Out at sea, gentle waves provide power for thousands of homes. In cities, dancefloor moves generate electricity for nightclubs. In the countryside, hikers use leg power to recharge their phones.
It is an alluring goal of clean, reliable power free from geo-political risks -- and scientists said it lies within reach, thanks to a smart way to harvest energy called tribo-electricity.
Researchers at the Georgia Institute of Technology said they had built a simple prototype device that converts stop-start movement into power.
Waves, walking and dancing -- even rainfall, computer keys or urban traffic -- could one day be harnessed to drive sensors, mobile gadgets or even electricity plants, they contend.
Zhong Lin Wang, a professor of materials science and engineering, described the invention a breakthrough. "Our technology can be used for large-scale energy harvesting, so that the energy we have wasted for centuries will be useful," he told AFP by email.
"Tribo-electric" is a modern term with ancient roots -- from the Greek word for "rub." Its electricity is created from friction between two substances causing a charge of electrons to be transferred from one to the other.
It commonly happens, for instance, when plastic-soled shoes are in contact with a nylon carpet, causing the snap of static discharge when one's hand touches a metal doorknob. Because tribo-electric is so unpredictable, it has been generally shunned as a power source.
The preferred method has been magnetic induction -- a turbine driven by nuclear- or fossil-powered steam or water.