pakistan in the summer of 2010 as disparate but linked climate-related events that taxed those societies.
It also cites the Nile River watershed as a place where climate-related conflict over water and farmland could arise as the combined populations of Egypt, Sudan and Ethiopia approach 300 million. South Korea and Saudi Arabia have purchased fertile land in the Nile watershed to produce crops to feed their people, but local forces could decide to seize the crops for their own use, potentially leading to international conflict, the report says.
The 18-month study is not the first such report from government agencies or research organizations to draw a direct link between climate change and national security concerns.
The National Intelligence Council produced a classified national intelligence estimate on climate change in 2008 and has issued a number of unclassified reports since then. The Pentagon and the White House have also highlighted the role of climate change in humanitarian crises and security threats.
The National Research Council recommends in the new report that all government agencies improve their ability to monitor the global climate and assess the risks to populations and critical resources around the world.
Yet Mr. Steinbruner said that as the need for more and better analysis is growing, government resources devoted to them are shrinking. Republicans in Congress objected to the C.I.A.’s creation of a climate change center and tried to deny money for it. The American weather satellite program is losing capability because of years of underfinancing and mismanagement, imperiling the ability to predict and monitor major storms.
Personal comment:
Following the previous post about hurricanes, another article by The NYT that strength the necessity to take into account the effects of climate extremes.
We've seen in the recent years projects taking into account floodings or higher levels of oceans. Probably should we also already consider more generally "climate extremes" (wind, floodings, rain, heat waves, etc.) that will occur more and more often at a global scale in the coming 50 years in the design of contemporary architectures, cities, landscapes and infrastructures. Undoubtedly a research project.
Monday, November 05. 2012
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The Land Art Generator Initiative just announced the winner of its 2012 design competition moments ago in New York City. "Scene Sensor", designed by artists James Murray and Shota Vashakmadze, is a striking piezoelectric energy-generating art project designed to be installed above and below the surface of the Staten Island park. — Inhabitat NYC
Via MIT Technology Review
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Using technology to cool the planet may be the only way to deal with the greenhouse gases already in the atmosphere, argues scientist David Keith.
By Kevin Bullis
David Keith spoke at MIT Technology Review’s EmTech conference this week.
Geoengineering—using technology to purposefully change the climate—is the only option for reducing the risk of climate change from greenhouse-gas emissions in the next few decades, says David Keith, a professor of public policy and applied physics at Harvard University. And he says that if it’s done in moderation, it could be much safer than some experts have argued. In fact, says Keith, effective methods of geoengineering are so cheap and easy that just about any country could do it—for better or worse.
Keith, speaking this week at MIT Technology Review’s annual EmTech conference, says it is already too late to avoid climate changes by reducing carbon emissions alone. The carbon dioxide that’s been released into the atmosphere by burning fossil fuels is already likely to cause significant harm, such as raising temperatures enough to hurt crop yields in many places. “If you want to, say, really stop the loss of Arctic sea ice or stop heat-stress crop losses over the next few decades, geoengineering is pretty much the only thing you can do,” he says (see “Why Climate Scientists Support Geoengineering Research”).
Keith’s preferred method of geoengineering is to shade the earth by injecting sulfate particles into the upper atmosphere, imitating a similar process that happens with large volcanic eruptions, which are known to temporarily cool the planet. The technique could be effective even if far less sulfate were injected than is currently emitted by fossil-fuel power plants. A million tons per year injected into the stratosphere would be enough—whereas 50 million tons are injected into the lower part of the atmosphere by coal plants, he says. (In the lower atmosphere, the sulfates are less effective at cooling because they stay airborne for shorter periods.)
One of the main objections to geoengineering is that the measures that might be taken to cool the planet won’t exactly offset the effects of carbon dioxide, so they could actually make things much worse—for example, by altering patterns of precipitation. Keith says recent climate models suggest that injecting sulfate particles into the upper reaches of the atmosphere might not affect precipitation nearly as much as others have warned.
“I propose that you start in about 2020, and you start very, very gradually increasing your amount of sulfate engineering so that you cut about in half the rate of warming,” he says. “Not eliminate it, but cut it about in half. Cutting it in half is a big benefit.”
One of the benefits could be increased crop production. Though some critics have worried that geoengineering would alter monsoon patterns that are key to agriculture in India, Keith says moderate geoengineering could actually boost crop productivity there by 20 percent, in part by reducing temperatures.
Keith and some of his colleagues recently hired engineers to estimate how much one approach to sulfate injection might work, and how much it might cost. It could be done at first with existing airplanes—certain business jets can fly high enough to inject the particles into the upper atmosphere. Eventually we would need new planes that can fly higher. All in all, once the procedure is scaled up it would cost about a billion dollars a year and require about 100 aircraft. That’s cheap enough for most countries to pull off on their own.
The fact that it’s easy isn’t necessarily a good thing, Keith says. There’s the potential that if one country does it, another might blame that country—rightly or wrongly—for ensuing bad weather (see “The Geoengineering Gambit”).
And there are also real concerns about the impact sulfates might have on the atmosphere (see Geoengineering May Be Necessary, Despite Its Perils). It’s known that sulfates can be involved in reactions that deplete the ozone layer. As the earth warms, water vapor levels are increasing, which could exacerbate the problem. Keith is proposing a test to discover quantitatively just what the effect of the injections could be. He would introduce small clouds of sulfate and water vapor into the stratosphere using balloons, and then carefully measure the reactions that take place.
And Keith acknowledges a concern many have had about geoengineering: that using it to offset problems from climate change will reduce the incentive to tackle the greenhouse-gas emissions at the root of the problem. Even if geoengineering is employed, reducing emissions will still be important. Sulfate injection does nothing to address the ocean acidification associated with increased levels of carbon dioxide in the atmosphere. And if emissions continue to grow, ever-increasing amounts of sulfate will be needed.
But Keith thinks the potential benefits might be worth the dangers. “We don’t know enough yet to start,” he says. “But the current balance of evidence is that doing this really would reduce risks. And for that reason, we’ve got to take it seriously. It really would be reckless not to look at something that could reduce risk like this could.”
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