3 p.m., March 17, 2011----The ocean's powerful winds make the coast an ideal location for a wind turbine. Ironically, it's that ocean air that presents a challenge to any turbine on or near the sea. The moist, salty air combined with a turbine's metallic materials can result in corrosion, a destructive process able to bring any power-generating source to a halt.
Stephen Dexter, professor of marine biosciences in the University of Delaware's College of Earth, Ocean, and Environment (CEOE), is working to address this threat to renewable energy production. He is overseeing a two-year, Department of Energy-supported corrosivity study at the site of UD's wind turbine, located at UD's Hugh R. Sharp Campus in Lewes.
“One of the primary reasons UD constructed the 2-megawatt wind turbine in 2010 was to facilitate scientific study of specific issues with this renewable energy source,” CEOE Dean Nancy Targett said. “This is one of multiple projects fulfilling that purpose and one that could benefit Delaware's pursuits in wind energy as well as those around the country and the globe.”
Studying corrosion has been a priority since the turbine's inception. Dexter is an expert on the topic -- he has extensively studied microbiologically influenced marine corrosion and is a well-known researcher in the field -- and corrosivity is a critical concern for the wind industry. Understanding its impacts will lead to continuing enhancements to turbine reliability and to decreased costs.
“One of the major issues is the cost per kilowatt-hour,” Dexter explained. “The reliability of the turbine and how long it lasts depend on the corrosivity of the site and the corrosion susceptibility of the materials used in construction. Corrosion itself is not the only thing that goes into reliability, but it is a big factor, and it has a direct bearing on your overall cost per kilowatt-hour for power generated.”
The first phase of the project began in September, 2010, when Dexter placed steel samples at three locations around the Lewes campus. Two sets are right near Roosevelt Inlet, one at ground level and one higher up. Another is at the base of the turbine, about 1,150 feet farther back from the water. This spring, Dexter plans to place samples at a fourth location, the top of the turbine. Those samples will be deployed when two graduate students earn final certification required to ascend to the top of the 255-foot tower.
Each site has 12 samples of ordinary steel often used to study atmospheric corrosion. Dexter will pull three samples from each site every six months. The process will allow him to compare the levels of corrosion over time, at the various heights, and at different distances from the water. More importantly, it will allow comparison between the Lewes site and locations up and down the East Coast where similar research has taken place. This ability will benefit those looking to establish their own wind turbines elsewhere by helping them predict the corrosivity of their own location.
“The idea is to calibrate corrosivity and link it to factors that are common to the coastal environment,” Dexter said. “This way, all somebody would have to do is measure the air quality parameters of a given site anywhere in the world and make a pretty good guess as to whether their site is more or less corrosive than ours and what they need to do about it, if anything.”
A second phase of the project will look at the susceptibility to corrosion of the Lewes turbine itself and the electronic control systems inside of it.
For this phase, Dexter will use specially designed probes that will tell him in real-time when corrosion begins to damage critical working parts throughout the turbine. Each probe will simulate a particular turbine component. It will be made of the same material, and it will be placed right next to the turbine part of interest. The probe will work by monitoring the electrical current going through it over time -- if the current for a certain voltage lessens, it tells Dexter corrosion has occurred on the probe and probably on the turbine component as well.
“If the current just stays the same all the time you know it's OK, but if it starts to decrease then you know that that type of material in the turbine environment is getting some damage,” he said, explaining that then turbine operators can either schedule maintenance of that component right when it needs it, or redesign it to be more durable.
That's what this project is all about, Dexter said, taking steps to try and make a turbine more durable by dealing with corrosion.
“The coast is a hostile environment from the mechanical and electrical points of view,” he said. “I'm interested in anything I can do to make power generation more efficient in the long run against this corrosion enemy that essentially affects everybody all the time.”
Article by Elizabeth Boyle