David Kirkpatrick

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 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 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 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 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 22, 2010

Improving the application of nanocoatings

Nanocoatings do a lot of good, particularly with making solar cells more efficient. The trick is they haven’t been too easy to apply to big areas. Researchers at Stanford have helped change that issue.

From the link:

Nanoscale wires, pores, bumps, and other textures can dramatically improve the performance of solar cells, displays, and even self-cleaning coatings. Now researchers at Stanford University have developed a simpler, cheaper way to add these features to large surfaces.

Nanoscale structures offer particular advantages in devices that interact with light. For example, a thin-film solar cell carpeted with nano pillars is more efficient because the pillars absorb more light and convert more of it into electricity. Other nanoscale textures offer similar advantages in optical devices like display backlights.

The problem is scaling up to large areas, says Yi Cui, a Stanford professor of materials science and engineering who led the new work. “Many methods are really complex and don’t solve the problem,” says Cui. Lithography can be used to carve out nanoscale features with precise dimensions, but it’s expensive and difficult. Simpler techniques, such as spin-coating a surface with nanoparticles or using acids to etch it with tiny holes, don’t allow for much precision.

Nanosphere smear: Using a spinning rod to deposit an ink suspension of silica nanospheres is a simple way to create bumpy, nanotextured coatings like these three.

Credit: ACS/Nano Letters

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

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.

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 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.

April 2, 2010

Black silicon bringing down the cost of efficient solar

Filed under: Science — Tags: , , , , — David Kirkpatrick @ 7:03 pm

The latest news in one of the two areas — cost in this case — solar needs to continue to see improvement for widespread use.

From the link:

A simple chemical treatment could replace expensive antireflective solar cell coatings, bringing down the cost of crystalline silicon panels. The treatment, a one-step dip in a chemical bath, creates a highly antireflective layer of black silicon on the surface of silicon wafers, and it would cost just pennies per watt, say researchers at the National Renewable Energy Laboratory (NREL). They’ve used it to create black silicon solar cells that match the efficiency of conventional silicon cells on the market.

Solar goes black: These two solar cells were fabricated on a silicon wafer treated to create an antireflective black silicon surface. The silvery areas around the cells are a different color because the highly absorbent black layer has been etched away.
Credit: Hao-Chih Yuan

February 17, 2010

Efficient thin-film solar through nanotech

Filed under: Business, Science — Tags: , , , , , — David Kirkpatrick @ 2:54 pm

A nanotechnology design improves the efficiency of thin-film solar cells. An important breakthrough in working to commercially viable solar power because thin-film cells are cheaper than photovoltaics, but efficiency has been an issue. The two key elements  in making solar energy widespread and a credible challenger to petroleum-based energy are lower costs (both in installation and maintenance) and higher efficiencies. Anything that works to combine those two elements is a step in the right direction.

I just love blog posts that combine nanotechnology and solar power.

From the link:

Thin-film solar cells are less expensive than traditional photovoltaics sliced from wafers, but they’re not as efficient at converting the energy in sunlight into electricity. Now a Newton, MA-based startup is developing a nanostructured design that overcomes one of the main constraints on the performance of thin-film solar cells. Solasta fabricates on arrays of nanopillars, rather than flat areas, boosting the efficiency of amorphous silicon solar cells to about 10 percent–still less than crystalline silicon panels, but more than the thin-film amorphous silicon panels on the market today. The company says that the design won’t require new equipment or materials and that it will license its technology to amorphous-silicon manufacturers at the end of this year.

Pillar power: This microscope image shows the layers of a solar cell built on a nanopillar substrate. The core of each pillar is coated first with metal, then amorphous silicon, and then a transparent conductive oxide.

Credit: Solasta

February 11, 2010

IBM comes up with solar breakthrough

Filed under: Business, Science — Tags: , , , , , — David Kirkpatrick @ 1:49 am

There’s been a lot of solar energy news to blog about lately. Nestled in this spate of announcements is a breakthrough at IBM — solar cells created from abundant materials, well a higher proportion of abundant elements, than previous cells. The practical result? Cheaper to produce cells that don’t lose anything in the efficiency department, and cost and efficiency are the two issues that will determine when solar power becomes a viable alternative energy source.

From the second link:

Researchers at IBM have increased the efficiency of a novel type of solar cell made largely from cheap and abundant materials by over 40 percent. According to an article published this week in the journal Advanced Materials, the new efficiency is 9.6 percent, up from the previous record of 6.7 percent for this type of solar cell, and near the level needed for commercial solar panels. The IBM solar cells also have the advantage of being made with an inexpensive ink-based process.

The new solar cells convert light into electricity using a semiconductor material made of copper, zinc, tin, and sulfur–all abundant elements–as well as the relatively rare element selenium (CZTS). Reaching near-commercial efficiency levels is a “breakthrough for this technology,” says Matthew Beard, a senior scientist at the National Renewable Energy Laboratory, who was not involved with the work.

Copper power: This prototype solar cell uses a copper-based material and has achieved record efficiencies for a cell of its kind.

Credit: IBM Research

Update — head below the fold for IBM’s release on the new solar cell. (more…)

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