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.
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.