University of Delaware Online Research Magazine
University of Delaware Online Research Magazine

ISSN 2150-5128

If we could capture it all for just 90 minutes, that beautiful shining star in the sky—our sun—would deliver enough power to satisfy this planet’s appetite for electricity for about a full year, scientists say.

 

In six days, the sun could deliver nearly a century of power—if demand remained constant. And if demand surges, as expected—well, give it another day or two.

If only.

Courtesy of NASA’s Solar Dynamics Observatory.

 

by | October 12, 2015

  Beth Miller

Science Writer, UD Office of Communications and Marketing

The vast majority of the sun’s extraordinary power remains out of reach—absorbed, deflected or otherwise inaccessible to today’s power-hungry masses—but University of Delaware researchers continue their quest to capture more, store more and deploy it more efficiently.

The University has been a center of pioneering solar research since before it was fashionable—before the oil embargo of 1973, before long lines formed to get rations of gasoline, before the nation had a Department of Energy or the word “green” became a badge of good stewardship.

And this is a great time to be in the middle of that work. Solar-generated energy, now representing a small fraction of the nation’s electricity supply, is a burgeoning industry, representing almost a third of the new capacity installed in 2014.

A time-lapse map on the Department of Energy’s website shows the surge from the utility perspective across the United States, starting in 1983 with zero solar plants online.

Ten years later, 10 plants were online with enough juice to power about 100,000 homes. By 2003, there were only 15 plants and enough power for about 103,000 homes. By 2013, though, there were 682 plants able to deliver power to 1.7 million homes. And when you include the hundreds of thousands of residential and commercial rooftops covered with solar panels, their installation is growing at over 50 percent per year, doubling every few years.

Among the resources available at IEC are over 12 systems for depositing a wide range of semiconducting, transparent or metallic thin-film layers on glass or flexible foils up to a foot wide; a digital scanning electron microscope; spectrophotometers; X-ray diffractometers, high power laser scanner, solar simulators, quantum efficiency and luminescence measurements, and an accelerated exposure facility.

UD’s Institute of Energy Conversion (IEC) focuses its research on solar energy technologies including cadmium telluride, copper indium gallium selenide and silicon—all of which have varying levels of efficiency and production costs.

Solar is expected to remain a growth industry as prices continue to drop—they have fallen 40–50 percent in the past five years in the U.S.—and the nation demonstrates a growing commitment to renewable energy sources as a way to address environmental concerns, political concerns and energy security.

The speed of that growth turns on resources and advances in technology, the kind that have been underway at the University of Delaware’s Institute of Energy Conversion (IEC) since 1972.

Karl Böer, Distinguished Professor Emeritus of Physics and Solar Energy, was at the forefront then, working on thin-film photovoltaics as the founder of the IEC, which has produced more than 45 patents in its 43 years.

Böer had come to Delaware in 1962 from Humboldt University of Berlin, Germany, which counted among its luminaries and lecturers such names as Karl Marx, Albert Einstein, Dietrich Bonhoeffer and a total of 40 Nobel laureates.

Böer’s work in physics took a sharp turn toward solar energy as he saw what was happening on the planet.
“If you are awake in the morning and know what’s going on, you know we can no longer burn coal and oil and so on,” said Böer, who now lives in Naples, Fla.

His early work in thin-film photovoltaics focused on solar cells made of layers of cadmium sulfide (CdS) and copper sulfide (Cu2S). Now, IEC focuses on other thin-film materials—cadmium telluride (CdTe), copper indium gallium selenide (CIGS) and amorphous silicon (a-Si).

Thin-film photovoltaics are extremely thin, using layers that start at a few nanometers (that’s a few billionths of a meter, not much wider than a strand of DNA). Compared to the more conventional silicon cells, thin-film materials are much lighter in weight and can be used in flexible applications. But those same properties mean they must be applied to and supported by another surface, which can add to their weight and affect other properties.

“You have to understand the fundamental properties of the material and the layers,” said physicist William Shafarman, senior scientist at IEC and an associate professor of materials science.

If you put thin-film materials between two sheets of glass, for example, you have to know how those materials will interact, how to control the properties of each and how to make such panels in reliable, industry-friendly ways.

IEC established several milestones in thin-film technology. It was the first laboratory to get 10 percent efficiency out of the materials, and it pioneered the “roll-to-roll” manufacturing process, exploiting the flexibility of thin films to develop a continuous rollout and cut production costs.

 

Solar One House
With support from Delmarva Power and Light, IEC built Solar One, a thin-film solar cell demonstration project, in 1973. It was the first experimental house to convert sunlight into both heat and electricity for domestic use and drew thousands of visitors.

 

Under Böer’s leadership, the IEC also built a thin-film solar cell demonstration project—a small house known as Solar One that had a sharply angled roof and still sits off South Chapel Street in Newark.

The house showed the practical potential of thin-film and passive solar technologies, producing both electricity and heat and—in the process—drawing thousands of visitors to Newark after its completion in 1973. The novelty made headlines with NBC News and Long Island, N.Y.’s Newsday, to name a few outlets, and Popular Science called it “the most technologically advanced solar house now in existence.”

Its glory days are past and the solar panels are gone, but the Solar One house still stands as an unassuming testament to the trailblazing work by UD researchers and their students.

At the IEC, an extensive and varied collection of solar panel samples is on display—probably the most substantial such collection in the world, according to Shafarman. The panels, each marked with the date of development and other information, are lined up for students and others to examine and compare.
The display and extensive research demonstrate that solar energy progress takes time. Some ideas produce a lot of hype, which “most of the time doesn’t pan out,” said Steven Hegedus, senior scientist at IEC and associate professor of electrical and computer engineering who has worked in solar research for more than 30 years.

“Remember, it takes 10 years or more for a technology to go from the laboratory to full-scale production,” he said. “There’s a lot of testing, validation, optimization. Making something once in the lab is hard. Making it day in, day out, thousands of modules a day, is really hard.”

But incremental progress has been a constant, he said.

Thin-film efficiency has doubled—to more than 20 percent, Shafarman said. But it still lags behind the standard silicon wafers, which are closer to 25 percent.

 

Thin-film solar cell
Thin-film solar cells, the focus of research at IEC, are much lighter than other materials and can be fabricated on glass or flexible foils. Above shows thin-film solar cells on glass fabricated at IEC. IEC has established several milestones
in thin-film technology.

 

Efficiency is an important problem for researchers and industry. When a system is said to be 25 percent efficient, it means it is converting a quarter of the power it absorbs. Seventy-five percent, in other words, goes unused.

Industry leaders often turn to IEC for help with performance issues or plans for a new product, and IEC has a strong team of scientists, graduate-level students and postdoctoral fellows with the training and experience to assist them. Shafarman said he and others often take calls from businesses looking for potential employees with strong solar credentials.

The IEC, directed since 1996 by physicist Robert Birkmire, professor of materials science and engineering, also participates in many Department of Energy initiatives and collaborates with other universities and national labs.

“There is still a need for new ideas,” Shafarman said, “and new ways to make solar cells with low-cost materials.”

Böer urges students to continue that quest and pursue a comprehensive understanding of the science and the systems.

“Look at the materials, the systems, understand the physics behind it,” he said. “Study solid state physics and solar energy. Study electrical energy and electrical engineering. Study solar engineering.”

And help the world catch more rays.

 

Steve Hegedus

His place in the sun

Steven Hegedus remembers the moment they flipped the solar switch at his Newark house on a February afternoon in 2007.

He and his wife were the first homeowners in town to install solar panels on their roof and Hegedus—senior scientist and a solar expert at the University of Delaware’s Institute of Energy Conversion—was keen to see what would happen.

They had turned off major systems in the house in case of an installation glitch. But there was no glitch, and shortly after the solar system went live, it was clear the tide had turned.

The rotating disk that was part of the electric meter now was slowing, slowing, slowing. Then it stopped and started turning in the opposite direction—in Hegedus’ favor— sending the surplus electricity from the solar array back to the grid.

“My wife and I were in the driveway going ‘woo-hoo!’” he said.

Since that day eight years ago, Hegedus’ power bills have dropped by about two-thirds. And his belief in the promise of solar power is stronger than ever, which is saying something.

With more than 30 years of research in photovoltaics, Hegedus is an expert in solar electricity and solar cell manufacturing and an associate professor of electrical and computer engineering. He was co-editor with Antonio Luque of Spain of the Handbook of Photovoltaic Science and Engineering, a standard in the field and an often-cited text.

“I wanted to be part of this movement that I’ve been doing research on,” he said. “It makes me a better proponent and advocate. I can use the data from my system, analyze it and show students in my class that our modeling actually works. When I go to talk to schools or churches that are thinking about going solar—I’ve done this. I took the leap.”

For the first few years after the system was installed, Hegedus says people would stop at the house, wanting to know more. He was glad to oblige.

Nine modules are on the roof of his house, each with 200-watt capacity. An inverter in the basement changes direct current to alternating current. Production varies with temperature, sunlight and time of day, Hegedus said.

It may be surprising to learn that the system’s peak production typically occurs on the coldest day of the year—a cloudless, bright winter sky with no humidity to scatter the sunlight. Plus, the solar panels are most efficient when it’s cold, Hegedus said.

Monthly averages, though, show July at the top, with longer days and the sun higher in the sky.

The only time the panels produce zero energy is when they are covered with snow, he said. And it typically slides off the next day due to the steep slope of his roof.

The panels have a life expectancy of about 25 years, he said, when they would still be producing a not-too-shabby 80 percent of their rated power.

“What other electronic device do we expect to be outside and functioning every day in the weather for 25 years? Streetlights maybe.”

Hegedus was on the roof with the installer to see that process in action and continues to monitor the system’s performance using the Delaware Environmental Observing System to track solar radiation data in his area.

He hopes IEC will increase its work on solar system performance analysis and reliability testing.

“These are important issues for the growth of the business and also important for students to learn as they go into the working world,” he said.

Learn more: www.udel.edu/iec

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