Stephanie Precourt/UW-Madison College of Engineering
Associate Professor Xudong Wang holds a prototype of the researchers’ energy harvesting technology, which uses wood pulp and harnesses nano fibers. The technology could be incorporated into flooring and convert footsteps on the flooring into usable electricity.
While solar and wind power continue to make clean-energy inroads into fueling our electric grid, both rely on favorable weather conditions to make their contribution. Now, a UW research team is developing an electricity-generating technology that could work rain or shine, breezy or calm. The simple act of people walking across floors embedded with treated wood fiber may one day make it possible for pedestrians to light their own walkway.
Xudong Wang, an associate professor of materials science and engineering at UW-Madison, his graduate student Chunhua Yao and his collaborator Zhiyong Can at the U.S. Forest Products Lab, neighboring the UW campus, are perfecting a way to turn tiny cellulose fibers in wood pulp into a triboelectric nanogenerator (TENG) that can harvest electricity from the environment.
The process involves chemically treating wood pulp fibers and creating thin neighboring layers in flooring that have different electric charges.
“We create very tiny gaps between the layers. When someone walks on the floor, the layers alternately touch and separate, and electrons transfer between them, producing electricity,” Wang says. “We add a thin metal sheet to collect the charge. It can be wired to the edge or bottom of the wood. The electron transfer between layers creates a charge imbalance that naturally wants to resolve itself — in contact with an external circuit, electricity is generated. Each electricity-producing layer would be about a millimeter thick, and extra modules could be added to boost energy output.”
TENG is not a new mechanical energy harvesting strategy, but until now it was not economically practical because it required costly ceramic or synthetic polymeric materials. Wang’s breakthrough is finding a way to generate electricity from wood pulp, which is cheap, abundant and renewable. The nano fibers in wood pulp could lead to energy-producing floors that are price-competitive with traditional wood flooring.
Wang’s floors would be most useful in areas where there is a lot of foot traffic, like hallways in malls, transportation terminals and stadiums. Right now, Wang says, his nanogenerators can produce a few milliwatts per step. A milliwatt is 1/1,000 of a watt. A typical laser pointer outputs about five milliwatts of light power.
“Used in the home, it might only power a night light, but if we put a piece of this material in front of each seat in Camp Randall,” says Wang, “and everyone stood up to cheer, that could power a hundred of the high-energy lights in the stadium.”
Wang’s team is at the cutting edge of a hot new green energy field, where waste energy is scavenged from human and manmade sources that exist all around us.
Wang’s TENG technology makes an affordable connection between sites rich in human activity and his patented coated wood pulp nano fibers. Wang has been working on the environmental mechanical energy harvesting concept since graduate school.
“This kind of research attracts many people because we all can see how our work can benefit humanity,” says Wang.
Wang’s plans include placing an educational prototype of his power floor in a high-traffic campus location to demonstrate its effectiveness and durability.
Lab tests have shown that the electricity-generating reaction can perform for millions of cycles. “We haven’t converted those numbers into years of service life for a floor yet,” says Wang, “but I think with appropriate design, it can definitely outlast the lifespan of the floorboards themselves.”
