New Technology Could Generate Energy From Every Step You Take
If you want to see the future of clean energy, just look in the mirror.
Scientists at MIT said Wednesday that they have devised a way to generate electricity from small human motions such as bending or walking.
While the idea of harvesting energy from small movements is not new, the researchers say they’ve made a significant breakthrough by figuring out a way to do so electrochemically, similar to how a typical lithium ion battery works, rather than mechanically.
“In our case, we have the two electrodes sandwiching a layer of electrolyte,” said Sangtae Kim, a materials scientist at MIT and lead author of the new study, published in the journal Nature Communications. “But we move the lithium ions between the electrodes by pressing or bending the material.”
The prototype device is a few centimeters wide and consists of two extremely thin layers of silicon film, each 75 nanometers thick, sandwiching a 25 micrometer-thick layer of electrolyte fluid, all supported by a paper-like base material.
“You can think of it as two water tanks, each containing a lot of lithium,” Kim said. “In between the tanks we have this layer of electrolyte where only lithium ions can pass. In a conventional battery we move the lithium ions by supplying electricity. In this case, we press one water tank, or electrode, and that moves the lithium ions from the one electrode to the other.”
The motion of the lithium creates the electric current and is more energy efficient than the most common micro-generation technologies, called piezoelectrics, he said. “For piezo, in almost all cases they are made of ceramic materials, which indicate that they don’t really conduct electricity,” Kim said. “So a vast amount of the electricity generated becomes heat.”
Piezo devices have another potential drawback for powering wearable devices: They create current only at the moment of movement. This works well when small motions are regular and high-frequency—such as vibrations from a piece of mechanical equipment. But human motion happens at a much slower rate of speed.
“One really characteristic feature of piezo is that the duration of the electricity lasts for very short time, about 15 milliseconds. If we have a mechanical input that moves really fast, like 20 times a second, a 20-hertz vibration source, it’s continuous,” Kim said. “Human walking is about one to two hertz, however.”
“We thought that if there was a way to generate electricity for the entire time the mechanism was being stepped on, that would be great,” he added.
The device generates about 100 microamps at 20 millivolts, a fraction of what would be needed to power even a low-power portable device, Kim said.
“Currently it’s only a laboratory version that tests the mechanisms and demonstrates the principles,” he added. “Our next step would be to stack these into the right engineering shape so that this can actually be used in real-life applications.”
One potential use that Kim envisions involves embedding the technology into roadbeds or sidewalks to generate power from the motions of cars and pedestrians. Such “smart highway” concepts have been floating around in recent years—there was even a crowdfunding campaign for a “solar roadway” in 2014—but have yet to become technologically or economically viable.
Jeff Feddersen, an adjunct professor in the Interactive Telecommunications Program at New York University, said the new device holds a lot of potential for harnessing micro movements into useful energy, although “it’s not going to remove any plugs from the wall” in the near future.
“But what I think it might do is open up horizons where it’s almost too sci-fi to make concrete predictions about,” Feddersen said.