CU professor tackles wind-power questions

Emeritus professor plays wind center's answer man

Palmer Carlin lets them down easy.

The newer ideas are perhaps 400 years old, he said. The older ones, more like 800 years old.

Carlin listened patiently to a recent caller's description of a revolutionary new wind turbine. When the man finished, Carlin asked, "Does it actually require wind to make it work?"

Palmer Carlin
Palmer Carlin, NREL National Wind Technology Center engineer and a CU electrical engineering professor emeritus, stands with a 75-foot wind turbine blade at the center south of Boulder. Jack Watson/For the Camera

No, the caller said, meaning it was a perpetual-motion machine.

"Well, I only talk about things that need wind," Carlin said, gently.

Carlin has worked for more than 20 years at the National Renewable Energy Laboratory's National Wind Technology Center south of Boulder, first as a consultant and then full-time after retiring as an electrical engineering professor at the University of Colorado. For years, Carlin did cutting-edge research on wind turbines.

He quantified the energy a turbine should be able to pull from a typical wind. He provided the experimental proof that variable-speed wind turbines - ubiquitous today - are indeed better than ones that operate at just one speed.

But now, at 83, the Boulder resident works part time, assisting projects and handling calls from garage inventors who think they have the next big idea in wind energy.

"He's very gentle about breaking the news to them that there's nothing new under the sun, and very good at communicating some simple laws and limits to the way things work," said Robert Thresher, director of the National Wind Technology Center.

The shape, size and mechanics of wind turbines have been painstakingly refined, leaving inventors with little room for improvement. The ideas tend to be either preindustrial or off-the-wall.

"Two guys are insisting on putting wind turbines at 30,000 feet," Carlin said. "I'm not sure the airline industry is going to like that."

Carlin can handle most inquiries without doing math. There are two classes of turbines; only one works well.

Lift machines function like airplane wings and produce rotor-tip speeds several times faster than wind speed, efficiently converting the wind's force into mechanically harvestable motion.

Modern wind turbines are lift machines. The Dutch windmills of the 1600s were lift machines.

Drag machines can never exceed wind speed, wasting force. There are many patents on drag machines.

"It shows you can patent anything," Carlin said.

In rare cases when an idea seems plausible, Carlin brings in Betz.

The Betz limit, published in 1926 by German physicist Albert Betz, says the maximum percentage of energy a machine can take from the wind is 59.3 percent. Modern turbines are up to 45 percent efficient, Carlin says - a high bar for a garage inventor to clear. Improving efficiency by a fraction of a percent is a big deal in wind-energy research, he said.

Thin, soft-spoken and courteous, Carlin has been known to show up at work dressed like Don Quixote on Betz's birthday. Because Betz was born on Dec. 25 - when NREL is largely deserted - Carlin celebrates whenever the whim strikes. He brings in a Safeway sheet cake adorned with a wind machine and the mathematical ratio thee-squared divided by two-cubed, which yields 59.3 percent.

On whether he has ever taken a promising idea from the public, Carlin paused.

"Not that I can think of," he said.