Highlight all of ASU's renewable energy research.

ASU professor advances research on water, contemporary Italian poetry

July 9, 2020

Serena Ferrando, assistant professor of environmental humanities and Italian at Arizona State University, is the discretionary funding winner from The College of Liberal Arts and Sciences' 2019–20 New Assistant Professor Workshop Series drawing and will be using the funds to advance her research on the intersection of water and literature. 

Her book in progress is titled "City of Water: The Poetic Geography of Modern Milan" and offers a novel and original ecocritical-cultural narrative of the relationship between poetry and nature in the city of Milan, Italy, and three Milanese poets. Ferrando’s work shows how during the 1920s and 1930s, Milan’s embrace of progress and modernity culminated in the controversial covering of the "navigli" (canals) to create roads and how, concurrently, a strong sense of nostalgia for the now-disappeared water emerged among the citizens. Download Full Image

Ferrando’s research on water and contemporary Italian poetry has birthed the Navigli Project (Instagram), an eco-digital interactive map of Milan’s waterways. She also studies environmental and experimental noisescapes and curates "Noisemakers!," a multimedia project that utilizes sound mapping to create a multisensory experience of the territory that is shared by a community. Her publications span from Italian literature to ecocriticism to digital humanities.

Students can enroll in her course, “City of Water: Uncovering Milan’s Aquatic Geographies” (ITA494/SLC494/CDH594), where they will explore the cultural history of water in Milan, Italy’s self-described “city of water,” in a multimedia environment that fosters an atmosphere of creative collaboration and encourages creative design. Students will generate searchable, annotated, thick maps of Milan and disseminate them outside the classroom and will also have the opportunity to see their work featured on the Navigli Project. The course will include a guest lecture by a renowned Milanese illustrator and two Milan-based film directors.

Taylor DiGiro

Communications and Marketing Intern, School of International Letters and Cultures

ASU solar energy startup shines in national competition

May 13, 2020

A bright idea developed through the Ira A. Fulton Schools of Engineering has been selected for the final stage of a national contest meant to expand solar energy manufacturing in the United States.

SunFlex Solar is a new startup venture co-founded by ASU Assistant Research Technologist Kate Fisher, Associate Professor Zachary Holman, Assistant Research Professor Zhengshan “Jason” Yu and doctoral student Barry Hartweg. The group entered its Sunfoil solar panel enhancement in the second round of the American-Made Solar Prize competition initiated by the National Renewable Energy Laboratory and the U.S. Department of Energy’s Solar Energy Technologies Office. Kate Fisher of SunFlex Solar inspects a solar panel SunFlex Solar co-founder Kate Fisher inspects the embossed aluminum foil at the heart of award-winning ASU solar energy innovation. Photo courtesy of SunFlex Solar Download Full Image

The foursome from the School of Electrical, Computer and Energy Engineering, one of the six Fulton Schools, learned in September that they had won $50,000 and a place among 20 semifinalists. By the end of March, SunFlex Solar was chosen as one of 10 finalists in the competition. The latter selection also came with $100,000 in prize money and an additional $75,000 in credit for development assistance from a network of national laboratories and component fabrication facilities.

The competition will announce two ultimate winners this summer, and each venture will receive half a million dollars to develop their innovation and an additional $75,000 in credit for laboratory and fabricator support. SunFlex Solar seeks to be one of those two winners through its novel method of enhancing solar panel efficiency at low cost.

“One leading technology that produces more power than industry-standard solar cells is called interdigitated back-contact, or IBC for short,” Fisher said. “IBC panels produce 6% more power than standard modules, but they are far too expensive for market application.”

That 6% may not sound significant, but it means a lot to the bottom line of solar power systems. Most expenses associated with solar installations are not the panels themselves, but so-called “balance of systems” costs. These comprise government permitting, inverter devices, panel racking, wiring and labor — and they represent five to 10 times more spend than the panels involved. As a consequence, any innovation that increases solar panel efficiency can reduce panel size and yield a multiplying effect in terms of lower costs across entire solar power systems.

Therefore, even a single-digit efficiency boost from IBC-based panels is meaningful, but the semiprecious metals used in their construction — silver and copper — make them too expensive. SunFlex Solar has solved this problem by developing a new method to make high-efficiency IBC panels at the same cost as lower-performing industry-standard panels by using an alternative material.

“Our Sunfoil solar panel replaces silver and copper in the IBC cells with aluminum foil,” Fisher said. “Our actual innovation is how the aluminum is integrated into the panel. In particular, we emboss the aluminum foil to form busbars that make electrical contact with the back of IBC solar cells. Then we weld these busbars to the cells with a laser, resulting in a robust interconnection.”

Holman points out that the innovation isn't just an idea. His research group at ASU devoted three years to develop this technology through a U.S. Department of Energy-funded project, and SunFlex Solar now has a patent application in process.

“Our next steps are to use prize money to purchase a laser and the materials to scale up from an initial single-cell example to create four-cell prototypes,” Holman said. “We then plan to use the voucher credit to test these prototypes with third parties. First is performance verification testing at the National Renewable Energy Laboratory in Colorado, and then outdoor power generation testing at Sandia National Laboratories in New Mexico.” 

With those validations complete, SunFlex Solar can partner with a module manufacturer to create industry-standard, 60-cell panels and move this ASU innovation into the marketplace.

“Our business model involves technology translation to an established panel manufacturer through a joint venture or acquisition,” Holman said. “SunFlex Solar brings our intellectual property and the technological expertise of our people. Our panel manufacturing partner will bring complementary capital, manufacturing capacity and supply and distribution chains.”

The success of ASU in the American-Made Solar Prize competition is not a first. Fulton Schools startup venture Crystal Sonic competed in the previous round of this contest, and it also reached finalist status for its development of a method to thinly slice expensive solar cell materials and dramatically reduce manufacturing costs. Yu was a member of that competition team, and he says that back-to-back successes for ASU are not a coincidence.

“ASU is unique in its ability to produce solar components — from cells to modules. We may be the only university in the U.S. with such comprehensive capacity,” he said. “And we have researchers across the whole spectrum of photovoltaic technologies who foster interdisciplinary learning and innovation. Actually, the opportunities represented by the facilities and researchers here are why I joined ASU.”

Hartweg shares the same reasoning for his doctoral work here, which has been more innovative than he expected.

“ASU was first on my list when applying to PhD programs because this university simply has the best and most established solar research groups,” he said. “But I had no expectation that I would be a part of a startup. That said, I'm learning a lot about the entrepreneurial aspect of taking a technology from a laboratory to a form that works for industry. And that's unique. Few people get the chance to learn these skills from an engineering program.”

Gary Werner

Science writer, Ira A. Fulton Schools of Engineering


Researchers develop new process to up solar cell performance

April 21, 2020

Experimental condensed matter physicists in the Department of Physics at the University of Oklahoma and an electrical engineering professor at Arizona State University have developed an approach to circumvent a major loss process that currently limits the efficiency of commercial solar cells.

Solar cells convert the sun’s energy into electricity and are the main component of solar panels and many types of electrical devices as broad-ranging as satellites and calculators. New solar energy approach Download Full Image

Members of the Photovoltaic Materials and Devices Group, led by Ian Sellers, University of Oklahoma associate professor in the Homer L. Dodge Department of Physics and Astronomy, along with theorists at Arizona State University led by David K. Ferry have demonstrated a breakthrough toward the development of a hot carrier solar cell.

A hot carrier solar cell is a device that would increase the efficiency of solar cells by more than 20%, which Sellers said would be a significant breakthrough for solar energy.

“Although this device has been the source of a considerable amount of research over the last 10 to 15 years, the realization of a practical solution has thus far eluded researchers with proof-of-principle demonstrations only presented under unrealistic conditions or in materials and structures not relevant for solar cell operation,” Sellers said.

Sellers says this new approach, recently published in the journal Nature Energy, demonstrates “significant progress in the realization of the hot carrier solar cell and the potential for ultrahigh-efficiency single junction semiconductor devices, which would revolutionize the field of photovoltaics and renewable energy generation.”

"The new approach arises from using an interdisciplinary approach where we bring proven ideas from other fields of semiconductor devices and use them in the solar cell arena," said Ferry, an emeritus engineering professor in ASU's School of Electrical, Computer and Electrical Engineering. "Working with the Oklahoma group has allowed us to move quickly toward the realization of these ideas."

Terry Grant

Media Relations Officer, Media Relations and Strategic Communications


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When will we move fossil fuels off the grid?

March 27, 2020

ASU sustainability scientist predicts a complete switch to renewable energy will most likely come at the turn of the century

For decades, the United States has attempted to wean itself from fossil fuels but with limited success. Coal, natural gas and oil still comprise about 80% of our energy supply, according to the U.S. Department of Energy.

It’s cheap, and it’s in abundant supply, but it’s not renewable energy.

Renewables accounted for almost 12% of U.S. energy consumption in 2019 and are slowly trending upward. But the transition is not happening fast enough in light of greenhouse gas emissions, climate change and global warming.

What will it take to get there?

“A globally concerted effort,” according to Arizona State University sustainability scientist Meng Tao.

A professor in ASU’s School of Electrical, Computer and Energy Engineering, Tao’s research covers a wide range of topics in sustainable and terawatt solar photovoltaics, including solar energy storage, solar charging of electric vehicles and solar-powered industrial electrolysis.

In the lead-up to Earth Day, ASU Now turned to Tao to discuss renewable energy, why our country is so dependent on fossil fuels, and how long it will take decarbonize the country.

Man with black hair smiling

Meng Tao

Question: What is renewable energy and how many different categories are there?

Answer: Renewable energy is energy that will not be depleted for the foreseeable future. There are six categories: solar energy, hydropower, biomass, wind, ocean energy (waves, current and tides) and geothermal energy. Notably, most of these renewable energy sources originate from solar energy, including hydropower, biomass, wind, ocean waves and ocean currents. Ocean tides are due to the gravitational effect of the moon. Geothermal energy is from the high-temperature Earth’s mantle.

Q: America wants renewable and solar power to replace energy that is reliant on fossil fuels, but how realistic is that and how much time are we talking about until a complete switch over?

A: It is hard to predict the future but my hope is that by 2050 half of the energy we use will be drawn from renewable sources and by 2100 we completely switch over to renewable energy. Unfortunately, this timeline is likely inadequate if we consider how fast Earth’s temperature is rising. We are facing a daunting but inevitable task. It is also important to remember that an America-alone action means little in this transition if 95% of the world’s population continues to depend on fossil fuels. We need a globally concerted effort.

Q: What is keeping us from reaching that goal?

A: There are multiple bottlenecks to our adoption of renewable energy. We have many promising technologies now but not every technology needed for us to live 100% on renewable energy today. For example, we do not know how to store summer solar energy for future winters or sell Arizonan solar energy to Sweden in the way that we buy Saudi oil for America. In other cases, the cost of the technologies is prohibitively high. The cost of solar systems has come down dramatically in the last 15 years, but if you consider the cost of a solar system with storage, it is more than doubled. Of course, there are also special interests, inertia in people’s mindset and behavior, and the huge financial barrier which all hinder our progress.

Q: What countries, in your opinion, are leading the way in using renewable and solar power and how can we better learn from them?

A: Several countries come to mind but I will just mention one: Sweden. I spent a year in Sweden as the Fulbright Distinguished Chair in Alternative Energy Technology and learnt firsthand about the Swedish experience. Public consensus in Sweden pushes government support and private investment into renewable energy. Now the electric grid in Sweden is 100% fossil fuel free: 45% from hydropower, 45% from nuclear energy and 10% from wind. The Swedish experience does not necessarily apply to other countries, as each country has its own unique combination of renewable energy sources, but achieving a public consensus is the first step in speeding up the transition.

Q: What are you doing at ASU to further the cause of renewable/solar energy?

A: My research focuses on sustainable solar technologies. It is ironic that we pursue solar energy for sustainability, but most of the solar technologies we have today are neither scalable nor sustainable. The roadblocks to sustainable solar technologies include the scarcity of the raw materials used in solar modules, the high energy consumption in producing solar modules, storage of intermittent solar energy, recyclability of end-of-life solar modules, in addition to cost and efficiency. We are developing technologies to remove these roadblocks, and our ultimate goal is to drive solar energy into a mainstream energy source by 2050.

Q: What are the most impactful trends for solar energy in the next 10 years?

A: My personal view is that there will be a shift in focus from cost and efficiency to systems, applications and sustainability. The scarce materials used in solar modules must be substituted with Earth-abundant materials. More energy-efficient methods for solar module production are in demand. Innovative storage technologies beyond batteries are needed for long-term storage and global trade of solar energy. Recycling of end-of-life solar modules is barely practiced today. In addition, systems and applications that take advantage of the intermittent nature of solar energy are desirable. Integration of solar energy with transportation electrification will certainly be pursued. The nexus of solar energy, water and food is a high priority for the growing population and prosperity. Grid integration of solar energy has been widely recognized. This is not an exhaustive list but just a few things which pop up first in my mind

Top photo: Renewable energy in action. Photo courtesy of Pixabay.

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ASU celebrates 50 years of Earth Day with 50 days of sustainability events

ASU community asked to take carbon-free pledge for Earth Month 2020.
March 10, 2020

University community urged to pledge to make an adjustment, big or small, for Carbon Free Day on April 15

The first Earth Day in 1970 was catalyzed at college campuses.

The event was launched after Americans were horrified by a massive oil spill off Santa Barbara, California, that killed thousands of animals, as well as the publication of the ground-breaking book “Silent Spring,” by Rachel Carson.

The date of the first Earth Day — April 22 — was chosen to express this newfound environmental awareness because it fell after spring break and before final exams, according to the Earth Day Network. Thousands of protests were held that day, with many on college campuses.

As the world marks the 50th anniversary of Earth Day this year, Arizona State University is taking 50 days to celebrate the beginning of the modern environmental movement. A new website lists events by and for the entire ASU community from March 12 through April 30, plus news stories, a historical timeline of Earth Day and a place to make a pledge for ASU’s Carbon Free Day on April 15, happening in conjunction with the Earth Day Festival on the Tempe campus. Visit earthmonth.asu.edu/events and scroll down for a day-by-day listing of events.

The Earth Month 2020 events, held across ASU’s campuses, range from one-hour webinars on sustainable bathroom practices to a "trading post" clothing swap, a chance to test drive electric vehicles at the West campus, an edible landscape tour and a discussion of the epically tree-hugging book “The Overstory” by Richard Powers. At the April 15 Earth Day Festival, student organizations and community partners will gather near the Memorial Union to showcase their work and celebrate the collective efforts of the ASU community. 

Everyone in the ASU community is asked to make a pledge for Carbon-Free Day on April 15, with options in travel, food and energy, according to Susan Norton, program manager for University Sustainability Practices at the Polytechnic campus.

“Throw away the right stuff and recycle the right stuff.”
— Michael Dalrymple, director of sustainability practices at ASU

“You could do ride sharing with co-workers, or using alternative transportation such as biking or bus or the light rail, if that works for you,” Norton said.

“You could create a meal plan for the week so you’re not doing those last-minute runs to the grocery store. Small things can add up.”

Moving toward a more plant-based diet and away from red meat is another way to reduce carbon, according to Michael Dalrymple, director of sustainability practices at ASU. The industrial production of beef in the U.S. adds to methane in the atmosphere as well as groundwater pollution.

One way to try a more plant-based diet is to experiment with some of the ethnic cuisines that are flourishing in the Valley, he said.

“There are a lot of cultures that put less emphasis on meat,” he said. “... It’s an opportunity to go out and try those plant-based foods that have lots of cool, different flavors where there might be some meat but it’s less.”

Dalrymple is also urging everyone at ASU to be more conscious of recycling.

“We can’t expect people to recycle if we don’t have the infrastructure, so now we the infrastructure and we have to get them to use it the right way,” he said. “Throw away the right stuff and recycle the right stuff.”

Even without deliberate effort, everyone living and working on ASU’s campuses is part of the university’s sustainability efforts, including the 90 solar panel arrays that not only generate power but also provide shade, cooling the campus. Other recent changes include:

• The university has been gradually converting patches of grass that are unused into low-water-use landscapes. “If the grass is providing a space for an event or for students to hang out, it hasn’t gone away. But those odd-shaped pieces that don’t serve any purpose have been converted,” he said.

• By Earth Day, on April 22, Aramark will eliminate all plastic straws on campus, switching to paper straws at all dining halls and Memorial Union vendors.

• The Orange Mall space outside the Student Pavilion has become the first fully SITES-certified landscape in Arizona, designed to reduce water and energy consumption, collect stormwater runoff and increase outdoor recreation opportunities.

• The university has just completed a two-year project to install 56 electric-vehicle charging stations.

Campus mall with solar panels

Solar installations around campus not only generate power but also provide shade, cooling the campus. Photo by ASU Now

Dalrymple recommends one small adjustment to get started on being more sustainable.

“We’re all hypocrites, not doing all the right things like walking or biking everywhere or being vegan,” he said.

“A lot of people don’t start because they think, ‘There’s no way I can live like that.’

“Don’t feel guilty. If your goal is to be a tiny bit less hypocritical every day, it’s amazing how much your life changes. Something that seemed daunting suddenly, six months later, doesn’t seem daunting anymore.”

Top photo: Solar panels cover the parking lot outside of the Desert Financial Arena on ASU's Tempe campus. Photo by ASU Now

Mary Beth Faller

Reporter , ASU Now


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Layered solar cell technology boosts efficiency, affordability

March 6, 2020

ASU researchers are pioneers in new solar cell technology

The future’s getting brighter for solar power. Researchers from Arizona State University and the University of Colorado Boulder have created a low-cost solar cell with one of the highest power-conversion efficiencies to date, by layering cells and using a unique combination of elements.

“Solar cell power-conversion efficiency is a key driver of the cost of solar power,” explained Zachary Holman, an associate professor in ASU’s School of Electrical, Computer and Energy Engineering and a co-author of a Science paper about the technology. “The installation of solar panels on your roof now costs five times more than the panels themselves, so you want to use the most efficient panels, which have the most efficient cells.”

The researchers took a perovskite solar cell, a crystal structure that's designed to harvest higher energy photons, and layered it on top of a silicon solar cell, which captures more photons in the infrared part of the spectrum — which is made up of radiant energy that we cannot see, but we can feel as heat.

“Silicon can be as efficient as 45% at converting low-energy photons,” said Zhengshan (Jason) Yu, an assistant research professor at Arizona State University and co-author of the paper. “Pairing (it) with a top cell that is efficient at converting high-energy photons can dramatically improve the overall device efficiency.”

Combined, the perovskite raises a 21% silicon solar cell up to an efficiency of 27% — increasing it by almost a third.

For years, silicon solar cells have been the standard in the solar power industry. But current silicon-based cells only convert 20–22% of the sun’s energy into usable electricity on average, and they max out at about 27%.

The average efficiency of solar panels is lower than the maximum efficiency, because no matter how good an individual solar cell is, connecting many of them in a large panel will cause a power loss of about three percentage points — kind of like a sports team only being as good as its average player. But if you can raise the overall efficiency, you don't have to install as many panels to get the same amount of power.

What dramatically improves efficiency is to put another solar cell on top of an existing one — and that's exactly what the researchers did.

An affordable secret formula

This isn’t the first time researchers have layered solar cells to gain efficiency. The concept, also known as tandem or multijunction solar cells, was first introduced in the 1970s — and the world record for solar cell efficiency is already over 45%. However, it came at a hefty price: $80,000 per square meter, due to the fact the cells were grown one atomic layer at a time, creating one big, single crystal. Probably not a cost the average homeowner or business can afford.

Holman, Yu and their fellow researchers are pioneers in a new direction of layered solar cells, using perovskites and silicon, which cost more than a hundred times less.

They started working in close collaboration with first co-author Michael McGehee, a professor in the Department of Chemical and Biological Engineering at CU Boulder, fewer than five years ago with the concept of using less expensive materials on top of the silicon. At first they achieved about 13% efficiency, but through technological improvements have been able to more than double that number.

Their secret formula involves a unique triple-halide alloy of chlorine, bromine and iodine.

Each solar cell material has a single wavelength, or color of light, that it best converts into electricity. Unique to perovskites, which are a family of materials, this best wavelength can be adjusted by swapping some elements in the crystal with others.

The addition of bromine, for example, can tune a perovskite so that its best wavelength is perfect for pairing with silicon in a tandem solar cell. However, when used with iodine and exposed to light, these elements don’t always stay in place. Previous studies have tried to use chlorine and iodine together, but due to the differing particle sizes of these elements, not enough chlorine could fit into the perovskite crystal structure. But by using different amounts of chlorine, bromine and iodine, the researchers figured out a way to shrink the crystal structure, allowing more chlorine to fit in — stabilizing and improving the cell’s efficiency. 

With the solar power market growing around 30% per year, cost and longevity are also major considerations for new technologies to become mainstream. Fortunately, perovskites are inexpensive and, even after 1,000 hours, or almost 42 days, of intensive light and heat testing, these new solar cells showed a minimal change in their initial efficiency.

Holman, Yu and McGehee are optimistic about the potential of this new perovskite material in tandem solar cells.

“We took a product that is responsible for a $30 billion a year industry and made it 30% better,” McGehee said. “That’s a big deal. “Not only has the team’s cell now surpassed the maximum efficiency of a silicon-only solar cell, we believe it can take us over 30% efficiency and that it can be stable.”

Additional authors of this study include Jixian Xu, co-first author and postdoctoral researcher; Jérémie Werner, postdoctoral researcher; and Daniel Witter, graduate student in chemical and biological engineering at the University of Colorado Boulder; Caleb Boyd, co-first author, visitor at the University of Colorado Boulder and NREL and graduate student at Stanford University; as well as researchers from the National Renewable Energy Laboratory and Stanford University.

Top photo:  Perovskite/silicon tandem solar cells created by ASU researchers are transforming mainstream silicon technology and lowering the cost of solar energy. Photo by Erika Gronek/ASU

Terry Grant

Media Relations Officer , Media Relations and Strategic Communications


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Dispelling the darkness leads Vijay Vittal to Regents Professor honor

February 7, 2020

ASU electrical engineer named top in his field

Vijay Vittal was inspired to go into power grid engineering during his undergrad days at the B.M.S. College of Engineering in Bengaluru, India.

“I took this course in power system analysis,” Vittal said. “It was a senior elective. The instructor was an excellent instructor. That’s what inspired me to take this field.”

He not only took it — he mastered it. Vittal is one of the newest faculty members at Arizona State University to be named a Regents Professor. The title is the highest academic honor, awarded to scholars who have made significant contributions to their field and are recognized nationally and internationally by peers.

The Ira A. Fulton Chair Professor of Electrical Engineering and ASU Foundation Professor in electric power systems in the School of Electrical, Computer and Energy Engineering, Vittal is an expert on large-scale power grids. He works on what is arguably the premier engineering problem of our time: how to integrate renewable energy sources like solar and wind into the existing grid. It’s a wicked problem. Hospitals can’t run on wind alone. With states and companies making commitments to transition to renewable energy sources, it’s a pressing problem. California now runs on 33% renewable energy sources.

“It’s a mixture of several problems, so we have to attack it from many viewpoints,” he said. “How do you account for proper grid performance when the resource itself is variable? … The goal always is reliable electricity at an affordable price. Economics plays a very big role. You cannot keep arbitrarily increasing the cost of energy.”

Vittal has developed pioneering methods for dealing with fluctuations on the grid because of renewable energy inputs. He has developed the theory and application of “islanding” to isolate parts of the power grid to prevent a disastrous cascade of outages.

He has won every significant distinction in his field. He has been named a fellow of the Institute of Electrical and Electronics Engineers and was elected to the U.S. National Academy of Engineering, the highest honor for engineers in the United States.

In the Arizona Board of Regents citation for his Regents Professorship, one reviewer said, “He is a leading researcher in power system dynamics. … MIT’s Technology Review identified 'power grid control' as one of the '10 emerging technologies that will change your world,' and cited Dr. Vittal as one of the five leading researchers in the world in preventing power system blackouts.”

Another reviewer stated, “Dr. Vittal is without question the No. 1 scholar globally in power system dynamics and is amongst a handful of scholars that lead the broader area of power system engineering in the world.”

Of all Vittal’s accomplishments, he is most proud of the students he has trained, many of whom have gone on to prestigious positions around the country and globe.

“They have gone out and become very successful,” he said. “My first PhD student was someone older than me. He came from Korea. … He had done his undergraduate degree and due to family circumstances had to go work. He actually changed his field and worked as a construction manager in the Middle East.”

When he was financially stable, he decided to go back to school and earn a master’s degree and PhD.

“When he finished, he went back to Korea, joined this place called Korea Electrotechnology Research Institute, became the vice president, and he eventually became the chief electricity regulator for South Korea,” Vittal said. “It was very satisfying.”

Vittal also is the director of the Power System Engineering Research Center. Headquartered at ASU, the center is a program of industry and university cooperation. There are 11 other universities and 30 member companies, mostly utilities and system operators.

They deal with the delivery of energy from the generation side until close to the customer — think big overhead power lines. They work on transmission design, analysis tools, hardware, algorithms and modeling, and cybersecurity. Gary Dirks, director of ASU's LightWorks, called the team “arguably the best transmission group in the country — perhaps even in the world.” 

Top photi: Regents Professor Vijay Vittal. Photo by Charlie Leight/ASU Now

Scott Seckel

Reporter , ASU Now


New tandem solar cell research enables greater returns from current energy infrastructure

February 7, 2020

Small changes can make a big difference. Powerful examples of this aphorism are new findings from the Holman Research Group within the Ira A. Fulton Schools of Engineering at Arizona State University.

Zachary Holman, an associate professor of electrical engineering, and members of his team have discovered how a microscopic alteration to industry-standard silicon wafers permits a significant enhancement to solar cell composition. The change can boost the efficiency of solar panels and lower the cost of energy production. The team’s findings have been published across two recent articles in the science journal Joule Zachary Holman in a laboratory Zachary Holman and his team have published new research that can significantly increase solar cell efficiency and lower energy costs. Photo by Deanna Dent/ASU Now Download Full Image

Almost all commercial solar panels, or modules, contain wafers made of silicon to absorb sunlight and convert it into electricity. But the inherent efficiency limits of silicon as an absorber are underwhelming.

“If you were to buy a module right now, the solar cells are probably going to offer 21% efficiency,” Holman said. This low figure reflects the fact that silicon works well only with light from a certain portion of the electromagnetic spectrum.

There are better alternatives, such as cells made from compounds like gallium arsenide. These mixed materials deliver very high cell efficiencies, but manufacturing costs are so high that their application is limited to satellites, for example.

Even so, the idea of fabricating multijunction cells, which are those with two or more different absorbers, presents a rich opportunity. At present, the terrestrial use of these composite cells is negligible, but the new research by Holman and his team offers a viable means to quickly bring two-junction, or tandem, cells into widespread use.

The innovation revolves around perovskites, a class of compounds named after the 19th-century Russian mineralogist Lev Perovski. They share a particular crystal structure and are formed from inexpensive substances including iodine, bromine, methylammonium, cesium and lead.

Perovskites are valuable to solar energy production because they efficiently absorb light from a different portion of the spectrum than is the case for silicon. Consequently, if successfully layered onto silicon wafers, the resulting tandem solar cells can yield higher efficiencies and, therefore, lower costs per unit of energy generated.

That said, previous work with perovskites was disappointing. Early versions of these compounds rapidly deteriorated when exposed to sunlight and oxygen.

“A decade ago, they lasted only minutes,” said Arthur Onno, a postdoctoral researcher with Holman’s group and a coauthor of one of the articles in Joule. “Now researchers can produce them to last for thousands of hours without degradation. It’s getting better and better.”

Two aspects of the new research by Holman and his team offer a promising route forward. One is altering the surface architecture of industry-standard silicon wafers to permit the creation of physically functional perovskite-silicon tandem cells. The other advance involves collecting light from both sides, or faces, of solar cells. This facilitates some chemical tweaking of the perovskites that, in turn, allows for an electrically more efficient tandem cell.

Today, commercial silicon wafers are finished with a rough texture. A magnified view would show that texture as little pyramids on the surface. These raised structures scatter the light that strikes the surface of the wafer and send it down for absorption and conversion into electricity. By contrast, a perfectly smooth silicon surface would reflect more light away and lose its benefit for energy production.

The problem for tandem cell fabrication is that those mini pyramids on the wafer surface are not small enough. A commercial silicon wafer is typically 150 micrometers thick, similar to a sheet of printer paper. Those textured pyramids on the wafer surface are only 3 to 10 micrometers high, but the layer of perovskite material applied to the top of the silicon is no more than a single micrometer.

“And when the pyramids are taller than the perovskite layer, they stick through the layer and kill the solar cell performance,” said Zhengshan (Jason) Yu, a Fulton Schools assistant research professor of electrical engineering and a coauthor of both articles in Joule. “This is why nobody tries to coat perovskite on these textured surfaces.”

The solution to this architectural problem is revealed by the new research from Holman and his group. They discovered that finishing silicon wafers to a finer surface texture, in which the pyramids are less than a micrometer tall, still scatters the light almost as effectively as standard-height pyramids. More notably, the wafers are smooth enough to allow successful application of the perovskite layer.

image of magnified material on a solar cell

Layering light-absorbing perovskite material on top of silicon in a solar cell requires that the silicon texture “pyramids” are no more than a micrometer (μm) tall. Photographer: Bo Chen/University of North Carolina

Creating current compatibility

Even with this physical pairing accomplished, there remains an electrical challenge. The benefit of pairing perovskites and silicon in a tandem architecture is that they work with different parts of the electromagnetic spectrum, so the combination can collect and convert more light into electricity than either material alone.

However, the different light-capturing characteristics of these two substances means that matching their current outputs is not straightforward. Since they are connected to each other in a series circuit, the lower performer will limit the current flow of the higher performer.

Specifically, the bandgap — or minimum energy threshold for light to make electrons available for conductance and energy creation — is fixed within silicon by its elemental composition. By contrast, the bandgap for perovskites is adjustable. But increasing the bandgap of perovskites to match that of silicon makes the former too physically unstable to use in any practical sense. Lowering or widening the bandgap for perovskites improves stability, but it sacrifices efficiency — and enhanced efficiency is the point of creating the tandem cell in the first place.

The Holman Research Group devised a solution by making the tandem cell bifacial. Bifaciality means using both sides of the solar cell to gather light. Bifacial cells are growing in commercial popularity, but they still represent fewer than 10% of cells in use. Moreover, bifacial tandem cells are currently nonexistent in the solar energy industry.

But the new study by the Holman group found that using the bottom of the silicon cell to collect light solved the current-matching problem.

“With our collaborators at the University of Iowa, we found that bifacial tandems can have a wide range of top-cell (perovskite) bandgaps and still have the same energy yield,” Yu said. “This synergy between tandem and bifacial technology now opens up new opportunities for ultra-high-energy-yield solar technologies.”

More immediately, the successful creation of the perovskite-silicon tandem cell by Holman’s team and collaborators at the University of North Carolina resulted in 26% efficiency — about a quarter more than current commercial single-absorber (silicon) cells.

“And while that 26% may not sound like much,” Holman said, “companies working in solar fight to secure improvements of even a fraction of a single percent.” So, this advance is notable, and Holman explains that the impact grows as you look beyond the cells or the panels.     

“Making solar panels a quarter more efficient decreases the cost of solar power by significantly more than a quarter,” he said. “The panels themselves may represent only 20% of the total system cost. The balance is paying someone to configure components around your chimney, for example, and to have an electrician hook it all up. Many of these costs scale with area: bigger is more expensive. So, if you have more efficient panels, you can generate the power that you need from a smaller area, and that really brings down total system costs. It’s a leverage effect.”

These results flow from Holman’s desire to tackle practical issues in the work that he leads at ASU.

“There are countless challenges that we could work on,” Holman said. “But I want to make sure that we focus on a subset of problems where the solutions matter. In this case, we sought to determine how to adapt a material for use in an existing system, and not the other way around.”

Gary Werner

Science writer, Ira A. Fulton Schools of Engineering


ASU honors students seeking participants for solar structure design competition

January 28, 2020

Are you a student who is interested in sustainability and having a solar powered outdoor study and hang-out space on the Arizona State University Tempe campus?

If this sparks your interest, you may want to sign up to assist two students from Barrett, The Honors College with their honors thesis project. In addition to helping with the project, you could get a cash award for your winning design. Sarah Desmond and Brock Williams Barrett, The Honors College students Sarah Desmond and Brock Williams. Download Full Image

Brock Williams, a senior conservation biology and ecology major with a minor in business management, and Sarah Desmond, a junior finance and marketing major with a minor in biology, are completing an honors thesis through Barrett with the Center for Entrepreneurship and the School for the Future of Innovation in Society.

Williams and Desmond are calling their project SolArt and inviting students from all ASU campuses to join a competition to design a structure to be built on a site on the ASU Tempe campus.

According to the SolART website, the focus of Williams’s and Desmond’s thesis “is to design and implement a competition at ASU where students would gain a voice in reclaiming the outdoor space and increasing the social value of energy. The design would utilize a sustainable solar energy source, bring social value to our community, and encourage people to want to spend time outdoors.”

Students may get more information about the competition and apply to participate on the project website. Feb. 6 is the deadline to apply. Based on the number of applicants, participants will be put into teams of three to four. Each team will work on creating and developing a design for an outdoor, solar powered space or structure. Participants will be offered workshops focusing on strategic planning, branding and positioning of their project, and learning about solar energy and how to implement it in their project.

The competition will run Feb. 7–9. Design, engineering and energy industry professionals will judge the projects. Each member of the winning team will receive a cash prize.

Williams said he and Desmond, with assistance from Changemaker Central at ASU, will work with the winning team to bring its design to the building phase.

Williams said the project concept came out of a survey of ASU students he and Desmond did last November focusing on students’ perceptions about being outdoors and what outdoor amenities they would like to see on campus.

“Our survey showed that students wanted more areas with renewable energy where they could work outdoors. Specifically, we got overwhelming response that students enjoyed being outside and wanted an outdoor space with solar-powered electrical outlets where they could charge their devices,” Williams said.

ASU students search for solutions to solar problems in Cyprus

December 26, 2019

Last summer, four Arizona State University students from the Ira A. Fulton Schools of Engineering participated in collaborative solar energy research as a part of the National Science Foundation’s International Research Experiences for Students program. The students joined Professor Andreas Spanias to spend four weeks at the KIOS Research and Innovation Center of Excellence at the University of Cyprus in the Republic of Cyprus.

The group featured students from multiple engineering disciplines — Jayden Booth, an electrical engineering graduate student; Emma Pedersen, aerospace engineering and computational mathematics double major; Jovita Chauvin, a computer science major; and Michael Oberdorf, an electrical engineering major and four-year U.S. Air Force veteran. They all work with Spanias at the Sensor, Signal and Information Processing Center, known as SenSIP, at ASU. University of Cyprus Associate Professor Elias Kyriakides (left), the Arizona State University students in the International Research Experiences for Students program (from left) Michael Oberdorf, Jayden Booth, Jovita Chauvin and Emma Pedersen along with Professor Andreas Spanias (fifth from left) visited the University of Cyprus Rector Tasos Christofides (right) in Nicosia. Photo by Christiana Koutsoulli/UCy KIOS communications Download Full Image

Spanias, an electrical engineering professor in the School of Electrical, Computer and Energy Engineering, is the founding director of the NSF Industry/University Cooperative Research Center SenSIP.

In Cyprus, the students worked in the lab of University of Cyprus Associate Professor Elias Kyriakides in the area of sensors and machine learning for solar energy monitoring performance, forecasting and anomaly detection applications. Kyriakides, who earned master’s and doctoral degrees in electrical engineering from ASU in 2001 and 2003 respectively, has been a longtime collaborator with Fulton Schools students and faculty.

The project promotes international multidisciplinary research in the areas of sustainability, power systems and signal processing with the aim of improving efficiency in photovoltaic power generation.

“Through this program, I learned how research is conducted in Cyprus,” Booth said. “I also had the chance to meet and interact with Cypriot researchers on a regular basis.”

By the end of the experience, the Fulton Schools students were trained in machine learning algorithms, producing and understanding solar analytics and creating algorithms and software to control solar arrays. They also learned how to effectively present their research results through various workshops including one held in Cyprus.

The challenging problem of fault detection and localization

In remote areas, hundreds or thousands of panels can contribute power to the electrical grid. If one of the panels has a fault, is underperforming or is soiled (by something like bird droppings), it becomes a challenging problem. In the event of a remote fault, technicians sometimes have to go out and remove a series of panels from the grid and use measuring equipment to localize which panel is experiencing problems. This becomes costly in terms of time, labor and travel expenses.

Spanias’ team at SenSIP is working on a related problem with solar panels — the issue of detecting and predicting shading patterns on a utility-scale solar array.

The NSF cyber-physical systems project at SenSIP addresses signal processing and communication problems associated with managing of solar energy production. Several new signal processing, machine learning, shading prediction and wireless communication methods are being developed for optimizing solar panel arrays using sensor actuators embedded in smart monitoring devices known as SMDs. SMDs have embedded sensors and are able to measure current, voltage, temperature and irradiance. They also have actuators (relays) that enable the ability to bypass panels or change configurations from series to parallel to optimize solar power output.

“Because of the massive deployment, you need statistical data analysis and machine learning algorithms to detect whether you have a fault or not,” Spanias said. “Sometimes partial or full shading will reduce the output of the system.”

In order to determine whether there is a fault or partial shading, one must run classification algorithms that are trained to detect certain types of faults. The analysis identifies the type of fault and, with the aid of actuators in the SMDs, can reduce or remedy the effects of a fault until technicians can do the necessary repairs at the facility if needed.

That, however, is only part of the story when it comes to optimizing power production.

With partial shading, it is possible to treat the array of solar panels and reconnect them in different ways. By reconnecting them, it is possible to recover some of the loss of energy output due to shading.

In Cyprus, the students addressed the problems shade may cause in solar arrays. There they gained access to solar array data, including data under different shading patterns. Using this data, they were able to simulate the shading effects on power output.

Currently, most solar panels are connected in series requiring the removal of the entire series of panels from the grid to repair a faulty panel; this is similar to strands of holiday lights where one bulb is removed and the entire strand goes out.

“Intelligent algorithms can try to solve this problem and can create a system to change connection topology for solar panels to maximize possible power,” Spanias said.

Partnering for global solutions

The students’ participation in the IRES program can be partly credited to Spanias’ long history of international collaborations in sensors and signal processing.

The connection between ASU and the University of Cyprus started in 2009 when Spanias received a joint grant from the European Union. There are currently multiple projects between the two universities focused on solar energy monitoring and control, a topic that SenSIP has been working on for many years.

The KIOS Research and Innovation Center of Excellence developed sensor technology for solar rooftop systems. With this technology and assistance from local companies, KIOS is able to monitor hundreds of household rooftop installations. 

One event that precipitated some of this work was the Fukushima nuclear accident in Japan in 2011. After the incident, officials wanted to place solar power facilities in the area to help replace the energy production capacity that had been lost in the region. But they also had to figure out how to monitor the solar panels as humans would not have been able to be sent in to monitor individual panels in the radioactive area. The solution was to create a method of remotely monitoring the panels and also be able to remotely repair issues without human exposure to the radiation.

The collaboration continues

More engineering students can look forward to participating in research at KIOS through the IRES program. The project has received funding for three years and will bring mutual benefits to both institutions. The research collaboration between the faculty and the students in both countries continues throughout the year, enabling the students to have a well-rounded research experience and complete their assigned projects.

Preliminary results from an evaluation of the IRES program by Wendy Barnard, an assistant research professor at ASU, found that students appreciated the opportunity to work with diverse groups of researchers.

“I thought this program would be a great way to apply the skills I had learned during the year into an international setting,” says Pedersen. “Getting to collaborate with researchers from the University of Cyprus was very exciting.”

In addition to their positive research experiences, evaluation results showed that students also enjoyed the cultural experiences they gained while in Cyprus. They visited archeological sites and beaches, interacted with people in the communities they visited and learned how to navigate their way around the country using local transportation.

“We had the opportunity to visit many cultural sites and talk with a diverse group of people from both within the university and out, which was very enriching,” says Pedersen.

The students reported that highlights outside of the lab included visiting the U.S. Embassy in Nicosia, Cyprus, where they met Sondra Sainsbury, Fulbright/alumni coordinator, and Glen Davis, public affairs officer. The students also met with several university administrators, including Tasos Christofides, rector of the University of Cyprus, and Marios Polycarpou, director of KIOS.

Both institutions look forward to continuing the collaboration and to having the next set of Fulton Schools students return to Cyprus in the summer of 2020.

The ASU SenSIP – UCy KIOS IRES program is funded by NSF award 1854273. Applications for the ASU SenSIP IRES program are scheduled to be available in mid-December. 

overhead view of four students in ancient ruins

As part of the IRES program, students visited cultural sites around Cyprus including a trip to the Tombs of the Kings in Paphos-Cyprus from the fourth century B.C. Photo courtesy of Emma Pedersen

Erik Wirtanen

Web content comm administrator, Ira A. Fulton Schools of Engineering