Edwin L. Aguirre
Wind energy as a source of electrical power is an attractive alternative to fossil fuels because it is clean, plentiful and renewable, and emits no greenhouse gases.
As of 2009, the United States has a total installed wind-energy generating capacity of nearly 25,400 million watts (MW), which is about a fifth of the world’s total capacity. In comparison, Germany produces 23,903 MW, Spain 16,740 MW, China 12,200 MW and India 9,645 MW.
Improvements in technology have led to a dramatic decrease in the cost of operating and maintaining wind farms in recent years, from $40 per megawatt-hours (MWh) to about $10/MWh. The U.S. Department of Energy (DOE) wants to improve the cost-effectiveness of wind power even further by cutting the price down to $5/MWh.
A team of researchers from UMass Lowell’s Mechanical Engineering Department recently received a two-year grant of about $500,000 from the DOE to help achieve that goal.
“Our project plans to make wind energy less expensive to produce and cheaper for consumers by minimizing manufacturing defects in wind turbine blades and avoiding costly repairs and downtime,” says Assoc. Prof. Christopher Niezrecki, co-director of the University’s Structural Dynamic and Acoustic Systems Laboratory. “Our goal is to better understand the cause, effect and detection of these defects.”
Prof. Julie Chen is the principal investigator (PI) for the project, while Niezrecki, Assoc. Prof. Peter Avitabile and Prof. James Sherwood are the co-PIs. Other collaborating institutions include the National Renewable Energy Laboratory (NREL), the Sandia National Laboratories and TPI Composites Inc.
Today’s commercial turbine blades are made of composite materials, mainly fiberglass, and each blade can span up to more than 100 meters (330 feet) in length. Structural defects usually encountered in the field include hairline cracks, wrinkles, waviness, voids, erosion, poor bonding or delamination in the fiberglass composite.
“Blade failures can result in significant downtime in a wind farm,” says Niezrecki. “Whenever a turbine is not operating, it’s losing money.”
The team hopes to validate its sensing techniques for detecting defects and improve the reliability and throughput, or yield, of the turbine blade.
“These techniques can be used for quality control during blade manufacturing, resulting in a reduction in the cost of blade fabrication and therefore the cost of energy generation,” he says.
There is no testing facility available on the UMass Lowell campus so all the tests will be conducted at the NREL facility in Arvada, Colo.
“Both static and dynamic fatigue tests will be performed,” says Niezrecki. “The University will be sending its sophisticated instrument the Aramis 3-D Digital Image Correlation System - to NREL for use by the UMass Lowell faculty there.”
In addition to the DOE grant, the team also recently received three-year $177,000 funding from the National Science Foundation (NSF) for structural stress-strain research. Niezrecki is the PI for the NSF project, with Chen and Avitabile as co-PIs.
“The goal of the NSF grant is to better understand dynamic stress and strain throughout a vibrating structure in operation using a limited number of sensors,” says Niezrecki. “This novel approach was developed by Dr. Avitabile here at UMass Lowell.”
He says the technique may ultimately be applied to monitoring the dynamic health of any large flexible composite structures, such as wind turbines blades, helicopter blades, bridges and aircraft wings and fuselage, for any sign of mechanical fatigue or failure.
“All the dynamic load testing and computer modeling will be done right here on the campus,” he says.