3D Printed Lenslets Used to Improve Efficiency and Cut Costs of Rooftop Solar Panels


Concentrated photovoltaics (CPV) are a technology that generates electricity from sunlight. You probably know that already, but now a team of researchers have worked on enabling CPV systems for rooftop use by combining photovoltaic cells and a 3D printed plastic lens array which not only reduces the size and weight, but also cuts the total cost of such systems.

Image 21 - CopyUsing miniaturized photovoltaic cells of gallium arsenide, the 3D printed plastic lens arrays, and a focusing mechanism which moves to track the sun, a traditional solar panel can be placed on the south-facing side of a building’s roof.

The researchers discovered that they could reach 70 percent optical efficiency — and they hope to reach 90 percent efficiency — using their design.

“The main benefit of printed optics for CPV is rapid prototyping and testing of initial concepts. The quality of the printed optics is sufficient for proof of concept,” said Noel Giebink, one of the authors of the research and an assistant professor of electrical engineering at Penn State University.

Image 22According to Geibink, focusing sunlight on the array of cells with the embedded 3D printed plastic ‘lenslet’ arrays means each of them in the top array acts like a tiny magnifying glass. Using their technique, they can intensify sunlight more than 200 times, and as the focal point moves with the sun over the course of a day, the middle solar cell sheet works by moving laterally in the center of the lenslet array.

“We partnered with colleagues at the University of Illinois because they are experts at making small, very efficient multi-junction solar cells,” said Giebink. “These cells are less than 1 square millimeter, made in large, parallel batches and then an array of them is transferred onto a thin sheet of glass or plastic.”

Previous tracking systems only functioned about two hours a day as the focal point moved out of the range of the solar cells. The researchers solved that problem and enabled solar focusing for a complete eight-hour period — and with a total movement of approximately 1 centimeter.

One of the arrays, a refractive surface, collimated the light while another which was coated with a reflective material reflects the collimated light onto the micro-cells.

argonneThe findings, by Jared Price, Xing Sheng, Bram Meulblok, John Rogers, and Giebink, were published in their paper, “Wide-angle planar microtracking for quasi-static microcell concentrating photovoltaics,” in the journal Nature Communications.

“Current CPV systems are the size of billboards and have to be pointed very accurately to track the sun throughout the day,” Giebink says. “You can’t put a system like this on your roof, which is where the majority of solar panels throughout the world are installed.”

The research was funded by the US Department of Energy.

Do you know of any other ways 3D printing is being used to move energy production systems forward? Let us know in the 3D Printed Lenslets forum thread on 3DPB.com.

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CPV Solar 1 Explanation_acrylic

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Efficient Triple-Junction Polymer Solar Cell Design Sets New Record


Triple Junc SC id36745_1. Copyright © Nanowerk

Organic solar cells are conventionally made from two materials: a donor and an acceptor, which facilitates an efficient charge separation. For the acceptor, the most commonly used molecule is one of the blue absorbing fullerenes. This leaves the absorption spectrum of the donor material responsible to cover as much as possible of the solar spectrum. But most organic semiconductors only have a small optical bandwidth.

Consequently, solar cells based on such materials only catch a small part of the solar spectrum. This problem can be overcome with a properly designed stacked or tandem configuration, in which several organic materials are tuned so that each absorbs a separate part of the spectrum, thereby increasing the efficiency of the overall device. High bandgap semiconductor materials are used to absorb the short wavelength radiation, with longer wavelength parts transmitted to subsequent semiconductors.

In this context, researchers have set great hopes in the development of multi-junction solar cells, hoping to substantially exceed the performance of single-junction organic photovoltaics. In theory, a solar cell with an infinite number of junctions could obtain a maximum power conversion efficiency (PCE) of nearly 87% under highly concentrated sun light.

The challenge is to develop a semiconductor material system that can attain a wide range of bandgaps and be grown with high crystalline quality. New research coming out of the Yang Yang lab at the University of California, Los Angeles (UCLA), one of the leading labs for organic tandem solar cell research, presents an efficient design for a triple-junction organic tandem solar cell featuring a configuration of bandgap energies designed to maximize the tandem photocurrent output.

The key innovation in this study, reported in the July 14, 2014 online edition of Advanced Materials (“An Efficient Triple-Junction Polymer Solar Cell Having a Power Conversion Efficiency Exceeding 11%”), is the demonstration of organic materials being able to mimic the record-setting efficiency of triple-junction structures in III-V solar cells. III-V based solar cells constructed with the industry-standard GaInP/GaInAs/Ge technology have achieved the highest energy conversion efficiencies of all solar cells, with the current record exceeding 40%.

“In III–V multijunction solar cells, the optimal arrangement for a high-current-output triple-junction tandem cell features one wide-bandgap absorber (2.0–1.85 eV), one medium-bandgap absorber (1.4–1.2 eV), and one low-bandgap absorber (1.0–0.7 eV)”, Chun-Chao Chen, a graduate student in Yang’s lab and first author of the paper, explains to Nanowerk. “This optimal design rule cannot be applied directly to organic solar cells, however, because of the lack of efficient donor materials having bandgaps as low as 1 eV. Therefore, we set out to determine a practical combination of bandgap energies for triple junctions to develop an efficient organic tandem solar cell structure.”

 

 

Layer stacks of a triple-junction tandem solar cell

Schematic representation of the complete device structure: Layer stacks of the triple-junction tandem solar cell in the inverted architecture. (Reprinted with permission by Wiley-VCH Verlag)

For their design, the team used three materials with different energy bandgaps (1.9, 1.58, and 1.4 eV) as electron donors, blended with fullerene derivatives. With this arrangement of bandgap energies, they fabricated a highly efficient triple-junction tandem solar cell having a PCE of 11% – exceeding the record efficiency of a double-junction tandem solar cell, previously demonstrated by Yang’s group as well.

Energy levels of various materials for solar cells

 

Energy levels of the materials investigated in this study. Values for ITO, ZnO, and WO3 were measured using ultraviolet photoelectron spectroscopy (UPS); other values were taken from the literature. (Reprinted with permission by Wiley-VCH Verlag)

 

The specific problem in triple-junction solar cells is the complicated optical interference effect between each subcell included in the tandem. “When there are two junctions in tandem, the optical effect is easy to resolve,” say the UCLA researchers. “However, when it comes to triple junctions, you can not use trial and error to find out the optimal layer thickness for absorption for each subcell.”

To solve this issue, and in order to understand how each subcell works and how much current it can deliver, the team carried out in-depth and detailed optical simulations for each subcell. Benefiting from this tool, they came up with a simple and effective structure for connecting the subcells in tandem solar cells. This interconnecting structure, made of WO3/PEDOT:PSS/ZnO, is completely solution processed, thus keeping the orthogonal processing advantage of organic solar cells unchanged – regardless of how many junctions are added.

According to the UCLA team, “this design significantly strengthens our faith in tandem structure for organic solar cell.” They also points out that one of the outcomes of this study is the message that innovations in device architecture can potentially push the efficiencies of organic solar cell technology into the realm of inorganic photovoltaics.

The team is confident that their experience and knowledge gained from designing tandem solar cells can be transferred to other photovoltaic technologies – e.g. hybrid solar cells; perovskite solar cell; CIGS solar cells. Last year, for instance, they have shown that tandem structures can be combined with existing semitransparent solar cell design can result in a doubling of efficiency (read more: “Transparent film could coat windows, smartphone screens with energy-harvesting material“).

Read more: Efficient triple-junction polymer solar cell design sets new record http://www.nanowerk.com/spotlight/spotid=36745.php#ixzz39Ya0Onsn

Graphene (Oxide) for New Solar Cells: Stronger, Cheaper .. Better?


Graphene Solar Cells 9138062484_ca590547c3_kThere remains a lot to learn on the frontiers of solar power research, particularly when it comes to new advanced materials which could change how we harness energy.

Under the guidance of Canada Research Chair in Materials Science with Synchrotron Radiation, Dr. Alexander Moewes, University of Saskatchewan researcher Adrian Hunt spent his PhD investigating graphene , a cutting-edge material that he hopes will shape the future of technology.

To understand graphene oxide, it is best to start with pure graphene, which is a single-layer sheet of carbon atoms in a honeycomb lattice that was first made in 2004 by Andre Geim and Kostya Novoselov at the University of Manchester – a discovery that earned the two physicists a Nobel Prize in 2010.

“It is incredibly thin, therefore it is incredibly transparent. It also has extremely high conductivity, it’s much better than copper, and it’s extremely strong, its tensile strength is even stronger than steel,” Hunt said.

“Air doesn’t damage it. It can’t corrode, it can’t degrade. It’s really stable.”

All of this makes graphene a great candidate for . In particular, its transparency and conductivity mean that it solves two problems of solar cells: first, light needs a good conductor in order to get converted into usable energy; secondly, the cell also has to be transparent for light to get through.CNT multiprv1_jpg71ec6d8c-a1e2-4de6-acb6-f1f1b0a66d46Larger

Most solar cells on the market use with a non-conductive glass protective layer to meet their needs.

“Indium is extremely rare, so it is becoming more expensive all the time. It’s the factor that will keep solar cells expensive in the future, whereas graphene could be very cheap. Carbon is abundant,” said Hunt.

Although graphene is a great conductor, it is not very good at collecting the electrical current produced inside the solar cell, which is why researchers like Hunt are investigating ways to modify graphene to make it more useful.

Graphene oxide, the focus of Hunt’s PhD work, has oxygen forced into the carbon lattice, which makes it much less conductive but more transparent and a better charge collector. Whether or not it will solve the solar panel problem is yet to be seen, and researchers in the field are building up their understanding of how the new material works.

Using X-ray scattering techniques at the REIXS and SGM beamlines at the Canadian Light Source, as well as a Beamline 8.0.1 at the Advanced Light Source, Hunt set out to learn more about how oxide groups attached to the graphene lattice changed it, and how in particular they interacted with charge-carrying graphene atoms.

“Graphene oxide is fairly chaotic. You don’t get a nice simple structure that you can model really easily, but I wanted to model graphene oxide and understand the interplay of these parts.”

Previous models had seemed simplistic to Hunt, and he wanted a model that would reflect graphene oxide’s true complexity.

Each different part of the graphene oxide has a unique electronic signature. Using the synchrotron, Hunt could measure where electrons were on the graphene, and how the different oxide groups modified that.

He showed that previous models were incorrect, which he hopes will help improve understanding of the effects of small shifts in oxidization.

Moreover, he studied how graphene oxide decays. Some of the oxide groups are not stable, and can group together to tear the lattice; others can react to make water. If graphene oxide device has water in it, and it is heated up, the water can actually burn the and produce carbon dioxide. It’s a pitfall that could be important to understand in the development of long-lasting solar cells, where sun could provide risky heat into the equation.

More research like this will be the key to harnessing graphene for solar power, as Hunt explains.

“There’s this complicated chain of interreactions that can happen over time, and each one of those steps needs to be addressed and categorized before we can make real progress.”

Explore further: Super-stretchable yarn is made of grapheme

Read more at: http://phys.org/news/2014-08-stronger-solar-cells-graphene-cusp.html#jCp

Genesis Nanotech Headlines Are Out!


Organ on a chip organx250Genesis Nanotech Headlines Are Out! Read All About It!

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SUBCOMMITTE EXAMINES BREAKTHROUGH NANOTECHNOLOGY OPPORTUNITIES FOR AMERICA

Chairman Terry: “Nanotech is a true science race between the nations, and we should be encouraging the transition from research breakthroughs to commercial development.”

WASHINGTON, DCThe Subcommittee on Commerce, Manufacturing, and Trade, chaired by Rep. Lee Terry (R-NE), today held a hearing on:

“Nanotechnology: Understanding How Small Solutions Drive Big Innovation.”

 

 

electron-tomography

“Great Things from Small Things!” … We Couldn’t Agree More!

 

Subcommittee Examines Breakthrough Nanotechnology Opportunities for America


Applications-of-Nanomaterials-Chart-Picture1SUBCOMMITTE EXAMINES BREAKTHROUGH NANOTECHNOLOGY OPPORTUNITIES FOR AMERICA
July 29, 2014

WASHINGTON, DCThe Subcommittee on Commerce, Manufacturing, and Trade, chaired by Rep. Lee Terry (R-NE), today held a hearing on “Nanotechnology: Understanding How Small Solutions Drive Big Innovation.” Nanotechnology is science, engineering, and technology conducted at the nanoscale, which is approximately 1 to 100 nanometers (one nanometer is a billionth of a meter). This technology brings great opportunities to advance a broad range of industries, bolster our U.S. economy, and create new manufacturing jobs. Members heard from several nanotech industry leaders about the current state of nanotechnology and the direction that it is headed.UNIVERSITY OF WATERLOO - New $5 million lab

“Just as electricity, telecommunications, and the combustion engine fundamentally altered American economics in the ‘second industrial revolution,’ nanotechnology is poised to drive the next surge of economic growth across all sectors,” said Chairman Terry.

 

 

Applications of Nanomaterials Chart Picture1

Dr. Christian Binek, Associate Professor at the University of Nebraska-Lincoln, explained the potential of nanotechnology to transform a range of industries, stating, “Virtually all of the national and global challenges can at least in part be addressed by advances in nanotechnology. Although the boundary between science and fiction is blurry, it appears reasonable to predict that the transformative power of nanotechnology can rival the industrial revolution. Nanotechnology is expected to make major contributions in fields such as; information technology, medical applications, energy, water supply with strong correlation to the energy problem, smart materials, and manufacturing. It is perhaps one of the major transformative powers of nanotechnology that many of these traditionally separated fields will merge.”

Dr. James M. Tour at the Smalley Institute for Nanoscale Science and Technology at Rice University encouraged steps to help the U.S better compete with markets abroad. “The situation has become untenable. Not only are our best and brightest international students returning to their home countries upon graduation, taking our advanced technology expertise with them, but our top professors also are moving abroad in order to keep their programs funded,” said Tour. “This is an issue for Congress to explore further, working with industry, tax experts, and universities to design an effective incentive structure that will increase industry support for research and development – especially as it relates to nanotechnology. This is a win-win for all parties.”

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Professor Milan Mrksich of Northwestern University discussed the economic opportunities of nanotechnology, and obstacles to realizing these benefits. He explained, “Nanotechnology is a broad-based field that, unlike traditional disciplines, engages the entire scientific and engineering enterprise and that promises new technologies across these fields. … Current challenges to realizing the broader economic promise of the nanotechnology industry include the development of strategies to ensure the continued investment in fundamental research, to increase the fraction of these discoveries that are translated to technology companies, to have effective regulations on nanomaterials, to efficiently process and protect intellectual property to ensure that within the global landscape, the United States remains the leader in realizing the economic benefits of the nanotechnology industry.”

James Phillips, Chairman & CEO at NanoMech, Inc., added, “It’s time for America to lead. … We must capitalize immediately on our great University system, our National Labs, and tremendous agencies like the National Science Foundation, to be sure this unique and best in class innovation ecosystem, is organized in a way that promotes nanotechnology, tech transfer and commercialization in dramatic and laser focused ways so that we capture the best ideas into patents quickly, that are easily transferred into our capitalistic economy so that our nation’s best ideas and inventions are never left stranded, but instead accelerated to market at the speed of innovation so that we build good jobs and improve the quality of life and security for our citizens faster and better than any other country on our planet.”

Chairman Terry concluded, “Nanotech is a true science race between the nations, and we should be encouraging the transition from research breakthroughs to commercial development. I believe the U.S. should excel in this area.”

– See more at: http://energycommerce.house.gov/press-release/subcommittee-examines-breakthrough-nanotechnology-opportunities-america#sthash.YnSzFU10.dpuf

A Molecular Approach to Solar Power: When the Sun Doesn’t Shine


SecondaryNewsImage_SolarThermal_01It’s an obvious truism, but one that may soon be outdated: The problem with solar power is that sometimes the sun doesn’t shine. Now a team at MIT and Harvard University has come up with an ingenious workaround — a material that can absorb the sun’s heat and store that energy in chemical form, ready to be released again on demand.

This solution is no solar-energy panacea: While it could produce electricity, it would be inefficient at doing so. But for applications where heat is the desired output — whether for heating buildings, cooking, or powering heat-based industrial processes — this could provide an opportunity for the expansion of solar power into new realms.

“It could change the game, since it makes the sun’s energy, in the form of heat, storable and distributable,” says Jeffrey Grossman, the Carl Richard Soderberg Associate Professor of Power Engineering at MIT, who is a co-author of a paper describing the new process in the journal Nature Chemistry. Timothy Kucharski, a postdoc at MIT and Harvard, is the paper’s lead author.

The principle is simple: Some molecules, known as photoswitches, can assume either of two different shapes, as if they had a hinge in the middle. Exposing them to sunlight causes them to absorb energy and jump from one configuration to the other, which is then stable for long periods of time.

But these photoswitches can be triggered to return to the other configuration by applying a small jolt of heat, light, or electricity — and when they relax, they give off heat. In effect, they behave as rechargeable thermal batteries: taking in energy from the sun, storing it indefinitely, and then releasing it on demand.

The working cycle of a solar thermal fuel is depicted in this illustration, using azobenzene as an example. When such a photoswitchable molecule absorbs a photon of light, it undergoes a structural rearrangement, capturing a portion of the photon’s energy as the energy difference between the two structural states. When the molecule is triggered to switch back to the lower-energy form, it releases that energy difference as heat. Illustration courtesy of the researchers

The new work is a follow-up to research by Grossman and his team three years ago, based on computer analysis. But translating that theoretical work into a practical material proved daunting: In order to reach the desired energy density — the amount of energy that can be stored in a given weight or volume of material — it is necessary to pack the molecules very close together, which proved to be more difficult than anticipated.

Grossman’s team tried attaching the molecules to carbon nanotubes (CNTs), but “it’s incredibly hard to get these molecules packed onto a CNT in that kind of close packing,” Kucharski says. But then they found a big surprise: Even though the best they could achieve was a packing density less than half of what their computer simulations showed they would need, the material nevertheless seemed to deliver the heat storage they were aiming for. Seeing a heat flow much greater than expected for the lower energy density prompted further investigation, Kucharski says.

After additional analysis, they realized that the photoswitching molecules, called azobenzene, protrude from the sides of the CNTs like the teeth of a comb. While the individual teeth were, indeed, twice as far apart as the researchers had hoped for, they were interleaved with azobenzene molecules attached to adjacent CNTs. The net result: The molecules were actually much closer to each other than expected.

The interactions between azobenzene molecules on neighboring CNTs make the material work, Kucharski says. While previous modeling showed that the packing of azobenzenes on the same CNT would provide only a 30 percent increase in energy storage, the experiments observed a 200 percent increase. New simulations confirmed that the effects of the packing between neighboring CNTs, as opposed to on a single CNT, explain the significantly larger enhancements.

This realization, Grossman says, opens up a wide range of possible materials for optimizing heat storage. Instead of searching for specific photoswitching molecules, the researchers can now explore various combinations of molecules and substrates. “Now we’re looking at whole new classes of solar thermal materials where you can enhance this interactivity,” he says.

Grossman says there are many applications where heat, not electricity, might be the desired outcome of solar power. For example, in large parts of the world the primary cooking fuel is wood or dung — which produces unhealthy indoor air pollution, and can contribute to deforestation. Solar cooking could alleviate that — and since people often cook while the sun isn’t out, being able to store heat for later use could be a big benefit.

Unlike fuels that are burned, this system uses material that can be continually reused. It produces no emissions and nothing gets consumed, Grossman says.

While further exploration of materials and manufacturing methods will be needed to create a practical system for production, Kucharski says, a commercial system is now “a big step closer.”

The adoption of carbon nanotubes to increase materials’ energy storage density is “clever,” says Yosuke Kanai, an assistant professor of chemistry at the University of North Carolina who was not involved in this work. He adds that the resulting increase in energy storage density “is surprising and remarkable.”

“This result provides additional motivation for researchers to design more and better photochromic compounds and composite materials that optimize the storage of solar energy in chemical bonds,” Kanai says.

The team also included MIT research scientist Nicola Ferralis, assistant professor of mechanical engineering Alexie Kolpak, and undergraduate Jennie Zheng, as well as Harvard professor Daniel Nocera. The work was supported by BP though the MIT Energy Initiative and the U.S. Department of Energy’s Advanced Research Projects Agency – Energy.

Source: By David L Chandler, Massachusetts Institute of Technology

Concentrated PV Startup Solar Junction Acquired by Saudis


CPV-image_2_310_224Chipmaker Solar Junction executed on its technical plans, but a growth market for concentrated PV never emerged. July 14, 2014

Solar Junction, a venture capital-funded solar startup that raised more than $30 million from investors Advanced Technology Ventures, Draper Fisher Jurvetson and New Enterprise Associates, has received a financial commitment from Saudi entity KACST (King Abdulaziz City for Science and Technology) and one of its investment arms, TAQNIA, according to sources close to the company.

A company founder spoke to GTM of an acquisition, as well as the identity of the new Saudi owner. The wheels started turning on this deal while original founder Jim Weldon was still CEO. Founder Vijit Sabnis, who replaced Weldon as CEO last year, would not provide any details. Weldon has declined to comment. KACST and TAQNIA have not responded to GTM’s inquiries.

Solar Junction executed on its technical goals, developing record-setting triple-junction solar cells in the lab for the concentrated photovoltaics (CPV) industry at a relatively modest burn rate. But building semiconductor components for an industry that doesn’t exist is not a workable business plan for a VC-funded firm.

CPV-image_2_310_224

Solar Junction hit an NREL-verified 44 percent cell efficiency (at 947 suns) in 2012, a world record that held until Sharp hit 44.4 percent for its triple-junction solar cell (at 302 suns). At one point, the firm was moving to a 6-inch production fabrication facility, partially funded by a U.S. DOE SUNPATH contract. The hope has been that more efficient compound semiconductors would improve the economics of CPV.

CPV has a few tens of megawatts in the field. The largest CPV deployment in North America is the 30-megawatt Alamosa site in Colorado owned by The Carlyle Group, with hardware from Amonix.

The few potentially viable commercial entrants in this technology-rich but economically challenged science include Soitec and China’s Suncore. Soitec has deeper corporate pockets and is vertically integrated, with CPV plants (at undisclosed costs) in the works in the U.S. and South Africa.

Amonix had to shut down its Las Vegas production facility in July 2012 and has rechristened itself as Arzon Solar with Amonix founder Vahan Garboushian in the CEO role. SolFocus shut down in 2013. GreenVolts went out of business in 2012. JDSU quietly exited the CPV cell market after acquiring QuantaSol. Energy Innovations, Soliant, Concentrator Optics and Skyline Solar’s low-concentration PV (LCPV) have all passed on.

Early-stage startups such as Morgan Solar, REhnu and Semprius still believe that CPV’s economic riddle can be solved. Solaria is still building or licensing LCPV. SunPower believes its C7 low-power concentrator product has potential in China. Cogenra’s combined heat and LCPV technology has a compelling business case.

Solar Junction CEO Sabnis told GTM in an earlier interview that no other PV technology has the headroom to improve its efficiency like multi-junction solar cells. Sabnis cited several studies showing 70 percent theoretical efficiencies from a 5- or 6-junction cell. More practically, he sees 50 percent cell efficiency as being achievable in two to four years, which could get DC module efficiencies to greater than 40 percent.

Weighted-average PV system prices hit $2.59 per watt in the fourth quarter of last year, according to GTM Research’s Solar Market Solar Market Insight report. Globally, large-scale project pricing is well under $2 per watt and regularly under $1.50 per watt, based on GTM Research’s latest figures. Those are the most important numbers for CPV vendors to keep in mind if they wish to compete in the solar industry.

 

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