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Streamlining Wind Energy

by Mikael Mulugeta

Corey Markfort (center) with members of his research team: (l to r) Pablo Carrica, Marcela Politano, Markfort, Shivendra Prakash, and Ezequiel Martin.

Early on a Friday morning, Mohsen Vahidzadeh stands under a radio tower in the southwest corner of the Kirkwood Community College campus. Overhead, more than a dozen sensors on the 350-foot tower track wind speed and direction, humidity, temperature, solar radiation, and even CO2 concentration. Vahidzadeh, a second-year PhD student at IIHR—Hydroscience & Engineering (IIHR), will collect the data and compare it with operational information from similar sensors affixed to Kirkwood’s 2.5 MW wind turbine on the north side of campus.

Using this data, Vahidzadeh and IIHR’s Corey Markfort, his faculty supervisor, hope to better understand how weather conditions affect the performance of wind turbines. That information will be crucial to build more accurate turbine flow models and optimize operation of turbines in less than ideal conditions. They plan to make the data publicly available online and use it in coursework for the University of Iowa’s (UI) Wind Energy Certificate program.

Environmental Flows

Markfort, who is also an assistant professor of civil and environmental engineering, studies environmental flows and wind energy. Unlike simple engineering flows, he says, environmental flows have two significant features that complicate measurements and forecasts. First, variations in topography and density due to temperature stratification (varying temperatures at different depths) cause a modeling challenge. Second, turbulence causes chaos. Markfort says we can see examples of turbulence in our daily lives, such as smoke rising from a smokestack or swirling flows in rivers. However, the technical problems stratified turbulence can produce are less obvious.

Turbulence is a frequently recurring problem in physics and engineering, says Markfort. “My wind energy research, which is about capturing kinetic energy from natural flow, takes these other factors into account.”

Markfort’s focus on wind energy grew out of his PhD studies of the atmospheric boundary layer — the layer closest to the Earth’s surface. While investigating how energy from the atmosphere mixes with lakes, he discovered a fascination with the complexities of harnessing wind energy. By understanding how land surface and complex terrain affect the wind, Markfort says we can also know where best to place wind turbines.

This is where the data collected by sensors at Kirkwood comes into play. Understanding how weather conditions affect turbines is one of several wind energy projects Markfort oversees. His objectives are to improve wind power plant performance and forecasting, and to better understand and mitigate the environmental impacts of turbines.

The Wind Energy Boom

In 2008, the Obama administration set a goal to double renewable energy production in the United States. This spurred new funding for wind energy research. “That’s a large part of what gave me the opportunity to research the interaction between wind and turbines, and how wind energy extraction affects the atmospheric boundary layer,” Markfort says.

IIHR’s innovative wind tunnel facilitates Markfort’s wind energy research.

Iowa already produces more than a third of its electricity from wind, and the state’s major electric utilities are on track to hit 80 percent within a decade. The national trend is also promising; the U.S. Department of Energy’s (DOE) Wind Vision report projects that the United States will meet 20 percent of its electricity needs with renewable wind power by 2030. This will require a workforce of approximately 380,000, up from the current estimate of 73,000. By 2050, the DOE predicts an increase to 600,000 jobs.

Markfort says scientists are rapidly overcoming the remaining challenges of wind energy. One of the most pressing challenges is to prevent wind turbines at the front of a wind farm from reducing the effectiveness of turbines behind them. Utilities typically arrange wind turbines in rows. However, when wind flows past a turbine, the region behind it experiences lower wind speeds. Power generation depends on high wind speeds. This can lead to significant losses, as high as 40% in some cases. Markfort says he and his team are trying to understand why.

“Right now, each turbine is designed to capture as much energy as it can for itself, even to the detriment of neighboring turbines,” says Markfort. “So we’re researching how to optimize the entire group so overall energy production is greater.”

Another persistent issue is the greater need for energy on the coasts. The strongest wind blows through the central United States, but highest demand for energy is on the coasts. Although offshore wind energy potential is substantial, significant challenges persist, including the cost of building offshore turbines. Nevertheless, offshore wind is becoming a focus in the United States, especially off the East Coast and on the Great Lakes.

To study offshore wind farming, IIHR recently developed a new experimental facility, the IIHR boundary layer wind-wave tunnel. In this facility, researchers conduct controlled experiments using state-of-art laser-based anemometry techniques to learn how offshore wind farms perform in the presence of surface waves and how they affect mixing at the Great Lakes and surface coastal oceans. Markfort and his team are hopeful this research will help move offshore wind farming forward.

By most measures, the future looks bright for renewable energy. Wind, hydro, bio, and solar energy present opportunities for significant improvements in air and water quality, public health, and the reduction of carbon emissions. Renewable energy is also a booming industry requiring a skilled workforce. Markfort says institutions such as the University of Iowa and Kirkwood Community College play a critical role in training this workforce.

Markfort’s research, and the work of others at IIHR and around the country, could help change how we generate electricity forever.

Last modified on May 30th, 2019
Posted on May 30th, 2019

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