While piezoelectric technologies don’t scale up as effectively as, say, a field of wind turbines, they do scale down. They can behave properly at the atomic level, and being able to generate electricity on the nano-scale has huge benefits for medicine, according to Amir Manbachi, a graduate student in clinical engineering at the University of Toronto. The body’s mechanical energy could be harvested to power permanent medical devices such as a pacemaker or a middle ear implant, thereby eliminating the need to perform invasive surgery to replace a battery every few years.
“The problem is that if you are doing a surgery like putting an implant in someone’s head, there’s no battery that provides energy for 20 years,” Manbachi says. “If we can come up with better ways of powering these implants, it’s going to change the whole medical industry.”
What works on the battlefield or the operating table isn’t necessarily practical for day-to-day uses. “Really the only market for these things is when you’re not attached to the grid,” Donelan says. “It’s unlikely that most people are going to wear [a knee brace] around New York City on a typical day to charge their cell phones.”
Nonetheless, one London-based start-up is working to make products that harvest ambient energy at a (somewhat) larger scale. Pavegen makes special tiles that absorb energy from pedestrians’ footfalls. CEO Laurence Kemball-Cook, an industrial design engineer, founded the company in 2009. He says Pavegen doesn’t publicly disclose how the technology works, but says the company uses a “hybrid” system of piezoelectricity and other harvesting technology.
During the 2012 Olympic Games in London, Pavegen installed tiles at a Tube station and captured almost 1 million footsteps, according to the company’s website. How much energy did that produce? Roughly 1.2 kilowatt hours. To put that number in perspective, 1.2 kilowatt hours would power one standard 100-watt incandescent light bulb for 12 hours, or a more energy-efficient 23-watt compact fluorescent bulb for 52 hours.
Kemball-Cook defends energy harvesting power, or what he calls “microgeneration,” despite its limitations compared to other forms of renewable energy. In a TED Talk he gave, Kemball-Cook said the average person has around 150 million footsteps in her lifetime, a total amount of energy that he said would power the average house for around three weeks. But when asked about how practical installing Pavegen tiles on a larger scale would be, Kemball-Cook was vague. “It’s a matter of scale, and you can’t scale in a day. ... You don’t want to sell 50,000 products in the first week of your business,” he says.
Another footfall-heavy environment Pavegen has taken advantage of is music festivals. In 2011, Pavegen set up an installation at Bestival, a music festival on the Isle of Wight. According to Pavegen, the installation captured 250,000 footsteps and helped charge 1,000 cell phones at the event—though it doesn’t say how much of a charge the installation gave. The company is planning to harvest the energy of 2,000 dancing people to help power an outdoor concert in Singapore. “I can’t guarantee that every single thing in the entire concert is going to be powered by Pavegen,” Kemball-Cook says, a bit optimistically. “But it’s going to be a serious amount of power.”
Products that harvest footfall energy aren’t limited to flooring. Tom Krupenkin, a mechanical engineering at the University of Wisconsin, is marketing a shoe insert that harvests and stores footfall energy to power personal electronics. Using his prototype, Krupenkin says it would take roughly two hours of walking to charge an average smart phone. He and his research partner, J. Ashley Taylor, are working with a “large shoe manufacturer” in the hopes of marketing their product to the general public in one to two years.
Harvesting the body’s energy isn’t a viable alternative to large-scale renewable energy options like wind and solar, but it has extremely useful applications in specific fields. What ambient energy harvesting can also do very effectively is show people how much we can rely on our own bodies to produce the energy we need. “We use so much more power than what we can produce on our own,” Donelan says. “That sounds so dire, but to put a positive spin on it, the way you use human power is not by having people produce electricity, but to use their own power to use less of it.”