“

A research team based out of the U.S. National Renewable Energy Laboratory (NREL), has developed a multi-junction solar cell that it says has broken an efficiency record. The research team partnered with the Swiss Center for Electronics and Microtechnology (CSEM) to create the so-called tandem solar cell, combining two layers of semiconductor material to absorb more of the solar spectrum.

In laboratory tests, the research team demonstrated that the solar cell could convert direct sunlight into electricity at 29.8% efficiency. David Young, a senior researcher at the NREL, points out that these results edged out the theoretical limit of 29.4% for mechanically stacked cells. In addition, the device works without having to concentrate sunlight with reflectors, which can increase efficiency in certain solar cells.  

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Each research center contributed part of the dual-junction solar cell, which combines III-V and crystalline silicon semiconductors. CSEM scientists developed a silicon sub-cell, on top of which NREL stacked a layer of gallium-indium phosphide (GaInP). The resulting device has a higher efficiency than either material by itself. The record efficiency for an individual crystalline silicon cell is 25.6%, and 20.8% for single-junction GaInP.

“We believe that silicon heterojunction technology [that combines different crystalline semiconductors] is today the most efficient silicon technology for application in tandem solar cells,” says Christophe Ballif, head of photovoltaic research at CSEM.

The researchers gave few additional details in a recent news release, but Young has submitted the team’s research paper to the IEEE Journal of Photovoltaics for publication. The experimental results were published in the journal Progress in Photovoltaics in an article reviewing solar cell designs and the highest efficiency in each category.

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The review, which includes solar cells up to three times more efficient than conventional solar panels, underlines the fact that efficiency is not everything for commercial solar cells. The highest efficiency ever recorded was 46% for a multi-junction device under highly concentrated sunlight. Soitec, a French company that makes photovoltaic semiconductors, engineered the solar cell in 2014. But the company has since stopped producing this technology.

Despite these higher efficiencies, multi-junction solar cells have been kept out of the commercial market by their complex structure and high manufacturing costs. These devices have typically been limited to satellites and other spacecraft. On the ground, they have to compete with the gradually falling cost of crystalline silicon, the most prevalent material for conventional solar cells. Mass-produced silicon cells are typically less than 20% efficient, but they are relatively cheap compared to the exotic material normally used in multi-junction cells.

The NREL, which is the primary research laboratory for the U.S. Energy Department, is examining several different semiconductor materials for solar cells. Last November, the laboratory found a way to significantly reduce the amount of energy lost to heat in perovskite-based solar cells. The discovery could one day lead to solar cells that convert up to two-thirds of sunlight to electricity.

The dual-junction research was funded in part by the Energy Department’s SunShot Initiative, a program aimed at making solar energy cost-competitive with fossil fuels. Additional funds were provided by the Swiss Confederation and Nano-Tera.ch, a Swiss green technology fund. 

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Hello! My name is Maria Guerra and I am the new Technology Editor on Electronic Design covering Analog/Power. I hold a bachelor’s degree in Electrical Engineering from Universidad Metropolitana in Caracas, Venezuela. Upon graduation, life circumstances brought me to the United States, where I earned a master’s degree in Electrical Engineering with a certificate in Wireless Communications at NYU Tandon School of Engineering.

Check out Maria’s Articles

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Over the course of my career, I have been involved in the oil and gas industry. In my hometown, I worked at Pequiven S.A., where I was responsible for estimating electric-circuit variables pertaining to the bottom of oil wells. Variables pertaining to the surface of oil wells were normalized and fed into a neural network for the estimation. In the UK, I worked for Kellogg, Brown, and Root Ltd. (KBR). While working there, one of the responsibilities that I enjoyed the most was giving technical support to the Electrical Engineering Group.

At KBR, I performed power systems studies (e.g., load-flow calculations, short-circuit analysis, motor-starting studies, harmonic studies, etc.) for different projects for both offshore and onshore designs. I communicated the results of those studies by writing technical reports, which I always found quite rewarding and challenging. Now I find myself in a similar situation: researching and reporting.

In my new role, I am going to have the chance to report on the latest information related to emerging technologies in the analog and power electronics world. I am also looking forward to sharing with our readers various learning resources that will help to refresh and reinforce engineering concepts.

I am particularly looking forward to talking about power-semiconductor technology trends. I would like our readers to be aware of what the industry leaders in the power electronics world have to offer in the areas of power management, charging, energy harvesting, power generation, and more. Among the hot topics that I plan to cover are electric/hybrid cars, renewable energy sources, and wireless charging technologies.

I’m based in Electronic Design’s New York City office and can be reached at maria.guerra@penton.com.

The European Organization for Nuclear Research (CERN) reported last month that two separate research teams may have discovered a new fundamental particle of matter. Despite the initial enthusiasm and skepticism of CERN physicists, it could take months for computers to comb through the ocean of data produced by the Large Hadron Collider and confirm that the particle actually exists.

As the physicists wait for more information to emerge, CERN’s information technology department is engaged in a different kind of research. Under the organization’s Openlab program, CERN has partnered with educational institutions and technology companies to ensure that, in the future, its computers are fast and efficient enough to sift through increasingly complex particle collisions.

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The latest project involves using new high-speed interconnects to link the thousands of processors in the CERN Data Center. Updating the interconnects will help to optimize its existing processing power—an alternative to adding more processors to increase its blunt force. The processors are designed to run algorithms that filter out uninteresting particle “collision events” in the Large Hadron Collider. The goal is to find unexpected interactions or anomalies that could suggest the presence of new particles.

CERN’s demand for faster processors stems mainly from the enormous amount of data produced by the Large Hadron Collider. The collider smashes particles together at near the speed of light and monitors the particle shards—for instance, those of the Higgs boson particle that was discovered in 2012—spraying in different directions. The shards leave behind traces in space that are recorded by “detectors” that take roughly 14 million snapshots per second of the particle interactions. These frames of data translate into about 3 gigabytes of data per second (about 25 petabytes or 25,000 terabytes per year).

At the core of the new interconnects is the high-speed communications standard RapidIO, which has been widely used to connect processors in cellular base stations and network servers. RapidIO can support up to 20 Gbits/s interconnects directly on processors without network interface controllers, adaptors, and software intervention.

According to Integrated Device Technology Inc. (IDT), which designed the interconnects for CERN, the latency of RapidIO can be as low as 100 ns between switches and less than one microsecond between processing nodes. The standard can be used to establish a connection between chips, boards, and chassis.

Although latency was the central concern, the new interconnect also help to reduce the data center’s massive power demands. Communication between processors on the same chip takes little energy (on the order of microwatts). But according to Barry Wood, principal product applications engineer at IDT, the communication between processors is significantly higher, from hundreds of milliwatts to watts. In supercomputers and servers, that can add up to hundreds of megawatts (MW).

The interconnect project underlines the creativity that has defined CERN’s information technology program over the years. In 1989, for instance, the organization created the World Wide Web as a way to distribute its research data. Building on its World Wide Web Technology, CERN invented grid computing in 2002 to process particle collision data using computer systems from around the world. Today, the Worldwide LHC Computing Grid sends information to 170 data centers in 42 countries.

CERN physicists will keep raising the energy at which the Large Hadron Collider fires protons in search of new particles that could reveal deeper physical laws. During its first two years running, the it fired protons to energies of about four trillion electron volts. But since restarting last June, after a two-year shutdown, CERN physicists have been firing protons with 6.5 trillion electron volts of energy. In order to find more esoteric particles, the collider will have to operate at higher energies, creating even more violent particle collisions. In turn, these collisions produce more data.

Before the shutdown, the data center was storing 1 gigabyte-per-second, with the occasional peak of 6 gigabytes-per-second, according to Alberto Pace, head of the Data and Storage Services in CERN's IT department. But now, “what was once our ‘peak’ will now be considered average, and we believe we could go up to 10 gigabytes-per-second,” he says.

The initial phase of the interconnect project will focus mainly on connecting a small number of processor nodes. But during the three-year research collaboration, IDT and CERN engineers have plans to build large scale computer systems and start using them to analyze data.

Shipping delays, quality failures and product delays can occur when your engineering and operations teams aren’t in sync. This whitepaper examines how an integrated cloud PLM system helps your product development teams have god-like visibility across their complete product lifecycle.

Dielectric constant, dissipation factor, dielectric strength, surface and volume resistivity are all fundamental electrical properties of epoxies. How they are measured, what values are desirable and how they react to changes in temperature, fillers and other variables are considered in this paper. The specific composition of resin and curing agents will also affect the electrical properties of a cured epoxy system. Three major types of curing agents are explained in this paper along with their benefits and trade-offs with respect to electrical properties

A new wireless sensor network being installed in Japan could help scientists more accurately predict the behavior of the country’s most active volcanoes. The system will gather enormous amounts of data used to forecast volcanic activity, identifying when it might be necessary to issue warnings or evacuations.

The sensor network, which will be installed around 47 volcanoes that the Japanese government has selected for around-the-clock observation, will measure several different variables. In addition to the seismic activity that almost always occurs before an eruption, the sensors will monitor gas emissions, topography changes, and vibrations in the air caused by rocks and ash spewing from the volcano.

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Japan sits on the western edge of the so-called “ring of fire,” an area around the Pacific Ocean where most of the earth’s volcanic eruptions and earthquakes occur. Sakurajima in southern Japan—which sits only miles from the roughly 600,000 people living in Kagoshima—has been erupting almost continuously for more than 50 years. Other volcanoes in the country are susceptible to “phreatic eruptions,” explosions of super-heated ground water that are notoriously difficult to detect.

In recent years, Japan has placed growing urgency on volcano monitoring. In late 2013, the eruption of Mount Ontakesan in central Japan killed 63 people and prompted the Japan Meteorological Agency, the state weather organization, to review into its volcano forecasting methods. Ultimately, it proposed adding new technology to the agency’s early warning system. It remains unclear whether the agency or a private company commissioned the new sensor network.

Because large populations often live in the shadow of Japan’s volcanoes, the sensor network was designed to provide a constant stream of real-time data. The system was built around LoRa technology, a wireless standard for sending data over long distances while consuming little power from end node batteries. The sensors are based on a LoRa transceiver from Semtech Corp., which it says can provide each sensor with at least five years of battery life. In addition, LoRa is capable of adapting data rates to ensure that data continues flowing from the sensors in spite of radio interference.

The information gathered by the sensors will be transmitted via LoRa gateways to manned monitoring stations located 5-10 km away from the volcanoes. LoRa, also known as LoRaWAN, operates using a chirp spread spectrum radio scheme, sending data through a series of gateways that serve as a bridge between the sensors and network servers.

LoRa is one of a growing number of low-power wide-area networks that are being designed to mine valuable data from advanced industrial systems and infrastructure. The standard can support more than one million uplink devices and up to around one hundred thousand downlink devices per access point. In rural areas the standard can stretch up to 15 km, while in urban areas, it can range from 2 to 5 km.

LoRa’s architecture allows for three kinds of end node devices, depending on the number of uplink and downlink channels. Class-A devices are bidirectional, with one scheduled uplink and two downlink windows. Class-B devices (also bidirectional) have additional downlink windows, while Class-C devices have receive links that are almost always open. The payload and range can be traded off.

Power distribution networks (PDNs), have become a key technology focus as the task of efficiently providing power to products becomes more difficult. Because PDNs are routed to all devices that need power, any noise or transients on power rails propagate throughout the system. This makes analyzing your system’s power integrity becomes even more important. See tips for power supply measurements and selecting the best tools for making these measurements in this application note.

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A research team from the Georgia Institute of Technology has developed a power management system that could allow fitness bands and smart watches to harvest energy from human motions like running, walking, or tapping your fingers.

The research, published last month in the journal Nature Communications, could significantly increase the efficiency of triboelectric generators—tiny electronic devices that convert body movements and mechanical vibrations into electricity. The team reports that their new power management system can increase the efficiency of these devices from about one percent up to 60%.

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Zhong Ling Wang, a professor in the Georgia Tech School of Materials Science and Engineering and member of the research team, led the development of the team's first triboelectric nanogenerators in 2012. Since then, Wang and his colleagues have invented several generators that take advantage of the triboelectric effect, or the property of certain materials to produce an electric current when rubbed against each other. Earlier this month, the research team developed a flag that could generate electricity by flapping in the wind. And last year, the researchers created a fabric that could harvest energy from human motion.

The new power management system has two stages. First, it captures alternating current from a triboelectric generator in a small capacitor. When the capacitor is full, a circuit funnels the electricity into a larger capacitor or battery. This second storage device then supplies direct current at the low voltages required for portable electronics and wearable devices.

The research could represent a major step toward solving the tricky problem of harvesting energy from irregular human motion. Ordinarily, alternating current can be converted into direct current using a transformer. But normal transformers require a constant number of cycles per second. By contrast, walking or finger tapping produce mechanical energy with fluctuating amplitude and variable frequencies.

The two-stage design of the new system can account for this problem, says Simiao Niu, a Georgia Tech graduate research assistant. “The first stage of our system is matched to the triboelectric nanogenerator,” he says, “and the second stage is matched to the application it will be powering.”

The power management system is capable of amplifying the very small electric current produced by triboelectric generators—up to 330 times more power output than the generator alone. When tested with finger tapping, the system generated a continuous direct current of 1.044 mW. The power management system needs a small amount of power to work, but the milliwatt-level power is more than enough to compensate, says Niu.

"It doesn't matter what kind of mechanical motion or what frequency of mechanical motion you have, as long as the energy input is high," says Niu. The system also helps to convert the high-voltage and low-current power from triboelectric generators for low-voltage, high-current portable electronics.

Wang says that the next step for the power management system, which has only been confirmed in a proof-of-concept experiment, will be to shrink the circuitry to the point where it can be used in an actual device. He adds that the system is also compatible with piezoelectric and pyroelectric generators, which also produce alternating current.

The international accord drafted by 195 countries at the Paris climate talks last year is focused on keeping the average global temperature increase below 1.5 degrees Celsius. The agreement will require not only using more renewable energy and reducing carbon emissions, but also a reevaluation of how a renewable power grid will work.

Now, a research team led by the Lawrence Livermore National Laboratory (LLNL) in California has proposed a new method for satisfying these requirements. Writing in the journal Mechanical Engineering, the researchers outlined a system that uses carbon emissions from power plants to store renewable energy for the power grid.

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The system, which the research team described as a vast underground battery, would store thermal energy in underground carbon dioxide reservoirs when demand on the power grid was low. The system would convert that energy into electricity and dispatch it to the power grid when demand is high.

The research comes as wind turbines, solar farms, and other renewable sources are increasingly being used in a power grid dominated by “baseload” power plants, which generate a constant flow of electricity. In contrast, the power output of renewable sources varies widely based on the time of day, seasons, location, and weather.

According to Thomas Buscheck, the paper’s author and director of LLNL’s Geochemical, Hydrological, and Environmental Science division, if “you want to store the large quantities of renewable energy necessary to balance seasonal supply-demand mismatches and store it efficiently, we believe the best way to do that is underground.”

The underground storage system involves pumping supercritical CO₂, a highly concentrated liquid version of carbon dioxide, into tunnels carved in sedimentary rock. Once underground, the highly pressurized CO₂ pushes brine trapped in the rock up production wells. At the surface, the brine can be heated by energy from concentrating solar power plants, wind turbines, and nuclear and other baseload power plants.

Once heated, the brine is sent into the reservoirs to store thermal energy. The geothermal heat and huge amount of pressure underground prevent significant heat loss. When renewable energy cannot fulfill power grid demands, the pressurized CO₂ and brine can both be released and their thermal energy converted to power. The brine could be used in a steam-powered generator, while the heated CO₂ could drive turbines by itself. Both fluids could be reheated and sent back down into the reservoirs.

Another benefit of the system is that it locks away CO₂ that would otherwise be released into the atmosphere, fueling climate change. Buscheck says at least four million tons of CO₂ could be stored underground each year over 30 years. That is equivalent to the CO₂ impact of a 600-megawatt coal plant. To relieve the enormous pressure of the stored CO₂, which will make it difficult to keep underground permanently, some of the brine could be removed to create water through desalination.

Burning fossil fuels to generate electricity accounts for about 31% of the carbon dioxide emissions in the United States—more than any other source, including transportation. This translates into more than two billion metric tons of carbon emissions per year, according a 2013 study by the Environmental Protection Agency.

Buscheck says the United States is a very suitable candidate for the new system, but his reasons are less about the country’s carbon footprint and more about its geology. The sedimentary rock formations required for this system cover about half of the United States, he says.

The project falls within the U.S. Energy Department's Grid Modernization program, which aims to integrate renewable energy sources into the grid, while making it more resilient and secure against cyberattacks. On Thursday, Energy Secretary Ernest Moniz announced that the laboratory would start 14 new power grid research projects this year. Buscheck and his LLNL colleagues worked on the project with researchers from Ohio State University, the University of Minnesota, and Terracoh Inc., a company that designs underground CO² storage systems.

The underground battery concept has been in development for seven years and has been validated in computer models, but Buscheck notes that more research is necessary. Fundamentally, however, “the concept is based on proven technology,” he says. “There are no showstoppers.”

Even though they have around three times the energy density of lead acid and NiMH, lithium-ion batteries can be very unstable. The Li-ion batteries in electric vehicles have been known to catch fire following accidents and front-end collisions. The Federal Aviation Administration has even considered a moratorium on shipping batteries for fear that they could ignite during flight.

Over the last month, as the press have raised the questions of their overall safety, and engineers have guaranteed that failures are extremely rare, two research projects have invented Li-ion batteries with internal fail-safes to prevent the catastrophic failures that cause them to catch fire.

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When severely damaged, overcharged due to a malfunction, or contaminated by metallic dust in the production process, Li-ion batteries can short-circuit and overheat. Too much heat triggers a chain reaction known as a thermal runaway, in which the flammable electrolyte inside the battery catches fire. Low-quality separators between the battery’s electrodes can also cause thermal runaways.

The most recent research to address these problems comes out of Stanford University. Researchers have developed a temperature sensor that can shut down the battery before it overheats, preventing a thermal runaway. In addition, the sensor is capable of restarting the battery automatically once it cools down.

Writing in the journal Nature Energy, the researchers said that they had based their design on wearable sensors for measuring body temperature. The sensor is made out of a thin film of elastic polyethelene, and embedded in the film are tiny nickel particles coated in graphene.

“We attached the polyethylene film to one of the battery electrodes so that an electric current could flow through it,” says Zheng Chen, lead author of the paper. “To conduct electricity, the spiky particles have to physically touch one another. But during thermal expansion, polyethylene stretches. That causes the particles to spread apart, making the film nonconductive so that electricity can no longer flow through the battery.”

The polyethylene film expands when the battery’s temperature is above 160°F, causing the spike to separate and the battery to shut down. When the temperature falls back under that threshold, the polyethylene contracts and the battery generates electricity again. The temperature threshold can be adjusted with different materials, according to the research team.

Another study from Penn State University takes a similar approach, using sensors to shut down the Li-ion battery at high temperatures. The Penn State team worked closely with large-format batteries—the kind used in electric vehicles and other gadgets—that require more power than cell phones and computers.

The team worked with a grant from the U.S. Department of Energy’s Computer Aided Engineering for Electric Drive Vehicle batteries (CAEBAT) project, underlining the need for Li-ion batteries that can survive accidents, as well as adapt to wide changes in weather and temperature. Its research was published in the journal Scientific Reports earlier this month.

The transition to electric vehicles will serve as one of the main tests of Li-ion battery safety. Automobile and battery companies are working to increase their energy density, at the same time making them smaller and lighter, in an attempt to extend the range of electric vehicles. At these higher densities, battery failures have the potential to cause more violent thermal runaways.

Chao-Yang Wang, a professor of mechanical, chemical, and materials engineering at Penn State, notes “you are compressing more and more energy into a smaller space, and you have to careful when you do that.”