The body electric: Harnessing human energy


By Emma Roller, SLATE

In The Matrix, human bodies are plugged into an elaborate grid where their energy is harvested to power our robot overlords. That nightmare scenario has its downsides, but practically speaking, human bodies do produce a lot of energy that goes untapped. Researchers are coming up with ways to convert that energy into electricity—power that could be used to charge your cell phone, transmit a wireless signal, or power a medical implant.

Wouldn't it be cool if you could charge your phone while you walk? (Photo provided by Bionic Power)

(Photo provided by Bionic Power)

The basis for some of this technology has been around for more than 130 years, starting with an experiment conducted in 1880 by brothers Pierre and Jacques Curie. They found that putting pressure on certain types of crystals could produce electricity. Piezoelectricity, or “pressure-driven electricity,” is created from ceramics or crystals such as quartz, zinc oxide, and titanium dioxide. Pressure redistributes these materials’ positive and negative charges. A camping stove or push-button lighter works by pressing down on a piezoelectric ceramic, which produces enough energy to spark a flame.

Energy harvesting is at work in most of the technologies we think of as renewable, such as solar power and wind power. But instead of the sun’s rays or the force of the wind, ambient energy harvesting captures our bodies’ kinetic energy.

Henry Sodano, a material sciences engineer at the University of Florida, has been researching human-action applications for piezoelectricity for 10 years. He developed a backpack equipped with shoulder straps made from piezoelectric materials. As the pack jostles up and down, the force exerted on the straps gets converted into electricity. Long-range hikers could use this to power small electrical devices on the trail.

The population that could benefit enormously from this type of technology is the military. Soldiers in the field are constantly grappling with their power sources, sometimes literally. They carry up to 28 pounds worth of batteries on a mission, according to Sodano—and that’s on top of body armor, ammunition, and other equipment. Using an energy-harvesting device would allow soldiers to power two-way radios, GPS devices, and headlamps without the added weight of batteries. The backpack technology isn’t being sold commercially, and like much of the technology in the field, it’s still in the development process.

Another energy-harvesting device the military is testing is a specialized knee brace developed by Max Donelan, a biomedical physiologist at Simon Fraser University in British Columbia. Donelan is also the chief science officer at Bionic Power, the company that makes the brace, which was spun off from Simon Fraser University in 2007. Bionic Power has R&D contracts with the military in both Canada and the United States, but the company is still one to two years away from putting the technology to use in the field. The brace is connected to a gearbox and a generator that converts the motion of the knee into electricity. Donelan says one minute of walking with the knee brace can generate enough energy for a 30-minute cell phone conversation.

“If you really want to get a lot of power from the body, you want to go to the powerhouses of the body,” Donelan says, such as the muscles that work with the knee joint.

Donelan compares his knee brace to a hybrid car’s regenerative braking. In a conventional car, the brakes act against the motor. In a hybrid car, the brakes reverse the motor and allow it to act as a generator. The system produces electricity that is stored in the car’s battery.

Donelan’s carbon-fiber knee brace will run roughly $1,000, not including the generator and battery. And while that is a prohibitive cost for most grid-dwellers, he says there’s a strong financial argument you can make to the military. Aside from the issue of weight, delivering batteries to the field can get expensive quickly—a 30-cent AA battery might have racked up $30 in external costs by the time it gets to its destination in Afghanistan.

Ambient energy harvesting has a lot of possible applications that just aren’t feasible for other types of renewable energy. One example is in the wake of a natural disaster, when rescue workers need quick access to power. Another is in developing countries without sophisticated power grids, where harvested human energy could be used to power anything from cell phones to coolers storing vaccines. This technology isn’t adults-only, either: The company Uncharted Play has invented an energy-harvesting soccer ball for children in developing countries to use. The ball stores the energy from getting kicked around during the day to power a built-in LED light at night.

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.”

Last modified: March 17, 2013