Engineering News at NC State

Dr. Salah M. Bedair (left) and Dr. Nadia El-Masry (center) want to make solar energy more cost-effective for consumers. The researchers do their work in labs on Centennial Campus. (Photo: Roger Winstead)

In 1979 a team led by Dr. Salah M. Bedair, professor of electrical and computer engineering at NC State University, revolutionized solar energy by creating a first-of-its-kind solar cell.

Now, in 2008, he’s trying to build upon that research. The results could make solar energy less expensive for consumers.

This time he’s accompanied by Dr. Nadia El-Masry, professor of materials science and engineering, and Dr. John Hauser, professor of electrical and computer engineering. Their goal of improving efficiency could make solar energy production more feasible on a large scale and finally practical and affordable for public use—a goal more than 20 years in the making.

When Bedair began working with his team in the late 1970s, solar cell efficiency was at about 16 percent—meaning the cell was only converting 16 percent of the sun’s energy into usable energy. Their goal was to increase this, and their work produced the first multiple-junction solar cell.

“Because solar radiation is made of different wavelengths,” Bedair explained, “the absorption of each wavelength has to be considered separately.”

The original structure they pioneered had two junctions, each capable of separately absorbing a different wavelength. After much research and improvement, the modern incarnation of that original structure is now produced by Spectrolab, a Boeing company. This cell has three junctions and yields 40 percent efficiency.

The ideal efficiency for a structure capable of absorbing every wavelength would be 70–80 percent, according to Bedair, and though this figure would be “nearly impossible” to achieve, they
still hope to improve efficiency by five percent by adding a fourth cell junction. The impact of that increase, he said, will have a huge and immediate impact on the energy market and consumers as solar energy becomes less expensive.

As Bedair pointed out, “at a solar cell station, producing tens of thousands of kilowatts, a five percent increase in efficiency means massive changes in energy production and cost efficiency.”

December 19, 2008

Harvesting the Sun

— NC State engineers are serious about making solar energy more affordable