By Kayt Sukel
When British drum and bass band Rudimental took the stage to kick off the Union of European Football Associations’ Champions League final in London’s Trafalgar Square on May 31, fans were ready. The energy, as so often experienced at live music events, was palpable. And thanks to the special dance floor, constructed with kinetic paving tiles, the dancing crowd produced more than 90,000 joules of energy during the show. That energy was then harvested to help power the show’s microphone and DJ booth.
Laurence Kemball-Cook, chief executive officer of Pavegen, the London-based company that provided the energy-harvesting tiles for the event, says there is great opportunity to use urban roads and sidewalks as new sources of renewable energy. After being fired from a large European energy company after failing to find a way to build solar-powered streetlights in dense, urban environments, he realized there might be another way forward: leveraging the city’s foot traffic.
“(Foot traffic) can work where other renewables, notably solar and wind, don’t,” says Kemball-Cook. “We have an abundant source of energy in our malls, our cities, our museums, our stadiums, our workplaces, and anywhere that people come together in urban environments. There’s an opportunity to use that energy.”
For more than a decade, academic researchers and startup companies have seen the potential in such an opportunity. Some are looking to harvest energy from footsteps, while others are looking to make use of the millions of miles of highways — and the traffic commonly found on such roads — to generate power.
Applications in asphalt
Any first-year physics student can recite the law of conservation of energy: Energy can neither be created nor destroyed, only transformed or converted from one form to another. In the case of driving, as vehicles travel across the asphalt or concrete, the resulting stress and vibrations produce mechanical energy. This process provides an opportunity for piezoelectric technologies, such as transducers, to convert this mechanical energy into clean electricity.
And researchers are developing new transducer devices to place within road materials to convert this energy. For instance, innovation commentator IP Watchdog named a new patent by researchers at the University of South Florida — a technology that sandwiches a layer of piezoelectric elements between two conductive asphalt layers and two nonconductive base asphalt layers that can harvest energy as vehicles travel over the road — as one of the top patents to watch in 2023.
The basic approach is one that researchers have been working on for some time, including Hao Wang, Ph.D., F.EMI, M.ASCE, an associate professor in the civil and environmental engineering department at Rutgers University’s Center for Advanced Infrastructure and Transportation. In 2019, he and his colleagues developed their own piezoelectric transducers with the power to transform roads and bridges into mini-power plants. An application based on that work was published in March, and the patent is pending.
“The challenge is the energy amount. It’s not that big,” Wang says.
Another issue, added John Haddock, Ph.D., M.ASCE, professor of civil engineering at Purdue University, who has also worked on energy-harvesting pavement applications, is that many of these technologies simply are not robust enough to withstand the wear and tear caused by the vehicles from which they are trying to collect the energy.
“They tend not to hold up very well to 80,000-pound semi-tractor trailers going over them,” Haddock says. “And then there’s the matter of skid resistance if such a system is on the pavement surface. If you’ve got an 80,000-pound truck bouncing around, the dynamic load becomes a real problem.”
It doesn’t necessarily get easier if the sensors or harvesting technologies are inside the pavement either, adds Wang.
“If you put (this transducer) in the asphalt, you are changing the integrity of the original roadway structure. We’re not sure what will happen,” Wang says. “Second, in case something is broken, you need to dig it up to repair it because it’s underneath (the surface). There’s a lot of uncertainty there.”
Despite these challenges, when asked which approach might be most promising for kinetic pavements, Haddock believes future asphalt-based materials that leverage nanosensors may be a way to overcome many of these obstacles. They could even, perhaps, harvest both solar and mechanical energy to produce clean energy from the nation’s roads. But it is going to take a lot more research to get there.
“I think we’re capable of developing a new material that you just put in the mix,” says Haddock. “Asphalt will be a great energy generator because it’s black and wants to absorb all the sunlight. There may be an additive developed we can simply add to an asphalt mixture to make it generate electricity.”
Starting small, building inspiration
In the meantime, however, Wang suggests that any current kinetic pavement technologies are best used in smaller applications — especially since the amount of energy produced by 100 m of energy-harvesting roadway is roughly the equivalent to the total battery power of three dozen mobile phones. Wang says that he and his collaborators are working on new applications not to generate energy for “grid purposes,” but to use for smart sensors or lighting devices in roadway applications.
“One application we are considering is using the energy to provide LED lighting on a warning or stop sign,” says Wang. “That kind of application is quite feasible.”
Kemball-Cook, for his part, believes that these smaller applications have the power to build big investments in future kinetic paving advances. He notes it is important that people understand what kinetic paving technologies can and cannot do — energy generation from “people-powered sidewalks” is governed by physics, after all, and “the physics rule everything.”
Pavegen’s kinetic paving installation off London’s Oxford Street stored enough energy to power LED lights using footsteps, says Kemball-Cook. And much like at the recent UEFA concert, these kinds of installations have the ability to inspire people to come together to help generate energy for their communities.
“We’ve seen people in Washington, D.C., outside DuPont Circle, jump up and down every day for hours,” he said. “They believe they are powering change in their city. And they know it’s only a small amount, but the way it connects to people’s hearts and souls is incredible to see in action. I think people are actively seeking out ways to take part in the climate change movement.”
The company has dozens of projects in more than 37 countries, and with continued improvements in their kinetic paving technologies, he and his team are continuing to look at new ways to scale up what their pavement tiles can do in the future — including moving from sidewalks to roadways.
Kayt Sukel is a science and technology writer based outside Houston, Texas.
This article first appeared in the September/October 2024 issue of Civil Engineering as “The Energy Beneath Us.”
