Solar Cell Efficiency Could Be Boosted by Minimizing Defects
Nano-cones could help neutralize manufacturing defects in solar cells
A new advance in solar cells that tips the surface with minuscule cone structures could neutralize manufacturing defects, boosting efficiency up to 80 percent.
In conventional solar panels, more than 50 percent of the charges generated by sunlight are lost due to defects, said Jun Xu, a researcher at the Department of Energy's Oak Ridge National Laboratory. The irregularities in the formation of the crystalline structure of solar cells can trap electrons and limit the transfer of sunlight to electrical energy.
SOLAR FLAWS: Manufacturing defects impair solar cells ability to turn sunlight into electricity, but a new technique might help minimize the flaws. Image: Stephan Kambor via Wikimedia Commons
This is why Xu and his team are looking at how nanocones -- cone-shaped structures one-millionth of a meter long -- can neutralize the burden of defects.
The negative-polarity nanocones are made of zinc oxide, and surrounded by a positive-polarity cadmium telluride semiconductor that absorbs sunlight. The three-dimensional cone structure acts as a junction between the zinc oxide and cadmium telluride, making for a smoother conversion of the solar charge to electricity.
The idea, said Xu, is not to "fix" the defects, but to make them irrelevant. With the nanocone structure, the team was able to increase the overall electric charge to overcome the pitfalls of defects.
"If [manufacturers] make a defect with no way to solve it, we make the defect less relevant," he said. "You need to increase the efficiency ... you need to be able to increase change of transport. With a nanocone structure, you can do that."
On a small level, the efficiency gains are relatively minor -- rising to 3.2 percent, compared to 1.8 percent for panels without the nanocones. But Xu believes this will pay off on a larger scale.
"Our efficiency is moderate in generation, but the difference between the two platforms is huge," he said, referring to the models with and without nanocones. In the real world, even a much smaller percentage increase would be an important achievement for solar.
"If we can reduce the defective material, and we can increase the efficiency about 15 or 10 percent," he said, "that would be a huge success."
Zinc oxide and cadmium telluride serve as relatively cheap materials to create nanocones, as well, said Xu, with the potential to reduce the cost of commercial solar panels if applied to silicon -- the most common material used for solar panels.
The research will be published in the Institute of Electrical and Electronics Engineers' IEEE Proceedings.
From Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500
Carbon Nanotubes Boost Power of Lithium Battery
A new battery demonstrated a power output 10 times higher, for its size, than what is expected of a conventional rechargeable lithium battery.
Imagine that the same rechargeable battery in your cell phone could power a device that requires 10 times the energy. That possibility may be closer than you think.
A battery created by researchers at Massachusetts Institute of Technology demonstrated an increased capacity for charge by roughly a third and a power output 10 times higher, for its size, than what is expected of a conventional rechargeable lithium battery. The results were published yesterday in Nature Nanotechnology.
The research team, led by Yang Shao-Horn, an associate professor of materials science and mechanical engineering, and Paula Hammond, professor of chemical engineering at MIT, achieved this by creating an entirely new kind of electrode -- in this case, by modifying the positive end of the conventional battery, which is called the cathode.
The collaboration began through graduate student Seung Woo Lee, studying fuel cells, who was advised by both Shao-Horn and Hammond. Lee defended his doctoral dissertation this spring.
Using commercially available carbon nanotubes -- hollow cylinders 50,000 times thinner than a human hair but composed of carbon atoms -- the team fabricated the cathode entirely out of the nanotubes put down in layers.
The large surface area of a nanotube allows it to store more charge than other types of carbon, such as graphite, but previous battery fabrication methods tended to obscure these surfaces.
Using the exposed surfaces allows more charge to be stored -- increasing capacity -- while also letting those charges migrate more easily -- increasing power.
The findings of this research challenge the conventional wisdom about what materials could be used in the cathode of a battery. It also stimulates discussion about what such powerful batteries could be used for.
Small scale experiments so far
Increased power output makes for a great capacitor as well, by efficiently storing charge and delivering that energy precisely when it is needed. Their work, Shao-Horn said, could "lead to a device with performance that bridges batteries and electrochemical capacitors."
So far, the thickest cathode the group has made for these experiments is only 3 micrometers -- 3 one-thousandths of a millimeter. This is tiny when compared to conventional lithium-ion batteries that have electrodes roughly 100 to 200 micrometers thick.
In their present form, Shao-Horn said, their cathode "could be ideal for microelectronic devices."
But these battery-capacitors are also useful in a number of other applications such as emergency power, "energy capture and power assist in cars, trucks and machinery requiring many start-stop cycles," said Shao-Horn. Successfully scaling up this design could dramatically reduce the inefficiencies in future lithium-ion batteries.
However, Shao-Horn preferred to err on the side of caution when peering into the future of this new technology, saying they are only just beginning to understand the underlying chemistry involved.
"Further work is required," said Shao-Horn, "to demonstrate that power and energy performance is maintained with thicker electrodes." A crucial next step of this research is to demonstrate an electrode with a thickness of 50 micrometers -- more than 10 times the size of what they made for their experiments.
The next phase is scaling it up
Doing so would allow the researchers to test whether the electrical properties of the carbon nanotubes can be successfully scaled up to greater and greater thicknesses. Potentially, Shao-Horn said, there is "no limit" on thickness. But in order to do this, Hammond's expertise in biomaterials will be essential.
The layer-by-layer fabrication technique used to make the 3-micrometer-thick carbon nanotube electrode described in the published paper was an extremely time-consuming process. For each layer of nanotubes, a sample had to be dipped into a solution awash with nanotubes.
Then, covered in the solution, the sample had to be left out for 15 to 20 minutes as gravity slowly pulled the nanotubes down through the liquid and onto the sample surface. This procedure had to be repeated about 400 times in order to pile up enough layers to reach a thickness of 3 micrometers.
To bring the layering process up to reasonable, commercially viable speeds, Hammond is appropriating an automatic spray technique she developed for producing layers of polymer materials.
"The spray method is 40 to 100 times faster," she said, taking only seconds to lay down each new layer of nanotubes rather than the 15 to 20 minutes it normally takes. The true test will come once much thicker electrodes are tested.
Other battery research from Shao-Horn's group has been highlighted in other ClimateWire stories.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500
| June 22, 2010
Navy’s Mach 8 Railgun Obliterates Record
There wasn’t much left of the 23-pound bullet, just a scalded piece of squat metal. That’s what happens when an enormous electromagnetic gun sends its ammo rocketing 5,500 feet in a single second.
The gun that fired the bullet is the Navy’s experimental railgun. The gun has no moving parts or propellants — just a king-sized burst of energy that sends a projectile flying. And today its parents at the Office of Naval Research sent 33 megajoules through it, setting a new world record and making it the most powerful railgun ever developed.
Reporters were invited to watch the test at the Dalghren Naval Surface Warfare Center. A tangle of two-inch thick coaxial cables hooked up to stacks of refrigerator-sized capacitors took five minutes to power juice into a gun the size of a schoolbus built in a warehouse. With a 1.5-million-ampere spark of light and a boom audible in a room 50 feet away, the bullet left the gun at a speed of Mach 8.
All that energy was “dump[ed] in 10 milliseconds,” says Charles Garrett, project manager at Dahlgren for the railgun.
But since there no explosion powering the projectile, why should the railgun have made any noise at all? Answer: the bullet went so fast it released a sonic boom.
Since 2005, the Navy has spent $211 million testing whether it can harness electromagnetic energy into a gun. The ultimate goal is to fire the gun at 64 megajoules, making it capable of sending a bullet 200 miles in six minutes. That’s 10 times farther than the Navy’s already-powerful guns can fire, keeping its ships far out of range of enemy anti-ship systems.
The Navy wants to put the railgun on a ship and power it through the ship’s batteries, something that’ll take years to develop. And since the gun’s power can be adjusted — it depends only on the batteries and the capacitors on board a ship, railgun scientists explained — it could theoretically be used to stop cruise missiles or even ballistic missiles.
That’s still a long way off. The Office of Science and Technology will keep running tests until 2017, largely for “thermal management,” says program manager Roger Ellis, basically to ensure that the materials used for the gun don’t get as fried as the bullet under the intense power generated. The Navy guesstimates that it’ll be ready for shipboard defense between 2020 and 2025.
Oh, and the last record holder for most powerful railgun? The same gun when it fired off a shot using 10.64 megajoules two years ago.
By Spencer Ackerman 
December 10, 2010
Green Patriot Posters Reinvigorate Environmental Message
Thumbing through the book's ecology-themed imagery, created by multimediators like Shepard Fairey and DJ Spooky, won't stab you in the gut with dogma — but it could tickle your conscience.
"Co-editor Dmitri Siegel and I started Green Patriot Posters because we felt the sustainability movement needs better images and messages to connect with people," co-editor Edward Morris told Wired.com in an e-mail interview. "It needs more positivity and urgency, and a better connection to values that aren't simply about nature and conservation, which not everybody cares about, but also jobs and a better future."
The visual meditations on sustainabili
ty and overload evoke World War II–era posters that inspired the campaign. The posters can be torn out of the book and plastered somewhere useful.
Click through the Green Patriot Posters gallery above for a taste of the book's alternately critical and cute graphics, along with comments from contributing artists.
"America is the child of the Enlightenment," Morris said. "Climate change is the ultimate challenge to that rationality. The risk of increased conflict, refugees, famine and economic failure are not debatable. Whatever country figures out newer, cheaper, safer forms of energy is the new economic superpower."
Do Green Patriot Posters' well-meaning media and urgent messages wake hearts and minds ready for a War on Terra? Fly your freak flag in the comments section below.
Keep Buying Shit
by Diego Gutiérrez
"To a graphic designer, there is no better reason to design than for a good cause," said Diego Gutiérrez. "At the same time, popular media and kitsch design have exhausted a cause like global warming. Since Al Gore's An Inconvenient Truth came out, it has become popular for commercial design to take green to the masses. Although for a good cause, these sorts of commercial iterations are still very often designed with fluff for fluffy brains — there is no true statement of the urgency with which we must act to keep our lifestyle or even the world as we know it."&
nbsp;
Sow
by Ben Barnes
"'Sow Cultivate Thrive' is a poster series developed around the concept of the victory garden posters of World War II, with a modern interpretation," said Ben Barnes. "Stylistically I wanted them to have an American militaristic feel, with the idea of taking action to plant a garden."
Problem Me, Solution Me
by Steve Le
"For a problem that was caused by us, we have the ability to clean up our mess and solve global warming," said Steve Le. "It is our world: We should treat it with the utmost care."
Join the Revolution
by Adam Gray
"Both the bike and the heart icon seem to have currency at the moment," said Green Patriot Posters editor Edward Morris. "[Adam] Gray combined both in this design, which evokes a peaceful sort of revolutionary vigor."
Simplicity Is the Key to Successful Living
by Nick Dewar
"I hope that America is entering a post–'greed is good' period," said illustrator Nick Dewar of his design, which first appeared in ReadyMade magazine in 2009. "I can't think of a single step that would change the nature of our society more than everyone abandoning their automobiles and cycling instead. There would be less dependence on oil, obesity levels would drop dramatically, and reflective bike clips would replace fancy ladies' purses as the current must-have fashion accessory."
Dead End
by Noel Douglas
"Dead End is part of a body of work made for the street protests during the 2009 G20 Summit in London, Copenhagen during COP15 and Bolivia during the People's Summit," said Noel Douglas. "Graphic communication can foreground the contradictions of capitalism, or open windows onto new worlds. But they must serve human and not commercial needs."
Power Up Windmill
by Shepard Fairey
"I believe very strongly that green energy is the only way for the United States to achieve energy independence, create valuable technology and protect the environment," Fairey said about this 2009 design for MoveOn.org. "I created this windmill image as a patriotic symbol of the green-energy mission."
Manifesto for a People's Republic of Antarctica
by DJ Spooky
"Antarctica has many faces," said Paul "DJ Spooky" Miller, who journeyed to Antarctica in 2007 and 2008 to shoot the multimedia meditation Terra Nova: Antarctica Sinfonia. "It's usually thought of as a huge pile of ice that somehow stays afloat at the bottom of the world. In different ages, before humanity had mapped out the world, it would have simply been beyond most maps and most ideas about what made up the geography of the world. Today, Antarctica persists as a symbol of the unknown, and possesses great symbolic strength."
As China Advances, Solar Start-Ups Strategize
Over the last two years, Chinese solar panel makers like Suntech and Yingli Green Energy have moved aggressively into the United States and now supply about 40 percent of the California market, according to Bloomberg New Energy Finance, a research firm.
China’s growing dominance of the global solar market has been on display in Los Angeles this week at the Solar Power International conference, one of the industry’s biggest annual get-togethers. In a vast exhibition hall, the booth of one Silicon Valley start-up, Solyndra, is surrounded by a sea of Chinese solar companies offering their wares.
As prices for conventional silicon-based solar panels plummet, pressure has increased on Silicon Valley start-ups like Solyndra that make a type of photovoltaic cell called copper indium gallium selenide, or CIGS. Though less efficient at converting sunlight into electricity, the promise of the technology was that it could be made cheaply – at least until the cost of conventional solar module prices fell 40 percent over the past year.
That led Solyndra to start production two months ahead of schedule at its new $733 million factory in Fremont, Calif., and to speed up development of its next-generation solar panel.
“It definitely puts more pressure on us to bring our costs down as quickly as possible by ramping up volume,” said Ben Bierman, Solyndra’s executive vice president for operations and engineering, as driverless carts shuttled stacks of photovoltaic parts to large orange robots at Fab 1, the company’s original factory.
Nathaniel Bullard, a solar analyst with Bloomberg New Energy Finance in San Francisco, said that success for high-tech Silicon Valley solar companies may depend on finding a big market niche they can dominate.
Solyndra, for instance, makes lightweight solar panels that snap together like Legos and can be installed on large commercial rooftops unable to support heavier conventional panels. On the roof of the company’s headquarters, Mr. Bierman recently gave me an advance look at its new solar panel, which is more powerful but requires far less labor to install.
Production started two months early at Solyndra’s solar panel factory in Fremont, Calif.
“We really took a lot of the cost out and accelerated development in response to the Chinese,” Mr. Bierman said.
China presents different challenges for SunPower, which was founded in 1985 and is the granddaddy of Silicon Valley solar companies.
SunPower makes conventional solar panels but has also pursued a high-technology strategy and says it produces the world’s most efficient photovoltaic modules. (Architects and fashion-forward homeowners also favor the company’s sleek jet-black panels.)
In recent years, SunPower has increasingly focused on building big photovoltaic power plants to supply electricity to utilities that put a premium on technological performance, reliability and a company’s ability to manage complex projects.
“In the old days, the saying was that nobody gets firedfor buying I.B.M.,” Thomas Werner, SunPower’s chief executive, said in an interview. “That’s what we want to be in solar, and we are in fact.”
He said that while SunPower competes on costs, it does not aim to be the lowest-cost manufacturer.
“We want to have the best technologies so that people buy us for the reasons they buy a company’s product like Apple,” Mr. Werner said. “I don’t want to be the iPhone without the apps.”