David Kirkpatrick

November 4, 2010

Transparent solar panels?

A very real possibility. This sounds like very promising technology.

The release:

Transparent Conductive Material Could Lead to Power-Generating Windows

Combines elements for light harvesting and electric charge transport over large, transparent areas

November 3, 2010

conjugated polymer honeycombClick on the image to download a high-resolution version.Top: Scanning electron microscopy image and zoom of conjugated polymer (PPV) honeycomb. Bottom (left-to-right): Confocal fluorescence lifetime images of conjugated honeycomb, of polymer/fullerene honeycomb double layer and of polymer/fullerene honeycomb blend. Efficient charge transfer within the whole framework is observed in the case of polymer/fullerene honeycomb blend as a dramatic reduction in the fluorescence lifetime.

UPTON, NY — Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and Los Alamos National Laboratory have fabricated transparent thin films capable of absorbing light and generating electric charge over a relatively large area. The material, described in the journal Chemistry of Materials, could be used to develop transparent solar panels or even windows that absorb solar energy to generate electricity.

The material consists of a semiconducting polymer doped with carbon-rich fullerenes. Under carefully controlled conditions, the material self-assembles to form a reproducible pattern of micron-size hexagon-shaped cells over a relatively large area (up to several millimeters).

“Though such honeycomb-patterned thin films have previously been made using conventional polymers like polystyrene, this is the first report of such a material that blends semiconductors and fullerenes to absorb light and efficiently generate charge and charge separation,” said lead scientist Mircea Cotlet, a physical chemist at Brookhaven’s Center for Functional Nanomaterials (CFN).

Furthermore, the material remains largely transparent because the polymer chains pack densely only at the edges of the hexagons, while remaining loosely packed and spread very thin across the centers. “The densely packed edges strongly absorb light and may also facilitate conducting electricity,” Cotlet explained, “while the centers do not absorb much light and are relatively transparent.”

Mircea CotletClick on the image to download a high-resolution version.Mircea Cotlet, Ranjith Krishna Pai, and Zhihua Xu (seated at the microscope).

“Combining these traits and achieving large-scale patterning could enable a wide range of practical applications, such as energy-generating solar windows, transparent solar panels, and new kinds of optical displays,” said co-author Zhihua Xu, a materials scientist at the CFN.

“Imagine a house with windows made of this kind of material, which, combined with a solar roof, would cut its electricity costs significantly. This is pretty exciting,” Cotlet said.

The scientists fabricated the honeycomb thin films by creating a flow of micrometer-size water droplets across a thin layer of the polymer/fullerene blend solution. These water droplets self-assembled into large arrays within the polymer solution. As the solvent completely evaporates, the polymer forms a hexagonal honeycomb pattern over a large area.

“This is a cost-effective method, with potential to be scaled up from the laboratory to industrial-scale production,” Xu said.

The scientists verified the uniformity of the honeycomb structure with various scanning probe and electron microscopy techniques, and tested the optical properties and charge generation at various parts of the honeycomb structure (edges, centers, and nodes where individual cells connect) using time-resolved confocal fluorescence microscopy.

The scientists also found that the degree of polymer packing was determined by the rate of solvent evaporation, which in turn determines the rate of charge transport through the material.

“The slower the solvent evaporates, the more tightly packed the polymer, and the better the charge transport,” Cotlet said.

“Our work provides a deeper understanding of the optical properties of the honeycomb structure. The next step will be to use these honeycomb thin films to fabricate transparent and flexible organic solar cells and other devices,” he said.

The research was supported at Los Alamos by the DOE Office of Science. The work was also carried out in part at the CFN and the Center for Integrated Nanotechnologies Gateway to Los Alamos facility. The Brookhaven team included Mircea Cotlet, Zhihua Xu, and Ranjith Krishna Pai. Collaborators from Los Alamos include Hsing-Lin Wang and Hsinhan Tsai, who are both users of the CFN facilities at Brookhaven, Andrew Dattelbaum from the Center for Integrated Nanotechnologies Gateway to Los Alamos facility, and project leader Andrew Shreve of the Materials Physics and Applications Division.

The Center for Functional Nanomaterials at Brookhaven National Laboratory and the Center for Integrated Nanotechnologies Gateway to Los Alamos facility are two of the five DOE Nanoscale Science Research Centers (NSRCs), premier national user facilities for interdisciplinary research at the nanoscale. Together the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative. The NSRCs are located at DOE’s Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge and Sandia and Los Alamos national laboratories.

 

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October 26, 2010

World’s largest solar installation coming to California

Via KurzweilAI.net — That’s some serious solar capacity.

US approves world’s biggest solar energy project in California

October 26, 2010 by Editor

The U.S. Department of Interior approved on Monday a permit for Solar Millennium, LLC to build the largest solar energy project in the world — four  plants at the cost of one billion dollars each — in southern California.

The project is expected to generate up to 1,000 Megawatts of energy, enough electricity to annually power more than 300,000 single-family homes, more than doubling the solar electricity production capacity of the U.S.

Once constructed, the Blythe facility will reduce CO2 emissions by nearly one million short tons per year, or the equivalent of removing more than 145,000 cars from the road. Additionally, because the facility is “dry-cooled,” it will use 90 percent less water than a traditional “wet-cooled” solar facility of this size. The Blythe facility will also help California take a major step toward achieving its goal of having one third of the state’s power come from renewable sources by the year 2020.

The entire Blythe Solar Power Project will generate a total of more than 7,500 jobs, including 1,000 direct jobs during the construction period, and thousands of additional indirect jobs in the community and throughout the supply chain. When the 1,000 MW facility is fully operational it will create more than 220 permanent jobs.

Adapted from materials provided by Solar Millennium, LLC.

 

 

 

October 20, 2010

Fresh drinking water through solar power

This has the potential to be a real game changer. Among all the other problems out there, one very pervasive issue that gets intermittent lip service is potable, or the lack thereof, water. A portable desalination device could save lives in a variety of situations.

From the link:

The portable system could also be used in remote areas where supplying energy and clean water can be logistically complex and expensive, such as desert locations or farms and small villages in developing countries.

Led by Steven Dubowsky, a professor in both the Department of Mechanical Engineering and the Department of Aeronautics and Astronautics, and graduate students Amy Bilton and Leah Kelley, the group built a small prototype of the system last spring to test algorithms they had developed to run it. They have since demonstrated that the prototype is capable of producing 80 gallons of water a day in a variety of weather conditions. They estimate that a larger version of the unit, which would cost about $8,000 to construct, could provide about 1,000 gallons of water per day. Dubowsky and his students also estimate that one C-130 cargo airplane could transport two dozen desalination units — enough to provide water for 10,000 people.

The team presented a paper reporting preliminary results about its prototype system last week at the EuroMed 2010-Desalination for Clean Water and Energy Conference.

October 13, 2010

3M is improving solar panels

Filed under: Business, Science, Technology — Tags: , , , , — David Kirkpatrick @ 9:34 am

This sounds like a pretty significant breakthrough.

From the link:

For years solar companies have wanted to make lightweight, flexible panels that are cheap to ship and easy to install (by unrolling them over large areas). But they’ve been held up by a lack of good and affordable glass substitutes.

Now 3M thinks it’s found a solution. This week the company unveiled a plastic film that it says can rival glass in its ability to protect the active materials in solar cells from the elements and save money for manufacturers and their customers.

The protective film is a multilayer, fluoropolymer-based sheet that can replace glass as the protective front cover of solar panels, says Derek DeScioli, business development manager for 3M’s renewable energy division. Manufacturers laminate the sheets onto the solar panels to seal them tight and shield them from moisture and other weather elements that can be deadly to the solar cells inside.

Solar protection: This polymer film seals out water far better than other plastics—it can protect solar panels for decades.
Credit: 3M

 

October 2, 2010

Quantum dots may lead to ultraefficient solar cells

This sounds promising.

From the link (emphasis mine):

Although researchers have steadily increased the amount of electricity that solar cells can produce, they face fundamental limits because of the physics involved in converting photons to electrons in semiconductor materials. Now researchers at the University of Wyoming have demonstrated that by using novel nanomaterials called quantum dots, it might be possible to exceed those limits and produce ultraefficient solar cells.

The theoretical limitation of solar cells has to do with the widely varying amounts of energy from photons in sunlight. The amount varies depending on the color of the light. No matter how energetic the incoming photons are, however, solar cells can only convert one photon into one electron with a given amount of energy. Any extra energy is lost as heat. Scientists have hypothesized that quantum dots, because of their unusual electronic properties, could convert some of this extra energy into electrons. They’ve calculated that this approach could increase the theoretical maximum efficiency of solar cells by about 50 percent.

Solar dots: A micrograph shows lead-sulfide quantum dots, each about five nanometers across, coating an electrode of titanium dioxide.
Credit: Science

September 6, 2010

Self-assembling and reassembling solar cells

Okay, just yesterday I blogged that a lot of the time the mundane “a ha” moment that puts together well-known materials and processes leads to scientific advancement (the case I was referring to in the post was a simple acid bath technique that made creating solar cells much cheaper). And then again sometimes the big sexy breakthrough gets the headline (as usual) and really deserves it.

If this technique for solar cells that self-assembles the light-harvesting element in the cell, and then breaks it down for re-assembly essentially copying what plants do in their chloroplast, is able to reach acceptable levels of efficiency, it will be an absolute game-changer. Instead of a solar cell that’s (hopefully) constantly bombarded with the full effect of the sun and constantly degrading under the solar assault, these cells will essentially be completely renewed by each reassembly. No degradation over time, just a brand new light-harvesting element with a relatively simple chemical process.

From the second link:

The system Strano’s team produced is made up of seven different compounds, including the carbon nanotubes, the phospholipids, and the proteins that make up the reaction centers, which under the right conditions spontaneously assemble themselves into a light-harvesting structure that produces an electric current. Strano says he believes this sets a record for the complexity of a self-assembling system. When a surfactant — similar in principle to the chemicals that BP has sprayed into the Gulf of Mexico to break apart oil — is added to the mix, the seven components all come apart and form a soupy solution. Then, when the researchers removed the surfactant by pushing the solution through a membrane, the compounds spontaneously assembled once again into a perfectly formed, rejuvenated photocell.

“We’re basically imitating tricks that nature has discovered over millions of years” — in particular, “reversibility, the ability to break apart and reassemble,” Strano says. The team, which included postdoctoral researcher Moon-Ho Ham and graduate student Ardemis Boghossian, came up with the system based on a theoretical analysis, but then decided to build a prototype cell to test it out. They ran the cell through repeated cycles of assembly and disassembly over a 14-hour period, with no loss of efficiency.

September 5, 2010

Acid bath creates cheaper solar cells

A relatively simple brute force manufacturing step creates solar cells at much lower cost. The big, sexy breakthroughs are great  and technological leaps are fun, but a lot of the time it’s the almost mundane “a ha” moment that puts together well-known materials and processes that take a technology to the next step. This particular discovery sounds very promising since it both reduces production costs and almost retains maximum solar efficiency.

From the link:

A new low-cost etching technique developed at the U.S. Department of Energy’s National Renewable Energy Laboratory can put a trillion holes in a silicon wafer the size of a compact disc.

As the tiny holes deepen, they make the silvery-gray silicon appear darker and darker until it becomes almost pure black and able to absorb nearly all colors of light the sun throws at it.

At room temperature, the black silicon wafer can be made in about three minutes. At 100 degrees F, it can be made in less than a minute.

The breakthrough by NREL scientists likely will lead to lower-cost  that are nonetheless more efficient than the ones used on rooftops and in solar arrays today.

R&D Magazine recently awarded the NREL team one of its R&D 100 awards for Black Silicon Nanocatalytic Wet-Chemical Etch. Called “the Oscars of Invention,” the R&D 100 awards recognize the most significant scientific breakthroughs of the year.

Also from the link (and conveniently making my point above about “almost mundane ‘a ha’ moment”s):

In a string of outside-the-box insights combined with some serendipity, Branz and colleagues Scott Ward, Vern Yost and Anna Duda greatly simplified that process.

Rather than laying the gold with vacuums and pumps, why not just spray it on? Ward suggested.

Rather than layering the gold and then adding the acidic mixture, why not mix it all together from the outset? Dada suggested.

In combination, those two suggestions yielded even better results.

A silver wafer reflects the face of NREL research scientist Hao-Chih Yuan, before the wafer is washed with a mix of acids. The acids etch holes, absorbing light and turning the wafer black. Credit: Dennis Schroeder

August 22, 2010

Keeping solar panels clean

By using technology developed for Mars missions. The budget for NASA gets debated, scoffed at and cut, but all too often people against giving NASA money forget how many products and processes developed for space travel ended up with solidly terrestrial applications.

The release:

Self-cleaning technology from Mars can keep terrestrial solar panels dust free

IMAGE: Researchers have developed technology for large-scale solar power installations to self-clean.

Click here for more information.

BOSTON, Aug. 22, 2010 — Find dusting those tables and dressers a chore or a bore? Dread washing the windows? Imagine keeping dust and grime off objects spread out over an area of 25 to 50 football fields. That’s the problem facing companies that deploy large-scale solar power installations, and scientists today presented the development of one solution — self-dusting solar panels ― based on technology developed for space missions to Mars.

In a report at the 240th National Meeting of the American Chemical Society (ACS), they described how a self-cleaning coating on the surface of solar cells could increase the efficiency of producing electricity from sunlight and reduce maintenance costs for large-scale solar installations.

“We think our self-cleaning panels used in areas of high dust and particulate pollutant concentrations will highly benefit the systems’ solar energy output,” study leader Malay K. Mazumder, Ph.D. said. “Our technology can be used in both small- and large-scale photovoltaic systems. To our knowledge, this is the only technology for automatic dust cleaning that doesn’t require water or mechanical movement.”

Mazumder, who is with Boston University, said the need for that technology is growing with the popularity of solar energy. Use of solar, or photovoltaic, panels increased by 50 percent from 2003 to 2008, and forecasts suggest a growth rate of at least 25 percent annually into the future. Fostering the growth, he said, is emphasis on alternative energy sources and society-wide concerns about sustainability (using resources today in ways that do not jeopardize the ability of future generations to meet their needs).

Large-scale solar installations already exist in the United States, Spain, Germany, the Middle East, Australia, and India. These installations usually are located in sun-drenched desert areas where dry weather and winds sweep dust into the air and deposit it onto the surface of solar panel. Just like grime on a household window, that dust reduces the amount of light that can enter the business part of the solar panel, decreasing the amount of electricity produced. Clean water tends to be scarce in these areas, making it expensive to clean the solar panels.

“A dust layer of one-seventh of an ounce per square yard decreases solar power conversion by 40 percent,” Mazumder explains. “In Arizona, dust is deposited each month at about 4 times that amount. Deposition rates are even higher in the Middle East, Australia, and India.”

Working with NASA, Mazumder and colleagues initially developed the self-cleaning solar panel technology for use in lunar and Mars missions. “Mars of course is a dusty and dry environment,” Mazumder said, “and solar panels powering rovers and future manned and robotic missions must not succumb to dust deposition. But neither should the solar panels here on Earth.”

The self-cleaning technology involves deposition of a transparent, electrically sensitive material deposited on glass or a transparent plastic sheet covering the panels. Sensors monitor dust levels on the surface of the panel and energize the material when dust concentration reaches a critical level. The electric charge sends a dust-repelling wave cascading over the surface of the material, lifting away the dust and transporting it off of the screen’s edges.

Mazumder said that within two minutes, the process removes about 90 percent of the dust deposited on a solar panel and requires only a small amount of the electricity generated by the panel for cleaning operations.

The current market size for solar panels is about $24 billion, Mazumder said. “Less than 0.04 percent of global energy production is derived from solar panels, but if only four percent of the world’s deserts were dedicated to solar power harvesting, our energy needs could be completely met worldwide. This self-cleaning technology can play an important role.”

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The American Chemical Society is a non-profit organization chartered by the U.S. Congress. With more than 161,000 members, ACS is the world’s largest scientific society and a global leader in providing access to chemistry-related research through its multiple databases, peer-reviewed journals and scientific conferences. Its main offices are in Washington, D.C., and Columbus, Ohio.

August 21, 2010

Cool tech news — solar powered toothbrush

And it uses an electron/mouth acid reaction to kill disease-causing bacteria and breakdown plaque instead of toothpaste. Very cool indeed, but I’m curious how the dental hygiene industry will react to the device?

From the link:

Dr. Kunio Komiyama, a dentistry professor emeritus at the University of Saskatchewan, designed the first model of the unconventional toothbrush 15 years ago. Today, Komiyama and his colleague Dr. Gerry Uswak are seeking recruits to test their newest model, the Soladey-J3X. The toothbrush, which is manufactured by the Shiken company of Japan, will soon be tested by 120 teenagers to see how it compares to a normal toothbrush.

The Soladey-J3X has a solar panel at its base that transmits electrons to the top of the toothbrush through a lead wire. The  react with acid in the mouth, creating a chemical reaction that breaks down  and kills . The toothbrush requires no toothpaste, and can operate with about the same amount of light as needed by a solar-powered calculator.

(And to answer a concern from the comment section on the toothbrush, the word “lead” in the second graf more than likely refers to a “leed” wire running between the solar panel and the top of the toothbrush, and not the heavy metal that’s been so excoriated.)

August 17, 2010

Nanotech and solar efficiency

Nanotechnology and solar energy get a lot of virtual ink around here, and I always enjoy getting the chance to blog about both topics in the same post. This study finds that incorporating quantum dots in photovoltaic solar cells through nanoscience should both increase the efficiency of the cells and reduce their cost. A win-win all the way around.

From the link:

As the fastest growing energy technology in the world, solar energy continues to account for more and more of the world’s energy supply. Currently, most commercial photovoltaic power comes from bulk semiconductor materials. But in the past few years, scientists have been investigating how semiconductor nanostructures can increase the efficiency of solar cells and the newer field of solar fuels.

Although there has been some controversy about just how much nanoscience can improve solar cells, a recent overview of this research by Arthur Nozik, a researcher at the National Renewable Energy Laboratory (NREL) and professor at the University of Colorado, shows that semiconductor nanostructures have significant potential for converting solar energy into electricity


August 10, 2010

Ten percent solar boost with a mere sticker

Filed under: Business, Science — Tags: , , , — David Kirkpatrick @ 12:39 am

And these things can be applied to solar installations in the field. Talk about a simple improvement that goes a long, long way. Solar efficiency tends to go up in tiny increments unless it involves some sort of materials or process breakthrough. This news really is impressive.

From the link:

The power output of solar panels can be boosted by 10 percent just by applying a big transparent sticker to the front. Developed by a small startup called Genie Lens Technologies, the sticker is a polymer film embossed with microstructures that bend incoming sunlight. The result: the active materials in the panels absorb more light, and convert more of it into electricity.

The technology is cheap and could lower the cost per watt of solar power. Also, unlike other technologies developed to improve solar panel performance, this one can be added to panels that have already been installed.

The polymer film does three main things, says Seth Weiss, CEO and cofounder of Genie Lens, based in Englewood, CO. It prevents light from reflecting off the surface of solar panels. It traps light inside the semiconductor materials that absorb light and convert it to electricity. And it redirects incoming light so that rather than passing through the thin semiconductor material, it travels along its surface, increasing the chances it will be absorbed.

Power film: A thin plastic sheet covered with microscopic structures is applied to the front of a solar panel to increase the amount of light it absorbs.
Credit: Genie Lens Technologies

August 9, 2010

Is solar power cheaper than nuclear?

Filed under: Business, Science, Technology — Tags: , , , , — David Kirkpatrick @ 9:04 pm

Surprisingly, maybe so.

From the link:

One of the issues associated with shifting from using fossil fuels to alternative energy sources is the cost. While adherents of alternative energy tout its benefits, many are skeptical, pointing out that such alternatives are just too expensive. Advocates of nuclear power point out that it is less polluting (if you don’t count storage of spent fuel) than fossil fuels, and that it costs less than alternatives like solar power.

A new study out of Duke University, though, casts doubt on the idea that  is cheaper than . Using information from North Carolina, the study shows that solar power may be more cost efficient than nuclear power. With costs dropping on the production of photovoltaic cells, and with solar cells becoming increasingly efficient, it appears that — in North Carolina at least — solar installations offer a viable alternative to nuclear power, which is the source for about 20% of the electricity in the U.S.

August 7, 2010

Beautiful space image — the sun in a solar flare

A solar flare from August 1, 2010 no less (last Sunday).

Enjoy …

On August 1, 2010, almost the entire Earth-facing side of the sun erupted in a tumult of activity. This image from the Solar Dynamics Observatory of the news-making solar event on August 1 shows the C3-class solar flare.

Great Ball of Fire

On August 1, 2010, almost the entire Earth-facing side of the sun erupted in a tumult of activity. This image from the Solar Dynamics Observatory of the news-making solar event on August 1 shows the C3-class solar flare (white area on upper left), a solar tsunami (wave-like structure, upper right), multiple filaments of magnetism lifting off the stellar surface, large-scale shaking of the solar corona, radio bursts, a coronal mass ejection and more.

This multi-wavelength extreme ultraviolet snapshot from the Solar Dynamics Observatory shows the sun’s northern hemisphere in mid-eruption. Different colors in the image represent different gas temperatures. Earth’s magnetic field is still reverberating from the solar flare impact on August 3, 2010, which sparked aurorae as far south as Wisconsin and Iowa in the United States. Analysts believe a second solar flare is following behind the first flare and could re-energize the fading geomagnetic storm and spark a new round of Northern Lights.

Credit: NASA/SDO/AIA

August 5, 2010

Selenium improves solar efficiency

I like the “anti-sunscreen” intro to this news on improving the efficiency of photovoltaic solar cells with selenium.

The release:

Selenium makes more efficient solar cells

This release is also available in Chinese.

IMAGE: This is a sunset over the Pacific Ocean as seen from Highway 1 south of Monterey, Calif. LBNL’s Marie Mayer, who took the photo, calls sunlight and water “two sustainable…

Click here for more information.

College Park, MD (August 3, 2010) — Call it the anti-sunscreen. That’s more or less the description of what many solar energy researchers would like to find — light-catching substances that could be added to photovoltaic materials in order to convert more of the sun’s energy into carbon-free electricity.

Research reported in the journal Applied Physics Letters, published by the American Institute of Physics (AIP), describes how solar power could potentially be harvested by using oxide materials that contain the element selenium. A team at the Lawrence Berkeley National Laboratory in Berkeley, California, embedded selenium in zinc oxide, a relatively inexpensive material that could be promising for solar power conversion if it could make more efficient use of the sun’s energy. The team found that even a relatively small amount of selenium, just 9 percent of the mostly zinc-oxide base, dramatically boosted the material’s efficiency in absorbing light.

“Researchers are exploring ways to make solar cells both less expensive and more efficient; this result potentially addresses both of those needs,” says author Marie Mayer, a fourth-year University of California, Berkeley doctoral student based out of LBNL’s Solar Materials Energy Research Group, which is working on novel materials for sustainable clean-energy sources.

Mayer says that photoelectrochemical water splitting, using energy from the sun to cleave water into hydrogen and oxygen gases, could potentially be the most exciting future application for her work. Harnessing this reaction is key to the eventual production of zero-emission hydrogen powered vehicles, which hypothetically will run only on water and sunlight. Like most researchers, Mayer isn’t predicting hydrogen cars on the roads in any meaningful numbers soon. Still, the great thing about solar power, she says, is that “if you can dream it, someone is trying to research it.”

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The article, “Band structure engineering of ZnO1-xSex alloys” by Marie A. Mayer, Derrick T. Speaks, Kin Man Yu, Samuel S. Mao, Eugene E. Haller, and Wladek Walukiewicz will appear in the journal Applied Physics Letters. See: http://apl.aip.org/applab/v97/i2/p022104_s1

ABOUT APPLIED PHYSICS LETTERS

Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics. Emphasizing rapid dissemination of key data and new physical insights, Applied Physics Letters offers prompt publication of new experimental and theoretical papers bearing on applications of physics phenomena to all branches of science, engineering, and modern technology. Content is published online daily, collected into weekly online and printed issues (52 issues per year). See: http://apl.aip.org/

ABOUT AIP

The American Institute of Physics is a federation of 10 physical science societies representing more than 135,000 scientists, engineers, and educators and is one of the world’s largest publishers of scientific information in the physical sciences. Offering partnership solutions for scientific societies and for similar organizations in science and engineering, AIP is a leader in the field of electronic publishing of scholarly journals. AIP publishes 12 journals (some of which are the most highly cited in their respective fields), two magazines, including its flagship publication Physics Today; and the AIP Conference Proceedings series. Its online publishing platform Scitation hosts nearly two million articles from more than 185 scholarly journals and other publications of 28 learned society publishers.

August 4, 2010

Lower cost solar cells

Yesterday I blogged about a new solar energy process that might supplant photovoltaics, at least in large-scale desert installations because of dramatically increased efficiency. Today it’s a breakthrough with photovoltaic solar cells in regards to production cost. I like seeing all this innovation is the solar space, especially since it’s a bit all over the map. Incremental improvement is always nice, but anytime research is going after all sorts of targets the odds of a major breakthrough go up.

From the second link:

One of the most promising technologies for making inexpensive but reasonably efficient solar photovoltaic cells just got much cheaper. Scientists at the University of Toronto in Canada have shown that inexpensive nickel can work just as well as gold for one of the critical electrical contacts that gather the electrical current produced by their colloidal quantum dot solar cells.

The change to nickel can reduce the cell’s already low material costs by 40 to 80 percent, says Lukasz Brzozowski, the director of the Photovoltaics Research Program in Professor Ted Sargent’s group. They present their research in the July 12, 2010 issue of Applied Physics Letters.

August 3, 2010

A completely new path to solar efficiency?

Maybe so. And if so this sounds very promising. I’ll go ahead and repeat my solar energy mantra — two things both have to happen before solar is truly economically viable: costs must come down quite a bit, and the efficiency has to at least be within spitting distance of petroleum and other traditional natural resources. This sounds like very good news on the efficiency front. Might even offer some cost benefits as well.

From the link:

Stanford engineers have figured out how to simultaneously use the light and heat of the sun to generate electricity in a way that could make solar power production more than twice as efficient as existing methods and potentially cheap enough to compete with oil.

Unlike photovoltaic technology currently used in  – which becomes less efficient as the temperature rises – the new process excels at higher temperatures.

Called ‘photon enhanced thermionic emission,’ or PETE, the process promises to surpass the efficiency of existing photovoltaic and thermal conversion technologies.

“This is really a conceptual breakthrough, a new  process, not just a new material or a slightly different tweak,” said Nick Melosh, an assistant professor of materials science and engineering, who led the research group. “It is actually something fundamentally different about how you can harvest energy.”

And the materials needed to build a device to make the process work are cheap and easily available, meaning the power that comes from it will be affordable.

A small PETE device made with cesium-coated gallium nitride glows while being tested inside an ultra-high vacuum chamber. The tests proved that the process simultaneously converted light and heat energy into electrical current. Credit: Photo courtesy of Nick Melosh, Stanford University

July 24, 2010

Solar plane stays aloft for two weeks

Due to my recent light blogging schedule this is not hot from the inbox, but it come through early yesterday morning. Pretty cool accomplishment, I’d say.

The release:

After 14 Nights in the Air, QinetiQ Prepares to Land its Zephyr Solar Powered Unmanned Aircraft

FARNBOROUGH, England, July 23, 2010/PRNewswire/ —

– With Photo

QinetiQ will today bring Zephyr
(http://www.qinetiq.com/home_farnborough_airshow/unmanned_air_systems/zephyr.html), its solar powered high-altitude long endurance (HALE) Unmanned Air System (UAS) back to earth after two weeks in the air – smashing a number of long-standing official and unofficial world records.

Zephyr was launched on 09 July and is currently still flying above the US Army’s Yuma Proving Ground in Arizona. Today Zephyr will have been aloft for 14 nights continuously, achieving the objective of the trial and setting a number of performance and altitude records. At this point QinetiQ’s Zephyr team in Yuma will bring the aircraft back to earth.

An official from the Federation Aeronautique Internationale (FAI) (http://www.fai.org/), the world air sports federation, has been monitoring progress at the Yuma Proving Ground and when Zephyr is back on the ground he looks set to be able to confirm a number of new world records. This includes quadrupling its own unofficial world record for longest duration unmanned flight (82 hours, 37 minutes set in 2008) and surpassing the current official world record for the longest flight for an unmanned air system (set at 30 hours 24 minutes by Northrop Grumman’s RQ-4A Global Hawk on 22 March 2001). Zephyr will also have flown longer, non-stop and without refuelling, than any other aeroplane – having significantly passed the Rutan Voyager milestone of 9 days (216 hours) 3 minutes and 44 seconds airborne, set in December 1986.

“Zephyr is the world’s first and only truly persistent aeroplane,” said Neville Salkeld, MD of QinetiQ’s UK Technology Solutions Group. “We are really proud of the team’s achievement which has been supported by expertise from across the QinetiQ business and beyond. We’ve now proved that this amazing aircraft is capable of providing a cost effective, persistent surveillance and communications capability measured in terms of weeks, if not months. Not only is Zephyr game-changing technology, it is also significantly more cost effective to manufacture and deploy than traditional aircraft and satellites.”

Easy to transport in a standard road transport container, once launched Zephyr can remain above a general area for weeks, if not months, at a time delivering vital capability at a fraction of the cost of satellites and significantly more cost effectively than other ‘conventionally powered’ manned or unmanned aircraft. Zephyr also does not need to return to base at regular intervals for re-fuelling or servicing which helps minimise the logistical supply chain, extending its operational capability and appeal. Its zero emissions also make it exceptionally environmentally friendly.

For the trial in Yuma Zephyr is carrying a communications payload configured to meet the needs of the UK Ministry of Defence. In addition to the obvious defence and security applications, commercial uses include environmental research; monitoring crops and pollution; providing tactical intelligence over disaster zones or forest fires; plus delivering mobile communications capabilities in remote areas.

Chris Kelleher, QinetiQ’s chief designer said: “We have designed, built and delivered what will be remembered as a milestone in aviation history. Zephyr will transform the delivery of current services such as communications, and lead to many new applications which are not possible or affordable by other means.

“The brand-new ‘production ready’ Zephyr airframe incorporates totally new approaches to aerodynamics, structures, propulsion, avionics, flight controls, power system management, thermal control, ground control station design and payload, as well as overall operating processes. Our outstanding team has brought this entire ‘one-shot’ flight together at the first time of asking, demonstrating we can operate both the aircraft and its ultra-light utility payload routinely for long duration flights.

“We’ve also had to design for temperatures of around plus 40 degrees C  on the ground to below minus 75 degrees C at altitude, ever changing  weather systems including storms and high winds – and Zephyr took them all  in its stride. It is a truly fantastic achievement.”

Launched by hand, the aircraft flies by day on solar power delivered by amorphous silicon solar arrays, supplied by Uni-Solar (http://www.uni-solar.com/), no thicker than sheets of paper that cover the aircraft’s wings. These are also used to recharge the lithium-sulphur batteries, supplied by Sion Power Inc (http://www.sionpower.com/), which are used to power the aircraft by night. Together they provide an extremely high power to weight ratio on a continuous day/night cycle, thereby delivering persistent on station capabilities.

Around 50% larger than the previous version, Zephyr incorporates an entirely new wing design with a total wingspan of 22.5m to accommodate more batteries that are combined with a totally new integrated power management system. The entirely new aerodynamic shape also helps to reduce drag and improve performance. Zephyr’s ultra-lightweight carbon fibre design means it weighs in at just over 50Kg.

– Zephyr launch video (http://www.youtube.com/watch?v=CT-DYeEP8dg)

– Zephyr pages on QinetiQ.com
(http://www.qinetiq.com/home_farnborough_airshow/unmanned_air_systems/zephyr.html)

– Zephyr launch release with additional hi-res photos
(http://www.qinetiq.com/home/newsroom/news_releases_homepage/2010/3rd_quarter/zephyr_2010.html)

A picture accompanying this release is available through the PA
Photowire. It can be downloaded from http://www.pa-mediapoint.press.net or
viewed at http://www.mediapoint.press.net or http://www.prnewswire.co.uk.

Source: QinetiQ

July 16, 2010

Solar plus nanotech equals lower cost cells

I always love covering news that combines solar and nanotechnology, particularly when the combo leads to lower costs for solar power. I’ve previously blogged about nanopillars leading increased solar efficiency.

From the first link:

A material with a novel nanostructure developed by researchers at the University of California, Berkeley could lead to lower-cost solar cells and light detectors. It absorbs light just as well as commercial thin-film solar cells but uses much less semiconductor material.

The new material consists of an array of nanopillars that are narrow at the top and thicker at the bottom. The narrow tops allow light to penetrate the array without reflecting off. The thicker bottom absorbs light so that it can be converted into electricity. The design absorbs 99 percent of visible light, compared to the 85 percent absorbed by an earlier design in which the nanopillars were the same thickness along their entire length. An ordinary flat film of the material would absorb only 15 percent of the light.

Thick and thin: A scanning electron microscope image shows dual-diameter light-trapping germanium nanopillars.

Credit: Ali Javey, UC Berkeley

July 13, 2010

Efficiency record for for large-area epitaxial thin-film silicon solar cells

Filed under: Business, Science — Tags: , , , — David Kirkpatrick @ 6:10 pm

Good solar news. I may sound like a broken record, but for solar to be market-viable two things have to happen — costs must come way down and efficiency must go way up. This is a step in the right direction.

From the link:

Imec scientists realized large-area (70cm2) epitaxial solar cells with efficiencies of up to 16.3% on high-quality substrates. And efficiencies of up to 14.7% were achieved on large-area low-quality substrates, showing the potential of thin-film epitaxial solar cells for industrial manufacturing. The results were achieved within imec’s silicon solar cell industrial affiliation program (IIAP) that explores and develops advanced process technologies aiming a sharp reduction in silicon use, whilst increasing cell efficiency and hence further lowering substantially the cost per Watt peak.

Imec large-area (70cm2) epitaxial solar cell with an efficiency of up to 16.3% on high-quality substrat

Colorado boasts first coal/solar hybrid power plant

Sounds like a great idea to begin integrating solar energy into viable power production.

From the link:

The first ever hybrid solar-coal power plant is now operating at Unit 2 of the Cameo Generating Station near Palisade in Colorado. The demonstration project was built by Xcel Energy as part of its new Innovative Clean Technology (ICT) Program, and is designed to decrease the use of coal, increase the plant’s efficiency, lower carbon dioxide emissions, and test the commercial viability of combining the two technologies.

The project was developed by Xcel Energy in conjunction with Abengoa Solar, which developed the solar parabolic trough technology that concentrates solar energy to produce heat. The demonstration project is expected to cut the use of coal at the power plant by around two or three percent, and could be scaled up to cut it by 10 percent.

July 4, 2010

Obama gives $2B to two solar companies

As a nation we must find energy sources beyond petroleum. Chiefly because it’s a finite resource and will eventually — and that eventually may be a long ways off — run out. And it is the root of almost every vexing military and statecraft problem the United States faces. The problem is oil, gas and coal are so incredibly cheap and efficient compared to any feasible alternative.

Solar power has seen breakthrough after breakthrough (see the link in the sidebar under “interesting blog topics”) over the last several years, and many of these breakthroughs affect the current solar marketplace so it’s not all pie-in-the-sky activity. One way to ramp up improvements in solar efficiency and lower practical costs is to infuse the R&D process with enough money to not have to pick and choose among untested ideas. This investment from the government will allow Abengoa Solar and Abound Solar Manufacturing to implement large solar installations, create some jobs along the way, and, yes, continue to improve solar energy as a viable alternative to petroleum.

This is good news to blog about on Independence Day. Kudos to President Obama.

From the link:

US President Barack Obama announced on Saturday the awarding of nearly two billion dollars to two solar energy companies that have agreed to build new power plants in the United States, creating thousands of new jobs.

“We’re going to keep fighting to advance our recovery,” Obama said in his weekly radio address. “And we’re going to keep competing aggressively to make sure the jobs and industries of the future are taking root right here in America.”

One of the companies, Abengoa Solar, has agreed to build one of the largest solar plants in the world in Arizona, which will create about 1,600 construction jobs. When completed, this plant will provide enough  to power 70,000 homes.

The other company, Abound Solar Manufacturing, is building two new plants, one in Colorado and one in Indiana.

US President Barack Obama (R) tours a solar energy centre in Arcadia, Florida in 2009. Obama has announced the awarding of nearly $2 bln to two solar energy companies that have agreed to build new power plants in the US, creating thousands of new jobs

June 17, 2010

Quantum dot research may lead to dramatic solar efficiency increase

Filed under: Science — Tags: , , , , — David Kirkpatrick @ 11:47 pm

This seems like a week full of a lot of good solar efficiency news. As I’ve written many, many times (hit the solar link in the sidebar), solar power needs continued breakthroughs in two areas to become market-viable — costs must continue to come down and efficiency needs to continue to increase. This news out of UT Austin points toward potential very dramatic efficiency increases.

From the link:

Conventional solar cell efficiency could be increased from the current limit of 30 percent to more than 60 percent, suggests new research on semiconductor nanocrystals, or quantum dots, led by chemist Xiaoyang Zhu at The University of Texas at Austin.

Zhu and his colleagues report their results in this week’s Science.

The scientists have discovered a method to capture the higher energy sunlight that is lost as heat in conventional .

The maximum efficiency of the silicon solar cell in use today is about 31 percent. That’s because much of the energy from sunlight hitting a solar cell is too high to be turned into usable electricity. That energy, in the form of so-called “hot ,” is lost as heat.

If the higher energy sunlight, or more specifically the hot electrons, could be captured, solar-to-electric power conversion efficiency could be increased theoretically to as high as 66 percent.

If you prefer the raw feed, here’s the release the linked story is based on.

June 16, 2010

Sanyo tops solar efficiency

Filed under: Business, Science — Tags: , , , , — David Kirkpatrick @ 8:54 pm

Impressive, over 20 percent energy conversion efficiency.

From the link:

The new N230 solar cell module is claimed to have an  of 20.7 percent, which makes it the most efficient solar module produced so far. The unprecedented efficiency was achieved by increasing the number of solar cell tabs from two to three and making each tab thinner. They also applied AG coated glass to the cells, and this reduces the amount of scattering and reflection of light. The increase in energy conversion efficiency could make the solar modules useful in areas with less than ideal amounts of sunshine.

June 15, 2010

The thick or thin solar question …

… has been solved by nanotech based on coaxial cable.

From the link:

“Many groups around the world are working on nanowire-type solar cells, most using crystalline semiconductors,” said co-author Michael Naughton, a professor of physics at Boston College. “This nanocoax cell architecture, on the other hand, does not require crystalline materials, and therefore offers promise for lower-cost solar power with ultrathin absorbers. With continued optimization, efficiencies beyond anything achieved in conventional planar architectures may be possible, while using smaller quantities of less costly material.”

Optically, the so-called nanocoax stands thick enough to capture light, yet its architecture makes it thin enough to allow a more efficient extraction of current, the researchers report in PSS’s Rapid Research Letters. This makes the nanocoax, invented at Boston College in 2005 and patented last year, a new platform for low cost, high efficiency solar power.

Boston College researchers report developing a “nanocoax” technology that can support a highly efficient thin film solar cell. This image shows a cross section of an array of nanocoax structures, which prove to be thick enough to absorb a sufficient amount of light, yet thin enough to extract current with increased efficiency, the researchers report in the journal Physica Status Solidi. Credit: Boston College

June 13, 2010

Japan deploys first solar sail in space

A long-time space travel concept becomes reality.

From the link:

Japan’s IKAROS has rolled out its solar sail, the first ever deployed in space. JAXA, the Japan Aerospace Exploration Agency, achieved the feat by rotating the craft rapidly and spinning the sail out by centrifugal force. IKAROS is the world’s first solar-powered spacecraft.

Hit the link up there for more illustrations.

June 2, 2010

Copper nanowires may improve solar cells and displays

This is an interesting use of nanotech because it looks like it might be market-ready much sooner than later, and as team member Benjamin Wiley puts it, “If we are going to have these ubiquitous electronics and solar cells we need to use materials that are abundant in the earth’s crust and don’t take much energy to extract.”

Also from the link:

A team of Duke University chemists has perfected a simple way to make tiny copper nanowires in quantity. The cheap conductors are small enough to be transparent, making them ideal for thin-film solar cells, flat-screen TVs and computers, and flexible displays.

“Imagine a foldable iPad,” said Benjamin Wiley, an assistant professor of chemistry at Duke. His team reports its findings online this week in .

Nanowires made of  perform better than carbon nanotubes, and are much cheaper than silver nanowires, Wiley said

May 12, 2010

Doubling organic solar cell efficiency …

Filed under: et.al. — Tags: , , , , , — David Kirkpatrick @ 12:39 pm

… with “light pipes.” If this research bears fruit it will be a major solar breakthrough — drastically increased efficiency coupled with lower cost manufacturing. A win-win.

From the link:

Researchers in North Carolina have developed a way to more than double the performance of organic solar cells by adding a layer of upright optical fibers that act as sunlight traps.

David Carroll, a professor of physics at Wake Forest University, led the development of a prototype solar cell incorporating the fibers. He is the chief scientist at a spinoff company called FiberCell that is developing a reel-to-reel manufacturing process to produce the cells. “We’re on the cusp of having working demonstrators that would convince someone to go into production with this,” said Carroll.

The best organic solar cells today are nearly 8 percent efficient, although efforts are ongoing to develop organic chemistries that would push the efficiency of such cells above 10 percent. But Carroll says improved chemistries alone won’t be enough to catch up to the performance of silicon cells. “The answer doesn’t lie in chemistry–it lies in the architecture of the cell itself,” he says. Carroll adds that the dollar-per-watt cost of manufacturing fiber-based organic cells should be about the same cost as for flat organic cells. “But they can be produced in a factory costing one-tenth that of a silicon foundry,” he says. This would make them much cheaper to produce than silicon cells.

Fiber forest: This prototype solar panel is covered with optical fibers. Photons bounce around inside the fibers before being absorbed, and this doubles the panel’s efficiency compared to regular organic cells.
Credit: Wake Forest University

May 1, 2010

Solar efficiency from a very unusual source

This is a somewhat surprising and actually interesting direction for solar efficiency research.

The release:

Purple Pokeberries hold secret to affordable solar power worldwide

Pokeberries – the weeds that children smash to stain their cheeks purple-red and that Civil War soldiers used to write letters home – could be the key to spreading solar power across the globe, according to researchers at Wake Forest University’s Center for Nanotechnology and Molecular Materials.

Nanotech Center scientists have used the red dye made from pokeberries to coat their efficient and inexpensive fiber-based solar cells. The dye acts as an absorber, helping the cell’s tiny fibers trap more sunlight to convert into power.

Pokeberries proliferate even during drought and in rocky, infertile soil. That means residents of rural Africa, for instance, could raise the plants for pennies. Then they could make the dye absorber for the extremely efficient fiber cells and provide energy where power lines don’t run, said David Carroll, Ph.D., the center’s director.

“They’re weeds,” Carroll said. “They grow on every continent but Antarctica.”

Wake Forest University holds the first patent for fiber-based photovoltaic, or solar, cells, granted by the European Patent Office in November. A spinoff company called FiberCell Inc. has received the license to develop manufacturing methods for the new solar cell.

The fiber cells can produce as much as twice the power that current flat-cell technology can produce. That’s because they are composed of millions of tiny, plastic “cans” that trap light until most of it is absorbed. Since the fibers create much more surface area, the fiber solar cells can collect light at any angle – from the time the sun rises until it sets.

To make the cells, the plastic fibers are stamped onto plastic sheets, with the same technology used to attach the tops of soft-drink cans. The absorber – either a polymer or a less-expensive dye – is sprayed on. The plastic makes the cells lightweight and flexible, so a manufacturer could roll them up and ship them cheaply to developing countries – to power a medical clinic, for instance.

Once the primary manufacturer ships the cells, workers at local plants would spray them with the dye and prepare them for installation. Carroll estimates it would cost about $5 million to set up a finishing plant – about $15 million less than it could cost to set up a similar plant for flat cells.

“We could provide the substrate,” he said. “If Africa grows the pokeberries, they could take it home.

“It’s a low-cost solar cell that can be made to work with local, low-cost agricultural crops like pokeberries and with a means of production that emerging economies can afford.”

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Wake Forest University’s Center for Nanotechnology and Molecular Materials uses revolutionary science to address the pressing needs of human society, from health care to green technologies. It is a shared resource serving academic, industrial and governmental researchers across the region.

April 21, 2010

Lowering the cost of thin-film solar

Yesterday I blogged about an efficiency breakthrough in thin-film solar cells, and now here’s more news on a cost breakthrough. I’m going to quote myself from the earlier post, “I keep hammering on the same point, but cost and efficiency in combination are the key to making solar a commercially viable option.” Be sure to hit the solar link in the “Interesting Blog Topics” box over on the sidebar for all my solar power blogging.

From the second link:

Advance made in thin-film solar cell technology

CORVALLIS, Ore. – Researchers have made an important breakthrough in the use of continuous flow microreactors to produce thin film absorbers for solar cells – an innovative technology that could significantly reduce the cost of solar energy devices and reduce material waste.

The advance was just reported in Current Applied Physics, a professional journal, by engineers from Oregon State University and Yeungnam University in Korea.

This is one of the first demonstrations that this type of technology, which is safer, faster and more economical than previous chemical solution approaches, could be used to continuously and rapidly deposit thin film absorbers for solar cells from such compounds as copper indium diselenide.

Previous approaches to use this compound – which is one of the leading photovoltaic alternatives to silicon-based solar energy devices – have depended on methods such as sputtering, evaporation, and electrodeposition. Those processes can be time-consuming, or require expensive vacuum systems or exotic chemicals that raise production costs.

Chemical bath deposition is a low-cost deposition technique that was developed more than a century ago. It is normally performed as a batch process, but changes in the growth solution over time make it difficult to control thickness. The depletion of reactants also limits the achievable thickness.

The technology invented at Oregon State University to deposit “nanostructure films” on various surfaces in a continuous flow microreactor, however, addresses some of these issues and makes the use of this process more commercially practical. A patent has been applied for on this approach, officials said.

“We’ve now demonstrated that this system can produce thin-film solar absorbers on a glass substrate in a short time, and that’s quite significant,” said Chih-hung Chang, an associate professor in the OSU School of Chemical, Biological and Environmental Engineering. “That’s the first time this has been done with this new technique.”

Further work is still needed on process control, testing of the finished solar cell, improving its efficiency to rival that of vacuum-based technology, and scaling up the process to a commercial application, Chang said.

Of some interest, researchers said, is that thin-film solar cells produced by applications such as this could ultimately be used in the creation of solar energy roofing systems. Conceptually, instead of adding solar panels on top of the roof of a residential or industrial building, the solar panel itself would become the roof, eliminating such traditional approaches as plywood and shingles.

“If we could produce roofing products that cost-effectively produced solar energy at the same time, that would be a game changer,” Chang said. “Thin film solar cells are one way that might work. All solar applications are ultimately a function of efficiency, cost and environmental safety, and these products might offer all of that.”

The research has been supported by the Process and Reaction Engineering Program of the National Science Foundation.

Related technology was also developed recently at OSU using nanostructure films as coatings for eyeglasses, which may cost less and work better than existing approaches. In that case, they would help capture more light, reduce glare and also reduce exposure to ultraviolet light. Scientists believe applications in cameras and other types of lenses are also possible.

More work such as this is expected to emerge from the new Oregon Process Innovation Center for Sustainable Solar Cell Manufacturing, a $2.7 million initiative based at OSU that will include the efforts of about 20 faculty from OSU, the University of Oregon, Portland State University and the Pacific Northwest National Laboratory.

Organizers of that initiative say they are aiming for “a revolution in solar cell processing and manufacturing” that might drop costs by as much as 50 percent while being more environmentally sensitive. In the process, they hope to create new jobs and industries in the Pacific Northwest.

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April 20, 2010

Nanophotonic technology and solar cell efficiency

Fascinating research on the upper limit of light absorption by solar cells. Utilizing nanophotonic technology and thin-film solar cells, the efficiency is given an impressive boost. I keep hammering on the same point, but cost and efficiency in combination are the key to making solar a commercially viable option. Throw in some short-term government subsidies (I know, I know) and we are getting close to that sweet spot.

From the link:

But things have changed since the 1980s, not least because it is now possible to make layers of silicon much thinner than the wavelength of the light they are expected to absorb and to carve intricate patterns in these layers. How does this nanophotonic technology change the effect of light trapping?

Today, Zongfu Yu and buddies at Stanford University in California, tackle this question and say that nanophotonics dramatically changes the game.

That’s basically because light trapping works in a different way on these scales. Instead of total internal reflection, light becomes trapped on the surface of nanolayers, which act like waveguides. This increases the amount of time the photons spend in the material and so also improves the chances of absorption.

Because of the geometry of the layers, some wavelengths are trapped better than others and this gives rise to resonances at certain frequencies.

What Yu and co show is that by designing the layers in a way that traps light effectively, it is possible to beat the old limit by a substantial margin.

Also from the link:

Physicists have long known that thinner solar cells are better in a number of ways: they use less material and so are cheaper to make and the electrons they produce are easier to collect making them potentially more efficient. Now they know that light trapping is more effective in thinner layers too.

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