What if your morning run could charge your phone for the day? What if even the touch of your fingers or rattling around in your pocket could power your smartphone? Engineers and scientists have long been interested in the idea of using the human body to generate energy, but not like the human-batteries you’ve seen in the Matrix. Rather, scientists are looking at ways to channel movement energy from the human body in to powering our devices. With the eyes of the world on clean energy and reducing our collective carbon footprint, the idea of powering our own world is an appealing thought experiment. But is it just a pipe dream?
One way in which companies have already begun to utilize the body is by turning exercise into energy. Millions of people go to gyms around the world every day to expel their excess calories in the name of health. What if all that energy could be harnessed to power our world? One gym in Sacramento, California spent $26,000 on exercise bikes that are designed to capture the energy generated by riding. The Sacramento Eco Fitness Gym sports 15 electricity-generating bikes from SportsArt, a company which began in Taiwan in 1978. These bikes look similar to traditional exercise machines, but when plugged in, a generator produces low-voltage AC from the pedaling motion of the rider. The bike then converts this voltage to DC, and back to a 60-hertz AC waveform. About 26% of the energy produced by the bike is used to power the machine, and the rest goes back in to the power grid.
However, these machines do not yet produce a significant amount of power. An advanced cyclist can product over 400 watts per hour, but most people aren’t preparing for the Tour de France and, on average, the machines produce between 50 and 150 watts in that time. Calculations show that, given 5 hours of daily use at 100 watts for every hour, these human batteries would produce only 183 kilowatt-hours per year — about $18 worth of electricity.
Portable energy harvesters have a similar story, but scientists are engineering some fascinating new ways to capture the energy we emit in our daily lives. At the Massachusetts Institute of Technology (MIT), Sangtae Kim from the Department of Materials Science and Engineering has been working on a paper-thin device that’s no larger than the size of a stamp, but which can harvest the energy generated by the human body. The device works by harnessing the stress put on the material by the body’s movements. The device is similar to a battery, with two conducting electrodes separated by a liquid electrolyte – but unlike a battery, Kim’s device uses the same compound for both electrodes, which creates an electrochemical reaction when stress is applied to the device. Then, when the device is unbent, a second reaction occurs, creating another flow of electrical current which generates electricity.
“Any motion is possible to harvest, but you wouldn’t want clothes full of harvesters. I would target the soles of shoes – that’s where the most energy is located,” explains Kim.
In 2012, David Carroll, a physics professor at Wake Forest University, embarked on a similar mission. He created Power Felt, a flexible fabric that can not only provide thermal insulation, but also conduct electricity. Carroll’s invention captures body heat and reuses it to charge phones. He believes that clothing made of Power Felt would be able to generate enough energy to run electronics like cell phones, ipods, and similar small items.
Small human power sources, like Carrol’s Power Felt or Kim’s flexible micro-generator are in high demand, which is expected to grow as wearable electronics like The Fitbit or Apple Watch, become more popular. According to IDC, a market research firm, shipments of wearable electronics are expected to increase from 113.2 million in 2017 to 222.3 million in 2021. Designers of these wearables like Apple and Google are on the hunt for technology that could keep these wearables running longer. Therefore, even though these devices are nowhere close to being able to keep your cell phone continuously charged, they could be useful in extending battery life for small gadgets.
Small devices doesn’t have to mean cell phones or cool gadgets, however. In 2011, A team of Swiss researchers led by biomedical engineer Alois Pfenniger is finding a way to harness the power in the deepest parts of the human body — the heart. The team is learning how to plant microturbines in human arteries, in order to power pacemakers, neurostimulators, blood pressure censors, and other internal medical devices. The microturbine works much like a hydroelectric plant by using blood flow through the artery to generate electricity. When tested, the most productive turbine generated about 800 microwatts of power – 80 times what a pacemakers needs to run (about 10 microwatts).
In 2017, researchers from the Laboratory of Advanced Materials at Fudan University in China came up with another solution that works a little differently. Called a “fluidic nanogenerator fiber,” or FFNG, it is a long fiber less than a millimeter thick that generates power from the movement of blood. It’s created by wrapping a polymer core with carbon nanotubes, which are microscopically thin structures of carbon atoms that conduct electricity better than copper. It generates electricity with a power conversion efficiency of up to 23.3 percent, beating out the more efficient solar panels which are only rated around 22.5 percent.
We may not be powering our grid with human batteries any time soon, but it’s more likely that individual buildings could implement them to decrease their carbon footprint in the near future. In addition, small batteries like the innovations mentioned above can help extend the life of small devices, and it’s clear that the market is turning the in the direction of alternative power to improve technology and make our devices more efficient. Perhaps in the distant future, we will find a way to power our world with nothing but the motion of our feet hitting the ground, but for now, this is just science fiction.