Taking the Uncertainty Out of Wind Energy

By Elizabeth Polsdofer, Iowa NSF EPSCoR

[PHOTO]Wind mills in field

Familiarity with the wind is a universal experience that transcends language, location, and time itself. Everyone has felt the joy of a cool breeze on a hot day and the chill of a cold, unexpected draft. We’ve delighted in watching wind dance in the grass, trees, and water while also fearfully locking our doors when its gentle dance has grown into a violent thrash. Even at its worse, we forgive the wind for its destruction and anger, embracing it as a long lost brother when it gently finds its way to us again.

Gaining a deeper understanding of wind and wind energy and increasing its attractiveness as a renewable energy resource is the goal of the Iowa NSF EPSCoR wind energy platform. Led by Provost Barry Butler at the University of Iowa, researchers at Iowa and Iowa State University are studying resource characterization, blade performance and reliability, green energy grids, and drivetrain design and optimization.

Wind turbines are an increasingly familiar sight on the American landscape, ushering in a new age of renewable energy. Iowa NSF EPSCoR researchers are working to increase reliability of wind turbines.

Why Study Wind Energy?

“Nowadays, wind energy is a green energy: clean and renewable, but we face many challenges. For example, many wind turbines are crashed or wrecked before their designed lifetime, so we are studying why they do not live to their designed lifetime,” said Weifei Hu, a graduate student and research assistant in the department of mechanical engineering at Iowa who studies the lesser known quantities of wind.The fact is wind turbines break much sooner than expected. To solve this problem scientists are not just looking at how to build a better turbine but also at the wind that tears their technology apart.

Before Hu came to the University of Iowa to study wind uncertainty, he studied wind turbine blades in South Korea. As a native to China, Hu has grown up watching wind energy farms in Western China heavily increase China’s capacity in renewable energy. “After I finished my masters I told my previous professor that I wanted to keep on doing research at the Ph.D. level,” recalled Hu. “He told me there is a good professor at the University of Iowa, that the professor is really famous, and his name is Kyung Choi. So I applied to the graduate program here and Kyung was very glad to accept me here.”

Choi, Roy J. Carver Professor in Mechanical Engineering, has been involved with wind energy research since May 2009 after seeing a real need to improve the wind energy systems. “My interest in renewable energy started when I learned that improving reliability of the wind energy system is critical for wind energy to compete with the fossil-fuel-based energy sources,” said Choi. “Reliability will reduce the cost of energy generated by the wind energy system.”

With the push to move toward renewable energies, Hu said the research he does now is key to his future. “I chose a great research topic and I can find a great job in the future either in the U.S. or China, he said. “I would prefer to find a faculty job at a university doing some teaching and research, but I think that for me finding an industry job is also a good choice because my research can be used in the wind energy industry.”

Why are Wind Turbines Falling Apart?

Understanding the nature of wind is one part of the wind energy equation. Once we’re sure we understand the wind, or at least have an idea how it behaves most of the time, we can begin to look at how to improve the wind turbine, those large machines that convert wind energy into electricity.

Hyunkyoo Cho, also a graduate student and research assistant in mechanical engineering, looks at uncertainties in vehicles. Like wind uncertainties, vehicle uncertainties measure the degree to which we do not know something about a vehicle. “I was studying structural analysis, but there’s a limit to what we can know about structural analysis. In reality there’s a limit, but we don’t know what that limit is. There are a lot of things we don’t know; they are all uncertainties.” 

Streamwise wind speed chartWhen asked to describe what he meant when he talked about “uncertainties,” Cho described a chair that was built for someone who weighed two hundred pounds or less. The question Cho is looking at is, at what weight above two hundred pounds can someone safely use the chair? When does the chair become unsafe to use? At 205 pounds? 210? That’s the key to building a better wind turbine, understanding how the uncertainty in the wind affects the uncertainty in the wind energy system. When does the wind turbine break? When does it not break?

Wind turbines undergo an immense amount of pressure from the wind in varying degrees and locations. Being a wind turbine is like being in a cylindrical shower full of shower heads everywhere. Some of the shower heads barely give out water and others shove with the pressure of a fire hose. A wind turbine blade needs to be able to holistically handle the various pressures the wind gives it and still perform well.

Iowa NSF EPSCoR scientists use computer programs to generate what the wind may be like on a given field. These simulations clearly show that wind turbines experience wind in a way that is not uniform or predictable. Image courtesy of Weifei Hu, University of Iowa.

“Wind turbines are supposed to withstand wind load for twenty years, but not all of them do. So Weifei [Hu] is figuring out where the wind-earth uncertainty is and how to characterize that uncertainty. If he finishes that, then we can consider that uncertainty to make a more reliable design,” explains Cho. “If someone can give me an uncertainty, then I can a make a design to satisfy that uncertainty.”

Aiding the Wind Energy Industry

When researchers are looking at wind energy in the lab they’re not just concerned with understanding new principles, but also in aiding the wind energy industry. “There are many wind energy companies in Iowa. The state has the second most wind energy production in U.S.  As a research university, we hope we can contribute to assist the state of Iowa in leading wind energy in U.S.,” said Choi. “The research in reliability-based design optimization with my students will help the wind energy to be competitive with the the fossil-fuel-based energy sources.”

Ed Hardee, Research Scientist, works to help develop the software scientists use to study reliability-based design. Interdisciplinary collaboration is a necessity to solve modern problems such as designing a better wind turbine. Hardee insists that although he does not work directly in wind energy research he still makes an invaluable contribution to the research team. “I am not directly involved in wind energy research. My background is not engineering, but rather mathematics and computer science. So I work on maintaining and enhancing the computer programs and tools our center has developed over the last twenty years to support the engineering students and staff in their research,” said Hardee. “Our group has worked on this wind energy project for the last couple of years. We hope our research leads to tools to assist the design of wind turbines that better deal with durability and reliability issues. In particular we want to contribute to the goal of wind turbines that reliably last in different conditions and environments, but at the same time weigh and cost as little as possible.”

The importance of their research and the need for renewable energy is not wasted on this hard working team. A common theme of wind energy as the future of Iowa is repeated as each scientist sees their research contributing to an industry that will mean a future of independence from fossil fuels. “Since resources are finite, I think we should focus on eco-friendly, reusable, sustainable energy and definitely wind energy is one of the strong candidate since it does not hurt nature much,” said Hyeongjin Song, a graduate student and research assistant at the University of Iowa.

The Iowa NSF EPSCoR Wind Energy Platform

Professor Kyung ChoiThe Iowa NSF EPSCoR project is helping to ensure that wind energy research at the Iowa Regent universities has the proper resources to realize its full potential. The effort gives researchers at the University of Iowa opportunities they would not otherwise have. “The EPSCoR funding will allow us to build a core resource in wind energy research by providing junior faculty members opportunities,” explained Choi, who is the drivetrain design and optimization plank leader for the wind energy platform.

“I see that my role as plank leader is in two different ways. First, as a plank leader in drivetrain design and optimization, I have to assist in developing the plank vision and integration, be a plank coordinator (organize plank meetings and other collaborative events), be a plank cheerleader (make connections and create opportunities for junior faculty members in maintaining excellent and relevant research),” said Choi. “On the other hand, with my research in reliability-based design optimization (RBDO), I have developed with my students RBDO software system that all wind energy plank researchers can use to optimize for reliability.”

Kyung Choi heads an Iowa EPSCoR research team investigating ways to make wind turbines more reliable. Choi, Carver Professor of Mechanical Engineering at the University of Iowa, is renowned for his work in reliability-based design optimization.