Innovation Is Blowing in the Wind
Alex Emanuel, professor of electrical and computer engineering, and PhD candidate Grazia Todeschini are exploring ways to use wind turbines, like the 600-kilowatt unit at Holy Name Central Jr./Sr. High School in Worcester, as active filters to clean harmful harmonic pollution from electric power.
by Ami Albernaz
President Obama's call for wind power to supply 20 percent of the country's electricity by 2030 underscores the need to improve the way we harness energy from the wind. At WPI, students and faculty have already begun to make important gains in wind power research, work that will help meet energy needs locally, across the country, and around the world in a more sustainable way.
Toward Cleaner Power
Alexander Emanuel, professor of electrical and computer engineering, who advised the Holy Name project, had begun examining wind generators a few years earlier as a cost-effective way to improve power quality. A leader in power systems research, Emanuel has spent much of his career studying harmonic pollution, a byproduct of the way in which modern electronic devices such as adjustable speed drives, arc furnaces, and fluorescent lights draw electricity. "Harmonics are harmful to power quality," Emanuel says. He believes wind generators can help counteract this pollution.
Most electrical equipment was built to operate with a clean sinusoidal current. When the electrical grid becomes polluted with harmonics, the sinusoidal waveform becomes distorted, reducing the life of transformers, overheating conductors, and degrading insulation. Compensators, also called active filters, can help cancel out harmonics, but they are expensive. The type of generators typically used in wind turbines (called doubly fed induction generators, or DFIGs) can do the job for far less, Emanuel says.
The notion of using wind turbines as active filters began with another undergraduate project. Emanuel co-advised a group of students who worked with National Grid USA to help it handle increasing electricity loads. The project raised the possibility of installing small-scale power generation devices—including wind turbines—near major consumers or at substations, through which electricity passes en route to powering homes.
Currently, Emanuel is working with doctoral candidate Grazia Todeschini to study how effectively the DFIGs in windmills can filter harmonics in the grid. Simulation studies have shown that the concept can work well, although the generators may need design modifications to optimize their ability to not only produce clean energy, but to clean up the power we all depend on.
The 262-foot-tall, 600-kilowatt wind turbine erected at Worcester's Holy Name Central Jr./Sr. High School in 2008 was a towering feat. Along with providing clean energy, the turbine should cut the school's electric bills by more than $4 million over its first 20 years of operation. The turbine was also the culmination of two years of work and planning by a group of WPI undergraduates who proved its feasibility and helped secure needed permits and funding. The project, which added a new dimension to WPI's work in wind power, was undergirded by a strong research foundation.
Building Better Turbines
Manufacturers of wind turbine parts face unique challenges, not least of which is producing components that are durable enough to withstand the inconstancy of wind and exposure to the elements. Given the fast pace of wind power growth in the United States and the nearly $16 billion invested in new wind power projects in 2008, the need for reliable, long-lasting components is no small matter.
To meet that challenge, researchers in WPI's materials science and engineering program are applying their extensive experience working with car and aircraft engines to improve the viability and reduce the cost of turbine gears and bearings. Typically, metal gears are produced through forging and heat treatment processes that can distort the metal. The sheer size of wind turbine gears (more than 10 times larger than car or aircraft gears), means more opportunity for distortion.
Richard Sisson, professor of mechanical engineering and head of WPI’s materials science and engineering program, and Diran Apelian, director of the WPI Metal Processing Institute, are testing several cost-effective manufacturing processes that may help produce gears closer to their intended shape while also making them more durable. They include powder metallurgy, commonly used in the aerospace industry, in which components are manufactured from forged powders; diffusion solidification technology, a casting technique; spray forming, in which molten metal is sprayed onto a substrate to make the desired shape; and cold spray, which is similar to spray forming, but uses room-temperature metal.
The researchers also aim to lower the costs of the heat treatment process, in which carbon is infused into the steel to harden it. This process, Sisson notes, is the most expensive in terms of time, energy, and gas consumption. The group will also be looking to control and reduce distortions that happen in the quenching process, in which the metal is cooled.
Sisson and Apelian will be using mathematical models to try to predict how well the different processes will work. The models will include information on heat transfers and metal and strains. If a particular technique seems to perform well, the researchers will test it out with actual gears. To advance this important work, WPI has teamed up with faculty from Northwestern University, Northern Illinois University, and other academic institutions. Together, they’re seeking funding from the U.S. Department of Energy in hopes of working with wind turbine manufacturers to improve system
operation, extend operating life, and reduce maintenance and repair costs.
Harnessing Sea Breezes
David Olinger, associate professor of mechanical engineering, is exploring a quicker way to implement large-scale wind projects. With a three-year, $300,000 award from the National Science Foundation, he and Gretar Tryggvason, professor and head of the Mechanical Engineering Department, are studying the feasibility of placing wind turbines on floating platforms far out at sea.
The idea is to circumvent environmental and aesthetic objections that have tied up plans for offshore wind farms located within sight of coastlines. Olinger and Tryggvason believe the right design for floating turbines located far offshore (where the winds are faster and steadier) could lead to more immediate construction. "We're hoping to determine the best design for a platform," Olinger says. He imagines the turbines being placed 10 to 25 miles offshore, in waters anywhere from 60 to 300 meters deep. Using computer simulations, the researchers will try to predict how various platform and turbine designs will hold up in a range of water and wind conditions. Eventually, they hope to test small-scale turbine models at Alden Research Laboratory in Holden, Mass.
Olinger's interest in wind power began a few years ago when he came across papers from the 1970s that proposed using kites for electricity generation. Kites are less expensive than turbines and can reach higher altitudes, where they can tap into greater wind speeds. They are also quieter than wind turbines and pose less of a threat to birds.
Dave Olinger, associate professor of mechanical engineering at right, is working with undergraduate and graduate students to develop a low-cost system that uses a windsurfing kite to generate power. He sits in a rig that translates the vertical movements of the kite into rotations of an electric generator or a grain grinder.
Olinger and a team of students have built a rig that turns the up-and-down motion of a 100-square-foot windsurfing kite into one kilowatt of electricity (enough to power a typical home). The kite moves a rocker arm connected to a clutch and flywheel from a rowing machine. The flywheel spins an electric generator, and the electricity can be used or stored in batteries. Energy provided by the kite can also be transferred to mechanical devices, such as a grain grinder. Olinger says the low-cost system might be a good way to power remote villages in developing countries.
The kite power team has tested the system on a Seabrook, N.H., beach. In 2007 the team won $10,000 from the Environmental Protection Agency to develop a kite power system for the agency's annual People, Prosperity, and the Planet Student Design Competition for Sustainability in Washington, D.C. Olinger estimates that two or three more years of testing are needed before the first real-world trial, perhaps at WPI's student project center in Namibia.
"We're hoping to determine the best design for a platform," Olinger says. He imagines the turbines being placed 10 to 25 miles offshore, in waters anywhere from 60 to 300 meters deep.