An inexpensive and simple method developed by University of Wisconsin–Madison materials engineers is able to convert footsteps into useable electricity, using panels made from wood pulp and nanofibers.
Xudong Wang, an associate professor of materials science and engineering at University of Wisconsin–Madison (UW-Madison), his graduate student Chunhua Yao, and their collaborators published details of the research in the journal Nano Energy.
Wang has developed a prototype of the technology which uses a common waste material: wood pulp. The pulp, which is already a common component of flooring, is partly made of cellulose nanofibres. When chemically treated, the nanofibers produce an electrical charge when they come into contact with untreated nanofibers. The energy can then be harnessed to power lights or charge batteries.
Wang’s research centres around using vibration to generate electricity. For years, he has been testing different materials that work best with a technology called a triboelectric nanogenerator (TENG). Triboelectricity is the same phenomenon that produces static electricity on clothing. Wang said that chemically treated cellulose nanofibers are a “simple, low-cost and effective alternative” for harnessing this broadly existing mechanical energy source.
Each functional portion inside the flooring has two differently charged materials — including the cellulose nanofibers – and would be a millimetre or less thick. The floor could include several layers for higher energy output.
Once the two materials are together electrons move from one to another based on their different electron affinity. The electron transfer creates a charge imbalance that naturally wants to right itself but as the electrons return, they pass through an external circuit. The energy that process creates is the end result of TENGs.
Wang says the TENG technology could be easily incorporated into all kinds of flooring once it’s ready for the market. Wang is now optimising the technology, and he hopes to build an educational prototype in a high-profile spot on the UW–Madison campus where he can demonstrate the concept.
“Our initial test in our lab shows that it works for millions of cycles without any problem,” Wang said. “We haven’t converted those numbers into year of life for a floor yet, but I think with appropriate design it can definitely outlast the floor itself.”
The UW-Madison team believe that the cheap, abundant and renewable waste product could be as affordable as conventional flooring materials. While there are other products that harness footstep energy, the researchers said they are “costly, non-recyclable, and impractical at a large scale”.
The UW–Madison team added that this kind of “roadside energy harvesting” could, in some settings, rival solar power — and it doesn’t depend on fair weather. Ideal locations to produce significant amounts of energy would include heavy traffic floors in hallways and places like stadiums and shopping centres.
The Wisconsin Alumni Research Foundation holds the patent to the technology.