Pedestrians walking across the floors of busy concourses expend plenty of energy. Researchers and building product manufacturers continue to search for ways to harness that energy to perform useful tasks from powering lights to providing intelligence on traffic flows.
A research team led by Xudong Wang, a University of Wisconsin–Madison professor of materials science and engineering, has developed a prototype wood floor designed to convert footsteps to electricity.
The 96-square-foot prototype is made from recycled wood pulp that’s been seeded with chemically-treated nanofibres. Together with embedded electrodes, the system creates static electricity, known as triboelectricity, under the pressure of footfalls. The energy is then harvested by wires running through the flooring.
Wang notes that the floor design represents a trade-off. Making the flooring material more resilient could improve energy harvests, but make walking difficult.
“We’re not harvesting so much power that it would drain the energy from the people walking across that section of flooring,” he says.
The prototype was placed in a busy hallway at a campus student centre traveled by thousands of pedestrians each day.
“In its current state of development, the technology doesn’t produce enough electricity to light up a building, but we are powering small LED lights at the test site,” Wang says. “Right now we’re thinking the most reasonable application is to use that electricity to run self-powered sensors in smart floors that could track foot traffic.”
Wang’s continuing research will focus on improving triboelectric materials as well as piezoelectric materials — composite materials generating electricity under pressure.
U.K.-based Pavegen Systems is taking a different approach to harvesting pedestrian energy. The company’s signature product consists of interlocking triangular tiles outfitted with pressure-activated flywheels at each apex.
“As people step on the tiles, their weight causes the top surface to vertically displace by between 5mm and 10mm,” says Will Brook, communications analyst with Pavegen. “This creates a downward pressure on the generators beneath, initiating a rotation in the electro-magnetic mechanisms to produce off-grid electrical energy and data.”
The triangular tile design maximizes the energy and data-generating potential of every footstep by allowing each generator to harvest energy through the corners of six adjacent tiles.
The tiles measure 19 inches along each edge and are made of glass-reinforced plastic, polyester resin and stainless steel. The tiles generate three joules of electrical energy per footstep or around five watts of power per person. One step can generate enough electricity to power a three-watt LED lightbulb for one second, or provide six seconds of talk time on an iPhone 8. Walking 144 steps can provide enough energy to power a Nissan Leaf for one metre.
Real-world applications powered by the system include LED lighting, sensors, and data capture and transmission.
“The Pavegen system can also integrate with batteries and capacitors to store and control the deployment of energy,” says Brook. “In DuPont Circle in Washington, D.C. batteries store the energy of around 10,000 people a day walking across three Pavegen walkways in the new Connecticut Avenue Overlook Park. This energy is then deployed at night to power the architectural lighting of the location, as well as providing a constant data feed to our client.”
Pavegen systems have been installed in 200 projects in 30 countries, including Harrods department store and Canary Wharf in London, and installations in France, Nigeria, South Africa, Brazil and Kazakhstan.
Brock notes that people walking across the tile system become personally engaged with the projects via an app that connects to smart phones using low-power Bluetooth beacons.
“The app enables people to see how much electrical energy they are generating and to convert this into rewards,” he says. “That allows people to interact with energy and sustainability in a way that they can’t with renewables like solar and wind. At our installations in London, Washington and elsewhere, we’ve observed people returning to the sites on a daily basis.”
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