Novel Quantum Photocell Could Boost Solar Cell Efficiency

Quantum Photocell Could Boost Solar Cell Efficiency

Photonics.com
Dec 2016

RIVERSIDE, Calif., Dec. 2, 2016 — A novel type of quantum heat engine photocell, which can help control the flow of energy in solar cells, could increase solar cell efficiency. The photocell has demonstrated the ability to regulate solar power conversion without requiring active feedback or adaptive control mechanisms. In contrast, conventional photovoltaic systems require voltage converters and feedback controllers to suppress fluctuations in solar power. 

Researchers from the University of California, Riverside (UCR) set out to design a simple photocell that could match the amount of solar power generated to the average power demand, and suppress energy fluctuations to avoid the accumulation of excess energy. 

“Plants have evolved to do this, but current affordable solar cells — which are at best 20 percent efficient — do not control these sudden changes in solar power,” said primary researcher Nathaniel Gabor. “That results in a lot of wasted energy and helps prevent wide-scale adoption of solar cells as an energy source.” 

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In a light harvesting quantum photocell, particles of light (photons) can efficiently generate electrons. When two absorbing channels are used, solar power entering the system through the two absorbers (a and b) efficiently generates power in the machine (M). Courtesy of Nathaniel Gabor and Tamar Melen.

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The researchers compared the theoretical minimum energy fluctuations in nanoscale quantum heat engine photocells: one in which the photocell absorbed one color of light, and the other in which the photocell absorbed two colors. They found that fluctuations were naturally suppressed in the two-channel photocell. Essentially, one channel absorbed at a wavelength at which the average input power was high, while the other channel absorbed at a wavelength at which the average input power was low. The photocell switched between high and low power to convert varying levels of solar energy into a steady-state output.

When the team applied its models to the measured solar spectrum on Earth’s surface, it discovered that the absorption of green light, the most radiant portion of the solar power spectrum per unit wavelength, provided no inherent regulatory benefit, a finding that led them to reject green light for use in a photocell whose primary role would be the regulation of energy flow. 

The team optimized the photocell parameters to reduce solar energy fluctuations and found that the absorption spectrum was nearly identical to the absorption spectrum observed in photosynthetic green plants. This discovery led the researchers to propose that the natural regulation of energy found in the quantum heat engine photocell could play a role in photosynthesis, possibly accounting for the predominance of green as a plant color.

Unrelated research has shown that some molecular structures in plants, including chlorophyll a and b molecules, could be important in preventing plants from accumulating excess energy. The molecular structure of the quantum heat engine photocell was found to be similar to the structure of photosynthetic molecules that incorporate pairs of chlorophyll.

Gabor and his team are potentially the first to connect quantum mechanical structure to the greenness of plants. Their work provides a set of tests for researchers aiming to verify natural regulation of solar energy. Additionally, their design allows regulation without active input, a process made possible by the photocell's quantum mechanical structure.

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Nathan Gabor's Laboratory of Quantum Materials Optoelectronics utilizes infrared laser spectroscopy techniques to explore natural regulation in quantum photocells composed of two-dimensional semiconductors. Courtesy of Max Grossnickle and QMO Lab.

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The research was published in Nano Letters (doi: 10.1021/acs.nanolett.6b03136)  

https://www.photonics.com/Article.aspx?AID=61393

Posted: Jun 21, 2016 Novel device to boost power output from solar panels (Nanowerk News) While recent advancements in solar cell technologies have significantly improved their sunlight-to-energy conversion efficiencies, without continued advancements in the actual panel technology, photovoltaic (PV) systems will never realize their maximum potential. This is because technological limitations prevent solar panels – which amplify and boost the electric current generated by multiple solar cells – from supplying all the electricity they generate to the electric grid. However, a team of researchers from the Masdar Institute may have discovered a way to overcome these technological limitations in the most popular PV connection system through a novel, low-cost and easy-to-install device that could significantly increase the amount of power generated by the system. “The problem occurs in series-connected solar panels (which is one of the most common ways of connecting solar panels for distributed PV systems), when solar modules are experiencing varying levels of irradiation or temperature. This can result from sporadic clouds, dust accumulation on the PV panels, or uneven air ventilation. In these instances, the current generated by each module is different,” explained Masdar Institute Research Engineer Omair Khan. “The low-performing solar modules affect the energy output of the entire string of solar panels, as the maximum power output is governed by the lowest current in the system. This means that if one solar module is shaded and thus generating a low current, and is connected in series to several good, high-performing modules, then the high-performing modules cannot operate at higher currents,” he added. Associate Professor Dr. Weidong Xiao and Research Engineer Omair Khan developed a gallium nitride-based device that fits inside a photovoltaic panel and can track each of the independently produced solar currents generated by a solar panel. The device developed by Khan and Masdar Institute Associate Professor of Electrical Engineering and Computer Science Dr. Weidong Xiao aims to optimize the power output of the series-connected solar panels. Series-connection is how the majority of PV panels are connected in a PV system and to electrical grids, including small-scale rooftop PVs and large-scale solar power plants. Series-connected solar panels direct the electrical currents produced by each submodule (usually three submodules form a solar panel) through the group, or “string”, of connected solar panels to the string’s centralized converter. The drawback of series-connected solar panels is that each panel needs to share the same electric current, which is set by the submodule with the lowest current. Khan and Dr. Xiao think they discovered a way to get around this “lowest current” limitation that series-connected solar panels face, through their device – called a “submodule integrated converter” – which tracks and feeds each of the three independently produced electrical currents for one solar module directly into the centralized converter, thus boosting the PV system’s overall power output, especially in the case of a current mismatch. It does this by capitalizing on the key properties of gallium nitride, which is the material used to make the converter’s switches. Gallium nitride’s high electrical conductivity is able to convert 99% of the power produced by each submodule into electricity for the centralized converter and enables the device to be made small enough to fit into the existing junction box on the back of each solar panel. Thus, the device can be easily installed into existing solar panels without needing to retrofit or re-build conventional solar panel systems. “By employing a dedicated converter to independently perform maximum power point tracking on each submodule, rather than the string of modules as a whole, means that the operating point of each submodule has no effect on the rest of the submodules in the system. Each converter extracts the maximum power possible from each submodule, thus maximizing the PV system’s energy-efficiency,” explained Khan. “Through this novel device, we are able to get more electricity out of conventional solar panels using a method that is easily scalable,” said Dr. Xiao. The researchers plan to optimize the product and develop a ready-to-install version that is capable of withstanding the UAE’s harsh weather. Khan and Dr. Xiao co-authored three journal papers on this research this year including two in the IEEE Transactions on Industrial Electronics and one in IEEE Transactions on Sustainable Energy. Source: By Erica Solomon, Masdar Institute http://www.nanowerk.com/news2/green/newsid=43751.php

This One Chart Says It All for the Future of Solar Energy

One graphic says so much about how far solar has come and how bright its future looks.

A friend and former colleague—my business partner from when I worked in solar—recently shared a graph showing the drop in the prices of solar panels and the growth in worldwide installations of solar.

http://ecowatch.com/2016/06/01/future-solar-energy/

Cooling Off A Hot Solar Cell For A High-Efficiency Solar Cell

For A High-Efficiency Solar Cell, Just Harnesses The “Coldness Of The Universe”

May 12th, 2016 by Tina Casey 

It doesn’t look like much right now, but Stanford University’s plywood-and-Mylar experimental solar cell apparatus could pave the way for a new, low-cost approach to boosting solar cell efficiency. The trick is to prevent the loss of efficiency that results when solar cells heat up. The solution, as described somewhat poetically by the research team, is to add a layer of material that enables the cell to access the “coldness of the universe.”

Cooling Off A Hot Solar Cell

The basic problem is that solar cells have two functions. They absorb photons to generate electricity, and they also retain heat. Only one of those two functions is desirable.

The skyward-facing position of solar cells does offer a way out, as described by the abstract forthe new Stanford solar cell study:

Because a solar absorber by necessity faces the sky, it also naturally has radiative access to the coldness of the universe. Therefore, in these applications it would be very attractive to directly use the sky as a heat sink while preserving solar absorption properties.

The Stanford research team hammered together a prototype model to demonstrate that you could engineer a protective, transparent layer or “blackbody” that enables the solar cell to function efficiently while funneling off excess heat into the vast sink of the universe.

The Stanford team based its blackbody on an atomic-thin wafer made from silica photonic crystal (silica is fancyspeak for quartz). If you have the right equipment you could DIY the same thing yourself. To engineer the crystal, the researchers etched holes into it to a depth of about 10 micrometers, tapering the holes slightly to act as funnels, with this result:

When placed on a silicon absorber under sunlight, such a blackbody preserves or even slightly enhances sunlight absorption, but reduces the temperature of the underlying silicon absorber by as much as 13 °C due to radiative cooling.

In the image below, the Stanford logo is actually under the photonic crystal, so yes, when Standford says visibly transparent they mean visibly transparent.

Image (A) shows the two of the experimental apparatuses on a campus rooftop. For their experiment, instead of using actual solar cells the team deployed “mock” solar cells, designed to absorb solar energy without generating electricity (the next step will be to test the silica layer on solar cells).

The four dots in the two apparatuses are solar absorbers. Moving from left to right, the first dot is an absorber with a silica layer but without the blackbody, and the second is an absorber with the silica photonic crystal blackbody. The third and fourth dots are plain absorbers for comparison.

Images (C) and (D) are from scanning electron microscopes, showing the structure of the silica photonic crystal.

Solar Cell Efficiency: Let’s Hear It For The 1%

The study will be formally presented in June at the Conference on Lasers and Electro-Optics in San Jose, California, under the title, “Radiative cooling of solar absorbers using a transparent photonic crystal thermal blackbody,” by Linxiao Zhu, Aaswath P. Raman and Shanhui Fan.

Meanwhile, the folks at The Optical Society have provided a plain-language rundown of how the new apparatus performs in terms of solar cell efficiency:

Because heat makes solar cells less efficient, the researchers predict their cooling layer could help solar cells turn approximately 1 percent more sunlight into electricity, a big boost from a relatively simple add-on.

Okay, so a one percent improvement sounds less than impressive at first take, but it represents a big step forward in the context of solar research and solar cell efficiency, where progress is measured in fractions of a percent.

In addition, the research team expects that the cooling effect will prevent degradation and help the solar cell last longer, and that will help lower the lifecycle, bottom line cost of solar power. That’s an important point because “soft costs” still account for a large proportion of the overall cost of solar power. Progress on solar cell efficiency is important, but other factors have also been contributing to the precipitous drop in solar prices.

But why stop at solar cells? The team anticipates that its finely tuned silica layer could also be used to save energy by deflecting excess heat from cars, buildings, and other surfaces.

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Images: via US National Institutes of Health, PubMed.gov.

 http://cleantechnica.com/2016/05/12/a-new-approach-to-solar-cell-efficiency-deploys-coolness-factor/

'Off-the-grid' solar cabin builder presents $12 innovation in solar power

PATRICK JODOIN, OTTAWA CITIZEN
More from Patrick Jodoin, Ottawa Citizen

Published on: April 16, 2016 | Last Updated: April 16, 2016 8:44 AM EDT

Algonquin College mechanical engineering student Joseph Dupuis — whose off-the-grid cabin went viral last spring — displays an early prototype of his solar tracking device in September 2015. PATRICK JODOIN / POSTMEDIA

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A local entrepreneur who made global headlines for his off-the-grid home last year is getting ready to unveil his latest unconventional solution in sustainable energy.

Algonquin College mechanical engineering student Joseph Dupuis was thrust into the spotlight last spring when the story of his solar-powered cabin made from shipping containers went viral.

This time around, Dupuis has assembled a team of students and built a prototype of what he said may be an innovation in solar technology: a solar tracking device that costs less to make than traditional solar power systems.

He was to present a working prototype at Algonquin’s Applied Research Day on Friday.

The difference between 29-year-old Dupuis’ device and a traditional system lies in its interior programming. The core concept of converting sunlight into electricity remains the same. 

“We came up with a tracking system that uses very, very inexpensive components,” said Dupuis. “These are components you can buy off the shelf at any electronics store.

“This technology that we developed is not new or groundbreaking in the sense that we invented new tech. However, we are using very affordable and simple components to achieve something that in the past would be too complex and costly for the average consumer.”

Instead of using expensive programmable logic controllers to track the sun — which sell for around $5,000, according to Dupuis, and require a strong understanding of electronics and complex software — his system uses a $12 microprocessing device called an Arduino, which can be purchased on Amazon. It can be programmed into a solar tracking device “with very basic understanding of coding and a simple computer,” said Dupuis.

“A fraction of the cost with still the same performance.”

Dupuis believes his device could make solar power more accessible to the average homeowner because of the potential cost difference. 

“We’re hoping to be able to market it as a very inexpensive way to make solar electricity,” he said.

Nick Harper of Barrie-based Home Energy Solutions believes that, at a glance, if Dupuis has invented a better “mouse-trap” in solar tracking — and his Arduino system does work — then such a cost-saving measure would be taken seriously in the solar energy industry. 

“If it’s a proven method that actually works,” said Harper, “then, in this industry, that always goes over well because most of the products are fairly expensive. If you can put something out into the market that brings the overall installation costs down, it could be a very good thing.”

Harper said in his 11 years in the renewable energy industry, he has seen many changes. Solar power went from a seasonal industry to year-round, for example.

Dupuis spent the past eight months working with a team of six electronic engineering students through Algonquin College’s Applied Research and Innovation to build and test a prototype. He said it has passed the tests and works.

The working prototype may be subject to further testing in the months to come. Dupuis is also in talks with Algonquin’s Perth, Ont. campus to install a full-scale, 20-panel model that will function as an electric car charging station.

“I really hope we can do the solar charging station,” said Kerry Milford, project manager of Applied Research and Innovation at Algonquin’s Perth campus. “We’d love to collaborate with Joseph and move forward on this.”

http://ottawacitizen.com/business/local-business/viral-off-the-grid-homeowner-returns-with-inexpensive-innovation-in-solar-power

Will Nanophotonics Save Solar Power Tech?

By Monica Heger

Posted 14 Apr 2016 | 18:00 GMT

Photo: iStockphoto

Nanophotonic technology could be the key to driving up the efficiencies of solar cells, making them feasible for widespread global deployment, say researchers from the FOM Institute for Atomic and Molecular Physics(AMOLF) in the Netherlands.

The researchers published a review article in Science today describing current solar technologies and their limitations with regards to efficiency. Silicon-based solar, which is now considered a mature technology, occupies about 90 percent of the photovoltaic market, the researchers wrote. Yet, over the last few years, silicon solar cells have realized only modest gains in efficiency, stalling out in the 20-percent range.

But, according to lead author Albert Polman, advances in nanophotonics could help increase efficiencies for single-junction solar cells to 40 percent and higher, and do so cost effectively. In addition, he said, the technology could be compatible not just with silicon, but any type of solar material.

“It's really an upcoming field,” Polman says.

Efficiency and cost are the two main barriers on solar, and often, one is compromised for the sake of the other, Polman says. Using less material, such as for thin-film solar cells, brings costs down, but drags efficiency down right along with it.

Nanophotonics can be applied to existing solar technologies to harness light more effectively to increase efficiency.

When sunlight hits a solar panel, a good amount of the potential energy is lost due to it being reflected and scattered, Polman says. But nanostructures incorporated into a panel can re-direct the scattered light within the solar cell, “so that the light travels back and forth within the cell and is trapped inside it,” he adds.

In the research described in the Science article, Polman's team calculated that the theoretical maximum efficiency for a single-junction monocrystalline silicon solar cell is 29.4 percent, although the majority of commercial silicon panels are multicrystalline silicon, which have efficiencies of around 20.8 percent. But that’s on paper. Thus far, the highest recorded experimental efficiency is 25.6 percent for monocrystalline silicon and 21.3 percent for multicrystalline silicon.  

Other materials don't fare much better. Solar cells made from gallium arsenide (GaAs) have the efficiency record for single-junction solar cells at 28.8 percent, but GaAs solar cells are expensive and mostly have niche applications for space and satellite technology, Polman says.

Meanwhile, less expensive materials like thin-film silicon, dye sensitized titanium dioxide, and organic solar, have not broken the 12-percent-efficiency mark.

Nanophotonic technology can help, though. Using printing techniques, nanstructures with improved light harnessing properties can be printed onto silicon-based solar cells, he said. Alternatively, cells can be designed with nanstructures incorporated into them from the beginning.

Polman's lab is currently conducting small-scale experiments using a printing technique to layer nanoscale structures onto silicon solar panels, he says, and is in the midst of building larger panels to test in the field.

Incorporating such nanostructures into silicon cells could help silicon reach beyond its maximum efficiency, but even greater gains will be realized when solar cells are built that combine different materials with nanostructures.

For instance, perovskite has recently been touted as a promising material for solar cell technology; demonstrations have shown that it can reach efficiencies of 20 percent. Polman says that layering perovskite on top of silicon could provide further advantages since the two materials capture different wavelengths of light. Earlier this year, researchers demonstrated that layering perovksite on top of a silicon solar cell boosted the efficiency by 7.3 percent. 

Incorporating nanostructures could provide a further boost by allowing researchers to “engineer the scattering of the light in a clever way,” he says.

Looking ahead, Polman says he envisions solar cells that make use of not just two materials, but three or four materials with complementary properties and nanophotonics to make the most use of the incoming sunlight.

“Further advances in nanophotovoltaics will lead to enhanced photocurrents, and thus enhanced efficiency, in several different PV materials and architectures,” the AMOLF team wrote, enabling “very large-scale penetration into our energy system.”

 http://spectrum.ieee.org/energywise/green-tech/solar/will-nanophotonics-save-pv

MIT Breakthrough Boosts Solar Panel Output

April 12th, 2016 by Steve Hanley 

 

UPDATED: April 12 at 2:30 pm. See update below.

A solar panel is an amazing thing. Put it in the sunshine and it makes electricity for free. No emissions, no noise, just clean renewable power. Add a bunch of them and some battery storage and you can have your own microgrid right at home and never pay a utility bill again. What’s not to like? The problem is, a solar panel doesn’t always perform at peak efficiency. It needs to be aligned correctly to take maximum advantage of the sun’s rays.

Image credit: MIT

Lots of factors affect how much electricity a solar panel makes. Which way it faces, the angle of the roof its on, what latitude it is at, what season of the year it is, how cold it is outside, and weather that obscures the sun all factor in. Under adverse conditions, it may make so little electricity it costs more than its worth.

Researchers at MIT think they have a solution. Instead of laying solar panels flat on a roof, they tried arranging them in various ways. They burned through a ton of supercomputer time trying to find the optimal arrangement. In the end, they came up with a way of arranging them in three dimensional patterns. By placing them vertically in towers, power output is two to twenty times greater than what a single panel with the same footprint mounted on a roof would produce.

The best part it, the biggest boost came in situations where tradition arrangements are least effective — locations far from the equator, in winter months, and on cloudy days. The new findings, based on both computer modeling and outdoor testing of real modules, have been published in the journal Energy and Environmental Science.

The basic physical reason for the improvement in power output and for the more uniform output over time is that the vertical surfaces in a 3D structure can collect much more sunlight during mornings, evenings and winters, when the sun is closer to the horizon, says co-author Marco Bernardi, a graduate student at MIT.

The complete 3D systems costs more to manufacture that traditional flat roof systems, but that cost can be offset by the greater amount of electricity created. Going vertical may also make it possible to install photovoltaics in areas where there is not enough room for a horizontal system.  An accordion-like tower could be shipped flat and easily assembled on site says Professor Jeremy Grossman. A tower could be installed in a parking lot to provide a charging station for electric vehicles, he says.

Not everything that works in the lab is commercially viable in the real world. But the MIT research is a promising new technology that may help expand the number of places where clean, renewable solar power can be used effectively.

Photo credit: Allegra Boverman/MIT News

UPDATE: Apparently, I am not terribly well versed in this subject. Two commenters have suggested there are inaccuracies in the story. Rather than argue a point in a subject in which I am weak (ask me anything about maintaining an MGB, though, and I’m your guy), I am going to recommend you review the comments posted by JamesWimberley and KenC.

If I understand their argument (and each seems well versed and well intentioned) the MIT “breakthough” only applies if these 3D towers cover the same area of a given roof that conventional flat solar panels would cover in a typical PV system. I have amended to the last sentence of the third paragraph in accordance with what I take those comments to mean.

Please read the comments and make up your own mind. If I have mislead anyone, it was not intentional.

http://gas2.org/2016/04/12/mit-breakthrough-boosts-solar-panel-output/