De overstap naar zonne-energie erg dichtbij?

quote:

Op zondag 12 februari 2012 22:21 schreef Bijvlagenzinvol het volgende:

[..]

Ik krijg ze morgen binnen, incl. 5 jaar garantie op de panelen zelf, dus kan me geen buil vallen. _{(Plus de gangbare 10 jaar garantie voor de 90% opbrengst en 25 jaar garantie voor de 80% opbrengst).}

Als ze naar mijn zin presteren dan volgend jaar 3400Wp op het echte dak, maar eerst even de kat uit de boom kijken.

Nice

Photovoltaic nanoshell "whispering galleries" trap light for more efficient solar cells

For those unfamiliar with the term, a "whispering gallery" is a round room designed in such a way that sound is carried around its perimeter - this allows a person standing on one side to hear words whispered by a person on the other. Now, scientists from Stanford University have developed a new type of photovoltaic material, that essentially does for sunlight what whispering galleries do for sound. Not only does the material have a structure that circulates light entering it, but it could also result in cheaper, less fragile, and less angle-sensitive solar panels.

The new material consists of tiny hollow spheres, made out of nanocrystalline-silicon. While nanocrystalline-silicon has good electrical efficiency and is able to stand up to the damaging effects of sunlight, is isn't particularly good at absorbing light - in past attempts at using it for photovoltaics, it has had to be thickly layered, which has in turn resulted in long manufacturing times. That's where the spheres - known as nanoshells - come into play.

To make the nanoshells, the scientists coated individual balls of silica with silicon, then used hydrofluoric acid to etch away the silica in the center. This left them with the hollow transparent nanoshells.

When sunlight enters one of them, instead of passing straight through, it gets trapped and is circulated several times within the nanoshell. This is a good thing, as the longer the light stays in contact with the nanocrystalline-silicon, the more energy the material can absorb.



In a side-by-side comparison with a flat layer of silicon, a layer of the nanoshells showed "significantly more absorption over a broader spectrum of light." When the nanoshells were subsequently stacked three layers deep, that improvement went up to 75 percent for certain important ranges of the solar spectrum.

Not only are they more efficient than nanocrystalline-silicon film, but they are easier to make - according to team member Yan Yao, "A micron-thick flat film of solid nanocrystalline-silicon can take a few hours to deposit, while nanoshells achieving similar light absorption take just minutes." They also require only about one-twentieth the amount of material, which translates into one-twentieth the cost and weight, too. This point could be particularly significant if the technology were used with other, rarer substances, such as tellurium or indium.

Additionally, the efficiency of the nanoshells isn't greatly affected by their angle to the Sun, so they could be used in locations where an optimal angle isn't always possible. Finally, layers of them are thin enough that they can stand up to twisting and bending, so they could possibly even be built into items such as sails or clothing.

A paper on the research was recently published in the journal Nature Communications.

http://www.zeitnews.org/e(...)ent-solar-cells.html

A Leap Forward for Plastic Solar Cells

A record-breaking polymer solar cell made by researchers at the University of California, Los Angeles, converts 10.6 percent of the energy in sunlight into electricity. The performance of the cell surpasses the previous record, 8.6 percent, set in July of last year by the same group.

Polymer solar cells are flexible, lightweight, and potentially inexpensive, but their performance lags behind that of conventional cells made from inorganic materials such as silicon. The goal of the researchers, led by Yang Yang, professor of materials science and engineering at UCLA, is to make a polymer solar cell that can compete with thin-film silicon cells. Yang's record-breaking cell, enabled by a new photovoltaic polymer developed by a Japanese company, Sumitomo Chemical, is a sign that researchers are getting better at making solar cells from these finicky materials.

The new plastic solar cell combines two layers that work with different bands of light—a polymer that works with visible light and one that works with infrared light. "The solar spectrum is very broad, from the near infrared through the infrared to the ultraviolet, and one single solar-cell component can't do it all," says Yang.



The best inorganic solar cells are also multilayer devices, but making multilayer organic solar cells has been difficult. Polymers can be printed from solution, like printing ink on paper, which is both a primary advantage of the technology and a liability, says Alan Heeger, who shared the Nobel Prize in 2000 for his co-discovery of conductive polymers. "There are no high temperatures involved, and manufacturing is simple," he says. But figuring out the right solvents to print each layer in a cell without bleeding into the one below it is tricky. The more layers, the more complex the problem becomes. Matching the electrical properties of each layer is also a challenge, as has been connecting them together.

Yang says he wants to make a polymer solar cell with an efficiency of 15 percent. He notes that efficiency numbers typically drop by about a third when solar cells are taken out of the lab and sold in working modules. A polymer solar cell that tests at 15 percent efficiency in the lab is likely to make a module with 10 percent efficiency, which Yang believes is good enough to compete with thin-film silicon solar.

http://www.zeitnews.org/e(...)tic-solar-cells.html

Revolutionary Sphelar Spherical Solar Cells Capture Sunlight From All Directions

Japanese company Kyosemi has developed a revolutionary spherical micro solar cell that is capable of capturing sunlight from all directions. Called the Sphelar, the cell shuns the traditional flat substrate photovoltaic design and opts for much more efficient shape – the sphere. While traditional flat solar cells are easy to design and produce, their main problem is that their efficiency relies on their relative position to the sun. While some companies have addressed this with motorized frames that follow the sun’s path, Kyosemi has gone for a completely new approach that doesn’t need costly motors to work.



Their innovative new Sphelar® is a matrix of tiny, spherical solar cells that are designed to absorb sunlight at any angle. This means not only more efficient energy production, but less power needed for motorization of solar cell frames. The design and geometry of Sphelar cells means that by harnessing reflected and indirect light, energy conversion is close to 20% efficiency – a target far beyond most flat photovoltaic technologies. Its design also makes Sphelar appropriate for applications at a variety of scales, including mobile electronic devices.

With innovation like this, it is no surprise that Japan is leading the world in solar power technology.

http://www.zeitnews.org/e(...)-all-directions.html

New design for a metamaterial could be far more efficient at capturing sunlight than existing solar cells

Metamaterials are a new class of artificial substances with properties unlike anything found in the natural world. Some have been designed to act as invisibility cloaks; others as superlenses, antenna systems or highly sensitive detectors. Now, researchers at MIT and elsewhere have found a way to use metamaterials to absorb a wide range of light with extremely high efficiency, which they say could lead to a new generation of solar cells or optical sensors.

Nicholas X. Fang, the Brit (1961) and Alex (1949) d’Arbeloff Career Development Associate Professor in Engineering Design in MIT's Department of Mechanical Engineering, says that most thin materials used to fully capture light are limited to a very narrow range of wavelengths and angles of incidence. The new design uses a pattern of wedge-shaped ridges whose widths are precisely tuned to slow and capture light of a wide range of wavelengths and angles of incidence.

These metamaterials can be extremely thin, saving weight and cost. Fang compares the tapered structures to the cochlea of the inner ear, which responds to different frequencies of sound at different points along its narrowing structure. “Our ears separate different frequencies and gather them at different depths,” he says; similarly, the metamaterial wedges harvest photons at different depths.

The actual structure of the material is etched from alternating layers of metal and an insulating material called a dielectric, whose response to polarized light can be varied by changing an electric field applied to the material. The creation of this new material is described in a paper to be published in a forthcoming issue of the journal Nano Letters. A preliminary version of Fang’s paper — co-authored with researchers at Zhejiang University and Taiyuan University in China, and the University of Illinois at Urbana-Champaign — is available online now.

Kin Hung Fung, an MIT postdoc and co-author of the Nano Letters paper, says, “What we have done is to design a multilayer sawtooth structure that can absorb a wide range of frequencies” with an efficiency of more than 95 percent. Previously, such efficiency could only be achieved with materials tuned to a very narrow band of wavelengths. “High-efficiency absorption has been achieved before, but this design has an extremely wide window” for colors of light, Fung says.



Metamaterials have been “a very hot topic this decade,” he says, “because they can help us to design functional materials that interact with light in unconventional ways.” By using the tuned metamaterial, he says, his team was able to slow light to less than one-hundredth of its normal speed in a vacuum, making it much easier to trap inside the material. “When something is going very fast, it’s difficult to catch it,” he says, “so we slow it down so it’s easier to absorb.”

The material can easily be fabricated using equipment that is already standard in conventional photovoltaic-cell manufacturing. Although the initial work was based on computer simulations, the team is now working on lab experiments to confirm their findings.

Besides solar cells, the design could be used to make efficient infrared detectors for a selected range of wavelengths. “We can selectively enhance the material’s interaction with infrared light at the wavelengths we want,” Fung says.

Fang says that by its nature, the material would be both a very efficient emitter and absorber of photons — so in addition to potential uses in new kinds of solar cells or infrared detectors, the material could be used for infrared-light emitting applications, such as devices for generating electricity from heat. In addition, the researchers say the principle can be scaled so that it could be used to capture or emit electromagnetic radiation at other wavelengths, such as microwave and terahertz frequencies. It could even be used to produce visible light with extremely low energy loss, creating a new kind of high-efficiency light bulb.

Richard Averitt, a professor of physics at Boston University who was not involved in this research, calls the sawtooth-shaped structure developed by this team “a unique and impressive approach toward realizing functional broadband absorbers” that could have applications in thermal detection and in light harvesting for energy applications. He cautions that further work is needed to ease fabrication and integration of the materials, but adds, “This is an intriguing slow-wave structure that should inspire new developments in this field.”

http://www.zeitnews.org/n(...)ing-solar-cells.html

Scientists Develop Ultra-thin Solar Cells

Austrian and Japanese researchers on Wednesday unveiled solar cells thinner than a thread of spider silk that are flexible enough to be wrapped around a single human hair.

The thin-film device, comprising electrodes on a plastic foil, is about 1.9 micrometers thick, a tenth the size of the thinnest solar cells currently available, the researchers said.

"The total thickness of this device is less than a typical thread of spider silk" the researchers said in a report carried by online science journal Nature Communications.

"Being ultra-thin means you don't feel its weight and it is elastic," said one of the researchers, Tsuyoshi Sekitani from the University of Tokyo.

"You could attach the device to your clothes like a badge to collect electricity (from the sun)... Elderly people who might want to wear sensors to monitor their health would not need to carry around batteries," Sekitani told AFP.

The research was done jointly by Martin Kaltenbrunner, Siegfried Bauer and other researchers from Johannes Kepler University of Austria as well as Sekitani and other contributors from University of Tokyo.



Sekitani said it was possible to make the cells bigger.

"Power generation by solar cells increases with their size. As this device is soft, it is less prone to damage by bending even if it gets bigger," he said.

Sekitani said the team hoped to increase the rate at which the device converts sunlight into electricity and put it to practical use in around five years.

http://www.zeitnews.org/e(...)hin-solar-cells.html

quote:

Op woensdag 11 april 2012 01:57 schreef Eyjafjallajoekull het volgende:
Japan is druk op zoek naar alternatieven nu ze geen kernenergie meer kunnen gebruiken..

http://inhabitat.com/kyoc(...)-largest-solar-farm/

[ afbeelding ]

Nice

Nog meer innovaties:

A Smarter Mirror for Cheaper Solar Power

Rather than try to reinvent the solar cell, startup Thermata has engineered a high-tech mirror to cut the cost of solar power.

The company, incubated at Idealabs, has completed initial testing on a system executives say can cut the cost of sun-tracking mirrors, or heliostats, in half using cameras and other digital technologies. Thermata plans to start beta testing the heliostats this year with potential customers, which are concentrating solar power technology companies, and with Sandia National Laboratories.

Thermata typifies a new breed of green-technology startup which is targeting a specific niche in energy using technologies from other fields. Its system uses a camera to detect the angle of heliostats and a mesh network of microprocessors to position each mirror with the ideal tilt. In a concentrating solar power plant, thousands or even millions of heliostats concentrate light onto a tower to produce steam, which turns a turbine to generate electricity.



"Instead of using calculations and past knowledge to infer where the mirror is, we can physically measure the angle and control it explicitly," said CEO Terry Bailey. "We've use intelligence instead of steel."

Heliostats now used at concentrating solar power plants are heavy-duty pieces of equipment, mounted on pylons to withstand high winds and connected via wires to control their motion.

Thermata's system is designed to be smaller, lighter, and operate wirelessly. There are eight heliostats on a "pod" with the mirrors' motors operated by small, two-watt photovoltaic solar panels, explained Chief Technology Officer Brad Hines.

Each mirror is equipped with four small "diffusers," or small square mirrors raised above the surface of the heliostat. A camera placed at a distance and out of the glare made by the heliostat takes pictures of the diffusers. Based on the light pattern and intensity, it can determine its location and optimize the tilt, Hines said.

Each heliostat has a microprocessor with a Zigbee wireless chip in it. Those nodes create a mesh network to send information to a central computer which dispatches information on the best position.

"The fact that we can talk to these heliostats wirelessly is a big part of the technology and that technology has only really become available in the last three or four year," Hines said. "That, combined with the optical processing, is what enabled our invention."

Small is beautiful

Having a smaller heliostat means lower costs, which is significant since heliostats are about 40 percent of the cost in solar power plant.

The size means mirrors can be closer to the ground and require less-expensive mounting, Hines said. Gears can be made out of plastic, rather than steel, and the heliostats can be handled by two people, making installation simpler. "We've taken what was traditionally aerospace engineering and we've turned it into automotive," Hines said.

As for the camera and optics, Hines said that digital imaging has progressed so much, the company can get ample imaging processing for under $25 or $30 and built-in image stabilization means cameras can operate on poles which move in the wind.

It's still not clear that Thermata's system will satisfy concentrating solar power developers' demands, but those companies, such as BrightSource Energy and SolarReserve, do need to lower their costs.

The dramatic drop in the cost of solar panels has forced some plant developers to drop solar thermal systems in favor of solar photovoltaics. Thermata's heliostats can also be used for enhanced oli recovery, where steam is injected in used oil wells to stimulate more flow.

Thermata estimates its smaller, cheaper heliostats can take roughly $100 million off of a $600 million solar power plant construction cost, based on savings on heliostats, wiring, and labor. The key is making smaller, lighter devices, something which solar engineers have long desired but has been difficult to do.

"As you go bigger, you get taller and then the wind becomes a significant factor to the design. Then you need yet more precision, more weight, and stiffness -- it's an escalating problem," said Bailey. "This breakthrough allows us to go small and low."

http://www.zeitnews.org/e(...)per-solar-power.html

Of deze dan:

Black Solar Cell Absorbs 99.7% of All Light

Scientists over at Natcore Tech have created what is now the "blackest" solar cell to date. While that might sound as trivial as creating a white iPhone, this is a fairly huge advancement in the world of solar technology. With an average reflectance of 0.3%, these black silicon wafers absorb more light than any other out there, which means more of the sun's energy is actually converted into energy.

By the way, reflectance is the ratio of reflected light to that of which actually hits the surface. So a reflectance of 0.3% means that only 0.3% of all light is reflected from the solar cell's surface and that the remaining 99.7% is absorbed.



This breakthrough makes industry standards such as anti-reflective coatings now obsolete. Those coatings perform poorly anyway, especially during morning and afternoon hours when the sun is at an angle. The black solar also outperforms standard cells on cloudy days.

“One of the ways this matters,” said Chuck Provini , the company’s CEO, “is that there isn’t a whole lot of difference between the electricity you get on a sunny day vs. a cloudy day. Diffused light won’t matter that much.”

Its higher energy output, combined with a lower cost using Natcore's patented process, could quickly make black silicon the global solar technology of choice.

Of course, with every new solar breakthrough comes the promise of grossly affordable solar cells and the clean tech utopia we've all been hoping for. I don't think this totally changes the game but it could lead to advancements that might. So I am hopeful.

One thing is for sure, this is the one instance where black is...the new black.

http://www.zeitnews.org/e(...)97-of-all-light.html

Of zullen we het anders gewoon met een satelliet naar de aarde sturen?

Proposed Satellite Would Beam Solar Power to Earth

PASADENA, Calif. — An energy-hungry Earth is in need of transformational and sustainable energy solutions, experts say.

For decades, researchers have been appraising the use of power-beaming solar-power satellites. But the projected cost, complexity and energy economics of the notion seemingly short-circuited the idea.

Now, a unique new approach has entered the scene, dubbed SPS-ALPHA, short for Solar Power Satellite via Arbitrarily Large PHased Array. Leader of the concept is John Mankins of Artemis Innovation Management Solutions of Santa Maria, Calif.

Mankins provided a detailed overview of the power-beaming concept here during the 2012 NASA Innovative Advanced Concepts meeting March 27-29. [Video: Beaming Power From Space]

The NIAC is under the wing of NASA's Office of the Chief Technologist, which is providing a technology and innovation focus for the space agency.

Huge platforms

Last August, Artemis Innovation Management Solutions was selected for a NASA NIAC award to dive into the details of what Mankins labels "the first practical solar-power satellite concept."



The project will be an energetic one-year study of the design. Mankins is drawing upon a 25-year career at NASA and Caltech's Jet Propulsion Laboratory, doing work that ranged from flight projects and space mission operations to systems-level innovation and advanced technology research.

Along with reviewing the conceptual feasibility of the SPS-ALPHA, the team will carry out select proof-of-concept technology experiments.

SPS-ALPHA is a novel "biomimetic" approach to the challenge of space solar power, Mankins told SPACE.com.

Biomimetic refers to human-made processes, substances, devices or systems that imitate nature. The booming field of biomimetics is of interest to researchers in nanotechnology, robotics, artificial intelligence, the medical industry and the military.

Megawatts of power

If successful, Mankins said that this project would make possible the construction of huge platforms from tens of thousands of small elements that can deliver remotely and affordably tens to thousands of megawatts using wireless power transmission to markets on Earth, as well as missions in space, Mankins said.

SPS-ALPHA uses a large array of individually controlled thin-film mirrors, outfitted on the curved surface of the satellite. These movable mirrors intercept and redirect incoming sunlight toward photovoltaic cells affixed to the backside of the solar power satellite's large array.

The Earth-pointing side of this large modular circular array is tiled with a collection of microwave-power transmission panels that generate the coherent, low-intensity beam of radio frequency energy and transmits that energy to Earth.

Mass production

According to Mankins, the SPS-ALPHA has several important advantages over past solar-power satellite approaches.

For example, this new approach eliminates the need for a large integrated power management and distribution system. That significantly reduces the projected cost of the platform, Mankins said during the NIAC gathering.

Moreover, the SPS-ALPHA concept, Mankins said, enables a solar-power satellite that can be assembled entirely from individual system elements that weigh no more than 110 to 440 pounds (50 to 200 kilograms), allowing all pieces to be mass produced at dramatically lower cost than traditional space systems. Therefore, a drastically reduced cost of the SPS system is realizable, he said.

"The current project will provide a detailed analytical understanding of the SPS-ALPHA concept, with supporting experiments," Mankins said. "The needed next steps are to develop a working prototype of one or more of the modules and demonstrate the assembled system in the field. Over the next several years, the goal is to realize a low-Earth orbit flight test of the system," he concluded.

Filmpje: http://www.space.com/9819-beaming-solar-power-space.html

http://www.zeitnews.org/e(...)-power-to-earth.html

“Photochemical upconversion” could allow conventional solar cells to break 40% efficiency

While the overall efficiency of conventional silicon solar cells has continued to improve in recent years, the technology faces a natural theoretical limit at around 33%. This is because the laws of physics prevent the cells from absorbing photons below a certain energy level, meaning that this low-energy light cannot be converted into electricity and is simply lost. Now researchers have found a way join two energy-poor red photons to form a single energy-rich yellow photon, allowing the harvesting of this part of the spectrum currently unused by single p-n junction crystalline silicon solar cells, and potentially enabling a record-breaking efficiency of 40%.

The technique, called “photochemical upconversion,” relies on two different types of molecules that are placed behind the solar cell in a solution to combine two low-energy photons into a single high-energy photon. The first type of molecule absorbs the energy-poor red photons, preventing them from escaping and storing them in a persistent state. This persistent state lasts long enough so that the energy can be transferred to a second, organic molecule when they encounter each other in the solution.



When two of these excited organic molecules then encounter each other, one returns to its base state and the other assumes a higher energy state. This higher-energy state is extremely short-lived, as the molecule then sends off a single yellow photon that is if a high enough energy to be absorbed by the solar cell.

"We are able to boost efficiency by forcing two energy-poor red photons in the cell to join and make one energy-rich yellow photon that can capture light, which is then turned into electricity," says University of Sydney Associate Professor Schmidt who developed the so-called “turbo for solar cells” with partners at Helmholtz Centre Berlin for Materials and Energy. “We now have a benchmark for the performance of an upconverting solar cell. We need to improve this several times, but the pathway is now clear."

The photochemical upconversion technique was detailed in the journal Energy & Environmental Science, earlier this year.

http://www.zeitnews.org/e(...)k-40-efficiency.html

Liquid Solar Cells Can Be Painted Onto Surfaces

Scientists at USC have developed a potential pathway to cheap, stable solar cells made from nanocrystals so small they can exist as a liquid ink and be painted or printed onto clear surfaces.

The solar nanocrystals are about four nanometers in size -- meaning you could fit more than 250,000,000,000 on the head of a pin -- and float them in a liquid solution, so "like you print a newspaper, you can print solar cells," said Richard L. Brutchey, assistant professor of chemistry at the USC Dornsife College of Letters, Arts and Sciences.

Brutchey and USC postdoctoral researcher David H. Webber developed a new surface coating for the nanocrystals, which are made of the semiconductor cadmium selenide. Their research is featured as a "hot article" this month in the international journal for inorganic chemistry Dalton Transactions.

Liquid nanocrystal solar cells are cheaper to fabricate than available single-crystal silicon wafer solar cells but are not nearly as efficient at converting sunlight to electricity. Brutchey and Webber solved one of the key problems of liquid solar cells: how to create a stable liquid that also conducts electricity.

In the past, organic ligand molecules were attached to the nanocrystals to keep them stable and to prevent them from sticking together. These molecules also insulated the crystals, making the whole thing terrible at conducting electricity.



"That has been a real challenge in this field," Brutchey said.

Brutchey and Webber discovered a synthetic ligand that not only works well at stabilizing nanocrystals, but actually builds tiny bridges connecting the nanocrystals to help transmit current.

With a relatively low-temperature process, the researchers' method also allows for the possibility that solar cells can be printed onto plastic instead of glass without any issues with melting -- resulting in a flexible solar panel that can be shaped to fit anywhere.

As they continue their research, Brutchey said he plans to work on nanocrystals built from materials other than cadmium, which is restricted in commercial applications due to toxicity.

"While the commercialization of this technology is still years away, we see a clear path forward toward integrating this into the next generation of solar cell technologies," Brutchey said.

http://www.zeitnews.org/e(...)d-onto-surfaces.html

Tesla and SolarCity Team Up to Create New Off-the-Grid Solar Power Storage System

Tesla may be best known for exceptionally good-looking electric sports cars, but their role in the automotive industry has honed their skills in battery-making too. Now, the company is teaming up with solar rental company SolarCity, and the pair is set to apply their battery know-how to create a complete off-the-grid kit for home solar power storage. The partnership could provide an easy (though potentially costly) way to overcome a long-standing problem: almost all solar systems are tied to and somewhat dependent on an electric grid. When the grid is off, the solar panels are out, and when the sun is off, there’s no solar power stored and you’re back on the electrical grid. And if both are out, you’re completely in the dark. But Tesla and SolarCity’s new off-the-shelf lithium-ion battery pack could just solve that once and for all.

Some solar users have overcome this problem with battery storage systems of their own. Gizmodo reports that these battery packs are often comprised of a gang of less than eco-friendly lead acid car batteries. Tesla has been working on developing lithium-ion batteries—the kind one typically finds in a laptop computer—for use in their electric vehicles. Through their partnership with SolarCity, a California-based company who provide solar panel lease options and full service installation in 12 states, Tesla hopes to provide a rack of these lithium-ion batteries which can be easily hooked up to SolarCity’s arrays of photovoltaic panels for a fully off-the-grid system.



The battery unit is presently displayed on SolarCity’s website, and takes the form of a wall-mounted unit which is “about the size of a solar-inverter,” and can be placed either inside or outside the home. SolarCity claims that “A fully charged battery will power basic home needs for a few days and a solar powered home can recharge the battery from the sun to run indefinitely,” enabling one to be “prepared for anything” from an average blip in the power supply to a natural disaster.

The partnership between the two companies began two years ago, when they received a $1.8 million grant from the California Public Utilities Commission to research a solar-storage battery unit. It’s somewhat of a family affair since Tesla’s CEO Elon Musk is the cousin of SolarCity co-founder and COO Peter Rive. In 2010 Rive commented to the New York Times that “We think in the years ahead this will be the default way that solar is installed. Getting the costs down, though, is not going to be an easy task.”

Solving the cost-effectiveness issue of the technology appears to be the project’s next step, as the companies are reportedly waiting for approval for subsidies from the California Public Utility Commission’s Self-Generation Incentive Program (SGIP), and federal investment tax credit (ITC) for clean power before rolling out the tech commercially.

http://www.zeitnews.org/t(...)-storage-system.html

Folding light: Wrinkles and twists boost power from solar panels

Taking their cue from the humble leaf, researchers have used microscopic folds on the surface of photovoltaic material to significantly increase the power output of flexible, low-cost solar cells.

The team, led by scientists from Princeton University, reported online April 22 in the journal Nature Photonics that the folds resulted in a 47 percent increase in electricity generation. Yueh-Lin (Lynn) Loo, the principal investigator, said the finely calibrated folds on the surface of the panels channel light waves and increase the photovoltaic material's exposure to light.

"On a flat surface, the light either is absorbed or it bounces back," said Loo, a professor of chemical and biological engineering at Princeton. "By adding these curves, we create a kind of wave guide. And that leads to a greater chance of the light's being absorbed."

The research team's work involves photovoltaic systems made of relatively cheap plastic. Current solar panels are typically made of silicon, which is both more brittle and more expensive than plastics. So far, plastic panels have not been practical for widespread use because their energy production has been too low. But researchers have been working to increase that efficiency with the goal of creating a cheap, tough and flexible source of solar power.

If researchers can increase the plastic panels' efficiency, the material could produce power from an array of surfaces from inserts in window panels to overlays on exterior walls or backpacks.

"It is flexible, bendable, light weight and low cost," Loo said.

In most cases, researchers have focused on increasing the efficiency of the plastic photovoltaic material itself. Recent developments have been promising: a team from UCLA recently announced a system with a 10.6 percent efficiency. That approaches the 10 to 15 percent level seen as the target for commercial development.

Loo said the folding method promises to increase those numbers. Because the technique works with most types of plastic photovoltaic materials, it should provide a boost to efficiency across the board.

"This is a very simple process that you can use with any material," she said. "We have tested it with other polymers and it works as well."

Jong Bok Kim, a postdoctoral researcher in chemical and biological engineering and the paper's lead author, explained in the Nature Photonics paper that the folds on the surface of the panels channel light waves through the material in much the same way that canals guide water through farmland. By curving the light through the material, the researchers essentially trap the light inside the photovoltaic material for a longer time, which leads to greater absorption of light and generation of energy.



"I expected that it would increase the photocurrent because the folded surface is quite similar to the morphology of leaves, a natural system with high light harvesting efficiency," said Kim, a postdoctoral researcher in chemical and biological engineering. "However, when I actually constructed solar cells on top of the folded surface, its effect was better than my expectations."

Although the technique results in an overall increase in efficiency, the results were particularly significant at the red side of the light spectrum, which has the longest wavelengths of visible light. The efficiency of conventional solar panels drops off radically as light's wavelength increases, and almost no light is absorbed as the spectrum approaches the infrared. But the folding technique increased absorption at this end of the spectrum by roughly 600 percent, the researchers found.

"If you look at the solar spectrum, there is a lot of sunlight out there that we are wasting," Loo said. "This is a way to increase efficiency."

The research team created the folded surface in Howard Stone's laboratory in the mechanical and aerospace engineering department by carefully curing a layer of liquid photographic adhesive with ultraviolet light. By controlling how fast different sections of the adhesive cured, the team was able to introduce stresses in the material and generate ripples in the surface. The shallower ripples were classified as wrinkles and the deeper ones are called folds. The team found that a surface containing a combination of wrinkles and folds produced the best results.

Although the math underlying the process is complex, the actual production is straightforward. Loo said it would be quite practical for industrial purposes.

"Everything hinges on the fact that you can reproduce the wrinkles and folds," Loo said. "By controlling the stresses, we can introduce more or fewer wrinkles and folds."

Another benefit of the process is that it increases the durability of the solar panels by relieving mechanical stresses from bending. The researchers found the panels with folded surfaces were able to retain their effectiveness after bending. A standard plastic panel's energy production would be diminished by 70 percent after undergoing bending.

Loo said the researchers drew their inspiration from leaves. Seemingly a simple object, the leaf is a miracle of natural engineering. Its green surface is perfectly constructed to bend and control light to ensure that a maximum amount of solar energy is absorbed to create energy and nutrients for the tree. Recent work by Pilnam Kim, a postdoctoral researcher in Stone's lab, provided insight into how these microscopic structures could be applied to synthetic devices.

"If you look at leaves very closely, they are not smooth, they have these sorts of structures," said Loo, who is deputy director of Princeton's Andlinger Center for Energy and the Environment. "We'd like to mimic this geometric effect in synthetic, man-made light-harvesting systems."

http://www.zeitnews.org/e(...)om-solar-panels.html