Page 32 - UD Research Magazine Vol5-No2

burn coal and oil and so on,” said Böer, who now lives in Naples, Fla.
His early work in thin-film photovol- taics focused on solar cells made of layers of cadmium sulfide (CdS) and copper sul- fide (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 conven- tional silicon cells, thin-film materials are
His place in the sun by Beth Miller
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 base- ment 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 produc- ing 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.
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 funda- mental 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.
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EVAN KRAPE