DOE Pulse
  • Number 403  |
  • December 16, 2013

Emery makes NREL the go-to place for solar cell characterization

NREL researcher Keith Emery uses a high-intensity pulse solar simulator to test a concentrator solar cell in his laboratory at NREL. This summer, Emery was presented the Cherry Award by the IEEE. Credit: Dennis Schroeder

NREL researcher Keith Emery uses a high-intensity
pulse solar simulator to test a concentrator solar
cell in his laboratory at NREL. This summer, Emery
was presented the Cherry Award by the IEEE.
Credit: Dennis Schroeder

Keith Emery always had amazing computer programming skills, but he lacked that special gift for creating solar cells. So, 30 years ago he switched to something more in his wheelhouse — characterizing and measuring the efficiency of solar cells and modules.

He succeeded so well, building a world-class testing facility at DOE's National Renewable Energy Laboratory (NREL), that he was recently given the annual William R. Cherry Award by the Institute of Electrical and Electronic Engineers (IEEE) — one of the most coveted awards in the world of solar photovoltaic (PV) energy.

Emery has a Teddy Roosevelt moustache and routinely climbs high rugged mountains in the Colorado Rockies. But the Cherry Award startled this usually unflappable man.

"I was very surprised," Emery said.

Others aren't surprised, citing his work to bring iron-clad certainty to the claims made by solar companies about the efficiency of their cells and modules — not to mention the 320 scientific publications he's written.

"Accredited measurements from Emery's laboratories are considered the gold standard by the U.S. and international PV communities," said NREL colleague Pete Sheldon, deputy director of the NCPV. "Keith has been a leader in cell and module performance measurement techniques that have been the foundation for the credibility of PV efficiency standards for a quarter century."

The award is named in honor of William R. Cherry, a founder of the PV community. The award recognizes an individual engineer or scientist who has devoted a part of his or her professional life to the advancement of the science and technology of photovoltaic energy conversion.

In the world of solar cells, a seemingly small improvement in efficiency is almost always a very big deal. Higher efficiency links directly to cost and helps solar cells compete with other forms of energy.

Before Emery brought strict standards and independent analysis to testing and measurement, claims of high efficiency would be published in the literature without any independent verification.

"We decided that independent verification was important for credibility," Emery said. He and his NREL colleagues standardized measurement techniques, testing cells and modules under identical environmental conditions. But that meant that companies didn't always like the efficiency numbers they were getting back from Emery's lab.

"The happiness factor was never in our favor," Emery said. "We were coming in with lower efficiencies than the customer expected."

Emery and his colleagues stuck to their guns, and soon certification from NREL was de rigueur in the solar cell world. "Our goal is to eliminate surprises," Emery said. "If the measurements on their end disagree with our measurements, we show them why. It's in everyone's best interest to know what the environment is."

The service is readily available so researchers and companies have equal access to the resources needed for independent efficiency measurement, he says. "We provide the same playing field for everyone. We have to thank the Energy Department for this. They've funded it. We've been able to offer the service to everybody from national labs to a lot of low-budget startups. They all get the same verification."

Emery’s interest in electronics goes back to seventh grade, when he made a five-tube amplifier out of a junk box hi-fi and a TV set. "I would have violated every safety rule we have at NREL, but that's a separate issue. I've always been interested in computers, going back to the days of paddle switches, punch cards, and paper tapes."

Emery started working with chemicals in community college, including some chemicals that are so potentially hazardous they're not even allowed in some research centers today. "Yes, I had fun with chemicals."

He earned his bachelor's and master's degrees at Michigan State University, where he fell under the tutelage of Stan Ovshinsky, whose pioneering work in amorphous silicon semiconductors set the course for many technologies and industries. More important to Emery, Ovshinsky introduced his young graduate students to energy-conservation devices, delivered a lecture on amorphous silicon, and "treated us like VIPs," springing for the occasional expensive meal.

That was in the 1970s, the first oil embargo and the first Earth Day, and Emery wanted a piece of the new excitement about renewable energy.

He was just short of his doctorate when NREL's predecessor, the Solar Energy Research Institute (SERI), offered him a job — impressed, by and large, by his computer skills. "I always had a knack for programming," he said. "Every lab that hired me wanted me for my programming. They didn't want me for anything else."

At SERI, Emery soon found that his expertise wasn't in making solar cells, but rather in testing them. "There's an art to making solar cells," he said. "I could deposit a good one in about 50 tries. The true artists can make them in about 10."

So, Emery developed the test equipment and put together the data-acquisition system for characterizing and measuring the efficiency of solar cells. Turns out, his programming skills were essential to computer-control measurements and numerical control of instruments. "That's what we needed to build our lab."

He has spent his career building the capabilities of that testing and characterization lab, making it one of a handful of premier measurement labs in the world — and the only place in the United States that sets primary standards for solar-cell characterization.

A few years back, Emery published a paper on how to artificially increase solar-cell efficiency — not to encourage cheating, but to warn journal editors to be suspicious of claims.

"There have only been three or four papers in the past 35 years that have made claims that were outright bogus," Emery said, lauding the solar community for its integrity. Still, editors need to be on the lookout for exaggerated claims.

New materials will have to be more efficient and more economical than silicon to make a big dent in the market, Emery says. "They have a huge learning curve to keep costs down," he said, referring to thin films, organic PV, amorphous silicon, and other products just now moving from national labs to private companies. On the other hand, the newer materials have a great chance of invading niche markets such as solar cells on clothes, on signs, or on things that shine and glow or are hit by a laser. The multi-junction cell, for example, has already proven its superiority in outer space.

When he's not at work, Emery enjoys the Colorado outdoors. Emery and his wife, Pat, just published a paper on their own solar house, for which Emery dug the ditches, painted, and installed the insulation.

And at work, he'll keep testing and measuring the products of extraordinary research, as he continues to keep his lab among the best in the world at measuring solar module capacity.

As for the Cherry Award, Emery gives much of the credit to the colleagues who work in his lab and who have on average about 16 years of service at NREL. "Take my team away, and I wouldn't have gotten this award — it's that simple."

Learn more about NREL's work in Photovoltaic Measurements and Characterization. — Bill Scanlon

Submitted by DOE's National Renewable Energy Laboratory